improve performance by precomputing parts of the AABB intersection algorithm

src/main/java/eu/jonahbauer/raytracing/Examples.java

@@ -1,9 +1,11 @@
 package eu.jonahbauer.raytracing;
 
-import eu.jonahbauer.raytracing.math.AABB;
 import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.color.ColorSpaces;
+import eu.jonahbauer.raytracing.render.spectrum.RGBAlbedoSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.RGBIlluminantSpectrum;
 import eu.jonahbauer.raytracing.render.texture.CheckerTexture;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
 import eu.jonahbauer.raytracing.render.camera.SimpleCamera;
 import eu.jonahbauer.raytracing.render.material.*;
 import eu.jonahbauer.raytracing.render.texture.ImageTexture;
@@ -50,13 +52,14 @@ public class Examples {
 
     public static @NotNull Example getSimpleScene(int height) {
         if (height <= 0) height = 675;
+        var cs = ColorSpaces.sRGB;
         return new Example(
                 new Scene(getSkyBox(), List.of(
-                        new Sphere(new Vec3(0, -100.5, -1.0), 100.0, new LambertianMaterial(new Color(0.8, 0.8, 0.0))),
+                        new Sphere(new Vec3(0, -100.5, -1.0), 100.0, new LambertianMaterial(cs.albedo(0.8, 0.8, 0.0))),
-                        new Sphere(new Vec3(0, 0, -1.2), 0.5, new LambertianMaterial(new Color(0.1, 0.2, 0.5))),
+                        new Sphere(new Vec3(0, 0, -1.2), 0.5, new LambertianMaterial(cs.albedo(0.1, 0.2, 0.5))),
                         new Sphere(new Vec3(-1.0, 0, -1.2), 0.5, new DielectricMaterial(1.5)),
                         new Sphere(new Vec3(-1.0, 0, -1.2), 0.4, new DielectricMaterial(1 / 1.5)),
-                        new Sphere(new Vec3(1.0, 0, -1.2), 0.5, new MetallicMaterial(new Color(0.8, 0.6, 0.2), 0.0))
+                        new Sphere(new Vec3(1.0, 0, -1.2), 0.5, new MetallicMaterial(cs.albedo(0.8, 0.6, 0.2)))
                 )),
                 SimpleCamera.builder()
                         .withImage(height * 16 / 9, height)
@@ -67,11 +70,16 @@ public class Examples {
     public static @NotNull Example getSpheres(int height) {
         if (height <= 0) height = 675;
 
+        var cs = ColorSpaces.sRGB;
+
         var rng = new Random(1);
         var objects = new ArrayList<Hittable>();
         objects.add(new Sphere(
                 new Vec3(0, -1000, 0), 1000,
-                new LambertianMaterial(new CheckerTexture(0.32, new Color(.2, .3, .1), new Color(.9, .9, .9)))
+                new LambertianMaterial(new CheckerTexture(0.32,
+                        new RGBAlbedoSpectrum(cs, new ColorRGB(.2, .3, .1)),
+                        new RGBAlbedoSpectrum(cs, new ColorRGB(.9, .9, .9))
+                ))
         ));
 
         for (int a = -11; a < 11; a++) {
@@ -83,13 +91,13 @@ public class Examples {
                 var rnd = rng.nextDouble();
                 if (rnd < 0.8) {
                     // diffuse
-                    var albedo = Color.multiply(Color.random(rng), Color.random(rng));
+                    var albedo = ColorRGB.random(rng).times(ColorRGB.random(rng));
-                    material = new LambertianMaterial(albedo);
+                    material = new LambertianMaterial(cs.albedo(albedo));
                 } else if (rnd < 0.95) {
                     // metal
-                    var albedo = Color.random(rng, 0.5, 1.0);
+                    var albedo = ColorRGB.random(rng, 0.5, 1.0);
                     var fuzz = rng.nextDouble() * 0.5;
-                    material = new MetallicMaterial(albedo, fuzz);
+                    material = new MetallicMaterial(cs.albedo(albedo), fuzz);
                 } else {
                     // glass
                     material = new DielectricMaterial(1.5);
@@ -100,8 +108,8 @@ public class Examples {
         }
 
         objects.add(new Sphere(new Vec3(0, 1, 0), 1.0, new DielectricMaterial(1.5)));
-        objects.add(new Sphere(new Vec3(-4, 1, 0), 1.0, new LambertianMaterial(new Color(0.4, 0.2, 0.1))));
+        objects.add(new Sphere(new Vec3(-4, 1, 0), 1.0, new LambertianMaterial(cs.albedo(0.4, 0.2, 0.1))));
-        objects.add(new Sphere(new Vec3(4, 1, 0), 1.0, new MetallicMaterial(new Color(0.7, 0.6, 0.5))));
+        objects.add(new Sphere(new Vec3(4, 1, 0), 1.0, new MetallicMaterial(cs.albedo(0.7, 0.6, 0.5))));
 
         var camera = SimpleCamera.builder()
                 .withImage(height * 16 / 9, height)
@@ -117,13 +125,14 @@ public class Examples {
 
     public static @NotNull Example getSquares(int height) {
         if (height <= 0) height = 600;
+        var cs = ColorSpaces.sRGB;
         return new Example(
                 new Scene(getSkyBox(), List.of(
-                        new Parallelogram(new Vec3(-3, -2, 5), new Vec3(0, 0, -4), new Vec3(0, 4, 0), new LambertianMaterial(new Color(1.0, 0.2, 0.2))),
+                        new Parallelogram(new Vec3(-3, -2, 5), new Vec3(0, 0, -4), new Vec3(0, 4, 0), new LambertianMaterial(cs.albedo(1.0, 0.2, 0.2))),
-                        new Parallelogram(new Vec3(-2, -2, 0), new Vec3(4, 0, 0), new Vec3(0, 4, 0), new LambertianMaterial(new Color(0.2, 1.0, 0.2))),
+                        new Parallelogram(new Vec3(-2, -2, 0), new Vec3(4, 0, 0), new Vec3(0, 4, 0), new LambertianMaterial(cs.albedo(0.2, 1.0, 0.2))),
-                        new Parallelogram(new Vec3(3, -2, 1), new Vec3(0, 0, 4), new Vec3(0, 4, 0), new LambertianMaterial(new Color(0.2, 0.2, 1.0))),
+                        new Parallelogram(new Vec3(3, -2, 1), new Vec3(0, 0, 4), new Vec3(0, 4, 0), new LambertianMaterial(cs.albedo(0.2, 0.2, 1.0))),
-                        new Parallelogram(new Vec3(-2, 3, 1), new Vec3(4, 0, 0), new Vec3(0, 0, 4), new LambertianMaterial(new Color(1.0, 0.5, 0.0))),
+                        new Parallelogram(new Vec3(-2, 3, 1), new Vec3(4, 0, 0), new Vec3(0, 0, 4), new LambertianMaterial(cs.albedo(1.0, 0.5, 0.0))),
-                        new Parallelogram(new Vec3(-2, -3, 5), new Vec3(4, 0, 0), new Vec3(0, 0, -4), new LambertianMaterial(new Color(0.2, 0.8, 0.8)))
+                        new Parallelogram(new Vec3(-2, -3, 5), new Vec3(4, 0, 0), new Vec3(0, 0, -4), new LambertianMaterial(cs.albedo(0.2, 0.8, 0.8)))
                 )),
                 SimpleCamera.builder()
                         .withImage(height, height)
@@ -136,12 +145,13 @@ public class Examples {
 
     public static @NotNull Example getLight(int height) {
         if (height <= 0) height = 225;
+        var cs = ColorSpaces.sRGB;
         return new Example(
                 new Scene(List.of(
-                        new Sphere(new Vec3(0, -1000, 0), 1000, new LambertianMaterial(new Color(0.2, 0.2, 0.2))),
+                        new Sphere(new Vec3(0, -1000, 0), 1000, new LambertianMaterial(cs.albedo(0.2, 0.2, 0.2))),
-                        new Sphere(new Vec3(0, 2, 0), 2, new LambertianMaterial(new Color(0.2, 0.2, 0.2))),
+                        new Sphere(new Vec3(0, 2, 0), 2, new LambertianMaterial(cs.albedo(0.2, 0.2, 0.2))),
-                        new Parallelogram(new Vec3(3, 1, -2), new Vec3(2, 0, 0), new Vec3(0, 2, 0), new DiffuseLight(new Color(4.0, 4.0, 4.0))),
+                        new Parallelogram(new Vec3(3, 1, -2), new Vec3(2, 0, 0), new Vec3(0, 2, 0), new DiffuseLight(cs.illuminant(4.0))),
-                        new Sphere(new Vec3(0, 7, 0), 2, new DiffuseLight(new Color(4.0, 4.0, 4.0)))
+                        new Sphere(new Vec3(0, 7, 0), 2, new DiffuseLight(cs.illuminant(4.0)))
                 )),
                 SimpleCamera.builder()
                         .withImage(height * 16 / 9, height)
@@ -155,10 +165,11 @@ public class Examples {
     public static @NotNull Example getCornellBox(int height) {
         if (height <= 0) height = 600;
 
-        var red = new LambertianMaterial(new Color(.65, .05, .05));
+        var cs = ColorSpaces.sRGB;
-        var white = new LambertianMaterial(new Color(.73, .73, .73));
+        var red = new LambertianMaterial(cs.albedo(.65, .05, .05));
-        var green = new LambertianMaterial(new Color(.12, .45, .15));
+        var white = new LambertianMaterial(cs.albedo(.73, .73, .73));
-        var light = new DiffuseLight(new Color(15.0, 15.0, 15.0));
+        var green = new LambertianMaterial(cs.albedo(.12, .45, .15));
+        var light = new DiffuseLight(cs.illuminant(15.0));
 
         return new Example(
                 new Scene(List.of(
@@ -182,10 +193,11 @@ public class Examples {
 
     public static @NotNull Example getCornellBoxSmoke(int height) {
         if (height <= 0) height = 600;
-        var red = new LambertianMaterial(new Color(.65, .05, .05));
+        var cs = ColorSpaces.sRGB;
-        var white = new LambertianMaterial(new Color(.73, .73, .73));
+        var red = new LambertianMaterial(cs.albedo(.65, .05, .05));
-        var green = new LambertianMaterial(new Color(.12, .45, .15));
+        var white = new LambertianMaterial(cs.albedo(.73, .73, .73));
-        var light = new DiffuseLight(new Color(7.0, 7.0, 7.0));
+        var green = new LambertianMaterial(cs.albedo(.12, .45, .15));
+        var light = new DiffuseLight(cs.illuminant(15.0));
 
         return new Example(
                 new Scene(List.of(
@@ -195,13 +207,13 @@ public class Examples {
                                 new Box(new Vec3(0, 0, 0), new Vec3(165, 330, 165), white)
                                         .rotateY(Math.toRadians(15))
                                         .translate(new Vec3(265, 0, 295)),
-                                0.01, new IsotropicMaterial(Color.BLACK)
+                                0.01, new IsotropicMaterial(cs.albedo(ColorRGB.BLACK))
                         ),
                         new ConstantMedium(
                                 new Box(new Vec3(0, 0, 0), new Vec3(165, 165, 165), white)
                                         .rotateY(Math.toRadians(-18))
                                         .translate(new Vec3(130, 0, 65)),
-                                0.01, new IsotropicMaterial(Color.WHITE)
+                                0.01, new IsotropicMaterial(cs.albedo(ColorRGB.WHITE))
                         )
                 )),
                 SimpleCamera.builder()
@@ -216,10 +228,11 @@ public class Examples {
     public static @NotNull Example getCornellBoxSphere(int height) {
         if (height <= 0) height = 600;
 
-        var red = new LambertianMaterial(new Color(.65, .05, .05));
+        var cs = ColorSpaces.sRGB;
-        var white = new LambertianMaterial(new Color(.73, .73, .73));
+        var red = new LambertianMaterial(cs.albedo(.65, .05, .05));
-        var green = new LambertianMaterial(new Color(.12, .45, .15));
+        var white = new LambertianMaterial(cs.albedo(.73, .73, .73));
-        var light = new DiffuseLight(new Color(7.0, 7.0, 7.0));
+        var green = new LambertianMaterial(cs.albedo(.12, .45, .15));
+        var light = new DiffuseLight(cs.illuminant(7.0));
         var glass = new DielectricMaterial(1.5);
 
         var room = new Box(new Vec3(0, 0, 0), new Vec3(555, 555, 555), white, white, red, green, white, null);
@@ -243,17 +256,18 @@ public class Examples {
     public static @NotNull Example getDiagramm(int height) {
         if (height <= 0) height = 450;
 
-        record Partei(String name, Color color, double stimmen) { }
+        var cs = ColorSpaces.sRGB;
+        record Partei(String name, ColorRGB color, double stimmen) { }
         var data = List.of(
-                new Partei("CDU", new Color(0x00, 0x4B, 0x76), 18.9),
+                new Partei("CDU",       new ColorRGB(0x004B76), 18.9),
-                new Partei("SPD", new Color(0xC0, 0x00, 0x3C), 25.7),
+                new Partei("SPD",       new ColorRGB(0xC0003C), 25.7),
-                new Partei("AfD", new Color(0x80, 0xCD, 0xEC), 10.3),
+                new Partei("AfD",       new ColorRGB(0x80CDEC), 10.3),
-                new Partei("FDP", new Color(0xF7, 0xBB, 0x3D), 11.5),
+                new Partei("FDP",       new ColorRGB(0xF7BB3D), 11.5),
-                new Partei("DIE LINKE", new Color(0x5F, 0x31, 0x6E), 4.9),
+                new Partei("DIE LINKE", new ColorRGB(0x5F316E), 4.9),
-                new Partei("GRÜNE", new Color(0x00, 0x85, 0x4A), 14.8),
+                new Partei("GRÜNE",     new ColorRGB(0x00854A), 14.8),
-                new Partei("CSU", new Color(0x00, 0x77, 0xB6), 5.2)
+                new Partei("CSU",       new ColorRGB(0x0077B6), 5.2)
         );
-        var white = new LambertianMaterial(new Color(.99, .99, .99));
+        var white = new LambertianMaterial(cs.albedo(.99, .99, .99));
 
         var count = data.size();
         var size = 75d;
@@ -273,12 +287,12 @@ public class Examples {
             objects.add(new Box(
                     new Vec3((i + 1) * spacing +       i * size, 0, spacing),
                     new Vec3((i + 1) * spacing + (i + 1) * size, partei.stimmen() * 15, spacing + size),
-                    new DielectricMaterial(1.5, partei.color())
+                    new DielectricMaterial(1.5, cs.albedo(partei.color()))
             ));
         }
 
         return new Example(
-                new Scene(new Color(1.25, 1.25, 1.25), objects),
+                new Scene(cs.illuminant().scale(1.25), objects),
                 SimpleCamera.builder()
                         .withImage(height * 16 / 9, height)
                         .withPosition(new Vec3(700, 250, 800))
@@ -293,7 +307,7 @@ public class Examples {
 
         return new Example(
                 new Scene(getSkyBox(), List.of(
-                        new Sphere(Vec3.ZERO, 2, new LambertianMaterial(new ImageTexture("/earthmap.jpg")))
+                        new Sphere(Vec3.ZERO, 2, new LambertianMaterial(new ImageTexture("earthmap.jpg", ColorSpaces.sRGB)))
                 )),
                 SimpleCamera.builder()
                         .withImage(height * 16 / 9, height)
@@ -326,12 +340,13 @@ public class Examples {
     public static @NotNull Example getFinal(int height) {
         if (height <= 0) height = 400;
 
+        var cs = ColorSpaces.sRGB;
         var objects = new ArrayList<Hittable>();
         var random = new Random(1);
 
         // boxes
         var boxes = new ArrayList<Hittable>();
-        var ground = new LambertianMaterial(new Color(0.48, 0.83, 0.53));
+        var ground = new LambertianMaterial(cs.albedo(0.48, 0.83, 0.53));
         for (int i = 0; i < 20; i++) {
             for (int j = 0; j < 20; j++) {
                 var w = 100.0;
@@ -349,31 +364,31 @@ public class Examples {
         // light
         objects.add(new Parallelogram(
                 new Vec3(123, 554, 147), new Vec3(300, 0, 0), new Vec3(0, 0, 265),
-                new DiffuseLight(new Color(7., 7., 7.))
+                new DiffuseLight(cs.illuminant(7.0))
         ));
 
         // spheres with different materials
-        objects.add(new Sphere(new Vec3(400, 400, 200), 50, new LambertianMaterial(new Color(0.7, 0.3, 0.1))));
+        objects.add(new Sphere(new Vec3(400, 400, 200), 50, new LambertianMaterial(cs.albedo(0.7, 0.3, 0.1))));
         objects.add(new Sphere(new Vec3(260, 150, 45), 50, new DielectricMaterial(1.5)));
-        objects.add(new Sphere(new Vec3(0, 150, 145), 50, new MetallicMaterial(new Color(0.8, 0.8, 0.9), 1.0)));
+        objects.add(new Sphere(new Vec3(0, 150, 145), 50, new MetallicMaterial(cs.albedo(0.8, 0.8, 0.9), 1.0)));
 
         // glass sphere filled with gas
         var boundary = new Sphere(new Vec3(360, 150, 145), 70, new DielectricMaterial(1.5));
         objects.add(boundary);
-        objects.add(new ConstantMedium(boundary, 0.2, new IsotropicMaterial(new Color(0.2, 0.4, 0.9))));
+        objects.add(new ConstantMedium(boundary, 0.2, new IsotropicMaterial(cs.albedo(0.2, 0.4, 0.9))));
 
         // put the world in a glass sphere
         objects.add(new ConstantMedium(
                 new Sphere(new Vec3(0, 0, 0), 5000, new DielectricMaterial(1.5)),
-                0.0001, new IsotropicMaterial(new Color(1., 1., 1.))
+                0.0001, new IsotropicMaterial(cs.albedo(1.0, 1.0, 1.0))
         ));
 
         // textures spheres
-        objects.add(new Sphere(new Vec3(400, 200, 400), 100, new LambertianMaterial(new ImageTexture("/earthmap.jpg"))));
+        objects.add(new Sphere(new Vec3(400, 200, 400), 100, new LambertianMaterial(new ImageTexture("earthmap.jpg", cs))));
         objects.add(new Sphere(new Vec3(220, 280, 300), 80, new LambertianMaterial(new PerlinTexture(0.2))));
 
         // box from spheres
-        var white = new LambertianMaterial(new Color(.73, .73, .73));
+        var white = new LambertianMaterial(cs.albedo(.73, .73, .73));
         var spheres = new ArrayList<Hittable>();
         for (int j = 0; j < 1000; j++) {
             spheres.add(new Sphere(new Vec3(random.nextDouble(165), random.nextDouble(165), random.nextDouble(165)), 10, white));
@@ -392,6 +407,9 @@ public class Examples {
     }
 
     private static @NotNull SkyBox getSkyBox() {
-        return SkyBox.gradient(new Color(0.5, 0.7, 1.0), Color.WHITE);
+        return SkyBox.gradient(
+                new RGBIlluminantSpectrum(ColorSpaces.sRGB, new ColorRGB(0.5, 0.7, 1.0)),
+                ColorSpaces.sRGB.illuminant()
+        );
     }
 }

src/main/java/eu/jonahbauer/raytracing/Main.java

@@ -1,10 +1,11 @@
 package eu.jonahbauer.raytracing;
 
-import eu.jonahbauer.raytracing.render.ImageFormat;
 import eu.jonahbauer.raytracing.render.canvas.Canvas;
-import eu.jonahbauer.raytracing.render.canvas.Image;
 import eu.jonahbauer.raytracing.render.canvas.LiveCanvas;
+import eu.jonahbauer.raytracing.render.canvas.XYZCanvas;
+import eu.jonahbauer.raytracing.render.image.PNGImageWriter;
 import eu.jonahbauer.raytracing.render.renderer.SimpleRenderer;
+import eu.jonahbauer.raytracing.render.color.ColorSpaces;
 import org.jetbrains.annotations.NotNull;
 
 import java.io.IOException;
@@ -23,6 +24,7 @@ public class Main {
 
         var renderer = SimpleRenderer.builder()
                 .withSamplesPerPixel(config.samples)
+                .withSpectralSamples(config.spectralSamples)
                 .withMaxDepth(config.depth)
                 .withIterative(config.iterative)
                 .withParallel(config.parallel)
@@ -30,21 +32,21 @@ public class Main {
 
         Canvas canvas;
         if (config.preview) {
-            var image = new LiveCanvas(new Image(camera.getWidth(), camera.getHeight()));
+            var image = new LiveCanvas(new XYZCanvas(camera.getWidth(), camera.getHeight()), ColorSpaces.sRGB);
             image.preview();
             canvas = image;
         } else {
-            canvas = new Image(camera.getWidth(), camera.getHeight());
+            canvas = new XYZCanvas(camera.getWidth(), camera.getHeight());
         }
 
         long time = System.nanoTime();
         renderer.render(camera, scene, canvas);
         System.out.printf("rendering finished after %dms", (System.nanoTime() - time) / 1_000_000);
 
-        ImageFormat.PNG.write(canvas, config.path);
+        PNGImageWriter.sRGB.write(canvas, config.path);
     }
 
-    private record Config(@NotNull Example example, @NotNull Path path, boolean preview, boolean iterative, boolean parallel, int samples, int depth) {
+    private record Config(@NotNull Example example, @NotNull Path path, boolean preview, boolean iterative, boolean parallel, int samples, int spectralSamples, int depth) {
         public static @NotNull Config parse(@NotNull String @NotNull[] args) {
             IntFunction<Example> example = null;
             Path path = null;
@@ -52,6 +54,7 @@ public class Main {
             boolean iterative = false;
             boolean parallel = false;
             int samples = 1000;
+            int spectralSamples = 4;
             int depth = 50;
             int height = -1;
 
@@ -80,6 +83,15 @@ public class Main {
                             throw fail("value " + args[i] + " is not a valid integer");
                         }
                     }
+                    case "--spectral-samples" -> {
+                        if (i + 1 == args.length) throw fail("missing value for parameter --spectral-samples");
+                        try {
+                            spectralSamples = Integer.parseInt(args[++i]);
+                            if (spectralSamples <= 0) throw fail("spectral samples must be positive");
+                        } catch (NumberFormatException ex) {
+                            throw fail("value " + args[i] + " is not a valid integer");
+                        }
+                    }
                     case "--depth" -> {
                         if (i + 1 == args.length) throw fail("missing value for parameter --depth");
                         try {
@@ -111,7 +123,7 @@ public class Main {
 
             if (example == null) example = Examples::getCornellBoxSmoke;
             if (path == null) path = Path.of("scene-" + System.currentTimeMillis() + ".png");
-            return new Config(example.apply(height), path, preview, iterative, parallel, samples, depth);
+            return new Config(example.apply(height), path, preview, iterative, parallel, samples, spectralSamples, depth);
         }
 
         private static @NotNull RuntimeException fail(@NotNull String message) {

src/main/java/eu/jonahbauer/raytracing/math/AABB.java

@@ -79,33 +79,37 @@ public record AABB(@NotNull Vec3 min, @NotNull Vec3 max) {
      * @return {@code true} iff the ray intersects this bounding box, {@code false} otherwise
      */
     public boolean hit(@NotNull Ray ray, @NotNull Range range) {
-        var origin = ray.origin();
+        var invDirection = ray.getInvDirection();
-        var direction = ray.direction();
+        var negInvOrigin = ray.getNegInvOrigin();
-        var invDirection = direction.inv();
+
-
+        var tminX = Math.fma(min.x(), invDirection.x(), negInvOrigin.x());
-        // calculate t values for intersection points of ray with planes through min
+        var tminY = Math.fma(min.y(), invDirection.y(), negInvOrigin.y());
-        var tmin = intersect(min(), origin, invDirection);
+        var tminZ = Math.fma(min.z(), invDirection.z(), negInvOrigin.z());
-        // calculate t values for intersection points of ray with planes through max
+
-        var tmax = intersect(max(), origin, invDirection);
+        var tmaxX = Math.fma(max.x(), invDirection.x(), negInvOrigin.x());
-
+        var tmaxY = Math.fma(max.y(), invDirection.y(), negInvOrigin.y());
-        // determine range of t for which the ray is inside this voxel
+        var tmaxZ = Math.fma(max.z(), invDirection.z(), negInvOrigin.z());
-        double tlmax = Double.NEGATIVE_INFINITY; // lower limit maximum
+
-        double tumin = Double.POSITIVE_INFINITY; // upper limit minimum
+        var tlmax = max(
-
+                Math.min(tminX, tmaxX),
-        for (int i = 0; i < 3; i++) {
+                Math.min(tminY, tmaxY),
-            // classify t values as lower or upper limit based on ray direction
+                Math.min(tminZ, tmaxZ)
-            if (direction.get(i) >= 0) {
+        );
-                // min is lower limit and max is upper limit
+        var tumin = min(
-                if (tmin[i] > tlmax) tlmax = tmin[i];
+                Math.max(tminX, tmaxX),
-                if (tmax[i] < tumin) tumin = tmax[i];
+                Math.max(tminY, tmaxY),
-            } else {
+                Math.max(tminZ, tmaxZ)
-                // max is lower limit and min is upper limit
+        );
-                if (tmax[i] > tlmax) tlmax = tmax[i];
+
-                if (tmin[i] < tumin) tumin = tmin[i];
+        return tlmax < tumin && tumin >= range.min() && tlmax <= range.max();
     }
+
+    private static double max(double a, double b, double c) {
+        return Math.max(a, Math.max(b, c));
     }
 
-        return tlmax < tumin && tumin >= range.min() && tlmax <= range.max();
+    private static double min(double a, double b, double c) {
+        return Math.min(a, Math.min(b, c));
     }
 
     /**

src/main/java/eu/jonahbauer/raytracing/math/IVec.java

@@ -0,0 +1,33 @@
+package eu.jonahbauer.raytracing.math;
+
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A vector-like object that implements the standard mathematical operations
+ * @param <T> the type
+ */
+public interface IVec<T extends IVec<T>> {
+    @Contract(pure = true)
+    double get(int i);
+
+    @Contract(pure = true)
+    @NotNull T plus(@NotNull T other);
+
+    @Contract(pure = true)
+    @NotNull T minus(@NotNull T other);
+
+    @Contract(pure = true)
+    @NotNull T times(@NotNull T other);
+
+    @Contract(pure = true)
+    @NotNull T times(double d);
+
+    @Contract(pure = true)
+    default @NotNull T div(double d) {
+        return times(1 / d);
+    }
+
+    @Contract(pure = true)
+    double @NotNull[] toArray();
+}

src/main/java/eu/jonahbauer/raytracing/math/IVec3.java

@@ -0,0 +1,47 @@
+package eu.jonahbauer.raytracing.math;
+
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A vector-like object with three components.
+ * @param <T> the type
+ */
+public interface IVec3<T extends Record & IVec3<T>> extends IVec<T> {
+    @Contract(pure = true)
+    default double component1() {
+        return toVec3().x();
+    }
+
+    @Contract(pure = true)
+    default double component2() {
+        return toVec3().y();
+    }
+
+    @Contract(pure = true)
+    default double component3() {
+        return toVec3().z();
+    }
+
+    @Override
+    @Contract(pure = true)
+    default double get(int i) {
+        return switch (i) {
+            case 0 -> component1();
+            case 1 -> component2();
+            case 2 -> component3();
+            default -> throw new IndexOutOfBoundsException(i);
+        };
+    }
+
+    @Contract(pure = true)
+    default @NotNull Vec3 toVec3() {
+        return new Vec3(component1(), component2(), component3());
+    }
+
+    @Override
+    @Contract(pure = true)
+    default double @NotNull [] toArray() {
+        return new double[] {component1(), component2(), component3()};
+    }
+}

src/main/java/eu/jonahbauer/raytracing/math/Matrix3.java

@@ -0,0 +1,255 @@
+package eu.jonahbauer.raytracing.math;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Objects;
+
+public record Matrix3(
+        double a11, double a12, double a13,
+        double a21, double a22, double a23,
+        double a31, double a32, double a33
+) {
+    public static @NotNull Matrix3 fromRows(@NotNull Vec3 @NotNull[] rows) {
+        if (rows.length != 3) throw new IllegalArgumentException();
+        return fromRows(rows[0], rows[1], rows[2]);
+    }
+
+    public static @NotNull Matrix3 fromRows(@NotNull Vec3 row0, @NotNull Vec3 row1, @NotNull Vec3 row2) {
+        return new Matrix3(
+                row0.x(), row0.y(), row0.z(),
+                row1.x(), row1.y(), row1.z(),
+                row2.x(), row2.y(), row2.z()
+        );
+    }
+
+    public static @NotNull Matrix3 fromColumns(@NotNull Vec3 @NotNull[] cols) {
+        if (cols.length != 3) throw new IllegalArgumentException();
+        return fromColumns(cols[0], cols[1], cols[2]);
+    }
+
+    public static @NotNull Matrix3 fromColumns(@NotNull Vec3 col0, @NotNull Vec3 col1, @NotNull Vec3 col2) {
+        return new Matrix3(
+                col0.x(), col1.x(), col2.x(),
+                col0.y(), col1.y(), col2.y(),
+                col0.z(), col1.z(), col2.z()
+        );
+    }
+
+    public static @NotNull Matrix3 fromArray(double @NotNull[] @NotNull[] array) {
+        return new Matrix3(
+                array[0][0], array[0][1], array[0][2],
+                array[1][0], array[1][1], array[1][2],
+                array[2][0], array[2][1], array[2][2]
+        );
+    }
+
+    public Matrix3() {
+        this(1, 1, 1);
+    }
+
+    public Matrix3(double a11, double a22, double a33) {
+        this(a11, 0, 0, 0, a22, 0, 0, 0, a33);
+    }
+
+    public @NotNull Matrix3 times(@NotNull Matrix3 other) {
+        return new Matrix3(
+                a11 * other.a11 + a12 * other.a21 + a13 * other.a31,
+                a11 * other.a12 + a12 * other.a22 + a13 * other.a32,
+                a11 * other.a13 + a12 * other.a23 + a13 * other.a33,
+                a21 * other.a11 + a22 * other.a21 + a23 * other.a31,
+                a21 * other.a12 + a22 * other.a22 + a23 * other.a32,
+                a21 * other.a13 + a22 * other.a23 + a23 * other.a33,
+                a31 * other.a11 + a32 * other.a21 + a33 * other.a31,
+                a31 * other.a12 + a32 * other.a22 + a33 * other.a32,
+                a31 * other.a13 + a32 * other.a23 + a33 * other.a33
+        );
+    }
+
+    public @NotNull Matrix3 times(double other) {
+        return new Matrix3(
+                a11 * other, a12 * other, a13 * other,
+                a21 * other, a22 * other, a23 * other,
+                a31 * other, a32 * other, a33 * other
+        );
+    }
+
+    public @NotNull Vec3 times(@NotNull Vec3 other) {
+        return new Vec3(
+                a11 * other.x() + a12 * other.y() + a13 * other.z(),
+                a21 * other.x() + a22 * other.y() + a23 * other.z(),
+                a31 * other.x() + a32 * other.y() + a33 * other.z()
+        );
+    }
+
+    public @NotNull Matrix3 plus(@NotNull Matrix3 other) {
+        return new Matrix3(
+                a11 + other.a11, a12 + other.a12, a13 + other.a13,
+                a21 + other.a21, a22 + other.a22, a23 + other.a23,
+                a31 + other.a31, a32 + other.a32, a33 + other.a33
+        );
+    }
+
+    public double det() {
+        return a11 * a22 * a33 + a12 * a23 * a31 + a13 * a21 * a32
+                - a13 * a22 * a31 - a23 * a32 * a11 - a33 * a12 * a21;
+    }
+
+    public @NotNull Matrix3 invert() {
+        var det = det();
+        if (det == 0) throw new IllegalStateException();
+        var t = 1 / det;
+        return new Matrix3(
+                t * (Math.fma( a22, a33, -a23 * a32)),
+                t * (Math.fma(-a12, a33,  a13 * a32)),
+                t * (Math.fma( a12, a23, -a13 * a22)),
+                t * (Math.fma(-a21, a33,  a23 * a31)),
+                t * (Math.fma( a11, a33, -a13 * a31)),
+                t * (Math.fma(-a11, a23,  a13 * a21)),
+                t * (Math.fma( a21, a32, -a22 * a31)),
+                t * (Math.fma(-a11, a32,  a12 * a31)),
+                t * (Math.fma( a11, a22, -a12 * a21))
+        );
+    }
+
+    public @NotNull Vec3 column(int i) {
+        return switch (i) {
+            case 0 -> new Vec3(a11, a21, a31);
+            case 1 -> new Vec3(a12, a22, a32);
+            case 2 -> new Vec3(a13, a23, a33);
+            default -> throw new IndexOutOfBoundsException(i);
+        };
+    }
+
+    public @NotNull Vec3 @NotNull[] columns() {
+        return new Vec3[] {
+                new Vec3(a11, a21, a31),
+                new Vec3(a12, a22, a32),
+                new Vec3(a13, a23, a33)
+        };
+    }
+
+    public @NotNull Vec3 row(int i) {
+        return switch (i) {
+            case 0 -> new Vec3(a11, a12, a13);
+            case 1 -> new Vec3(a21, a22, a23);
+            case 2 -> new Vec3(a31, a32, a33);
+            default -> throw new IndexOutOfBoundsException(i);
+        };
+    }
+
+    public @NotNull Vec3 @NotNull[] rows() {
+        return new Vec3[] {
+                new Vec3(a11, a12, a13),
+                new Vec3(a21, a22, a23),
+                new Vec3(a31, a32, a33)
+        };
+    }
+
+    public double @NotNull[] @NotNull[] toArray() {
+        return new double[][] {
+                {a11, a12, a13},
+                {a21, a22, a23},
+                {a31, a32, a33}
+        };
+    }
+
+    public double get(int i, int j) {
+        Objects.checkIndex(i, 3);
+        Objects.checkIndex(j, 3);
+        var idx = 3 * i + j;
+        return switch (idx) {
+            case 0 -> a11;
+            case 1 -> a12;
+            case 2 -> a13;
+            case 3 -> a21;
+            case 4 -> a22;
+            case 5 -> a23;
+            case 6 -> a31;
+            case 7 -> a32;
+            case 8 -> a33;
+            default -> throw new AssertionError();
+        };
+    }
+
+    /**
+     * Performs lower-upper decomposition with partial pivoting (LUP decomposition) on {@code this} matrix.
+     * @param tolerance a small tolerance number to detect failure when the matrix is near degenerate
+     * @see <a href="https://en.wikipedia.org/w/index.php?title=LU_decomposition&oldid=1213102558#C_code_example">LU decomposition — Wikipedia, The Free Encyclopedia</a>
+     */
+    public @NotNull LUPDecomposition decompose(double tolerance) {
+        // unit permutation matrix
+        var perm = new int[] {0, 1, 2, 3};
+        var A = toArray();
+        var N = 3;
+
+        for (int i = 0; i < N; i++) {
+            double maxA = 0.0;
+            int imax = i;
+
+            for (int k = i; k < N; k++) {
+                double absA = Math.abs(A[k][i]);
+                if (absA > maxA) {
+                    maxA = absA;
+                    imax = k;
+                }
+            }
+
+            if (maxA < tolerance) throw new IllegalArgumentException("matrix is degenerate");
+
+            if (imax != i) {
+                // pivoting P
+                int j = perm[i];
+                perm[i] = perm[imax];
+                perm[imax] = j;
+
+                // pivoting rows of A
+                var ptr = A[i];
+                A[i] = A[imax];
+                A[imax] = ptr;
+
+                // counting pivots starting from N (for determinant)
+                perm[3]++;
+            }
+
+            for (int j = i + 1; j < N; j++) {
+                A[j][i] /= A[i][i];
+
+                for (int k = i + 1; k < N; k++) {
+                    A[j][k] -= A[j][i] * A[i][k];
+                }
+            }
+        }
+
+        return new LUPDecomposition(fromArray(A), perm);
+    }
+
+    public record LUPDecomposition(@NotNull Matrix3 matrix, int @NotNull[] permutation) {
+
+        /**
+         * Solves the equation {@code Ax = b} where {@code A} is the matrix that {@code this} decomposition was derived
+         * from.
+         * @param b the right hand side vector
+         * @return the solution vector
+         */
+        public @NotNull Vec3 solve(@NotNull Vec3 b) {
+            var N = 3;
+            var x = new double[N];
+            for (int i = 0; i < N; i++) {
+                x[i] = b.get(permutation[i]);
+
+                for (int k = 0; k < i; k++) {
+                    x[i] -= matrix.get(i, k) * x[k];
+                }
+            }
+
+            for (int i = N - 1; i >= 0; i--) {
+                for (int k = i + 1; k < N; k++) {
+                    x[i] -= matrix.get(i, k) * x[k];
+                }
+
+                x[i] /= matrix.get(i, i);
+            }
+            return new Vec3(x[0], x[1], x[2]);
+        }
+    }
+}

src/main/java/eu/jonahbauer/raytracing/math/Ray.java

@@ -1,16 +1,97 @@
 package eu.jonahbauer.raytracing.math;
 
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
+import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Objects;
 
-public record Ray(@NotNull Vec3 origin, @NotNull Vec3 direction) {
+public final class Ray {
-    public Ray {
+    private final @NotNull Vec3 origin;
-        Objects.requireNonNull(origin, "origin");
+    private final @NotNull Vec3 direction;
-        Objects.requireNonNull(direction, "direction");
+    private final @NotNull SampledWavelengths lambda;
+
+    private final @NotNull Vec3 inv;
+    private final @NotNull Vec3 negInvOrigin;
+
+    public Ray(@NotNull Vec3 origin, @NotNull Vec3 direction) {
+        this(origin, direction, SampledWavelengths.EMPTY);
+    }
+
+    public Ray(@NotNull Vec3 origin, @NotNull Vec3 direction, @NotNull SampledWavelengths lambda) {
+        this.origin = Objects.requireNonNull(origin, "origin");
+        this.direction = Objects.requireNonNull(direction, "direction");
+        this.lambda = Objects.requireNonNull(lambda, "lambda");
+
+        this.inv = direction.inv();
+        this.negInvOrigin = inv.neg().times(origin);
+    }
+
+    private Ray(@NotNull Vec3 origin, @NotNull Vec3 direction, @NotNull SampledWavelengths lambda, @NotNull Vec3 inv, @NotNull Vec3 negInvOrigin) {
+        this.origin = origin;
+        this.direction = direction;
+        this.lambda = lambda;
+        this.inv = inv;
+        this.negInvOrigin = negInvOrigin;
     }
 
     public @NotNull Vec3 at(double t) {
         return Vec3.fma(t, direction, origin);
     }
+
+    public @NotNull Ray with(@NotNull HitResult hit, @NotNull Vec3 direction) {
+        return new Ray(hit.position(), direction, lambda);
+    }
+
+    public @NotNull Ray with(@NotNull Vec3 origin, @NotNull Vec3 direction) {
+        return new Ray(origin, direction, lambda);
+    }
+
+    public @NotNull Ray with(@NotNull SampledWavelengths lambda) {
+        return new Ray(origin, direction, lambda, inv, negInvOrigin);
+    }
+
+    public @NotNull Vec3 origin() {
+        return origin;
+    }
+
+    public @NotNull Vec3 direction() {
+        return direction;
+    }
+
+    public @NotNull SampledWavelengths lambda() {
+        return lambda;
+    }
+
+    public @NotNull Vec3 getInvDirection() {
+        return inv;
+    }
+
+    public @NotNull Vec3 getNegInvOrigin() {
+        return negInvOrigin;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj == this) return true;
+        if (obj == null || obj.getClass() != this.getClass()) return false;
+        var that = (Ray) obj;
+        return Objects.equals(this.origin, that.origin) &&
+                Objects.equals(this.direction, that.direction) &&
+                Objects.equals(this.lambda, that.lambda);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(origin, direction, lambda);
+    }
+
+    @Override
+    public @NotNull String toString() {
+        return "Ray[" +
+                "origin=" + origin + ", " +
+                "direction=" + direction + ", " +
+                "lambda=" + lambda + ']';
+    }
+
 }

src/main/java/eu/jonahbauer/raytracing/math/Vec3.java

@@ -7,10 +7,8 @@ import java.util.random.RandomGenerator;
 
 import static eu.jonahbauer.raytracing.Main.DEBUG;
 
-public record Vec3(double x, double y, double z) {
+public record Vec3(double x, double y, double z) implements IVec3<Vec3> {
     public static final Vec3 ZERO = new Vec3(0, 0, 0);
-    public static final Vec3 MAX = new Vec3(Double.MAX_VALUE, Double.MAX_VALUE, Double.MAX_VALUE);
-    public static final Vec3 MIN = new Vec3(-Double.MAX_VALUE, -Double.MAX_VALUE, -Double.MAX_VALUE);
     public static final Vec3 UNIT_X = new Vec3(1, 0, 0);
     public static final Vec3 UNIT_Y = new Vec3(0, 1, 0);
     public static final Vec3 UNIT_Z = new Vec3(0, 0, 1);
@@ -62,7 +60,7 @@ public record Vec3(double x, double y, double z) {
      * @return the reflected vector
      */
     public static @NotNull Vec3 reflect(@NotNull Vec3 vec, @NotNull Vec3 normal) {
-        var factor = - 2 * normal.times(vec);
+        var factor = - 2 * normal.dot(vec);
         return Vec3.fma(factor, normal, vec);
     }
 
@@ -75,7 +73,7 @@ public record Vec3(double x, double y, double z) {
      */
     public static @NotNull Optional<Vec3> refract(@NotNull Vec3 vec, @NotNull Vec3 normal, double ri) {
         vec = vec.unit();
-        var cosTheta = Math.min(- vec.times(normal), 1.0);
+        var cosTheta = Math.min(- vec.dot(normal), 1.0);
         var sinTheta = Math.sqrt(1 - cosTheta * cosTheta);
         if (ri * sinTheta > 1) return Optional.empty();
 
@@ -162,10 +160,22 @@ public record Vec3(double x, double y, double z) {
         );
     }
 
+    public static @NotNull Vec3 fma(@NotNull Vec3 a, @NotNull Vec3 b, @NotNull Vec3 c) {
+        return new Vec3(
+                Math.fma(a.x(), b.x(), c.x()),
+                Math.fma(a.y(), b.y(), c.y()),
+                Math.fma(a.z(), b.z(), c.z())
+        );
+    }
+
     public static double tripleProduct(@NotNull Vec3 a, @NotNull Vec3 b, @NotNull Vec3 c) {
         return a.x * b.y * c.z + a.y * b.z * c.x + a.z * b.x * c.y - c.x * b.y * a.z - c.y * b.z * a.x - c.z * b.x * a.y;
     }
 
+    /*
+     * Math
+     */
+
     public @NotNull Vec3 plus(double x, double y, double z) {
         return new Vec3(this.x + x, this.y + y, this.z + z);
     }
@@ -179,6 +189,7 @@ public record Vec3(double x, double y, double z) {
      * @param other a vector
      * @return the sum of this and the other vector
      */
+    @Override
     public @NotNull Vec3 plus(@NotNull Vec3 other) {
         return new Vec3(this.x + other.x, this.y + other.y, this.z + other.z);
     }
@@ -188,49 +199,58 @@ public record Vec3(double x, double y, double z) {
      * @param other a vector
      * @return the difference of this and the other vector
      */
+    @Override
     public @NotNull Vec3 minus(@NotNull Vec3 other) {
         return new Vec3(this.x - other.x, this.y - other.y, this.z - other.z);
     }
 
-    /**
-     * Computes the scalar product of this and another vector
-     * @param other a vector
-     * @return the scalar product
-     */
-    public double times(@NotNull Vec3 other) {
-        return this.x * other.x + this.y * other.y + this.z * other.z;
-    }
-
     /**
      * Multiplies this vector with a scalar
      * @param t a scalar
      * @return the product of this vector and the scalar
      */
+    @Override
     public @NotNull Vec3 times(double t) {
         return new Vec3(this.x * t, this.y * t, this.z * t);
     }
 
     /**
-     * Negates this vector.
+     * Multiplies this vector with another vector component-wise.
-     * {@return the negated vector}
+     * @param other a vector
+     * @return the component-wise product of this vector and the other vector
      */
-    public @NotNull Vec3 neg() {
+    @Override
-        return new Vec3(-x, -y, -z);
+    public @NotNull Vec3 times(@NotNull Vec3 other) {
+        return new Vec3(this.x * other.x, this.y * other.y, this.z * other.z);
     }
 
     /**
-     * Inverts each component of this vector.
+     * Divides this vector by a scalar
-     * @return the inverted vector.
+     * @param t a scalar
+     * @return this vector divided by the scalar
      */
-    public @NotNull Vec3 inv() {
+    @Override
-        return new Vec3(1 / x, 1 / y, 1 / z);
+    public @NotNull Vec3 div(double t) {
+        return times(1 / t);
     }
 
     /**
-     * Computes the cross-product of this and another vector
+     * Computes the scalar product of this and another vector
      * @param other a vector
-     * @return the cross-product
+     * @return the scalar product
      */
+    public double dot(@NotNull Vec3 other) {
+        return this.x * other.x + this.y * other.y + this.z * other.z;
+    }
+
+    public @NotNull Vec3 neg() {
+        return new Vec3(-x, -y, -z);
+    }
+
+    public @NotNull Vec3 inv() {
+        return new Vec3(1 / x, 1 / y, 1 / z);
+    }
+
     public @NotNull Vec3 cross(@NotNull Vec3 other) {
         return new Vec3(
                 Math.fma(this.y, other.z, - other.y * this.z),
@@ -239,15 +259,6 @@ public record Vec3(double x, double y, double z) {
         );
     }
 
-    /**
-     * Divides this vector by a scalar
-     * @param t a scalar
-     * @return this vector divided by the scalar
-     */
-    public @NotNull Vec3 div(double t) {
-        return new Vec3(this.x / t, this.y / t, this.z / t);
-    }
-
     /**
      * {@return the squared length of this vector}
      */
@@ -279,17 +290,28 @@ public record Vec3(double x, double y, double z) {
         return div(Math.sqrt(squared));
     }
 
-    /**
+    /*
-     * {@return the n-th component of this vector}
+     * Accessors
-     * @param axis the component index
      */
-    public double get(int axis) {
+
-        return switch (axis) {
+    @Override
-            case 0 -> x;
+    public double component1() {
-            case 1 -> y;
+        return x;
-            case 2 -> z;
+    }
-            default -> throw new IndexOutOfBoundsException(axis);
+
-        };
+    @Override
+    public double component2() {
+        return y;
+    }
+
+    @Override
+    public double component3() {
+        return z;
+    }
+
+    @Override
+    public @NotNull Vec3 toVec3() {
+        return this;
     }
 
     public @NotNull Vec3 withX(double x) {

src/main/java/eu/jonahbauer/raytracing/render/ImageFormat.java

@@ -1,134 +0,0 @@
-package eu.jonahbauer.raytracing.render;
-
-import eu.jonahbauer.raytracing.render.canvas.Canvas;
-import eu.jonahbauer.raytracing.render.canvas.Image;
-import org.jetbrains.annotations.NotNull;
-
-import java.io.*;
-import java.nio.charset.StandardCharsets;
-import java.nio.file.Files;
-import java.nio.file.Path;
-import java.util.zip.CRC32;
-import java.util.zip.CheckedOutputStream;
-import java.util.zip.DeflaterOutputStream;
-import java.util.zip.InflaterInputStream;
-
-public enum ImageFormat {
-    PPM {
-        @Override
-        public void write(@NotNull Canvas image, @NotNull OutputStream out) throws IOException {
-            try (var writer = new BufferedWriter(new OutputStreamWriter(out, StandardCharsets.US_ASCII))) {
-                writer.write("P3\n");
-                writer.write(String.valueOf(image.getWidth()));
-                writer.write(" ");
-                writer.write(String.valueOf(image.getHeight()));
-                writer.write("\n255\n");
-
-                var it = image.pixels().iterator();
-                while (it.hasNext()) {
-                    var color = it.next();
-                    writer.write(String.valueOf(color.red()));
-                    writer.write(" ");
-                    writer.write(String.valueOf(color.green()));
-                    writer.write(" ");
-                    writer.write(String.valueOf(color.blue()));
-                    writer.write("\n");
-                }
-            }
-        }
-    },
-    PNG {
-        private static final byte[] MAGIC = new byte[] { (byte) 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
-        private static final int IHDR_LENGTH = 13;
-        private static final int IHDR_TYPE = 0x49484452;
-        private static final int IDAT_TYPE = 0x49444154;
-        private static final int IEND_TYPE = 0x49454E44;
-        private static final int IEND_CRC = 0xAE426082;
-
-        @Override
-        public void write(@NotNull Canvas image, @NotNull OutputStream out) throws IOException {
-            try (var data = new NoCloseDataOutputStream(out); var _ = data.closeable()) {
-                data.write(MAGIC);
-
-                writeIHDR(image, data);
-                writeIDAT(image, data);
-                writeIEND(image, data);
-            }
-        }
-
-        private void writeIHDR(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
-            data.writeInt(IHDR_LENGTH);
-            try (
-                    var crc = new CheckedOutputStream(data, new CRC32());
-                    var ihdr = new DataOutputStream(crc)
-            ) {
-                ihdr.writeInt(IHDR_TYPE);
-                ihdr.writeInt(image.getWidth()); // image width
-                ihdr.writeInt(image.getHeight()); // image height
-                ihdr.writeByte(8); // bit depth
-                ihdr.writeByte(2); // color type
-                ihdr.writeByte(0); // compression method
-                ihdr.writeByte(0); // filter method
-                ihdr.writeByte(0); // interlace method
-                ihdr.flush();
-                data.writeInt((int) crc.getChecksum().getValue());
-            }
-        }
-
-        private void writeIDAT(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
-            try (
-                    var baos = new ByteArrayOutputStream();
-                    var crc = new CheckedOutputStream(baos, new CRC32());
-                    var idat = new DataOutputStream(crc)
-            ) {
-                idat.writeInt(IDAT_TYPE);
-
-                try (var deflate = new DataOutputStream(new DeflaterOutputStream(idat))) {
-                    var pixels = image.pixels().iterator();
-                    for (int i = 0; pixels.hasNext(); i = (i + 1) % image.getWidth()) {
-                        if (i == 0) deflate.writeByte(0); // filter type
-                        var pixel = pixels.next();
-                        deflate.writeByte(pixel.red());
-                        deflate.writeByte(pixel.green());
-                        deflate.writeByte(pixel.blue());
-                    }
-                }
-
-                var bytes = baos.toByteArray();
-                data.writeInt(bytes.length - 4); // don't include type in length
-                data.write(bytes);
-                data.writeInt((int) crc.getChecksum().getValue());
-            }
-        }
-
-        private void writeIEND(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
-            data.writeInt(0);
-            data.writeInt(IEND_TYPE);
-            data.writeInt(IEND_CRC);
-        }
-
-        private static class NoCloseDataOutputStream extends DataOutputStream {
-            public NoCloseDataOutputStream(OutputStream out) {
-                super(out);
-            }
-
-            @Override
-            public void close() {
-                // do nothing
-            }
-
-            public Closeable closeable() {
-                return super::close;
-            }
-        }
-    },
-    ;
-
-    public void write(@NotNull Canvas image, @NotNull Path path) throws IOException {
-        try (var out = Files.newOutputStream(path)) {
-            write(image, out);
-        }
-    }
-
-    public abstract void write(@NotNull Canvas image, @NotNull OutputStream out) throws IOException;
-}

src/main/java/eu/jonahbauer/raytracing/render/canvas/Canvas.java

@@ -1,22 +1,37 @@
 package eu.jonahbauer.raytracing.render.canvas;
 
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.function.Function;
-import java.util.stream.IntStream;
-import java.util.stream.Stream;
-
 public interface Canvas {
+    /**
+     * {@return the width of this canvas}
+     */
     int getWidth();
+
+    /**
+     * {@return the height of this canvas}
+     */
     int getHeight();
 
-    void set(int x, int y, @NotNull Color color);
+    /**
-    @NotNull Color get(int x, int y);
+     * Adds a sample to this canvas
+     * @param x the pixel x coordinate
+     * @param y the pixel y coordinate
+     * @param n the index of the sample
+     * @param spectrum the sampled spectrum
+     * @param lambda the sampled wavelengths
+     */
+    void add(int x, int y, int n, @NotNull SampledSpectrum spectrum, @NotNull SampledWavelengths lambda);
 
-    default @NotNull Stream<Color> pixels() {
+    /**
-        return IntStream.range(0, getHeight())
+     * {@return the color at a given pixel}
-                .mapToObj(y -> IntStream.range(0, getWidth()).mapToObj(x -> get(x, y)))
+     * @param x the pixel x coordinate
-                .flatMap(Function.identity());
+     * @param y the pixel y coordinate
-    }
+     * @param cs the color space of the output
+     */
+    @NotNull ColorRGB getRGB(int x, int y, @NotNull ColorSpace cs);
 }

src/main/java/eu/jonahbauer/raytracing/render/canvas/Image.java

@@ -1,58 +0,0 @@
-package eu.jonahbauer.raytracing.render.canvas;
-
-import eu.jonahbauer.raytracing.render.texture.Color;
-import org.jetbrains.annotations.NotNull;
-
-import java.awt.image.BufferedImage;
-import java.util.Objects;
-
-public final class Image implements Canvas {
-    private final int width;
-    private final int height;
-
-    private final Color[][] data;
-
-    public Image(int width, int height) {
-        this.width = width;
-        this.height = height;
-
-        if (width <= 0) throw new IllegalArgumentException("width must be positive");
-        if (height <= 0) throw new IllegalArgumentException("height must be positive");
-
-        this.data = new Color[height][width];
-    }
-
-    public Image(@NotNull BufferedImage image) {
-        this(image.getWidth(), image.getHeight());
-
-        for (int y = 0; y < height; y++) {
-            for (int x = 0; x < width; x++) {
-                this.data[y][x] = new Color(image.getRGB(x, y));
-            }
-        }
-    }
-
-    @Override
-    public int getWidth() {
-        return width;
-    }
-
-    @Override
-    public int getHeight() {
-        return height;
-    }
-
-    @Override
-    public @NotNull Color get(int x, int y) {
-        Objects.checkIndex(x, width);
-        Objects.checkIndex(y, height);
-        return Objects.requireNonNullElse(this.data[y][x], Color.BLACK);
-    }
-
-    @Override
-    public void set(int x, int y, @NotNull Color color) {
-        Objects.checkIndex(x, width);
-        Objects.checkIndex(y, height);
-        this.data[y][x] = Objects.requireNonNull(color);
-    }
-}

src/main/java/eu/jonahbauer/raytracing/render/canvas/LiveCanvas.java

@@ -1,6 +1,9 @@
 package eu.jonahbauer.raytracing.render.canvas;
 
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
 import org.jetbrains.annotations.NotNull;
 
 import javax.swing.*;
@@ -12,10 +15,12 @@ import java.awt.image.BufferedImage;
 public final class LiveCanvas implements Canvas {
     private final @NotNull Canvas delegate;
     private final @NotNull BufferedImage image;
+    private final @NotNull ColorSpace cs;
 
-    public LiveCanvas(@NotNull Canvas delegate) {
+    public LiveCanvas(@NotNull Canvas delegate, @NotNull ColorSpace cs) {
         this.delegate = delegate;
         this.image = new BufferedImage(delegate.getWidth(), delegate.getHeight(), BufferedImage.TYPE_INT_RGB);
+        this.cs = cs;
     }
 
     @Override
@@ -29,15 +34,16 @@ public final class LiveCanvas implements Canvas {
     }
 
     @Override
-    public void set(int x, int y, @NotNull Color color) {
+    public void add(int x, int y, int n, @NotNull SampledSpectrum spectrum, @NotNull SampledWavelengths lambda) {
-        delegate.set(x, y, color);
+        delegate.add(x, y, n, spectrum, lambda);
+        var color = cs.encode(delegate.getRGB(x, y, cs));
         var rgb = color.red() << 16 | color.green() << 8 | color.blue();
         image.setRGB(x, y, rgb);
     }
 
     @Override
-    public @NotNull Color get(int x, int y) {
+    public @NotNull ColorRGB getRGB(int x, int y, @NotNull ColorSpace cs) {
-        return delegate.get(x, y);
+        return delegate.getRGB(x, y, cs);
     }
 
     public @NotNull Thread preview() {

src/main/java/eu/jonahbauer/raytracing/render/canvas/RGBCanvas.java

@@ -0,0 +1,76 @@
+package eu.jonahbauer.raytracing.render.canvas;
+
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import org.jetbrains.annotations.NotNull;
+
+import java.awt.image.BufferedImage;
+import java.util.Objects;
+
+public final class RGBCanvas implements Canvas {
+    private final int width;
+    private final int height;
+
+    private final @NotNull ColorSpace cs;
+    private final @NotNull ColorRGB[][] data;
+
+    public RGBCanvas(int width, int height, @NotNull ColorSpace cs) {
+        this.width = width;
+        this.height = height;
+        this.cs = Objects.requireNonNull(cs);
+
+        if (width <= 0) throw new IllegalArgumentException("width must be positive");
+        if (height <= 0) throw new IllegalArgumentException("height must be positive");
+
+        this.data = new ColorRGB[height][width];
+    }
+
+    public RGBCanvas(@NotNull BufferedImage image, @NotNull ColorSpace cs) {
+        this(image.getWidth(), image.getHeight(), cs);
+
+        for (int y = 0; y < height; y++) {
+            for (int x = 0; x < width; x++) {
+                this.data[y][x] = new ColorRGB(image.getRGB(x, y));
+            }
+        }
+    }
+
+    @Override
+    public int getWidth() {
+        return width;
+    }
+
+    @Override
+    public int getHeight() {
+        return height;
+    }
+
+    @Override
+    public void add(int x, int y, int n, @NotNull SampledSpectrum spectrum, @NotNull SampledWavelengths lambda) {
+        assert x < width;
+        assert y < height;
+
+        var rgb = spectrum.toRGB(lambda, cs);
+        data[y][x] = ColorRGB.average(data[y][x], rgb, n);
+    }
+
+    @Override
+    public @NotNull ColorRGB getRGB(int x, int y, @NotNull ColorSpace cs) {
+        if (cs == this.cs) return get(x, y);
+        return cs.toRGB(this.cs.toXYZ(get(x, y)));
+    }
+
+    public @NotNull ColorRGB get(int x, int y) {
+        assert x < width;
+        assert y < height;
+        return Objects.requireNonNullElse(data[y][x], ColorRGB.BLACK);
+    }
+
+    public void set(int x, int y, @NotNull ColorRGB color) {
+        assert x < width;
+        assert y < height;
+        data[y][x] = Objects.requireNonNull(color);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/canvas/XYZCanvas.java

@@ -0,0 +1,74 @@
+package eu.jonahbauer.raytracing.render.canvas;
+
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.ColorXYZ;
+import org.jetbrains.annotations.NotNull;
+
+import java.awt.image.BufferedImage;
+import java.util.Objects;
+
+public final class XYZCanvas implements Canvas {
+    private final int width;
+    private final int height;
+
+    private final @NotNull ColorXYZ[][] data;
+
+    public XYZCanvas(int width, int height) {
+        this.width = width;
+        this.height = height;
+
+        if (width <= 0) throw new IllegalArgumentException("width must be positive");
+        if (height <= 0) throw new IllegalArgumentException("height must be positive");
+
+        this.data = new ColorXYZ[height][width];
+    }
+
+    public XYZCanvas(@NotNull BufferedImage image, @NotNull ColorSpace cs) {
+        this(image.getWidth(), image.getHeight());
+
+        for (int y = 0; y < height; y++) {
+            for (int x = 0; x < width; x++) {
+                data[y][x] = cs.toXYZ(new ColorRGB(image.getRGB(x, y)));
+            }
+        }
+    }
+
+    @Override
+    public int getWidth() {
+        return width;
+    }
+
+    @Override
+    public int getHeight() {
+        return height;
+    }
+
+    @Override
+    public void add(int x, int y, int n, @NotNull SampledSpectrum spectrum, @NotNull SampledWavelengths lambda) {
+        assert x < width;
+        assert y < height;
+
+        var xyz = spectrum.toXYZ(lambda);
+        data[y][x] = ColorXYZ.average(get(x, y), xyz, n);
+    }
+
+    public @NotNull ColorXYZ get(int x, int y) {
+        assert x < width;
+        assert y < height;
+        return Objects.requireNonNullElse(data[y][x], ColorXYZ.BLACK);
+    }
+
+    @Override
+    public @NotNull ColorRGB getRGB(int x, int y, @NotNull ColorSpace cs) {
+        return cs.toRGB(get(x, y));
+    }
+
+    public void set(int x, int y, @NotNull ColorXYZ color) {
+        assert x < width;
+        assert y < height;
+        data[y][x] = Objects.requireNonNull(color);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/Chromaticity.java

@@ -0,0 +1,9 @@
+package eu.jonahbauer.raytracing.render.color;
+
+/**
+ * A pair of chromaticity coordinates in the xyY color space
+ * @param x the x coordinate
+ * @param y the y coordinate
+ */
+public record Chromaticity(double x, double y) {
+}

src/main/java/eu/jonahbauer/raytracing/render/color/ColorRGB.java

@@ -0,0 +1,115 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.math.IVec3;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Random;
+
+public record ColorRGB(double r, double g, double b) implements IVec3<ColorRGB> {
+    public static final @NotNull ColorRGB BLACK = new ColorRGB(0.0, 0.0, 0.0);
+    public static final @NotNull ColorRGB WHITE = new ColorRGB(1.0, 1.0, 1.0);
+
+    public static @NotNull ColorRGB random(@NotNull Random random) {
+        return new ColorRGB(random.nextDouble(), random.nextDouble(), random.nextDouble());
+    }
+
+    public static @NotNull ColorRGB random(@NotNull Random random, double min, double max) {
+        var span = max - min;
+        return new ColorRGB(
+                Math.fma(random.nextDouble(), span, min),
+                Math.fma(random.nextDouble(), span, min),
+                Math.fma(random.nextDouble(), span, min)
+        );
+    }
+
+    public ColorRGB(int rgb) {
+        this(((rgb >> 16) & 0xFF) / 255d, ((rgb >> 8) & 0xFF) / 255d, (rgb & 0xFF) / 255d);
+    }
+
+    public ColorRGB {
+        assert Double.isFinite(r) : "r must be finite";
+        assert Double.isFinite(g) : "g must be finite";
+        assert Double.isFinite(b) : "b must be finite";
+    }
+
+    /*
+     * Math
+     */
+
+    public static @NotNull ColorRGB average(@NotNull ColorRGB current, @NotNull ColorRGB next, int index) {
+        return lerp(current, next, 1d / index);
+    }
+
+    public static @NotNull ColorRGB lerp(@NotNull ColorRGB a, @NotNull ColorRGB b, double t) {
+        if (t < 0) return a;
+        if (t > 1) return b;
+        return new ColorRGB(
+                Math.fma(t, b.r - a.r, a.r),
+                Math.fma(t, b.g - a.g, a.g),
+                Math.fma(t, b.b - a.b, a.b)
+        );
+    }
+
+    public static @NotNull ColorRGB fma(@NotNull ColorRGB a, @NotNull ColorRGB b, @NotNull ColorRGB c) {
+        return new ColorRGB(
+                Math.fma(a.r, b.r, c.r),
+                Math.fma(a.g, b.g, c.g),
+                Math.fma(a.b, b.b, c.b)
+        );
+    }
+
+    @Override
+    public @NotNull ColorRGB plus(@NotNull ColorRGB other) {
+        return new ColorRGB(r + other.r, g + other.g, b + other.b);
+    }
+
+    @Override
+    public @NotNull ColorRGB minus(@NotNull ColorRGB other) {
+        return new ColorRGB(r - other.r, g - other.g, b - other.b);
+    }
+
+    @Override
+    public @NotNull ColorRGB times(double d) {
+        return new ColorRGB(r * d, g * d, b * d);
+    }
+
+    @Override
+    public @NotNull ColorRGB times(@NotNull ColorRGB other) {
+        return new ColorRGB(r * other.r, g * other.g, b * other.b);
+    }
+
+    /*
+     * Accessors
+     */
+
+    public int red() {
+        return toInt(r);
+    }
+
+    public int green() {
+        return toInt(g);
+    }
+
+    public int blue() {
+        return toInt(b);
+    }
+
+    private static int toInt(double value) {
+        return Math.clamp((int) (255.99 * value), 0, 255);
+    }
+
+    @Override
+    public double component1() {
+        return r;
+    }
+
+    @Override
+    public double component2() {
+        return g;
+    }
+
+    @Override
+    public double component3() {
+        return b;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/ColorSpace.java

@@ -0,0 +1,164 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.math.Matrix3;
+import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.spectrum.*;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Objects;
+
+/**
+ * An RGB color space.
+ */
+public final class ColorSpace {
+    private final @NotNull Chromaticity r;
+    private final @NotNull Chromaticity g;
+    private final @NotNull Chromaticity b;
+    private final @NotNull Chromaticity w;
+    private final @NotNull DenselySampledSpectrum illuminant;
+
+    private final @NotNull ColorXYZ R;
+    private final @NotNull ColorXYZ G;
+    private final @NotNull ColorXYZ B;
+    private final @NotNull ColorXYZ W;
+
+    private final @NotNull Matrix3 XYZfromRGB;
+    private final @NotNull Matrix3 RGBfromXYZ;
+    private final @NotNull SpectrumTable RGBtoSpectrumTable;
+    private final @NotNull TransferFunction transferFunction;
+
+    public ColorSpace(
+            @NotNull Chromaticity r, @NotNull Chromaticity g, @NotNull Chromaticity b,
+            @NotNull Spectrum illuminant, @NotNull SpectrumTable table, @NotNull TransferFunction transferFunction
+    ) {
+        this.r = Objects.requireNonNull(r, "r");
+        this.g = Objects.requireNonNull(g, "g");
+        this.b = Objects.requireNonNull(b, "b");
+        this.illuminant = new DenselySampledSpectrum(illuminant);
+        this.RGBtoSpectrumTable = table; // no null-check
+        this.transferFunction = transferFunction; // no null-check
+
+        this.W = illuminant.toXYZ();
+        this.w = W.xy();
+
+        this.R = new ColorXYZ(r);
+        this.G = new ColorXYZ(g);
+        this.B = new ColorXYZ(b);
+        var rgb = new Matrix3(
+                R.x(), G.x(), B.x(),
+                R.y(), G.y(), B.y(),
+                R.z(), G.z(), B.z()
+        );
+        var C = rgb.invert().times(W.toVec3());
+
+        this.XYZfromRGB = rgb.times(new Matrix3(C.x(), C.y(), C.z()));
+        this.RGBfromXYZ = XYZfromRGB.invert();
+    }
+
+    /*
+     * Conversions
+     */
+
+    public @NotNull ColorRGB toRGB(@NotNull ColorXYZ xyz) {
+        var out = RGBfromXYZ.times(xyz.toVec3());
+        return new ColorRGB(out.x(), out.y(), out.z());
+    }
+
+    public @NotNull ColorXYZ toXYZ(@NotNull ColorRGB rgb) {
+        var out = XYZfromRGB.times(rgb.toVec3());
+        return new ColorXYZ(out);
+    }
+
+    public @NotNull Vec3 toCIELab(@NotNull ColorRGB rgb) {
+        return toCIELab(toXYZ(rgb));
+    }
+
+    public @NotNull Vec3 toCIELab(@NotNull ColorXYZ xyz) {
+        return new Vec3(
+                116 * cieLabCbrt(xyz.y() / W.y()) - 16,
+                500 * (cieLabCbrt(xyz.x() / W.x()) - cieLabCbrt(xyz.y() / W.y())),
+                200 * (cieLabCbrt(xyz.y() / W.y()) - cieLabCbrt(xyz.z() / W.z()))
+        );
+    }
+
+    private static double cieLabCbrt(double x) {
+        var delta = 6.0 / 29.0;
+        if (x > delta * delta * delta) {
+            return Math.cbrt(x);
+        } else {
+            return x / (delta * delta * 3.0) + (4.0 / 29.0);
+        }
+    }
+
+    public @NotNull ColorRGB encode(@NotNull ColorRGB rgb) {
+        return transferFunction.encode(rgb);
+    }
+
+    public @NotNull ColorRGB decode(@NotNull ColorRGB rgb) {
+        return transferFunction.decode(rgb);
+    }
+
+    /*
+     * Spectrum
+     */
+
+    public @NotNull SigmoidPolynomial toPolynomial(@NotNull ColorRGB rgb) {
+        return RGBtoSpectrumTable.get(new ColorRGB(
+                Math.max(0, rgb.r()),
+                Math.max(0, rgb.g()),
+                Math.max(0, rgb.b())
+        ));
+    }
+
+    public @NotNull Spectrum toSpectrum(@NotNull ColorRGB rgb, @NotNull Spectrum.Type type) {
+        return switch (type) {
+            case ALBEDO -> new RGBAlbedoSpectrum(this, rgb);
+            case ILLUMINANT -> new RGBIlluminantSpectrum(this, rgb);
+            case UNBOUNDED -> new RGBUnboundedSpectrum(this, rgb);
+        };
+    }
+
+    public @NotNull Spectrum albedo(double r, double g, double b) {
+        return albedo(new ColorRGB(r, g, b));
+    }
+
+    public @NotNull Spectrum albedo(@NotNull ColorRGB rgb) {
+        return toSpectrum(rgb, Spectrum.Type.ALBEDO);
+    }
+
+    public @NotNull Spectrum illuminant(double intensity) {
+        return illuminant.scale(intensity);
+    }
+
+    public @NotNull Spectrum illuminant(double r, double g, double b) {
+        return illuminant(new ColorRGB(r, g, b));
+    }
+
+    public @NotNull Spectrum illuminant(@NotNull ColorRGB rgb) {
+        return toSpectrum(rgb, Spectrum.Type.ILLUMINANT);
+    }
+
+    /*
+     * Accessors
+     */
+
+    public @NotNull Chromaticity r() {
+        return r;
+    }
+
+    public @NotNull Chromaticity g() {
+        return g;
+    }
+
+    public @NotNull Chromaticity b() {
+        return b;
+    }
+
+    public @NotNull Chromaticity w() {
+        return w;
+    }
+
+    public @NotNull DenselySampledSpectrum illuminant() {
+        return illuminant;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/ColorSpaces.java

@@ -0,0 +1,44 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+import java.io.UncheckedIOException;
+import java.util.Objects;
+
+public final class ColorSpaces {
+    // Rec. ITU-R BT.709.3
+    public static final @NotNull ColorSpace sRGB = new ColorSpace(
+            new Chromaticity(0.6400, 0.3300),
+            new Chromaticity(0.3000, 0.6000),
+            new Chromaticity(0.1500, 0.0600),
+            Spectra.D65, read("sRGB_spectrum.bin"), TransferFunctions.sRGB
+    );
+    // P3-D65 (display)
+    public static final @NotNull ColorSpace DCI_P3 = new ColorSpace(
+            new Chromaticity(0.680, 0.320),
+            new Chromaticity(0.265, 0.690),
+            new Chromaticity(0.150, 0.060),
+            Spectra.D65, read("DCI_P3_spectrum.bin"), TransferFunctions.sRGB
+    );
+    // ITU-R Rec BT.2020
+    public static final @NotNull ColorSpace Rec2020 = new ColorSpace(
+            new Chromaticity(0.708, 0.292),
+            new Chromaticity(0.170, 0.797),
+            new Chromaticity(0.131, 0.046),
+            Spectra.D65, read("Rec2020_spectrum.bin"), null
+    );
+
+    private static @NotNull SpectrumTable read(@NotNull String name) {
+        try (var in = ColorSpaces.class.getResourceAsStream("/eu/jonahbauer/raytracing/colorspace/" + name)) {
+            return SpectrumTable.read(Objects.requireNonNull(in));
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
+    }
+
+    private ColorSpaces() {
+        throw new UnsupportedOperationException();
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/ColorXYZ.java

@@ -0,0 +1,111 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.math.IVec3;
+import eu.jonahbauer.raytracing.math.Vec3;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A CIE XYZ color
+ */
+public record ColorXYZ(double x, double y, double z) implements IVec3<ColorXYZ> {
+    public static final double CIE_Y_INTEGRAL = 106.85689500000002;
+
+    public static final @NotNull ColorXYZ BLACK = new ColorXYZ(0, 0, 0);
+    public static final @NotNull ColorXYZ WHITE = new ColorXYZ(0, 1, 0);
+
+    public ColorXYZ(@NotNull Chromaticity chromaticity) {
+        this(chromaticity, 1);
+    }
+
+    public ColorXYZ(@NotNull Chromaticity chromaticity, double Y) {
+        this(
+                chromaticity.y() == 0 ? 0 : Y * chromaticity.x() / chromaticity.y(),
+                chromaticity.y() == 0 ? 0 : Y,
+                chromaticity.y() == 0 ? 0 : Y * (1 - chromaticity.x() - chromaticity.y()) / chromaticity.y()
+        );
+    }
+
+    public ColorXYZ(@NotNull Vec3 vec) {
+        this(vec.x(), vec.y(), vec.z());
+    }
+
+    public ColorXYZ {
+        assert Double.isFinite(x) : "x must be finite";
+        assert Double.isFinite(y) : "y must be finite";
+        assert Double.isFinite(z) : "z must be finite";
+    }
+
+    /*
+     * Math
+     */
+
+    public static @NotNull ColorXYZ average(@NotNull ColorXYZ a, @NotNull ColorXYZ b, int index) {
+        return lerp(a, b, 1d / index);
+    }
+
+    public static @NotNull ColorXYZ lerp(@NotNull ColorXYZ a, @NotNull ColorXYZ b, double t) {
+        if (t < 0) return a;
+        if (t > 1) return b;
+        return new ColorXYZ(
+                Math.fma(t, b.x - a.x, a.x),
+                Math.fma(t, b.y - a.y, a.y),
+                Math.fma(t, b.z - a.z, a.z)
+        );
+    }
+
+    public static @NotNull ColorXYZ fma(@NotNull ColorXYZ a, @NotNull ColorXYZ b, @NotNull ColorXYZ c) {
+        return new ColorXYZ(
+                Math.fma(a.x, b.x, c.x),
+                Math.fma(a.y, b.y, c.y),
+                Math.fma(a.z, b.z, c.z)
+        );
+    }
+
+    @Override
+    public @NotNull ColorXYZ plus(@NotNull ColorXYZ other) {
+        return new ColorXYZ(x + other.x, y + other.y, z + other.z);
+    }
+
+    @Override
+    public @NotNull ColorXYZ minus(@NotNull ColorXYZ other) {
+        return new ColorXYZ(x - other.x, y - other.y, z - other.z);
+    }
+
+    @Override
+    public @NotNull ColorXYZ times(@NotNull ColorXYZ other) {
+        return new ColorXYZ(x * other.x, y * other.y, z * other.z);
+    }
+
+    @Override
+    public @NotNull ColorXYZ times(double d) {
+        return new ColorXYZ(x * d, y * d, z * d);
+    }
+
+    /*
+     * Accessors
+     */
+
+    public double average() {
+        return (x + y + z) / 3;
+    }
+
+    public @NotNull Chromaticity xy() {
+        var factor = 1 / (x + y + z);
+        return new Chromaticity(factor * x, factor * y);
+    }
+
+    @Override
+    public double component1() {
+        return x;
+    }
+
+    @Override
+    public double component2() {
+        return y;
+    }
+
+    @Override
+    public double component3() {
+        return z;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/SigmoidPolynomial.java

@@ -0,0 +1,34 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
+
+/**
+ * A function of the form {@code s(p(x))} where {@code p} is a polynomial of second degree and {@code s} is the sigmoid
+ * function <code>s(x) = 0.5 + x / (2 * sqrt(1 + x^2))</code>.
+ * <p>
+ * A function of this form is used to generate a {@link Spectrum} from an RGB value.
+ *
+ * @param c0 the coefficient of the quadratic term
+ * @param c1 the coefficient of the linear term
+ * @param c2 the coefficient of the constant term
+ */
+public record SigmoidPolynomial(double c0, double c1, double c2) {
+
+    public double get(double x) {
+        var p = Math.fma(Math.fma(c0, x, c1), x, c2);
+        if (!Double.isFinite(p)) return p > 0 ? 1 : 0;
+        return Math.fma(.5 * p, 1 / Math.sqrt(Math.fma(p, p, 1)), .5);
+    }
+
+    public double max() {
+        // evaluate at the edges
+        var result = Math.max(get(Spectrum.LAMBDA_MIN), get(Spectrum.LAMBDA_MAX));
+        var lambda = -c1 / (2 * c0);
+        if (lambda >= 360 && lambda <= 830) {
+            // evaluate at the vertex
+            return Math.max(result, get(lambda));
+        } else {
+            return result;
+        }
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/SpectrumTable.java

@@ -0,0 +1,142 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.io.*;
+import java.util.Arrays;
+
+/**
+ * A table of sigmoid polynomials used to convert between RGB values and spectra.
+ * <p>
+ * The rgb values are renormalized to xyz coordinates with {@code z} being the largest of the rgb components, and
+ * {@code x} and {@code y} being the other two rgb components divided by {@code z}. By this construction, {@code x},
+ * {@code y} and {@code z} are all in the range [0, 1] which allows for better use of the samples in a fixed grid.
+ * The {@code z} coordinate is additionally remapped using {@link #zNodes} to improve sampling at both ends of the scale.
+ * <p>
+ * The coefficients of the sigmoid functions are stored in a flattened five-dimensional array with indices as described
+ * in {@link #coefficients}.
+ */
+public final class SpectrumTable {
+    private final int resolution;
+
+    /**
+     * the remapped {@code z} values
+     */
+    private final double[] zNodes;
+
+    /**
+     * the stored coefficients as a flattened five-dimensional array with the following indices
+     * <ol>
+     *     <li>the component index of the biggest rgb component</li>
+     *     <li>the {@code z} coordinate</li>
+     *     <li>the {@code y} coordinate</li>
+     *     <li>the {@code x} coordinate</li>
+     *     <li>the coefficient index</li>
+     * </ol>
+     */
+    private final double[] coefficients;
+
+    public static void write(@NotNull SpectrumTable table, @NotNull OutputStream out) throws IOException {
+        var dos = new DataOutputStream(out);
+        dos.writeInt(table.resolution);
+        for (double z : table.zNodes) {
+            dos.writeDouble(z);
+        }
+        for (double c : table.coefficients) {
+            dos.writeDouble(c);
+        }
+        dos.flush();
+    }
+
+    public static @NotNull SpectrumTable read(@NotNull InputStream in) throws IOException {
+        var dis = new DataInputStream(in);
+        var resolution = dis.readInt();
+        var nodes = new double[resolution];
+        for (int i = 0; i < resolution; i++) {
+            nodes[i] = dis.readDouble();
+        }
+        var table = new double[3 * resolution * resolution * resolution * 3];
+        for (int i = 0; i < table.length; i++) {
+            table[i] = dis.readDouble();
+        }
+        return new SpectrumTable(resolution, nodes, table);
+    }
+
+    SpectrumTable(int resolution, double @NotNull[] zNodes, double[] coefficients) {
+        this.resolution = resolution;
+        this.zNodes = zNodes;
+        this.coefficients = coefficients;
+
+        // check input array lengths
+        if (zNodes.length != resolution) {
+            throw new IllegalArgumentException("length of zNodes must be equal to the RESOLUTION");
+        }
+        if (coefficients.length != 3 * resolution * resolution * resolution * 3) {
+            throw new IllegalArgumentException("coefficients length must be 3 * RESOLUTION * RESOLUTION * RESOLUTION * 3");
+        }
+        // check ascending zNodes
+        for (int i = 1; i < resolution; i++) {
+            if (zNodes[i - 1] >= zNodes[i]) {
+                throw new IllegalArgumentException("zNodes must be in increasing order");
+            }
+        }
+        if (zNodes[0] != 0.0 || zNodes[zNodes.length - 1] != 1.0) {
+            throw new IllegalArgumentException("zNodes must start with 0.0 and end with 1.0");
+        }
+    }
+
+    public @NotNull SigmoidPolynomial get(@NotNull ColorRGB color) {
+        // handle uniform rgb values
+        if (color.r() == color.g() && color.g() == color.b()) {
+            return new SigmoidPolynomial(0, 0, (color.r() - .5) / Math.sqrt(color.r() * (1 - color.r())));
+        }
+
+        // find maximum component and compute remapped component values
+        var max = color.r() > color.g()
+                ? (color.r() > color.b() ? 0 : 2)
+                : (color.g() > color.b() ? 1 : 2);
+
+        var z = color.get(max);
+        var x = color.get((max + 1) % 3) * (resolution - 1) / z;
+        var y = color.get((max + 2) % 3) * (resolution - 1) / z;
+
+        // compute integer indices and offsets for coefficient interpolation
+        int xi = Math.min((int) x, resolution - 2);
+        int yi = Math.min((int) y, resolution - 2);
+        int zi = Arrays.binarySearch(zNodes, z);
+        if (zi < 0) {
+            zi = -zi - 2;
+        } else if (zi > 0) {
+            zi = zi - 1;
+        }
+
+        var dx = x - xi;
+        var dy = y -yi;
+        var dz = (z - zNodes[zi]) / (zNodes[zi + 1] - zNodes[zi]);
+
+        // trilinearly interpolate sigmoid polynomial coefficients
+        var c = new double[3];
+        for (int i = 0; i < 3; i++) {
+            c[i] = lerp(dz,
+                        lerp(dy,
+                             lerp(dx, get(max, zi + 0, yi + 0, xi + 0, i), get(max, zi + 0, yi + 0, xi + 1, i)),
+                             lerp(dx, get(max, zi + 0, yi + 1, xi + 0, i), get(max, zi + 0, yi + 1, xi + 1, i))
+                        ),
+                        lerp(dy,
+                             lerp(dx, get(max, zi + 1, yi + 0, xi + 0, i), get(max, zi + 1, yi + 0, xi + 1, i)),
+                             lerp(dx, get(max, zi + 1, yi + 1, xi + 0, i), get(max, zi + 1, yi + 1, xi + 1, i))
+                        )
+            );
+        }
+
+        return new SigmoidPolynomial(c[0], c[1], c[2]);
+    }
+
+    private double get(int l, int z, int y, int x, int i) {
+        return coefficients[(((l * resolution + z) * resolution + y) * resolution + x) * 3 + i];
+    }
+
+    private static double lerp(double t, double a, double b) {
+        return Math.fma(t, b, Math.fma(-t, a, a));
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/SpectrumTableGenerator.java

@@ -0,0 +1,204 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import eu.jonahbauer.raytracing.math.Matrix3;
+import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.stream.IntStream;
+
+/**
+ * Generates a lookup table for RGB to spectrum conversion.
+ * <p>
+ * The spectrum for each RGB value is a {@link SigmoidPolynomial} with coefficients such that the round trip error
+ * from converting the RGB value to a spectrum and back is minimized.
+ * <p>
+ * <img src="doc-files/rgb2spectrum.png">
+ */
+public final class SpectrumTableGenerator {
+    private static final double EPSILON = 1e-4;
+    private static final int ITERATIONS = 15;
+
+    private final int resolution = 64;
+    private final @NotNull ColorSpace cs;
+
+    public static void main(String[] args) throws IOException {
+        var generator = new SpectrumTableGenerator(ColorSpaces.DCI_P3);
+        var table = generator.generate();
+
+        try (var out = Files.newOutputStream(Path.of("DCI_P3_spectrum.bin"))) {
+            SpectrumTable.write(table, out);
+        }
+    }
+
+    public SpectrumTableGenerator(@NotNull ColorSpace cs) {
+        this.cs = Objects.requireNonNull(cs);
+    }
+
+    public @NotNull SpectrumTable generate() {
+        var scale = new double[resolution];
+        for (int i = 0; i < scale.length; i++) {
+            var t = (double) i / (resolution - 1);
+            scale[i] = smoothstep(smoothstep(t));
+        }
+
+        var table = new double[3 * resolution * resolution * resolution * 3];
+
+        for (int l0 = 0; l0 < 3; l0++) {
+            var l = l0;
+            IntStream.range(0, resolution).parallel().forEach(i -> {
+                System.out.println("l = " + l + ", i = " + i);
+                var x = (double) i / (resolution - 1);
+                for (int j = 0; j < resolution; j++) {
+                    var y = (double) j / (resolution - 1);
+
+                    var start = resolution / 5;
+
+                    var c = new double[3];
+                    for (int k = start; k < resolution; k++) {
+                        var z = scale[k];
+                        var idx = ((((l * resolution + k) * resolution) + j) * resolution + i) * 3;
+                        var color = getColor(l, x, y, z);
+                        generate(color, c, table, idx);
+                    }
+
+                    Arrays.fill(c, 0);
+                    for (int k = start; k >= 0; --k) {
+                        var z = scale[k];
+                        var idx = ((((l * resolution + k) * resolution) + j) * resolution + i) * 3;
+                        var color = getColor(l, x, y, z);
+                        generate(color, c, table, idx);
+                    }
+                }
+            });
+        }
+        return new SpectrumTable(resolution, scale, table);
+    }
+
+    private void generate(@NotNull ColorRGB rgb, double @NotNull[] c, double @NotNull[] out, int offset) {
+        gaussNewton(rgb, c, ITERATIONS);
+        double c0 = 360.0, c1 = 1.0 / (830.0 - 360.0);
+        double A = c[0], B = c[1], C = c[2];
+        out[offset] = A * c1 * c1;
+        out[offset + 1] = B * c1 - 2 * A * c0 * c1 * c1;
+        out[offset + 2] = C - B * c0 * c1 + A * c0 * c0 * c1 * c1;
+    }
+
+    /**
+     * Use Gauss-Newton algorithm to calculate coefficients {@code c} of a {@link SigmoidPolynomial} such that the round
+     * trip error from converting the {@code rgb} value to a spectrum and back is minimized.
+     * @param rgb the input color
+     * @param c the coefficients, used as initial values and output
+     * @param it the number of iterations
+     */
+    private void gaussNewton(@NotNull ColorRGB rgb, double @NotNull[] c, int it) {
+        var bestQuality = Double.POSITIVE_INFINITY;
+        var bestCoefficients = new double[3];
+
+        for (int i = 0; i < it; ++i) {
+            var polynomial = new SigmoidPolynomial(c[0], c[1], c[2]);
+            var residual = getResidual(rgb, polynomial);
+            var jacobian = getJacobian(rgb, polynomial);
+
+            var delta = jacobian.decompose(1e-15).solve(residual);
+            for (int j = 0; j < 3; ++j) {
+                c[j] -= delta.get(j);
+            }
+
+            // catch runaway
+            double max = Math.max(Math.max(c[0], c[1]), c[2]);
+            if (max > 200) {
+                for (int j = 0; j < 3; ++j) {
+                    c[j] *= 200 / max;
+                }
+            }
+
+            var quality = residual.squared();
+            if (quality <= 1e-6) {
+                return;
+            } else if (quality < bestQuality) {
+                bestQuality = quality;
+                System.arraycopy(c, 0, bestCoefficients, 0, 3);
+            }
+        }
+
+        System.arraycopy(bestCoefficients, 0, c, 0, 3);
+    }
+
+    /**
+     * Calculates the Jacobian matrix of the {@code polynomial}.
+     */
+    private @NotNull Matrix3 getJacobian(@NotNull ColorRGB rgb, @NotNull SigmoidPolynomial polynomial) {
+        var jac = new double[3][3];
+
+        // central finite difference coefficients for first derivative with sixth-order accuracy
+        var factors = new double[] { -1d/60, 3d/20, -3d/4, 0, 3d/4, -3d/20,	1d/60 };
+
+        for (int i = 0; i < 3; i++) {
+            var derivative = Vec3.ZERO;
+            for (int d = - factors.length / 2, j = 0; j < factors.length; d++, j++) {
+                if (factors[j] == 0) continue;
+                var tmp = switch (i) {
+                    case 0 -> new SigmoidPolynomial(polynomial.c0() + d * EPSILON, polynomial.c1(), polynomial.c2());
+                    case 1 -> new SigmoidPolynomial(polynomial.c0(), polynomial.c1() + d * EPSILON, polynomial.c2());
+                    case 2 -> new SigmoidPolynomial(polynomial.c0(), polynomial.c1(), polynomial.c2() + d * EPSILON);
+                    default -> throw new AssertionError();
+                };
+                var r = getResidual(rgb, tmp);
+                derivative = Vec3.fma(factors[j], r, derivative);
+            }
+
+            for (int j = 0; j < 3; j++) {
+                jac[j][i] = derivative.get(j) / EPSILON;
+            }
+        }
+
+        return new Matrix3(
+                jac[0][0], jac[0][1], jac[0][2],
+                jac[1][0], jac[1][1], jac[1][2],
+                jac[2][0], jac[2][1], jac[2][2]
+        );
+    }
+
+    /**
+     * Calculates the difference between the RGB color and the result of converting the RGB color to a spectrum using
+     * the given coefficients, illuminating it with the color space's standard illuminant, and converting it back to an
+     * RBG color. The output is a vector in CIE Lab color space.
+     */
+    private @NotNull Vec3 getResidual(@NotNull ColorRGB rgb, @NotNull SigmoidPolynomial polynomial) {
+        var out = new SigmoidPolynomialSpectrum(polynomial, cs).toXYZ();
+        return cs.toCIELab(rgb).minus(cs.toCIELab(out));
+    }
+
+
+    private static double smoothstep(double x) {
+        return x * x * (3.0 - 2.0 * x);
+    }
+
+    private static @NotNull ColorRGB getColor(int l, double x, double y, double z) {
+        var rgb = new double[3];
+        rgb[l] = z;
+        rgb[(l + 1) % 3] = x * z;
+        rgb[(l + 2) % 3] = y * z;
+        return new ColorRGB(rgb[0], rgb[1], rgb[2]);
+    }
+
+    private record SigmoidPolynomialSpectrum(@NotNull SigmoidPolynomial polynomial, @NotNull ColorSpace cs) implements Spectrum {
+
+        @Override
+        public double max() {
+            return polynomial.max();
+        }
+
+        @Override
+        public double get(double lambda) {
+            var l = (lambda - Spectrum.LAMBDA_MIN) / (Spectrum.LAMBDA_MAX - Spectrum.LAMBDA_MIN);
+            return polynomial.get(l) * cs.illuminant().get(lambda);
+        }
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/color/TransferFunction.java

@@ -0,0 +1,8 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import org.jetbrains.annotations.NotNull;
+
+public interface TransferFunction {
+    @NotNull ColorRGB decode(@NotNull ColorRGB rgb);
+    @NotNull ColorRGB encode(@NotNull ColorRGB rgb);
+}

src/main/java/eu/jonahbauer/raytracing/render/color/TransferFunctions.java

@@ -0,0 +1,50 @@
+package eu.jonahbauer.raytracing.render.color;
+
+import org.jetbrains.annotations.NotNull;
+
+public final class TransferFunctions {
+    public static final @NotNull TransferFunction sRGB = new ComponentTransferFunction() {
+        @Override
+        protected double encode(double value) {
+            if (value <= 0.0031308) return 12.92 * value;
+            return 1.055 * Math.pow(value, 1. / 2.4) - 0.055;
+        }
+
+        @Override
+        protected double decode(double value) {
+            if (value <= 0.04045) return value / 12.92;
+            return Math.pow((value + 0.055) / 1.055, 2.4d);
+        }
+    };
+
+    public static final @NotNull TransferFunction LINEAR = new TransferFunction() {
+        @Override
+        public @NotNull ColorRGB encode(@NotNull ColorRGB rgb) {
+            return rgb;
+        }
+
+        @Override
+        public @NotNull ColorRGB decode(@NotNull ColorRGB rgb) {
+            return rgb;
+        }
+    };
+
+    private TransferFunctions() {
+        throw new UnsupportedOperationException();
+    }
+
+    private abstract static class ComponentTransferFunction implements TransferFunction {
+        @Override
+        public final @NotNull ColorRGB decode(@NotNull ColorRGB rgb) {
+            return new ColorRGB(decode(rgb.r()), decode(rgb.g()), decode(rgb.b()));
+        }
+
+        @Override
+        public final @NotNull ColorRGB encode(@NotNull ColorRGB rgb) {
+            return new ColorRGB(encode(rgb.r()), encode(rgb.g()), encode(rgb.b()));
+        }
+
+        protected abstract double encode(double value);
+        protected abstract double decode(double value);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/image/ImageWriter.java

@@ -0,0 +1,19 @@
+package eu.jonahbauer.raytracing.render.image;
+
+import eu.jonahbauer.raytracing.render.canvas.Canvas;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.IOException;
+import java.io.OutputStream;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public interface ImageWriter {
+    default void write(@NotNull Canvas image, @NotNull Path path) throws IOException {
+        try (var out = Files.newOutputStream(path)) {
+            write(image, out);
+        }
+    }
+
+    void write(@NotNull Canvas canvas, @NotNull OutputStream out) throws IOException;
+}

src/main/java/eu/jonahbauer/raytracing/render/image/PNGImageWriter.java

@@ -0,0 +1,107 @@
+package eu.jonahbauer.raytracing.render.image;
+
+import eu.jonahbauer.raytracing.render.canvas.Canvas;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.ColorSpaces;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.*;
+import java.util.Objects;
+import java.util.zip.CRC32;
+import java.util.zip.CheckedOutputStream;
+import java.util.zip.DeflaterOutputStream;
+
+public class PNGImageWriter implements ImageWriter {
+    public static final @NotNull PNGImageWriter sRGB = new PNGImageWriter(ColorSpaces.sRGB);
+
+    private static final byte[] MAGIC = new byte[] { (byte) 0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A };
+    private static final int IHDR_LENGTH = 13;
+    private static final int IHDR_TYPE = 0x49484452;
+    private static final int IDAT_TYPE = 0x49444154;
+    private static final int IEND_TYPE = 0x49454E44;
+    private static final int IEND_CRC = 0xAE426082;
+
+    private final @NotNull ColorSpace cs;
+
+    public PNGImageWriter(@NotNull ColorSpace cs) {
+        this.cs = Objects.requireNonNull(cs, "cs");
+    }
+
+    @Override
+    public void write(@NotNull Canvas image, @NotNull OutputStream out) throws IOException {
+        try (var data = new NoCloseDataOutputStream(out); var _ = data.closeable()) {
+            data.write(MAGIC);
+
+            writeIHDR(image, data);
+            writeIDAT(image, data);
+            writeIEND(image, data);
+        }
+    }
+
+    private void writeIHDR(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
+        data.writeInt(IHDR_LENGTH);
+        try (
+                var crc = new CheckedOutputStream(data, new CRC32());
+                var ihdr = new DataOutputStream(crc)
+        ) {
+            ihdr.writeInt(IHDR_TYPE);
+            ihdr.writeInt(image.getWidth()); // image width
+            ihdr.writeInt(image.getHeight()); // image height
+            ihdr.writeByte(8); // bit depth
+            ihdr.writeByte(2); // color type
+            ihdr.writeByte(0); // compression method
+            ihdr.writeByte(0); // filter method
+            ihdr.writeByte(0); // interlace method
+            ihdr.flush();
+            data.writeInt((int) crc.getChecksum().getValue());
+        }
+    }
+
+    private void writeIDAT(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
+        try (
+                var baos = new ByteArrayOutputStream();
+                var crc = new CheckedOutputStream(baos, new CRC32());
+                var idat = new DataOutputStream(crc)
+        ) {
+            idat.writeInt(IDAT_TYPE);
+
+            try (var deflate = new DataOutputStream(new DeflaterOutputStream(idat))) {
+                for (int y = 0; y < image.getHeight(); y++) {
+                    deflate.writeByte(0); // filter type
+                    for (int x = 0; x < image.getWidth(); x++) {
+                        var pixel = cs.encode(image.getRGB(x, y, cs));
+                        deflate.writeByte(pixel.red());
+                        deflate.writeByte(pixel.green());
+                        deflate.writeByte(pixel.blue());
+                    }
+                }
+            }
+
+            var bytes = baos.toByteArray();
+            data.writeInt(bytes.length - 4); // don't include type in length
+            data.write(bytes);
+            data.writeInt((int) crc.getChecksum().getValue());
+        }
+    }
+
+    private void writeIEND(@NotNull Canvas image, @NotNull DataOutputStream data) throws IOException {
+        data.writeInt(0);
+        data.writeInt(IEND_TYPE);
+        data.writeInt(IEND_CRC);
+    }
+
+    private static class NoCloseDataOutputStream extends DataOutputStream {
+        public NoCloseDataOutputStream(OutputStream out) {
+            super(out);
+        }
+
+        @Override
+        public void close() {
+            // do nothing
+        }
+
+        public Closeable closeable() {
+            return super::close;
+        }
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/image/PPMImageWriter.java

@@ -0,0 +1,46 @@
+package eu.jonahbauer.raytracing.render.image;
+
+import eu.jonahbauer.raytracing.render.canvas.Canvas;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.ColorSpaces;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.nio.charset.StandardCharsets;
+import java.util.Objects;
+
+public class PPMImageWriter implements ImageWriter {
+    public static final PPMImageWriter sRGB = new PPMImageWriter(ColorSpaces.sRGB);
+
+    private final @NotNull ColorSpace cs;
+
+    public PPMImageWriter(@NotNull ColorSpace cs) {
+        this.cs = Objects.requireNonNull(cs, "cs");
+    }
+
+    @Override
+    public void write(@NotNull Canvas image, @NotNull OutputStream out) throws IOException {
+        try (var writer = new BufferedWriter(new OutputStreamWriter(out, StandardCharsets.US_ASCII))) {
+            writer.write("P3\n");
+            writer.write(String.valueOf(image.getWidth()));
+            writer.write(" ");
+            writer.write(String.valueOf(image.getHeight()));
+            writer.write("\n255\n");
+
+            for (int y = 0; y < image.getHeight(); y++) {
+                for (int x = 0; x < image.getWidth(); x++) {
+                    var color = cs.encode(image.getRGB(x, y, cs));
+                    writer.write(String.valueOf(color.red()));
+                    writer.write(" ");
+                    writer.write(String.valueOf(color.green()));
+                    writer.write(" ");
+                    writer.write(String.valueOf(color.blue()));
+                    writer.write("\n");
+                }
+            }
+        }
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/material/DielectricMaterial.java

@@ -2,7 +2,7 @@ package eu.jonahbauer.raytracing.render.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
@@ -11,34 +11,75 @@ import java.util.Objects;
 import java.util.Optional;
 import java.util.random.RandomGenerator;
 
-public record DielectricMaterial(double refractionIndex, @NotNull Texture texture) implements Material {
+public record DielectricMaterial(@NotNull RefractiveIndex ri, @NotNull Texture texture) implements Material {
-    public DielectricMaterial(double refractionIndex) {
-        this(refractionIndex, Color.WHITE);
-    }
-
     public DielectricMaterial {
+        Objects.requireNonNull(ri, "ri");
         Objects.requireNonNull(texture, "texture");
     }
 
+    public DielectricMaterial(@NotNull RefractiveIndex ri) {
+        this(ri, Spectra.WHITE);
+    }
+
+    public DielectricMaterial(double ri) {
+        this(new ConstantRefractiveIndex(ri), Spectra.WHITE);
+    }
+
+    public DielectricMaterial(double ri, @NotNull Texture texture) {
+        this(new ConstantRefractiveIndex(ri), texture);
+    }
+
     @Override
     public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit, @NotNull RandomGenerator random) {
-        var ri = hit.isFrontFace() ? (1 / refractionIndex) : refractionIndex;
+        var ri = switch (this.ri) {
+            case ConstantRefractiveIndex(var x) -> x;
+            case RefractiveIndex x -> x.get(ray.lambda().collapse());
+        };
+        if (hit.isFrontFace()) ri = 1 / ri;
 
-        var cosTheta = Math.min(- ray.direction().unit().times(hit.normal()), 1.0);
+        var cosTheta = Math.min(- ray.direction().unit().dot(hit.normal()), 1.0);
-        var reflectance = reflectance(cosTheta);
+        var reflectance = reflectance(cosTheta, ri);
         var reflect = reflectance > random.nextDouble();
 
         var newDirection = (reflect ? Optional.<Vec3>empty() : Vec3.refract(ray.direction(), hit.normal(), ri))
                 .orElseGet(() -> Vec3.reflect(ray.direction(), hit.normal()));
 
         var attenuation = texture.get(hit);
-        return Optional.of(new SpecularScatterResult(attenuation, new Ray(hit.position(), newDirection)));
+        return Optional.of(new SpecularScatterResult(attenuation, ray.with(hit, newDirection)));
     }
 
-    private double reflectance(double cos) {
+    private double reflectance(double cos, double ri) {
         // use schlick's approximation for reflectance
-        var r0 = (1 - refractionIndex) / (1 + refractionIndex);
+        var r0 = (1 - ri) / (1 + ri);
         r0 = r0 * r0;
         return r0 + (1 - r0) * (1 - cos) * (1 - cos) * (1 - cos) * (1 - cos) * (1 - cos);
     }
+
+    @FunctionalInterface
+    public interface RefractiveIndex {
+        double get(double lambda);
+    }
+
+    public record ConstantRefractiveIndex(double ri) implements RefractiveIndex {
+
+        @Override
+        public double get(double lambda) {
+            return ri;
+        }
+    }
+
+    public record SellmeierRefractiveIndex(
+            double B1, double B2, double B3,
+            double C1, double C2, double C3
+    ) implements RefractiveIndex {
+
+        @Override
+        public double get(double lambda) {
+            var l2 = lambda * lambda * 1E-6; // square and convert to µm
+            var x = 1 + B1 * l2 / (l2 - C1)
+                      + B2 * l2 / (l2 - C2)
+                      + B3 * l2 / (l2 - C3);
+            return Math.sqrt(x);
+        }
+    }
 }

src/main/java/eu/jonahbauer/raytracing/render/material/DiffuseLight.java

@@ -1,22 +1,27 @@
 package eu.jonahbauer.raytracing.render.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Objects;
 import java.util.Optional;
 import java.util.random.RandomGenerator;
 
 public record DiffuseLight(@NotNull Texture texture) implements Material {
+    public DiffuseLight {
+        Objects.requireNonNull(texture, "texture");
+    }
+
     @Override
     public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit, @NotNull RandomGenerator random) {
         return Optional.empty();
     }
 
     @Override
-    public @NotNull Color emitted(@NotNull HitResult hit) {
+    public @NotNull Spectrum emitted(@NotNull HitResult hit) {
         return texture.get(hit);
     }
 }

src/main/java/eu/jonahbauer/raytracing/render/material/DirectionalMaterial.java

@@ -2,7 +2,8 @@ package eu.jonahbauer.raytracing.render.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
@@ -40,11 +41,11 @@ public final class DirectionalMaterial implements Material {
             if (back != null) return back.scatter(ray, hit, random);
         }
         // let the ray pass through without obstruction
-        return Optional.of(new SpecularScatterResult(Color.WHITE, new Ray(ray.at(hit.t()), ray.direction())));
+        return Optional.of(new SpecularScatterResult(Spectra.WHITE, ray.with(hit, ray.direction())));
     }
 
     @Override
-    public @NotNull Color emitted(@NotNull HitResult hit) {
+    public @NotNull Spectrum emitted(@NotNull HitResult hit) {
         if (hit.isFrontFace()) {
             if (front != null) return front.emitted(hit);
         } else {
@@ -56,7 +57,7 @@ public final class DirectionalMaterial implements Material {
     private record DirectionalTexture(@Nullable Texture front, @Nullable Texture back) implements Texture {
 
         @Override
-        public @NotNull Color get(double u, double v, @NotNull Vec3 p) {
+        public @NotNull Spectrum get(double u, double v, @NotNull Vec3 p) {
             throw new UnsupportedOperationException();
         }
 

src/main/java/eu/jonahbauer/raytracing/render/material/IsotropicMaterial.java

@@ -2,15 +2,20 @@ package eu.jonahbauer.raytracing.render.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.render.renderer.pdf.SphereProbabilityDensityFunction;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
 
+import java.util.Objects;
 import java.util.Optional;
 import java.util.random.RandomGenerator;
 
-public record IsotropicMaterial(@NotNull Color albedo) implements Material {
+public record IsotropicMaterial(@NotNull Spectrum albedo) implements Material {
+    public IsotropicMaterial {
+        Objects.requireNonNull(albedo, "albedo");
+    }
+
     @Override
     public @NotNull Optional<ScatterResult> scatter(@NotNull Ray ray, @NotNull HitResult hit, @NotNull RandomGenerator random) {
         return Optional.of(new PdfScatterResult(albedo(), new SphereProbabilityDensityFunction()));

src/main/java/eu/jonahbauer/raytracing/render/material/Material.java

@@ -2,7 +2,9 @@ package eu.jonahbauer.raytracing.render.material;
 
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.render.renderer.pdf.ProbabilityDensityFunction;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
@@ -30,10 +32,10 @@ public interface Material {
 
     /**
      * {@return the color emitted for a given hit}
-     * @implSpec the default implementation returns {@linkplain Color#BLACK black}, i.e. no emission
+     * @implSpec the default implementation returns {@linkplain ColorRGB#BLACK black}, i.e. no emission
      */
-    default @NotNull Color emitted(@NotNull HitResult hit) {
+    default @NotNull Spectrum emitted(@NotNull HitResult hit) {
-        return Color.BLACK;
+        return Spectra.BLACK;
     }
 
     /**
@@ -48,7 +50,7 @@ public interface Material {
      * @param attenuation the attenuation of the scattered light ray
      * @param ray the scattered light ray
      */
-    record SpecularScatterResult(@NotNull Color attenuation, @NotNull Ray ray) implements ScatterResult {
+    record SpecularScatterResult(@NotNull Spectrum attenuation, @NotNull Ray ray) implements ScatterResult {
         public SpecularScatterResult {
             Objects.requireNonNull(attenuation, "attenuation");
             Objects.requireNonNull(ray, "ray");
@@ -62,7 +64,7 @@ public interface Material {
      * @param attenuation the attenuation of the scattered light ray
      * @param pdf the probability density function
      */
-    record PdfScatterResult(@NotNull Color attenuation, @NotNull ProbabilityDensityFunction pdf) implements ScatterResult {
+    record PdfScatterResult(@NotNull Spectrum attenuation, @NotNull ProbabilityDensityFunction pdf) implements ScatterResult {
         public PdfScatterResult {
             Objects.requireNonNull(attenuation, "attenuation");
             Objects.requireNonNull(pdf, "pdf");

src/main/java/eu/jonahbauer/raytracing/render/material/Materials.java

@@ -0,0 +1,25 @@
+package eu.jonahbauer.raytracing.render.material;
+
+import eu.jonahbauer.raytracing.render.color.ColorSpaces;
+import eu.jonahbauer.raytracing.render.material.DielectricMaterial.SellmeierRefractiveIndex;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
+import eu.jonahbauer.raytracing.render.texture.CheckerTexture;
+import org.jetbrains.annotations.NotNull;
+
+public final class Materials {
+    public static final @NotNull Material GLASS = new DielectricMaterial(new SellmeierRefractiveIndex(
+            1.0361212, 0.231792344, 1.01046945,
+            6.00069867E-3, 2.00179144E-2, 1.03560653E2
+    ));
+
+    public static final @NotNull Material MIRROR = new MetallicMaterial(ColorSpaces.sRGB.albedo(0.7, 0.7, 0.7));
+
+    public static final @NotNull Material DEBUG = new DirectionalMaterial(
+            new LambertianMaterial(new CheckerTexture(50.0, ColorSpaces.sRGB.albedo(1.0, 0.0, 1.0), Spectra.BLACK)),
+            new LambertianMaterial(new CheckerTexture(50.0, ColorSpaces.sRGB.albedo(1.0, 1.0, 1.0), Spectra.BLACK))
+    );
+
+    private Materials() {
+        throw new UnsupportedOperationException();
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/material/MetallicMaterial.java

@@ -28,6 +28,6 @@ public record MetallicMaterial(@NotNull Texture texture, double fuzz) implements
             newDirection = Vec3.fma(fuzz, Vec3.random(random), newDirection.unit());
         }
         var attenuation = texture.get(hit);
-        return Optional.of(new SpecularScatterResult(attenuation, new Ray(hit.position(), newDirection)));
+        return Optional.of(new SpecularScatterResult(attenuation, ray.with(hit, newDirection)));
     }
 }

src/main/java/eu/jonahbauer/raytracing/render/renderer/Renderer.java

@@ -2,13 +2,13 @@ package eu.jonahbauer.raytracing.render.renderer;
 
 import eu.jonahbauer.raytracing.render.camera.Camera;
 import eu.jonahbauer.raytracing.render.canvas.Canvas;
-import eu.jonahbauer.raytracing.render.canvas.Image;
+import eu.jonahbauer.raytracing.render.canvas.XYZCanvas;
 import eu.jonahbauer.raytracing.scene.Scene;
 import org.jetbrains.annotations.NotNull;
 
 public interface Renderer {
-    default @NotNull Image render(@NotNull Camera camera, @NotNull Scene scene) {
+    default @NotNull Canvas render(@NotNull Camera camera, @NotNull Scene scene) {
-        var image = new Image(camera.getWidth(), camera.getHeight());
+        var image = new XYZCanvas(camera.getWidth(), camera.getHeight());
         render(camera, scene, image);
         return image;
     }

src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java

@@ -1,13 +1,13 @@
 package eu.jonahbauer.raytracing.render.renderer;
 
-import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.render.material.Material;
 import eu.jonahbauer.raytracing.render.renderer.pdf.TargetingProbabilityDensityFunction;
 import eu.jonahbauer.raytracing.render.renderer.pdf.MixtureProbabilityDensityFunction;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
 import eu.jonahbauer.raytracing.render.camera.Camera;
 import eu.jonahbauer.raytracing.render.canvas.Canvas;
+import eu.jonahbauer.raytracing.render.spectrum.SampledWavelengths;
 import eu.jonahbauer.raytracing.scene.Scene;
 import org.jetbrains.annotations.NotNull;
 
@@ -21,7 +21,10 @@ import static eu.jonahbauer.raytracing.Main.DEBUG;
 public final class SimpleRenderer implements Renderer {
     private final int sqrtSamplesPerPixel;
     private final int maxDepth;
-    private final double gamma;
+
+    private final int spectralSamples;
+    private final SampledSpectrum black;
+    private final SampledSpectrum white;
 
     private final boolean parallel;
     private final boolean iterative;
@@ -37,7 +40,10 @@ public final class SimpleRenderer implements Renderer {
     private SimpleRenderer(@NotNull Builder builder) {
         this.sqrtSamplesPerPixel = (int) Math.sqrt(builder.samplesPerPixel);
         this.maxDepth = builder.maxDepth;
-        this.gamma = builder.gamma;
+
+        this.spectralSamples = builder.spectralSamples;
+        this.black = new SampledSpectrum(spectralSamples, 0);
+        this.white = new SampledSpectrum(spectralSamples, 1);
 
         this.parallel = builder.parallel;
         this.iterative = builder.iterative;
@@ -77,18 +83,11 @@ public final class SimpleRenderer implements Renderer {
                     for (int x = 0; x < camera.getWidth(); x++) {
                         var ray = camera.cast(x, y, sif, sjf, sqrtSamplesPerPixel, random);
                         var c = getColor(scene, ray, random);
-                        canvas.set(x, y, Color.average(canvas.get(x, y), c, sample));
+                        canvas.add(x, y, sample, c, ray.lambda());
                     }
                 });
             }
         }
-
-        // apply gamma correction
-        getScanlineStream(camera.getHeight(), parallel).forEach(y -> {
-            for (int x = 0; x < camera.getWidth(); x++) {
-                canvas.set(x, y, Color.gamma(canvas.get(x, y), gamma));
-            }
-        });
     }
 
     /**
@@ -101,19 +100,18 @@ public final class SimpleRenderer implements Renderer {
         getScanlineStream(camera.getHeight(), parallel).forEach(y -> {
             var random = splittable.split();
             for (int x = 0; x < camera.getWidth(); x++) {
-                var color = Color.BLACK;
                 int i = 0;
                 for (int sj = 0; sj < sqrtSamplesPerPixel; sj++) {
                     for (int si = 0; si < sqrtSamplesPerPixel; si++) {
-                        var ray = camera.cast(x, y, si, sj, sqrtSamplesPerPixel, random);
+                        var lambda = SampledWavelengths.uniform(random.nextDouble(), spectralSamples);
+                        var ray = camera.cast(x, y, si, sj, sqrtSamplesPerPixel, random).with(lambda);
                         if (DEBUG) {
                             System.out.println("Casting ray " + ray + " through pixel (" + x + "," + y + ") at subpixel (" + si + "," + sj + ")...");
                         }
                         var c = getColor(scene, ray, random);
-                        color = Color.average(color, c, ++i);
+                        canvas.add(x, y, ++i, c, ray.lambda());
                     }
                 }
-                canvas.set(x, y, Color.gamma(color, gamma));
             }
         });
     }
@@ -121,19 +119,19 @@ public final class SimpleRenderer implements Renderer {
     /**
      * {@return the color of the given ray in the given scene}
      */
-    private @NotNull Color getColor(@NotNull Scene scene, @NotNull Ray ray, @NotNull RandomGenerator random) {
+    private @NotNull SampledSpectrum getColor(@NotNull Scene scene, @NotNull Ray ray, @NotNull RandomGenerator random) {
         return getColor0(scene, ray, maxDepth, random);
     }
 
-    private @NotNull Color getColor0(@NotNull Scene scene, @NotNull Ray ray, int depth, @NotNull RandomGenerator random) {
+    private @NotNull SampledSpectrum getColor0(@NotNull Scene scene, @NotNull Ray ray, int depth, @NotNull RandomGenerator random) {
-        var color = Color.BLACK;
+        var color = black;
-        var attenuation = Color.WHITE;
+        var attenuation = white;
 
         while (depth-- > 0) {
-            var optional = scene.hit(ray);
+            var optional = scene.hit(ray, random);
             if (optional.isEmpty()) {
                 var background = scene.getBackgroundColor(ray);
-                color = Color.add(color, Color.multiply(attenuation, background));
+                color = SampledSpectrum.fma(attenuation, background, color);
                 if (DEBUG) {
                     System.out.println("  Hit background: " + background);
                 }
@@ -145,13 +143,13 @@ public final class SimpleRenderer implements Renderer {
                 System.out.println("  Hit " + hit.target() + " at t=" + hit.t() + " (" + hit.position() + ")");
             }
             var material = hit.material();
-            var emitted = material.emitted(hit);
+            var emitted = material.emitted(hit).sample(ray.lambda());
-            if (DEBUG && !Color.BLACK.equals(emitted)) {
+            if (DEBUG && !black.equals(emitted)) {
                 System.out.println("  Emitted: " + emitted);
             }
 
             var result = material.scatter(ray, hit, random);
-            color = Color.add(color, Color.multiply(attenuation, emitted));
+            color = SampledSpectrum.fma(attenuation, emitted, color);
 
             if (result.isEmpty()) {
                 if (DEBUG) {
@@ -162,7 +160,7 @@ public final class SimpleRenderer implements Renderer {
 
             switch (result.get()) {
                 case Material.SpecularScatterResult(var a, var scattered) -> {
-                    attenuation = Color.multiply(attenuation, a);
+                    attenuation = attenuation.times(a.sample(ray.lambda()));
                     ray = scattered;
 
                     if (DEBUG) {
@@ -171,8 +169,8 @@ public final class SimpleRenderer implements Renderer {
                 }
                 case Material.PdfScatterResult(var a, var pdf) -> {
                     if (scene.getTargets() == null) {
-                        attenuation = Color.multiply(attenuation, a);
+                        attenuation = attenuation.times(a.sample(ray.lambda()));
-                        ray = new Ray(hit.position(), pdf.generate(random));
+                        ray = new Ray(hit.position(), pdf.generate(random), ray.lambda());
 
                         if (DEBUG) {
                             System.out.println("  Pdf scattering with albedo " + a);
@@ -187,8 +185,8 @@ public final class SimpleRenderer implements Renderer {
 
                         var factor = idealPdf / actualPdf;
 
-                        attenuation = Color.multiply(attenuation, Color.multiply(a, factor));
+                        attenuation = attenuation.times(a.sample(ray.lambda()).times(factor));
-                        ray = new Ray(hit.position(), direction);
+                        ray = new Ray(hit.position(), direction, ray.lambda());
 
                         if (DEBUG) {
                             System.out.println("  Pdf scattering with albedo " + a + " and factor " + factor);
@@ -216,14 +214,14 @@ public final class SimpleRenderer implements Renderer {
      * are encoded in the longs lower and upper 32 bits respectively.
      */
     private static @NotNull IntStream getScanlineStream(int height, boolean parallel) {
-        var stream = IntStream.range(0, height);
+        var stream = IntStream.range(0, height).map(i -> height - i - 1);
         return parallel ? stream.parallel() : stream;
     }
 
     public static class Builder {
         private int samplesPerPixel = 100;
         private int maxDepth = 10;
-        private double gamma = 2.0;
+        private int spectralSamples = 4;
         private boolean parallel = true;
         private boolean iterative = false;
 
@@ -239,9 +237,9 @@ public final class SimpleRenderer implements Renderer {
             return this;
         }
 
-        public @NotNull Builder withGamma(double gamma) {
+        public @NotNull Builder withSpectralSamples(int samples) {
-            if (gamma <= 0 || !Double.isFinite(gamma)) throw new IllegalArgumentException("gamma must be positive");
+            if (samples <= 0) throw new IllegalArgumentException("samples must be positive");
-            this.gamma = gamma;
+            this.spectralSamples = samples;
             return this;
         }
 

src/main/java/eu/jonahbauer/raytracing/render/renderer/pdf/CosineProbabilityDensityFunction.java

@@ -15,7 +15,7 @@ public record CosineProbabilityDensityFunction(@NotNull Vec3 normal) implements
 
     @Override
     public double value(@NotNull Vec3 direction) {
-        var cos = normal.times(direction);
+        var cos = normal.dot(direction);
         return Math.max(0, cos / Math.PI);
     }
 

src/main/java/eu/jonahbauer/raytracing/render/spectrum/BlackbodySpectrum.java

@@ -0,0 +1,45 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+public final class BlackbodySpectrum implements Spectrum {
+    /**
+     * the speed of light in m/s
+     */
+    private static final double c = 299792458d;
+
+    /**
+     * the planck constant in m^2*kg/s
+     */
+    private static final double h = 6.62607015E-34;
+
+    /**
+     * the boltzmann constant in m^2*kg/s^2/K
+     */
+    private static final double k = 1.380649E-23;
+
+    /**
+     * wien's displacement constant in m*K
+     */
+    private static final double b = 2.897771995E-3;
+
+    private final double T;
+    private final double factor;
+
+    public BlackbodySpectrum(double T) {
+        if (T < 0) throw new IllegalArgumentException("T must be non-negative");
+        this.T = T;
+        this.factor = 1 / get(b / T);
+    }
+
+    @Override
+    public double max() {
+        return 1;
+    }
+
+    @Override
+    public double get(double lambda) {
+        lambda *= 1E-9;
+        var l2 = lambda * lambda;
+        var x = h * c / (lambda * k * T);
+        return 2 * h * c * c / (l2 * l2 * lambda) / (Math.exp(x) - 1) * factor;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/ConstantSpectrum.java

@@ -0,0 +1,17 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+/**
+ * A constant spectrum.
+ * @param c the constant value
+ */
+public record ConstantSpectrum(double c) implements Spectrum {
+    @Override
+    public double max() {
+        return c;
+    }
+
+    @Override
+    public double get(double lambda) {
+        return c;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/DenselySampledSpectrum.java

@@ -0,0 +1,51 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Arrays;
+
+/**
+ * A spectrum sampled in one nanometer intervals.
+ */
+public final class DenselySampledSpectrum implements Spectrum {
+    private final double[] samples;
+    private final int min;
+
+    private final double max;
+
+    public DenselySampledSpectrum(@NotNull Spectrum spectrum) {
+        this(spectrum, LAMBDA_MIN, LAMBDA_MAX);
+    }
+
+    public DenselySampledSpectrum(@NotNull Spectrum spectrum, int min, int max) {
+        if (max - min + 1 <= 0) throw new IllegalArgumentException("samples must not be empty");
+        this.samples = new double[max - min + 1];
+        var maxValue = 0d;
+        for (int lambda = min, i = 0; lambda <= max; lambda++, i++) {
+            var sample = spectrum.get(lambda);
+            if (sample > maxValue) maxValue = sample;
+            this.samples[i] = sample;
+        }
+        this.min = min;
+        this.max = maxValue;
+    }
+
+    public DenselySampledSpectrum(double @NotNull[] samples, int lambdaMin) {
+        if (samples.length == 0) throw new IllegalArgumentException("samples must not be empty");
+        this.samples = Arrays.copyOf(samples, samples.length);
+        this.min = lambdaMin;
+        this.max = Arrays.stream(this.samples).max().orElseThrow();
+    }
+
+    @Override
+    public double max() {
+        return max;
+    }
+
+    @Override
+    public double get(double lambda) {
+        int offset = (int) Math.round(lambda) - min;
+        if (offset < 0 || offset >= samples.length) return 0;
+        return samples[offset];
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/PiecewiseLinearSpectrum.java

@@ -0,0 +1,48 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import java.util.Arrays;
+
+public final class PiecewiseLinearSpectrum implements Spectrum {
+    private final double[] lambdas;
+    private final double[] values;
+    private final double max;
+
+    public PiecewiseLinearSpectrum(double[] lambdas, double[] values) {
+        if (lambdas.length != values.length) {
+            throw new IllegalArgumentException("lambdas and values must have the same length");
+        }
+
+        this.lambdas = Arrays.copyOf(lambdas, lambdas.length);
+        this.values = Arrays.copyOf(values, values.length);
+
+        var max = 0d;
+        for (int i = 1; i < this.lambdas.length; i++) {
+            if (this.lambdas[i] <= this.lambdas[i - 1]) {
+                throw new IllegalArgumentException("lambdas must be in increasing order");
+            }
+            if (this.values[i] < 0) {
+                throw new IllegalArgumentException("values must be non-negative");
+            } else if (this.values[i] > max) {
+                max = this.values[i];
+            }
+        }
+        this.max = max;
+    }
+
+    @Override
+    public double max() {
+        return max;
+    }
+
+    @Override
+    public double get(double lambda) {
+        if (lambdas.length == 0 || lambda < lambdas[0] || lambda > lambdas[lambdas.length - 1]) return 0;
+        if (lambda == lambdas[lambdas.length - 1]) return values[values.length - 1];
+
+        var i = Arrays.binarySearch(lambdas, lambda);
+        if (i < 0) i = -i - 1;
+
+        var t = (lambda - lambdas[i]) / (lambdas[i + 1] - lambdas[i]);
+        return (1 - t) * values[i] + t * values[i + 1];
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/RGBAlbedoSpectrum.java

@@ -0,0 +1,27 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.SigmoidPolynomial;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import org.jetbrains.annotations.NotNull;
+
+public final class RGBAlbedoSpectrum implements Spectrum {
+    private final @NotNull SigmoidPolynomial polynomial;
+
+    public RGBAlbedoSpectrum(@NotNull ColorSpace cs, @NotNull ColorRGB rgb) {
+        if (rgb.r() < 0 || rgb.r() > 1 || rgb.g() < 0 || rgb.g() > 1 || rgb.b() < 0 || rgb.b() > 1) {
+            throw new IllegalArgumentException();
+        }
+        this.polynomial = cs.toPolynomial(rgb);
+    }
+
+    @Override
+    public double max() {
+        return polynomial.max();
+    }
+
+    @Override
+    public double get(double lambda) {
+        return polynomial.get(lambda);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/RGBIlluminantSpectrum.java

@@ -0,0 +1,36 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.SigmoidPolynomial;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import org.jetbrains.annotations.NotNull;
+
+/**
+ * A spectrum based on an RGB color used as an illuminant. The spectrum is adjusted to account for the color space's
+ * standard illuminant.
+ */
+public final class RGBIlluminantSpectrum implements Spectrum {
+    private final double scale;
+    private final @NotNull SigmoidPolynomial polynomial;
+    private final @NotNull Spectrum illuminant;
+
+    public RGBIlluminantSpectrum(@NotNull ColorSpace cs, @NotNull ColorRGB rgb) {
+        if (rgb.r() < 0 || rgb.g() < 0 || rgb.b() < 0) {
+            throw new IllegalArgumentException();
+        }
+        var max = Math.max(rgb.r(), Math.max(rgb.g(), rgb.b()));
+        this.scale = 2 * max;
+        this.polynomial = cs.toPolynomial(scale != 0 ? rgb.div(scale) : ColorRGB.BLACK);
+        this.illuminant = cs.illuminant();
+    }
+
+    @Override
+    public double max() {
+        return scale * polynomial.max() * illuminant.max();
+    }
+
+    @Override
+    public double get(double lambda) {
+        return scale * polynomial.get(lambda) * illuminant.get(lambda);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/RGBUnboundedSpectrum.java

@@ -0,0 +1,30 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.SigmoidPolynomial;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import org.jetbrains.annotations.NotNull;
+
+public final class RGBUnboundedSpectrum implements Spectrum {
+    private final double scale;
+    private final @NotNull SigmoidPolynomial polynomial;
+
+    public RGBUnboundedSpectrum(@NotNull ColorSpace cs, @NotNull ColorRGB rgb) {
+        if (rgb.r() < 0 || rgb.g() < 0 || rgb.b() < 0) {
+            throw new IllegalArgumentException();
+        }
+        var max = Math.max(rgb.r(), Math.max(rgb.g(), rgb.b()));
+        this.scale = 2 * max;
+        this.polynomial = cs.toPolynomial(scale != 0 ? rgb.div(scale) : ColorRGB.BLACK);
+    }
+
+    @Override
+    public double max() {
+        return scale * polynomial.max();
+    }
+
+    @Override
+    public double get(double lambda) {
+        return scale * polynomial.get(lambda);
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/SampledSpectrum.java

@@ -0,0 +1,139 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.math.IVec;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.ColorXYZ;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Arrays;
+
+// TODO use Vector API to parallelize operations
+public final class SampledSpectrum implements IVec<SampledSpectrum> {
+    private final double @NotNull[] values;
+
+    public SampledSpectrum(@NotNull SampledWavelengths lambdas, @NotNull Spectrum spectrum) {
+        var values = new double[lambdas.size()];
+        for (int i = 0; i < values.length; i++) {
+            values[i] = spectrum.get(lambdas.get(i));
+        }
+        this.values = values;
+    }
+
+    public SampledSpectrum(int count, double value) {
+        var values = new double[count];
+        Arrays.fill(values, value);
+        this.values = values;
+    }
+
+    private SampledSpectrum(double @NotNull[] values) {
+        this.values = values;
+    }
+
+    /*
+     * Math
+     */
+
+    public static @NotNull SampledSpectrum fma(@NotNull SampledSpectrum a, @NotNull SampledSpectrum b, @NotNull SampledSpectrum c) {
+        var out = new double[a.values.length];
+        for (int i = 0; i < a.values.length; i++) {
+            out[i] = Math.fma(a.values[i], b.values[i], c.values[i]);
+        }
+        return new SampledSpectrum(out);
+    }
+
+    public static @NotNull SampledSpectrum lerp(@NotNull SampledSpectrum a, @NotNull SampledSpectrum b, double t) {
+        if (t < 0) return a;
+        if (t > 1) return b;
+        var out = new double[a.values.length];
+        for (int i = 0; i < a.values.length; i++) {
+            out[i] = Math.fma(t, b.values[i] - a.values[i], a.values[i]);
+        }
+        return new SampledSpectrum(out);
+    }
+
+    @Override
+    public @NotNull SampledSpectrum plus(@NotNull SampledSpectrum other) {
+        var out = new double[other.values.length];
+        for (int i = 0; i < other.values.length; i++) {
+            out[i] = values[i] + other.values[i];
+        }
+        return new SampledSpectrum(out);
+    }
+
+    @Override
+    public @NotNull SampledSpectrum minus(@NotNull SampledSpectrum other) {
+        var out = new double[other.values.length];
+        for (int i = 0; i < other.values.length; i++) {
+            out[i] = values[i] - other.values[i];
+        }
+        return new SampledSpectrum(out);
+    }
+
+    @Override
+    public @NotNull SampledSpectrum times(@NotNull SampledSpectrum other) {
+        var out = new double[other.values.length];
+        for (int i = 0; i < other.values.length; i++) {
+            out[i] = values[i] * other.values[i];
+        }
+        return new SampledSpectrum(out);
+    }
+
+    @Override
+    public @NotNull SampledSpectrum times(double d) {
+        var out = new double[values.length];
+        for (int i = 0; i < values.length; i++) {
+            out[i] = values[i] * d;
+        }
+        return new SampledSpectrum(out);
+    }
+
+    @Override
+    public double @NotNull [] toArray() {
+        return Arrays.copyOf(values, values.length);
+    }
+
+    /*
+     * Accessors
+     */
+
+    @Override
+    public double get(int index) {
+        return values[index];
+    }
+
+    public int size() {
+        return values.length;
+    }
+
+    /*
+     * Object
+     */
+
+    @Override
+    public boolean equals(Object obj) {
+        return obj instanceof SampledSpectrum o && Arrays.equals(values, o.values);
+    }
+
+    @Override
+    public int hashCode() {
+        return Arrays.hashCode(values);
+    }
+
+    @Override
+    public @NotNull String toString() {
+        return "SampledSpectrum[values=" + Arrays.toString(values) + "]";
+    }
+
+    /*
+     * Conversions
+     */
+
+    public @NotNull ColorXYZ toXYZ(@NotNull SampledWavelengths lambdas) {
+        return lambdas.toXYZ(this);
+    }
+
+    public @NotNull ColorRGB toRGB(@NotNull SampledWavelengths lambdas, @NotNull ColorSpace cs) {
+        return cs.toRGB(toXYZ(lambdas));
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/SampledWavelengths.java

@@ -0,0 +1,120 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.render.color.ColorXYZ;
+import org.jetbrains.annotations.Contract;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Arrays;
+
+/**
+ * A set of sampled wavelength that can be tracked together.
+ */
+public final class SampledWavelengths {
+    public static final SampledWavelengths EMPTY = new SampledWavelengths(new double[0], new double[0]);
+
+    private final double @NotNull[] lambdas;
+    private final double @NotNull[] pdf;
+
+    public static @NotNull SampledWavelengths uniform(double rng, int count) {
+        return uniform(rng, count, Spectrum.LAMBDA_MIN, Spectrum.LAMBDA_MAX);
+    }
+
+    public static @NotNull SampledWavelengths uniform(double rng, int count, double min, double max) {
+        var lambdas = new double[count];
+
+        // choose first sample at random
+        lambdas[0] = (1 - rng) * min + rng * max;
+
+        // choose next samples in equal intervals, wrapping if necessary
+        var delta = (max - min) / count;
+        for (int i = 1; i < count; i++) {
+            lambdas[i] = lambdas[i - 1] + delta;
+            if (lambdas[i] > max) {
+                lambdas[i] = min + (lambdas[i] - max);
+            }
+        }
+
+        var pdf = new double[count];
+        Arrays.fill(pdf, 1 / (max - min));
+        return new SampledWavelengths(lambdas, pdf);
+    }
+
+    private SampledWavelengths(double @NotNull[] lambdas, double @NotNull[] pdf) {
+        this.lambdas = lambdas;
+        this.pdf = pdf;
+    }
+
+    @Contract(pure = true)
+    public double get(int index) {
+        return lambdas[index];
+    }
+
+    @Contract(pure = true)
+    public int size() {
+        return lambdas.length;
+    }
+
+    /**
+     * Terminates the secondary wavelengths. This method should be called after a wavelength-dependent operation like
+     * refraction that makes it incorrect to track multiple wavelengths together.
+     */
+    @Contract(mutates = "this")
+    public double collapse() {
+        if (pdf.length >= 2 || pdf[1] != 0) {
+            Arrays.fill(pdf, 1, pdf.length, 0d);
+            pdf[0] /= pdf.length;
+        }
+        return lambdas[0];
+    }
+
+    /*
+     * Object
+     */
+
+    @Override
+    public boolean equals(Object obj) {
+        return obj instanceof SampledWavelengths o && Arrays.equals(lambdas, o.lambdas) && Arrays.equals(pdf, o.pdf);
+    }
+
+    @Override
+    public int hashCode() {
+        return 31 * Arrays.hashCode(lambdas) + Arrays.hashCode(pdf);
+    }
+
+    @Override
+    public @NotNull String toString() {
+        return "SampledWavelengths[lambdas=" + Arrays.toString(lambdas) + ", pdf=" + Arrays.toString(pdf) + "]";
+    }
+
+    /*
+     * Conversions
+     */
+
+    @NotNull
+    ColorXYZ toXYZ(@NotNull SampledSpectrum spectrum) {
+        var x = Spectra.X.sample(this);
+        var y = Spectra.Y.sample(this);
+        var z = Spectra.Z.sample(this);
+
+        return new ColorXYZ(
+                toXYZ0(spectrum, x) / ColorXYZ.CIE_Y_INTEGRAL,
+                toXYZ0(spectrum, y) / ColorXYZ.CIE_Y_INTEGRAL,
+                toXYZ0(spectrum, z) / ColorXYZ.CIE_Y_INTEGRAL
+        );
+    }
+
+    private double toXYZ0(@NotNull SampledSpectrum spectrum, @NotNull SampledSpectrum cie) {
+        var avg = 0d;
+        for (int i = 0; i < spectrum.size(); i++) {
+            var pdf = this.pdf[i];
+            double value;
+            if (pdf == 0) {
+                value = 0;
+            } else {
+                value = spectrum.get(i) * cie.get(i) / pdf;
+            }
+            avg = Math.fma(1d / (i + 1), value - avg, avg);
+        }
+        return avg;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/ScaledSpectrum.java

@@ -0,0 +1,15 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import org.jetbrains.annotations.NotNull;
+
+public record ScaledSpectrum(@NotNull Spectrum spectrum, double scale) implements Spectrum {
+    @Override
+    public double max() {
+        return spectrum.max() * scale;
+    }
+
+    @Override
+    public double get(double lambda) {
+        return spectrum.get(lambda) * scale;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/Spectra.java

@@ -0,0 +1,410 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.render.color.ColorXYZ;
+import org.jetbrains.annotations.NotNull;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.io.UncheckedIOException;
+import java.nio.charset.StandardCharsets;
+import java.util.ArrayList;
+
+public final class Spectra {
+    private static final String PATH_PREFIX = "/eu/jonahbauer/raytracing/spectrum/";
+
+    /**
+     * the CIE XYZ color matching curve for X
+     */
+    public static final Spectrum X = new DenselySampledSpectrum(new PiecewiseLinearSpectrum(CIE_XYZ.CIE_lambda, CIE_XYZ.CIE_X));
+    /**
+     * the CIE XYZ color matching curve for Y
+     */
+    public static final Spectrum Y = new DenselySampledSpectrum(new PiecewiseLinearSpectrum(CIE_XYZ.CIE_lambda, CIE_XYZ.CIE_Y));;
+    /**
+     * the CIE XYZ color matching curve for Z
+     */
+    public static final Spectrum Z = new DenselySampledSpectrum(new PiecewiseLinearSpectrum(CIE_XYZ.CIE_lambda, CIE_XYZ.CIE_Z));;
+    /**
+     * the CIE standard illuminant D50
+     * @see <a href="https://doi.org/10.25039/CIE.DS.hjfjmt59">CIE 2022, CIE standard illuminant D65, International Commission on Illumination (CIE), Vienna, Austria, DOI: 10.25039/CIE.DS.hjfjmt59</a>
+     */
+    public static final Spectrum D50 = read("CIE_std_illum_D50.csv", true);
+    /**
+     * the CIE standard illuminant D65
+     * @see <a href="https://doi.org/10.25039/CIE.DS.etgmuqt5">CIE 2022, Relative spectral power distributions of CIE standard illuminants A, D65 and D50 (wavelengths in standard air) (data table), International Commission on Illumination (CIE), Vienna, Austria, DOI:10.25039/CIE.DS.etgmuqt5</a>
+     */
+    public static final Spectrum D65 = read("CIE_std_illum_D65.csv", true);
+
+    public static final Spectrum BLACK = new ConstantSpectrum(0);
+    public static final Spectrum WHITE = new ConstantSpectrum(1);
+
+    private static @NotNull Spectrum read(@NotNull String path, boolean normalize) {
+        var lambda = new ArrayList<Double>();
+        var values = new ArrayList<Double>();
+
+        try (
+                var is = Spectra.class.getResourceAsStream(PATH_PREFIX + path);
+                var in = new BufferedReader(new InputStreamReader(is, StandardCharsets.US_ASCII))
+        ) {
+            String line;
+            while ((line = in.readLine()) != null) {
+                var parts = line.split(",");
+                lambda.add(Double.parseDouble(parts[0]));
+                values.add(Double.parseDouble(parts[1]));
+            }
+        } catch (IOException e) {
+            throw new UncheckedIOException(e);
+        }
+
+        var pls = new PiecewiseLinearSpectrum(
+                lambda.stream().mapToDouble(Double::doubleValue).toArray(),
+                values.stream().mapToDouble(Double::doubleValue).toArray()
+        );
+        if (normalize) {
+            return pls.scale(ColorXYZ.CIE_Y_INTEGRAL / Util.innerProduct(pls, Spectra.Y));
+        } else {
+            return pls;
+        }
+    }
+
+    private Spectra() {
+        throw new UnsupportedOperationException();
+    }
+
+    /**
+     * @see <a href="https://doi.org/10.25039/CIE.DS.xvudnb9b">CIE 2018, CIE 1931 colour-matching functions , 2 degree observer (data table),
+     * International Commission on Illumination (CIE), Vienna, Austria,
+     * DOI:10.25039/CIE.DS.xvudnb9b</a>
+     */
+    private static final class CIE_XYZ {
+        private static final double[] CIE_lambda = {
+                360, 361, 362, 363, 364, 365, 366, 367, 368, 369, 370, 371, 372, 373, 374, 375, 376,
+                377, 378, 379, 380, 381, 382, 383, 384, 385, 386, 387, 388, 389, 390, 391, 392, 393,
+                394, 395, 396, 397, 398, 399, 400, 401, 402, 403, 404, 405, 406, 407, 408, 409, 410,
+                411, 412, 413, 414, 415, 416, 417, 418, 419, 420, 421, 422, 423, 424, 425, 426, 427,
+                428, 429, 430, 431, 432, 433, 434, 435, 436, 437, 438, 439, 440, 441, 442, 443, 444,
+                445, 446, 447, 448, 449, 450, 451, 452, 453, 454, 455, 456, 457, 458, 459, 460, 461,
+                462, 463, 464, 465, 466, 467, 468, 469, 470, 471, 472, 473, 474, 475, 476, 477, 478,
+                479, 480, 481, 482, 483, 484, 485, 486, 487, 488, 489, 490, 491, 492, 493, 494, 495,
+                496, 497, 498, 499, 500, 501, 502, 503, 504, 505, 506, 507, 508, 509, 510, 511, 512,
+                513, 514, 515, 516, 517, 518, 519, 520, 521, 522, 523, 524, 525, 526, 527, 528, 529,
+                530, 531, 532, 533, 534, 535, 536, 537, 538, 539, 540, 541, 542, 543, 544, 545, 546,
+                547, 548, 549, 550, 551, 552, 553, 554, 555, 556, 557, 558, 559, 560, 561, 562, 563,
+                564, 565, 566, 567, 568, 569, 570, 571, 572, 573, 574, 575, 576, 577, 578, 579, 580,
+                581, 582, 583, 584, 585, 586, 587, 588, 589, 590, 591, 592, 593, 594, 595, 596, 597,
+                598, 599, 600, 601, 602, 603, 604, 605, 606, 607, 608, 609, 610, 611, 612, 613, 614,
+                615, 616, 617, 618, 619, 620, 621, 622, 623, 624, 625, 626, 627, 628, 629, 630, 631,
+                632, 633, 634, 635, 636, 637, 638, 639, 640, 641, 642, 643, 644, 645, 646, 647, 648,
+                649, 650, 651, 652, 653, 654, 655, 656, 657, 658, 659, 660, 661, 662, 663, 664, 665,
+                666, 667, 668, 669, 670, 671, 672, 673, 674, 675, 676, 677, 678, 679, 680, 681, 682,
+                683, 684, 685, 686, 687, 688, 689, 690, 691, 692, 693, 694, 695, 696, 697, 698, 699,
+                700, 701, 702, 703, 704, 705, 706, 707, 708, 709, 710, 711, 712, 713, 714, 715, 716,
+                717, 718, 719, 720, 721, 722, 723, 724, 725, 726, 727, 728, 729, 730, 731, 732, 733,
+                734, 735, 736, 737, 738, 739, 740, 741, 742, 743, 744, 745, 746, 747, 748, 749, 750,
+                751, 752, 753, 754, 755, 756, 757, 758, 759, 760, 761, 762, 763, 764, 765, 766, 767,
+                768, 769, 770, 771, 772, 773, 774, 775, 776, 777, 778, 779, 780, 781, 782, 783, 784,
+                785, 786, 787, 788, 789, 790, 791, 792, 793, 794, 795, 796, 797, 798, 799, 800, 801,
+                802, 803, 804, 805, 806, 807, 808, 809, 810, 811, 812, 813, 814, 815, 816, 817, 818,
+                819, 820, 821, 822, 823, 824, 825, 826, 827, 828, 829, 830
+        };
+
+
+        private static final double[] CIE_X = {
+                // CIE X function values
+                0.0001299000,   0.0001458470,   0.0001638021,   0.0001840037,   0.0002066902,
+                0.0002321000,   0.0002607280,   0.0002930750,   0.0003293880,   0.0003699140,
+                0.0004149000,   0.0004641587,   0.0005189860,   0.0005818540,   0.0006552347,
+                0.0007416000,   0.0008450296,   0.0009645268,   0.001094949,    0.001231154,
+                0.001368000,    0.001502050,    0.001642328,    0.001802382,    0.001995757,
+                0.002236000,    0.002535385,    0.002892603,    0.003300829,    0.003753236,
+                0.004243000,    0.004762389,    0.005330048,    0.005978712,    0.006741117,
+                0.007650000,    0.008751373,    0.01002888,     0.01142170,     0.01286901,
+                0.01431000,     0.01570443,     0.01714744,     0.01878122,     0.02074801,
+                0.02319000,     0.02620736,     0.02978248,     0.03388092,     0.03846824,
+                0.04351000,     0.04899560,     0.05502260,     0.06171880,     0.06921200,
+                0.07763000,     0.08695811,     0.09717672,     0.1084063,      0.1207672,
+                0.1343800,      0.1493582,      0.1653957,      0.1819831,      0.1986110,
+                0.2147700,      0.2301868,      0.2448797,      0.2587773,      0.2718079,
+                0.2839000,      0.2949438,      0.3048965,      0.3137873,      0.3216454,
+                0.3285000,      0.3343513,      0.3392101,      0.3431213,      0.3461296,
+                0.3482800,      0.3495999,      0.3501474,      0.3500130,      0.3492870,
+                0.3480600,      0.3463733,      0.3442624,      0.3418088,      0.3390941,
+                0.3362000,      0.3331977,      0.3300411,      0.3266357,      0.3228868,
+                0.3187000,      0.3140251,      0.3088840,      0.3032904,      0.2972579,
+                0.2908000,      0.2839701,      0.2767214,      0.2689178,      0.2604227,
+                0.2511000,      0.2408475,      0.2298512,      0.2184072,      0.2068115,
+                0.1953600,      0.1842136,      0.1733273,      0.1626881,      0.1522833,
+                0.1421000,      0.1321786,      0.1225696,      0.1132752,      0.1042979,
+                0.09564000,     0.08729955,     0.07930804,     0.07171776,     0.06458099,
+                0.05795001,     0.05186211,     0.04628152,     0.04115088,     0.03641283,
+                0.03201000,     0.02791720,     0.02414440,     0.02068700,     0.01754040,
+                0.01470000,     0.01216179,     0.009919960,    0.007967240,    0.006296346,
+                0.004900000,    0.003777173,    0.002945320,    0.002424880,    0.002236293,
+                0.002400000,    0.002925520,    0.003836560,    0.005174840,    0.006982080,
+                0.009300000,    0.01214949,     0.01553588,     0.01947752,     0.02399277,
+                0.02910000,     0.03481485,     0.04112016,     0.04798504,     0.05537861,
+                0.06327000,     0.07163501,     0.08046224,     0.08973996,     0.09945645,
+                0.1096000,      0.1201674,      0.1311145,      0.1423679,      0.1538542,
+                0.1655000,      0.1772571,      0.1891400,      0.2011694,      0.2133658,
+                0.2257499,      0.2383209,      0.2510668,      0.2639922,      0.2771017,
+                0.2904000,      0.3038912,      0.3175726,      0.3314384,      0.3454828,
+                0.3597000,      0.3740839,      0.3886396,      0.4033784,      0.4183115,
+                0.4334499,      0.4487953,      0.4643360,      0.4800640,      0.4959713,
+                0.5120501,      0.5282959,      0.5446916,      0.5612094,      0.5778215,
+                0.5945000,      0.6112209,      0.6279758,      0.6447602,      0.6615697,
+                0.6784000,      0.6952392,      0.7120586,      0.7288284,      0.7455188,
+                0.7621000,      0.7785432,      0.7948256,      0.8109264,      0.8268248,
+                0.8425000,      0.8579325,      0.8730816,      0.8878944,      0.9023181,
+                0.9163000,      0.9297995,      0.9427984,      0.9552776,      0.9672179,
+                0.9786000,      0.9893856,      0.9995488,      1.0090892,      1.0180064,
+                1.0263000,      1.0339827,      1.0409860,      1.0471880,      1.0524667,
+                1.0567000,      1.0597944,      1.0617992,      1.0628068,      1.0629096,
+                1.0622000,      1.0607352,      1.0584436,      1.0552244,      1.0509768,
+                1.0456000,      1.0390369,      1.0313608,      1.0226662,      1.0130477,
+                1.0026000,      0.9913675,      0.9793314,      0.9664916,      0.9528479,
+                0.9384000,      0.9231940,      0.9072440,      0.8905020,      0.8729200,
+                0.8544499,      0.8350840,      0.8149460,      0.7941860,      0.7729540,
+                0.7514000,      0.7295836,      0.7075888,      0.6856022,      0.6638104,
+                0.6424000,      0.6215149,      0.6011138,      0.5811052,      0.5613977,
+                0.5419000,      0.5225995,      0.5035464,      0.4847436,      0.4661939,
+                0.4479000,      0.4298613,      0.4120980,      0.3946440,      0.3775333,
+                0.3608000,      0.3444563,      0.3285168,      0.3130192,      0.2980011,
+                0.2835000,      0.2695448,      0.2561184,      0.2431896,      0.2307272,
+                0.2187000,      0.2070971,      0.1959232,      0.1851708,      0.1748323,
+                0.1649000,      0.1553667,      0.1462300,      0.1374900,      0.1291467,
+                0.1212000,      0.1136397,      0.1064650,      0.09969044,     0.09333061,
+                0.08740000,     0.08190096,     0.07680428,     0.07207712,     0.06768664,
+                0.06360000,     0.05980685,     0.05628216,     0.05297104,     0.04981861,
+                0.04677000,     0.04378405,     0.04087536,     0.03807264,     0.03540461,
+                0.03290000,     0.03056419,     0.02838056,     0.02634484,     0.02445275,
+                0.02270000,     0.02108429,     0.01959988,     0.01823732,     0.01698717,
+                0.01584000,     0.01479064,     0.01383132,     0.01294868,     0.01212920,
+                0.01135916,     0.01062935,     0.009938846,    0.009288422,    0.008678854,
+                0.008110916,    0.007582388,    0.007088746,    0.006627313,    0.006195408,
+                0.005790346,    0.005409826,    0.005052583,    0.004717512,    0.004403507,
+                0.004109457,    0.003833913,    0.003575748,    0.003334342,    0.003109075,
+                0.002899327,    0.002704348,    0.002523020,    0.002354168,    0.002196616,
+                0.002049190,    0.001910960,    0.001781438,    0.001660110,    0.001546459,
+                0.001439971,    0.001340042,    0.001246275,    0.001158471,    0.001076430,
+                0.0009999493,   0.0009287358,   0.0008624332,   0.0008007503,   0.0007433960,
+                0.0006900786,   0.0006405156,   0.0005945021,   0.0005518646,   0.0005124290,
+                0.0004760213,   0.0004424536,   0.0004115117,   0.0003829814,   0.0003566491,
+                0.0003323011,   0.0003097586,   0.0002888871,   0.0002695394,   0.0002515682,
+                0.0002348261,   0.0002191710,   0.0002045258,   0.0001908405,   0.0001780654,
+                0.0001661505,   0.0001550236,   0.0001446219,   0.0001349098,   0.0001258520,
+                0.0001174130,   0.0001095515,   0.0001022245,   0.00009539445,  0.00008902390,
+                0.00008307527,  0.00007751269,  0.00007231304,  0.00006745778,  0.00006292844,
+                0.00005870652,  0.00005477028,  0.00005109918,  0.00004767654,  0.00004448567,
+                0.00004150994,  0.00003873324,  0.00003614203,  0.00003372352,  0.00003146487,
+                0.00002935326,  0.00002737573,  0.00002552433,  0.00002379376,  0.00002217870,
+                0.00002067383,  0.00001927226,  0.00001796640,  0.00001674991,  0.00001561648,
+                0.00001455977,  0.00001357387,  0.00001265436,  0.00001179723,  0.00001099844,
+                0.00001025398,  0.000009559646, 0.000008912044, 0.000008308358, 0.000007745769,
+                0.000007221456, 0.000006732475, 0.000006276423, 0.000005851304, 0.000005455118,
+                0.000005085868, 0.000004741466, 0.000004420236, 0.000004120783, 0.000003841716,
+                0.000003581652, 0.000003339127, 0.000003112949, 0.000002902121, 0.000002705645,
+                0.000002522525, 0.000002351726, 0.000002192415, 0.000002043902, 0.000001905497,
+                0.000001776509, 0.000001656215, 0.000001544022, 0.000001439440, 0.000001341977,
+                0.000001251141
+        };
+
+        private static final double[] CIE_Y = {
+                // CIE Y function values
+                0.000003917000,  0.000004393581,  0.000004929604,  0.000005532136,  0.000006208245,
+                0.000006965000,  0.000007813219,  0.000008767336,  0.000009839844,  0.00001104323,
+                0.00001239000,   0.00001388641,   0.00001555728,   0.00001744296,   0.00001958375,
+                0.00002202000,   0.00002483965,   0.00002804126,   0.00003153104,   0.00003521521,
+                0.00003900000,   0.00004282640,   0.00004691460,   0.00005158960,   0.00005717640,
+                0.00006400000,   0.00007234421,   0.00008221224,   0.00009350816,   0.0001061361,
+                0.0001200000,    0.0001349840,    0.0001514920,    0.0001702080,    0.0001918160,
+                0.0002170000,    0.0002469067,    0.0002812400,    0.0003185200,    0.0003572667,
+                0.0003960000,    0.0004337147,    0.0004730240,    0.0005178760,    0.0005722187,
+                0.0006400000,    0.0007245600,    0.0008255000,    0.0009411600,    0.001069880,
+                0.001210000,     0.001362091,     0.001530752,     0.001720368,     0.001935323,
+                0.002180000,     0.002454800,     0.002764000,     0.003117800,     0.003526400,
+                0.004000000,     0.004546240,     0.005159320,     0.005829280,     0.006546160,
+                0.007300000,     0.008086507,     0.008908720,     0.009767680,     0.01066443,
+                0.01160000,      0.01257317,      0.01358272,      0.01462968,      0.01571509,
+                0.01684000,      0.01800736,      0.01921448,      0.02045392,      0.02171824,
+                0.02300000,      0.02429461,      0.02561024,      0.02695857,      0.02835125,
+                0.02980000,      0.03131083,      0.03288368,      0.03452112,      0.03622571,
+                0.03800000,      0.03984667,      0.04176800,      0.04376600,      0.04584267,
+                0.04800000,      0.05024368,      0.05257304,      0.05498056,      0.05745872,
+                0.06000000,      0.06260197,      0.06527752,      0.06804208,      0.07091109,
+                0.07390000,      0.07701600,      0.08026640,      0.08366680,      0.08723280,
+                0.09098000,      0.09491755,      0.09904584,      0.1033674,       0.1078846,
+                0.1126000,       0.1175320,       0.1226744,       0.1279928,       0.1334528,
+                0.1390200,       0.1446764,       0.1504693,       0.1564619,       0.1627177,
+                0.1693000,       0.1762431,       0.1835581,       0.1912735,       0.1994180,
+                0.2080200,       0.2171199,       0.2267345,       0.2368571,       0.2474812,
+                0.2586000,       0.2701849,       0.2822939,       0.2950505,       0.3085780,
+                0.3230000,       0.3384021,       0.3546858,       0.3716986,       0.3892875,
+                0.4073000,       0.4256299,       0.4443096,       0.4633944,       0.4829395,
+                0.5030000,       0.5235693,       0.5445120,       0.5656900,       0.5869653,
+                0.6082000,       0.6293456,       0.6503068,       0.6708752,       0.6908424,
+                0.7100000,       0.7281852,       0.7454636,       0.7619694,       0.7778368,
+                0.7932000,       0.8081104,       0.8224962,       0.8363068,       0.8494916,
+                0.8620000,       0.8738108,       0.8849624,       0.8954936,       0.9054432,
+                0.9148501,       0.9237348,       0.9320924,       0.9399226,       0.9472252,
+                0.9540000,       0.9602561,       0.9660074,       0.9712606,       0.9760225,
+                0.9803000,       0.9840924,       0.9874812,       0.9903128,       0.9928116,
+                0.9949501,       0.9967108,       0.9980983,       0.9991120,       0.9997482,
+                1.0000000,       0.9998567,       0.9993046,       0.9983255,       0.9968987,
+                0.9950000,       0.9926005,       0.9897426,       0.9864444,       0.9827241,
+                0.9786000,       0.9740837,       0.9691712,       0.9638568,       0.9581349,
+                0.9520000,       0.9454504,       0.9384992,       0.9311628,       0.9234576,
+                0.9154000,       0.9070064,       0.8982772,       0.8892048,       0.8797816,
+                0.8700000,       0.8598613,       0.8493920,       0.8386220,       0.8275813,
+                0.8163000,       0.8047947,       0.7930820,       0.7811920,       0.7691547,
+                0.7570000,       0.7447541,       0.7324224,       0.7200036,       0.7074965,
+                0.6949000,       0.6822192,       0.6694716,       0.6566744,       0.6438448,
+                0.6310000,       0.6181555,       0.6053144,       0.5924756,       0.5796379,
+                0.5668000,       0.5539611,       0.5411372,       0.5283528,       0.5156323,
+                0.5030000,       0.4904688,       0.4780304,       0.4656776,       0.4534032,
+                0.4412000,       0.4290800,       0.4170360,       0.4050320,       0.3930320,
+                0.3810000,       0.3689184,       0.3568272,       0.3447768,       0.3328176,
+                0.3210000,       0.3093381,       0.2978504,       0.2865936,       0.2756245,
+                0.2650000,       0.2547632,       0.2448896,       0.2353344,       0.2260528,
+                0.2170000,       0.2081616,       0.1995488,       0.1911552,       0.1829744,
+                0.1750000,       0.1672235,       0.1596464,       0.1522776,       0.1451259,
+                0.1382000,       0.1315003,       0.1250248,       0.1187792,       0.1127691,
+                0.1070000,       0.1014762,       0.09618864,      0.09112296,      0.08626485,
+                0.08160000,      0.07712064,      0.07282552,      0.06871008,      0.06476976,
+                0.06100000,      0.05739621,      0.05395504,      0.05067376,      0.04754965,
+                0.04458000,      0.04175872,      0.03908496,      0.03656384,      0.03420048,
+                0.03200000,      0.02996261,      0.02807664,      0.02632936,      0.02470805,
+                0.02320000,      0.02180077,      0.02050112,      0.01928108,      0.01812069,
+                0.01700000,      0.01590379,      0.01483718,      0.01381068,      0.01283478,
+                0.01192000,      0.01106831,      0.01027339,      0.009533311,     0.008846157,
+                0.008210000,     0.007623781,     0.007085424,     0.006591476,     0.006138485,
+                0.005723000,     0.005343059,     0.004995796,     0.004676404,     0.004380075,
+                0.004102000,     0.003838453,     0.003589099,     0.003354219,     0.003134093,
+                0.002929000,     0.002738139,     0.002559876,     0.002393244,     0.002237275,
+                0.002091000,     0.001953587,     0.001824580,     0.001703580,     0.001590187,
+                0.001484000,     0.001384496,     0.001291268,     0.001204092,     0.001122744,
+                0.001047000,     0.0009765896,    0.0009111088,    0.0008501332,    0.0007932384,
+                0.0007400000,    0.0006900827,    0.0006433100,    0.0005994960,    0.0005584547,
+                0.0005200000,    0.0004839136,    0.0004500528,    0.0004183452,    0.0003887184,
+                0.0003611000,    0.0003353835,    0.0003114404,    0.0002891656,    0.0002684539,
+                0.0002492000,    0.0002313019,    0.0002146856,    0.0001992884,    0.0001850475,
+                0.0001719000,    0.0001597781,    0.0001486044,    0.0001383016,    0.0001287925,
+                0.0001200000,    0.0001118595,    0.0001043224,    0.00009733560,   0.00009084587,
+                0.00008480000,   0.00007914667,   0.00007385800,   0.00006891600,   0.00006430267,
+                0.00006000000,   0.00005598187,   0.00005222560,   0.00004871840,   0.00004544747,
+                0.00004240000,   0.00003956104,   0.00003691512,   0.00003444868,   0.00003214816,
+                0.00003000000,   0.00002799125,   0.00002611356,   0.00002436024,   0.00002272461,
+                0.00002120000,   0.00001977855,   0.00001845285,   0.00001721687,   0.00001606459,
+                0.00001499000,   0.00001398728,   0.00001305155,   0.00001217818,   0.00001136254,
+                0.00001060000,   0.000009885877,  0.000009217304,  0.000008592362,  0.000008009133,
+                0.000007465700,  0.000006959567,  0.000006487995,  0.000006048699,  0.000005639396,
+                0.000005257800,  0.000004901771,  0.000004569720,  0.000004260194,  0.000003971739,
+                0.000003702900,  0.000003452163,  0.000003218302,  0.000003000300,  0.000002797139,
+                0.000002607800,  0.000002431220,  0.000002266531,  0.000002113013,  0.000001969943,
+                0.000001836600,  0.000001712230,  0.000001596228,  0.000001488090,  0.000001387314,
+                0.000001293400,  0.000001205820,  0.000001124143,  0.000001048009,  0.0000009770578,
+                0.0000009109300, 0.0000008492513, 0.0000007917212, 0.0000007380904, 0.0000006881098,
+                0.0000006415300, 0.0000005980895, 0.0000005575746, 0.0000005198080, 0.0000004846123,
+                0.0000004518100
+        };
+
+        private static final double[] CIE_Z = {
+                // CIE Z function values
+                0.0006061000,   0.0006808792,   0.0007651456,   0.0008600124,   0.0009665928,
+                0.001086000,    0.001220586,    0.001372729,    0.001543579,    0.001734286,
+                0.001946000,    0.002177777,    0.002435809,    0.002731953,    0.003078064,
+                0.003486000,    0.003975227,    0.004540880,    0.005158320,    0.005802907,
+                0.006450001,    0.007083216,    0.007745488,    0.008501152,    0.009414544,
+                0.01054999,     0.01196580,     0.01365587,     0.01558805,     0.01773015,
+                0.02005001,     0.02251136,     0.02520288,     0.02827972,     0.03189704,
+                0.03621000,     0.04143771,     0.04750372,     0.05411988,     0.06099803,
+                0.06785001,     0.07448632,     0.08136156,     0.08915364,     0.09854048,
+                0.1102000,      0.1246133,      0.1417017,      0.1613035,      0.1832568,
+                0.2074000,      0.2336921,      0.2626114,      0.2947746,      0.3307985,
+                0.3713000,      0.4162091,      0.4654642,      0.5196948,      0.5795303,
+                0.6456000,      0.7184838,      0.7967133,      0.8778459,      0.9594390,
+                1.0390501,      1.1153673,      1.1884971,      1.2581233,      1.3239296,
+                1.3856000,      1.4426352,      1.4948035,      1.5421903,      1.5848807,
+                1.6229600,      1.6564048,      1.6852959,      1.7098745,      1.7303821,
+                1.7470600,      1.7600446,      1.7696233,      1.7762637,      1.7804334,
+                1.7826000,      1.7829682,      1.7816998,      1.7791982,      1.7758671,
+                1.7721100,      1.7682589,      1.7640390,      1.7589438,      1.7524663,
+                1.7441000,      1.7335595,      1.7208581,      1.7059369,      1.6887372,
+                1.6692000,      1.6475287,      1.6234127,      1.5960223,      1.5645280,
+                1.5281000,      1.4861114,      1.4395215,      1.3898799,      1.3387362,
+                1.2876400,      1.2374223,      1.1878243,      1.1387611,      1.0901480,
+                1.0419000,      0.9941976,      0.9473473,      0.9014531,      0.8566193,
+                0.8129501,      0.7705173,      0.7294448,      0.6899136,      0.6521049,
+                0.6162000,      0.5823286,      0.5504162,      0.5203376,      0.4919673,
+                0.4651800,      0.4399246,      0.4161836,      0.3938822,      0.3729459,
+                0.3533000,      0.3348578,      0.3175521,      0.3013375,      0.2861686,
+                0.2720000,      0.2588171,      0.2464838,      0.2347718,      0.2234533,
+                0.2123000,      0.2011692,      0.1901196,      0.1792254,      0.1685608,
+                0.1582000,      0.1481383,      0.1383758,      0.1289942,      0.1200751,
+                0.1117000,      0.1039048,      0.09666748,     0.08998272,     0.08384531,
+                0.07824999,     0.07320899,     0.06867816,     0.06456784,     0.06078835,
+                0.05725001,     0.05390435,     0.05074664,     0.04775276,     0.04489859,
+                0.04216000,     0.03950728,     0.03693564,     0.03445836,     0.03208872,
+                0.02984000,     0.02771181,     0.02569444,     0.02378716,     0.02198925,
+                0.02030000,     0.01871805,     0.01724036,     0.01586364,     0.01458461,
+                0.01340000,     0.01230723,     0.01130188,     0.01037792,     0.009529306,
+                0.008749999,    0.008035200,    0.007381600,    0.006785400,    0.006242800,
+                0.005749999,    0.005303600,    0.004899800,    0.004534200,    0.004202400,
+                0.003900000,    0.003623200,    0.003370600,    0.003141400,    0.002934800,
+                0.002749999,    0.002585200,    0.002438600,    0.002309400,    0.002196800,
+                0.002100000,    0.002017733,    0.001948200,    0.001889800,    0.001840933,
+                0.001800000,    0.001766267,    0.001737800,    0.001711200,    0.001683067,
+                0.001650001,    0.001610133,    0.001564400,    0.001513600,    0.001458533,
+                0.001400000,    0.001336667,    0.001270000,    0.001205000,    0.001146667,
+                0.001100000,    0.001068800,    0.001049400,    0.001035600,    0.001021200,
+                0.001000000,    0.0009686400,   0.0009299200,   0.0008868800,   0.0008425600,
+                0.0008000000,   0.0007609600,   0.0007236800,   0.0006859200,   0.0006454400,
+                0.0006000000,   0.0005478667,   0.0004916000,   0.0004354000,   0.0003834667,
+                0.0003400000,   0.0003072533,   0.0002831600,   0.0002654400,   0.0002518133,
+                0.0002400000,   0.0002295467,   0.0002206400,   0.0002119600,   0.0002021867,
+                0.0001900000,   0.0001742133,   0.0001556400,   0.0001359600,   0.0001168533,
+                0.0001000000,   0.00008613333,  0.00007460000,  0.00006500000,  0.00005693333,
+                0.00004999999,  0.00004416000,  0.00003948000,  0.00003572000,  0.00003264000,
+                0.00003000000,  0.00002765333,  0.00002556000,  0.00002364000,  0.00002181333,
+                0.00002000000,  0.00001813333,  0.00001620000,  0.00001420000,  0.00001213333,
+                0.00001000000,  0.000007733333, 0.000005400000, 0.000003200000, 0.000001333333,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000, 0.000000000000,
+                0.000000000000
+        };
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/Spectrum.java

@@ -0,0 +1,79 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import eu.jonahbauer.raytracing.math.Ray;
+import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.color.ColorXYZ;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.texture.Texture;
+import eu.jonahbauer.raytracing.scene.HitResult;
+import eu.jonahbauer.raytracing.scene.SkyBox;
+import org.jetbrains.annotations.NotNull;
+
+public interface Spectrum extends Texture, SkyBox {
+    int LAMBDA_MIN = 360;
+    int LAMBDA_MAX = 830;
+
+    /**
+     * {@return the maximum value of <code>this</code> spectrum over the range of wavelengths}
+     */
+    double max();
+
+    /**
+     * {@return the value of <code>this</code> spectrum at a given wavelength}
+     * @param lambda the wavelength in nanometers
+     */
+    double get(double lambda);
+
+    default @NotNull Spectrum scale(double scale) {
+        return new ScaledSpectrum(this, scale);
+    }
+
+    default @NotNull SampledSpectrum sample(@NotNull SampledWavelengths lambdas) {
+        return new SampledSpectrum(lambdas, this);
+    }
+
+    default @NotNull ColorXYZ toXYZ() {
+        return new ColorXYZ(
+                Util.innerProduct(Spectra.X, this) / ColorXYZ.CIE_Y_INTEGRAL,
+                Util.innerProduct(Spectra.Y, this) / ColorXYZ.CIE_Y_INTEGRAL,
+                Util.innerProduct(Spectra.Z, this) / ColorXYZ.CIE_Y_INTEGRAL
+        );
+    }
+
+    default @NotNull ColorRGB toRGB(@NotNull ColorSpace cs) {
+        return cs.toRGB(toXYZ());
+    }
+
+    /*
+     * Texture
+     */
+
+    @Override
+    default @NotNull Spectrum get(@NotNull HitResult hit) {
+        return this;
+    }
+
+    @Override
+    default @NotNull Spectrum get(double u, double v, @NotNull Vec3 p) {
+        return this;
+    }
+
+    @Override
+    default boolean isUVRequired() {
+        return false;
+    }
+
+    /*
+     * SkyBox
+     */
+
+    @Override
+    default @NotNull SampledSpectrum getColor(@NotNull Ray ray) {
+        return this.sample(ray.lambda());
+    }
+
+    enum Type {
+        ALBEDO, ILLUMINANT, UNBOUNDED
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/spectrum/Util.java

@@ -0,0 +1,17 @@
+package eu.jonahbauer.raytracing.render.spectrum;
+
+import org.jetbrains.annotations.NotNull;
+
+final class Util {
+    private Util() {
+        throw new UnsupportedOperationException();
+    }
+
+    public static double innerProduct(@NotNull Spectrum f, @NotNull Spectrum g) {
+        var integral = 0.0;
+        for (var lambda = Spectrum.LAMBDA_MIN; lambda <= Spectrum.LAMBDA_MAX; lambda++) {
+            integral += f.get(lambda) * g.get(lambda);
+        }
+        return integral;
+    }
+}

src/main/java/eu/jonahbauer/raytracing/render/texture/CheckerTexture.java

@@ -1,12 +1,13 @@
 package eu.jonahbauer.raytracing.render.texture;
 
 import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import org.jetbrains.annotations.NotNull;
 
 public record CheckerTexture(double scale, @NotNull Texture even, @NotNull Texture odd) implements Texture {
 
     @Override
-    public @NotNull Color get(double u, double v, @NotNull Vec3 p) {
+    public @NotNull Spectrum get(double u, double v, @NotNull Vec3 p) {
         var x = (int) Math.floor(p.x() / scale);
         var y = (int) Math.floor(p.y() / scale);
         var z = (int) Math.floor(p.z() / scale);

src/main/java/eu/jonahbauer/raytracing/render/texture/Color.java

@@ -1,130 +0,0 @@
-package eu.jonahbauer.raytracing.render.texture;
-
-import eu.jonahbauer.raytracing.math.Ray;
-import eu.jonahbauer.raytracing.math.Vec3;
-import eu.jonahbauer.raytracing.scene.SkyBox;
-import org.jetbrains.annotations.NotNull;
-
-import java.util.Random;
-
-import static eu.jonahbauer.raytracing.Main.DEBUG;
-
-public record Color(double r, double g, double b) implements Texture, SkyBox {
-    public static final @NotNull Color BLACK = new Color(0.0, 0.0, 0.0);
-    public static final @NotNull Color WHITE = new Color(1.0, 1.0, 1.0);
-    public static final @NotNull Color RED = new Color(1.0, 0.0, 0.0);
-    public static final @NotNull Color GREEN = new Color(0.0, 1.0, 0.0);
-    public static final @NotNull Color BLUE = new Color(0.0, 0.0, 1.0);
-
-    public static @NotNull Color lerp(@NotNull Color a, @NotNull Color b, double t) {
-        if (t < 0) return a;
-        if (t > 1) return b;
-        return new Color(
-                (1 - t) * a.r + t * b.r,
-                (1 - t) * a.g + t * b.g,
-                (1 - t) * a.b + t * b.b
-        );
-    }
-
-    public static @NotNull Color multiply(@NotNull Color a, @NotNull Color b) {
-        return new Color(a.r() * b.r(), a.g() * b.g(), a.b() * b.b());
-    }
-
-    public static @NotNull Color multiply(@NotNull Color a, double b) {
-        return new Color(a.r() * b, a.g() * b, a.b() * b);
-    }
-
-    public static @NotNull Color add(@NotNull Color a, @NotNull Color b) {
-        return new Color(a.r() + b.r(), a.g() + b.g(), a.b() + b.b());
-    }
-
-    public static @NotNull Color random(@NotNull Random random) {
-        return new Color(random.nextDouble(), random.nextDouble(), random.nextDouble());
-    }
-
-    public static @NotNull Color random(@NotNull Random random, double min, double max) {
-        var span = max - min;
-        return new Color(
-                Math.fma(random.nextDouble(), span, min),
-                Math.fma(random.nextDouble(), span, min),
-                Math.fma(random.nextDouble(), span, min)
-        );
-    }
-
-    public static @NotNull Color average(@NotNull Color current, @NotNull Color next, int index) {
-        var factor = 1d / index;
-        return new Color(
-                Math.fma(factor, next.r() - current.r(), current.r()),
-                Math.fma(factor, next.g() - current.g(), current.g()),
-                Math.fma(factor, next.b() - current.b(), current.b())
-        );
-    }
-
-    public static @NotNull Color gamma(@NotNull Color color, double gamma) {
-        if (gamma == 1.0) {
-            return color;
-        } else if (gamma == 2.0) {
-            return new Color(
-                    Math.sqrt(color.r()),
-                    Math.sqrt(color.g()),
-                    Math.sqrt(color.b())
-            );
-        } else {
-            return new Color(
-                    Math.pow(color.r(), 1 / gamma),
-                    Math.pow(color.g(), 1 / gamma),
-                    Math.pow(color.b(), 1 / gamma)
-            );
-        }
-    }
-
-    public Color(int rgb) {
-        this((rgb >> 16) & 0xFF, (rgb >> 8) & 0xFF, rgb & 0xFF);
-    }
-    
-    public Color(int red, int green, int blue) {
-        this(red / 255f, green / 255f, blue / 255f);
-    }
-
-    public Color {
-        if (DEBUG) {
-            if (!Double.isFinite(r) || !Double.isFinite(g) || !Double.isFinite(b)) {
-                throw new IllegalArgumentException("r, g and b must be finite");
-            }
-            if (r < 0 || g < 0 || b < 0) {
-                throw new IllegalArgumentException("r, g and b must be non-negative");
-            }
-        }
-    }
-
-    public int red() {
-        return toInt(r);
-    }
-
-    public int green() {
-        return toInt(g);
-    }
-
-    public int blue() {
-        return toInt(b);
-    }
-
-    @Override
-    public @NotNull Color get(double u, double v, @NotNull Vec3 p) {
-        return this;
-    }
-
-    @Override
-    public @NotNull Color getColor(@NotNull Ray ray) {
-        return this;
-    }
-
-    @Override
-    public boolean isUVRequired() {
-        return false;
-    }
-
-    private static int toInt(double value) {
-        return Math.clamp((int) (255.99 * value), 0, 255);
-    }
-}

src/main/java/eu/jonahbauer/raytracing/render/texture/ImageTexture.java

@@ -1,7 +1,9 @@
 package eu.jonahbauer.raytracing.render.texture;
 
 import eu.jonahbauer.raytracing.math.Vec3;
-import eu.jonahbauer.raytracing.render.canvas.Image;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
+import eu.jonahbauer.raytracing.render.color.ColorSpace;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import org.jetbrains.annotations.NotNull;
 
 import javax.imageio.ImageIO;
@@ -10,22 +12,32 @@ import java.io.IOException;
 import java.io.UncheckedIOException;
 import java.util.Objects;
 
-public record ImageTexture(@NotNull Image image) implements Texture {
+public final class ImageTexture implements Texture {
+    private static final String PATH_PREFIX = "/eu/jonahbauer/raytracing/textures/";
 
-    public ImageTexture {
+    private final int width;
-        Objects.requireNonNull(image, "image");
+    private final int height;
-    }
+    private final @NotNull Spectrum[][] spectra;
+
+    public ImageTexture(@NotNull BufferedImage image, @NotNull ColorSpace cs, @NotNull Spectrum.Type type) {
+        this.width = image.getWidth();
+        this.height = image.getHeight();
+        this.spectra = new Spectrum[height][width];
 
-    public ImageTexture(@NotNull BufferedImage image) {
+        for (int y = 0; y < height; y++) {
-        this(new Image(image));
+            for (int x = 0; x < width; x++) {
+                var rgb = cs.decode(new ColorRGB(image.getRGB(x, y)));
+                spectra[y][x] = cs.toSpectrum(rgb, type);
+            }
+        }
     }
 
-    public ImageTexture(@NotNull String path) {
+    public ImageTexture(@NotNull String path, @NotNull ColorSpace cs) {
-        this(read(path));
+        this(read(path), cs, Spectrum.Type.ALBEDO);
     }
 
     private static @NotNull BufferedImage read(@NotNull String path) {
-        try (var in = Objects.requireNonNull(ImageTexture.class.getResourceAsStream(path))) {
+        try (var in = Objects.requireNonNull(ImageTexture.class.getResourceAsStream(PATH_PREFIX + path))) {
             return ImageIO.read(in);
         } catch (IOException ex) {
             throw new UncheckedIOException(ex);
@@ -33,11 +45,11 @@ public record ImageTexture(@NotNull Image image) implements Texture {
     }
 
     @Override
-    public @NotNull Color get(double u, double v, @NotNull Vec3 p) {
+    public @NotNull Spectrum get(double u, double v, @NotNull Vec3 p) {
         u = Math.clamp(u, 0, 1);
         v = 1 - Math.clamp(v, 0, 1);
-        int x = (int) (u * (image.getWidth() - 1));
+        int x = (int) (u * (width - 1));
-        int y = (int) (v * (image.getHeight() - 1));
+        int y = (int) (v * (height - 1));
-        return image.get(x, y);
+        return spectra[y][x];
     }
 }

src/main/java/eu/jonahbauer/raytracing/render/texture/PerlinTexture.java

@@ -1,6 +1,8 @@
 package eu.jonahbauer.raytracing.render.texture;
 
 import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Objects;
@@ -11,11 +13,11 @@ import java.util.random.RandomGenerator;
 public final class PerlinTexture implements Texture {
     private static final int POINT_COUNT = 256;
     private static final @NotNull Random RANDOM = new Random();
-    private static final @NotNull DoubleFunction<Color> GREYSCALE = t -> new Color(t, t, t);
+    private static final @NotNull DoubleFunction<Spectrum> GREYSCALE = Spectra.WHITE::scale;
 
     private final double scale;
     private final int turbulence;
-    private final @NotNull DoubleFunction<Color> color;
+    private final @NotNull DoubleFunction<Spectrum> color;
 
     private final int mask;
     private final Vec3[] randvec;
@@ -35,12 +37,12 @@ public final class PerlinTexture implements Texture {
         this(scale, turbulence, GREYSCALE);
     }
 
-    public PerlinTexture(double scale, int turbulence, @NotNull DoubleFunction<Color> color) {
+    public PerlinTexture(double scale, int turbulence, @NotNull DoubleFunction<Spectrum> color) {
         this(scale, turbulence, color, POINT_COUNT, RANDOM);
     }
 
     public PerlinTexture(
-            double scale, int turbulence, @NotNull DoubleFunction<Color> color,
+            double scale, int turbulence, @NotNull DoubleFunction<Spectrum> color,
             int count, @NotNull RandomGenerator random
     ) {
         if ((count & (count - 1)) != 0) throw new IllegalArgumentException("count must be a power of two");
@@ -118,7 +120,7 @@ public final class PerlinTexture implements Texture {
     }
 
     @Override
-    public @NotNull Color get(double u, double v, @NotNull Vec3 p) {
+    public @NotNull Spectrum get(double u, double v, @NotNull Vec3 p) {
         var noise = getNoise(p, turbulence);
         var t = Math.fma(0.5, Math.sin(Math.PI * noise), 0.5);
         return color.apply(t);

src/main/java/eu/jonahbauer/raytracing/render/texture/Texture.java

@@ -1,6 +1,7 @@
 package eu.jonahbauer.raytracing.render.texture;
 
 import eu.jonahbauer.raytracing.math.Vec3;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import org.jetbrains.annotations.NotNull;
 
@@ -8,7 +9,7 @@ public interface Texture {
     /**
      * {@return the color of <code>this</code> texture for a hit}
      */
-    default @NotNull Color get(@NotNull HitResult hit) {
+    default @NotNull Spectrum get(@NotNull HitResult hit) {
         return get(hit.u(), hit.v(), hit.position());
     }
 
@@ -18,7 +19,7 @@ public interface Texture {
      * @param v the texture v coordinate
      * @param p the position
      */
-    @NotNull Color get(double u, double v, @NotNull Vec3 p);
+    @NotNull Spectrum get(double u, double v, @NotNull Vec3 p);
 
     /**
      * Returns whether {@link #get(double, double, Vec3)} uses the {@code u} and/or {@code v} parameters.

src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java

@@ -7,10 +7,10 @@ import eu.jonahbauer.raytracing.render.material.Material;
 import eu.jonahbauer.raytracing.render.texture.Texture;
 import org.jetbrains.annotations.NotNull;
 
-import java.util.Objects;
+import java.util.random.RandomGenerator;
 
 /**
- * The result of a {@linkplain Hittable#hit(Ray, Range) hit}.
+ * The result of a {@linkplain Hittable#hit(Ray, Range, RandomGenerator) hit}.
  * @param t the {@code t} value at which the hit occurs
  * @param position the position of the hit
  * @param normal the surface normal at the hit position
@@ -24,10 +24,6 @@ public record HitResult(
         double t, @NotNull Vec3 position, @NotNull Vec3 normal, @NotNull Hittable target,
         @NotNull Material material, double u, double v, boolean isFrontFace
 ) implements Comparable<HitResult> {
-    public HitResult {
-        Objects.requireNonNull(position, "position");
-        normal = normal.unit();
-    }
 
     public @NotNull HitResult withPositionAndNormal(@NotNull Vec3 position, @NotNull Vec3 normal) {
         return new HitResult(t, position, normal, target, material, u, v, isFrontFace);

src/main/java/eu/jonahbauer/raytracing/scene/Hittable.java

@@ -9,15 +9,16 @@ import eu.jonahbauer.raytracing.scene.transform.Translate;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Optional;
+import java.util.random.RandomGenerator;
 
 public interface Hittable {
     @NotNull Range FORWARD = new Range(0.001, Double.POSITIVE_INFINITY);
 
     /**
-     * @see #hit(Ray, Range)
+     * @see #hit(Ray, Range, RandomGenerator)
      */
-    default @NotNull Optional<HitResult> hit(@NotNull Ray ray) {
+    default @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull RandomGenerator random) {
-        return hit(ray, FORWARD);
+        return hit(ray, FORWARD, random);
     }
 
     /**
@@ -31,7 +32,7 @@ public interface Hittable {
      * @return the result of the hit test, containing (among others) the value {@code t} such that {@code ray.at(t)} is
      *         a point on {@code this} hittable
      */
-    @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range);
+    @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @NotNull RandomGenerator random);
 
     /**
      * {@return the axis-aligned bounding box of this hittable}

src/main/java/eu/jonahbauer/raytracing/scene/Scene.java

@@ -2,7 +2,8 @@ package eu.jonahbauer.raytracing.scene;
 
 import eu.jonahbauer.raytracing.math.AABB;
 import eu.jonahbauer.raytracing.math.Ray;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.Spectra;
 import eu.jonahbauer.raytracing.scene.util.HittableBinaryTree;
 import eu.jonahbauer.raytracing.scene.util.HittableCollection;
 import org.jetbrains.annotations.NotNull;
@@ -11,6 +12,7 @@ import org.jetbrains.annotations.Nullable;
 import java.util.ArrayList;
 import java.util.List;
 import java.util.Objects;
+import java.util.random.RandomGenerator;
 
 public final class Scene extends HittableCollection {
     private final @NotNull HittableCollection objects;
@@ -23,7 +25,7 @@ public final class Scene extends HittableCollection {
     }
 
     public Scene(@NotNull List<? extends @NotNull Hittable> objects, @Nullable List<? extends @NotNull Target> targets) {
-        this(Color.BLACK, objects, targets);
+        this(Spectra.BLACK, objects, targets);
     }
 
     public Scene(@NotNull SkyBox background, @NotNull List<? extends @NotNull Hittable> objects) {
@@ -41,8 +43,8 @@ public final class Scene extends HittableCollection {
     }
 
     @Override
-    public void hit(@NotNull Ray ray, @NotNull State state) {
+    public void hit(@NotNull Ray ray, @NotNull State state, @NotNull RandomGenerator random) {
-        objects.hit(ray, state);
+        objects.hit(ray, state, random);
     }
 
     @Override
@@ -54,7 +56,7 @@ public final class Scene extends HittableCollection {
         return targets;
     }
 
-    public @NotNull Color getBackgroundColor(@NotNull Ray ray) {
+    public @NotNull SampledSpectrum getBackgroundColor(@NotNull Ray ray) {
         return background.getColor(ray);
     }
 }

src/main/java/eu/jonahbauer/raytracing/scene/SkyBox.java

@@ -1,21 +1,27 @@
 package eu.jonahbauer.raytracing.scene;
 
 import eu.jonahbauer.raytracing.math.Ray;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.spectrum.SampledSpectrum;
+import eu.jonahbauer.raytracing.render.spectrum.Spectrum;
 import org.jetbrains.annotations.NotNull;
 
 @FunctionalInterface
 public interface SkyBox {
-    @NotNull Color getColor(@NotNull Ray ray);
+    @NotNull SampledSpectrum getColor(@NotNull Ray ray);
 
-    static @NotNull SkyBox gradient(@NotNull Color top, @NotNull Color bottom) {
+    static @NotNull SkyBox gradient(@NotNull Spectrum top, @NotNull Spectrum bottom) {
         return ray -> {
             // altitude from -pi/2 to pi/2
             var alt = Math.copySign(
-                    Math.acos(ray.direction().withY(0).unit().times(ray.direction().unit())),
+                    Math.acos(ray.direction().withY(0).unit().dot(ray.direction().unit())),
                     ray.direction().y()
             );
-            return Color.lerp(bottom, top, alt / Math.PI + 0.5);
+
+            return SampledSpectrum.lerp(
+                    top.sample(ray.lambda()),
+                    bottom.sample(ray.lambda()),
+                    alt / Math.PI + 0.5
+            );
         };
     }
 }

src/main/java/eu/jonahbauer/raytracing/scene/hittable2d/Hittable2D.java

@@ -7,9 +7,11 @@ import eu.jonahbauer.raytracing.render.material.Material;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import eu.jonahbauer.raytracing.scene.Hittable;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.Optional;
+import java.util.random.RandomGenerator;
 
 public abstract class Hittable2D implements Hittable {
     protected final @NotNull Vec3 origin;
@@ -31,23 +33,23 @@ public abstract class Hittable2D implements Hittable {
         var n = u.cross(v);
         if (n.squared() < 1e-8) throw new IllegalArgumentException();
         this.normal = n.unit();
-        this.d = origin.times(normal);
+        this.d = origin.dot(normal);
         this.w = n.div(n.squared());
     }
 
     @Override
-    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @Nullable RandomGenerator random) {
-        var denominator = ray.direction().times(normal);
+        var denominator = ray.direction().dot(normal);
         if (Math.abs(denominator) < 1e-8) return Optional.empty(); // parallel
 
-        var t = (d - ray.origin().times(normal)) / denominator;
+        var t = (d - ray.origin().dot(normal)) / denominator;
         if (!range.surrounds(t)) return Optional.empty();
 
         var position = ray.at(t);
         var p = position.minus(origin);
 
-        var alpha = w.times(p.cross(v));
+        var alpha = w.dot(p.cross(v));
-        var beta = w.times(u.cross(p));
+        var beta = w.dot(u.cross(p));
         if (!isInterior(alpha, beta)) return Optional.empty();
 
         var frontFace = denominator < 0;
@@ -58,10 +60,10 @@ public abstract class Hittable2D implements Hittable {
     }
 
     protected double hit0(@NotNull Ray ray, @NotNull Range range) {
-        var denominator = ray.direction().times(normal);
+        var denominator = ray.direction().dot(normal);
         if (Math.abs(denominator) < 1e-8) return Double.NaN; // parallel
 
-        var t = (d - ray.origin().times(normal)) / denominator;
+        var t = (d - ray.origin().dot(normal)) / denominator;
         if (!range.surrounds(t)) return Double.NaN;
 
         var position = ray.at(t);

src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Box.java

@@ -48,7 +48,7 @@ public final class Box implements Hittable, Target {
     }
 
     @Override
-    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @Nullable RandomGenerator random) {
         // based on AABB#hit with additional detection of the side hit
         var origin = ray.origin();
         var direction = ray.direction();
@@ -103,13 +103,13 @@ public final class Box implements Hittable, Target {
             t = tmin;
             side = entry;
             frontFace = true;
-            material = materials[side.ordinal()];
+            material = materials[entry.ordinal()];
             normal = side.normal;
         } else if (range.surrounds(tmax) && materials[exit.ordinal()] != null) {
             t = tmax;
             side = exit;
             frontFace = false;
-            material = materials[side.ordinal()];
+            material = materials[exit.ordinal()];
             normal = side.normal.neg();
         } else {
             return Optional.empty();
@@ -130,7 +130,7 @@ public final class Box implements Hittable, Target {
     @Override
     public double getProbabilityDensity(@NotNull Vec3 origin, @NotNull Vec3 direction) {
         if (contains(origin)) return 1 / (4 * Math.PI);
-        if (hit(new Ray(origin, direction)).isEmpty()) return 0;
+        if (hit(new Ray(origin, direction), null).isEmpty()) return 0;
 
         var solidAngle = 0d;
         for (var s : Side.values()) {

src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java

@@ -10,15 +10,16 @@ import eu.jonahbauer.raytracing.scene.Hittable;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Optional;
+import java.util.random.RandomGenerator;
 
 public record ConstantMedium(@NotNull Hittable boundary, double density, @NotNull IsotropicMaterial material) implements Hittable {
 
     @Override
-    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @NotNull RandomGenerator random) {
-        var hit1 = boundary.hit(ray, Range.UNIVERSE);
+        var hit1 = boundary.hit(ray, Range.UNIVERSE, random);
         if (hit1.isEmpty()) return Optional.empty();
 
-        var hit2 = boundary.hit(ray, new Range(hit1.get().t() + 0.0001, Double.POSITIVE_INFINITY));
+        var hit2 = boundary.hit(ray, new Range(hit1.get().t() + 0.0001, Double.POSITIVE_INFINITY), random);
         if (hit2.isEmpty()) return Optional.empty();
 
         var tmin = Math.max(range.min(), hit1.get().t());
@@ -28,7 +29,7 @@ public record ConstantMedium(@NotNull Hittable boundary, double density, @NotNul
 
         var length = ray.direction().length();
         var distance = length * (tmax - tmin);
-        var hitDistance = - Math.log(Math.random()) / density;
+        var hitDistance = - Math.log(random.nextDouble()) / density;
         if (hitDistance > distance) return Optional.empty();
 
         var t = tmin + hitDistance / length;

src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Sphere.java

@@ -9,6 +9,7 @@ import eu.jonahbauer.raytracing.scene.HitResult;
 import eu.jonahbauer.raytracing.scene.Hittable;
 import eu.jonahbauer.raytracing.scene.Target;
 import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
 
 import java.util.Objects;
 import java.util.Optional;
@@ -40,13 +41,13 @@ public final class Sphere implements Hittable, Target {
     }
 
     @Override
-    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @Nullable RandomGenerator random) {
         var t = hit0(ray, range);
         if (Double.isNaN(t)) return Optional.empty();
 
         var position = ray.at(t);
         var normal = Vec3.fma(invRadius, position, normalizedCenter);
-        var frontFace = normal.times(ray.direction()) < 0;
+        var frontFace = normal.dot(ray.direction()) < 0;
 
         double u;
         double v;
@@ -70,7 +71,7 @@ public final class Sphere implements Hittable, Target {
         var oc = ray.origin().minus(center);
 
         var a = ray.direction().squared();
-        var h = ray.direction().times(oc);
+        var h = ray.direction().dot(oc);
         var c = oc.squared() - radius * radius;
 
         var discriminant = h * h - a * c;

src/main/java/eu/jonahbauer/raytracing/scene/transform/RotateY.java

@@ -62,7 +62,7 @@ public sealed class RotateY extends Transform {
 
         var newOrigin = transform(origin);
         var newDirection = transform(direction);
-        return new Ray(newOrigin, newDirection);
+        return new Ray(newOrigin, newDirection, ray.lambda());
     }
 
     @Override

src/main/java/eu/jonahbauer/raytracing/scene/transform/Transform.java

@@ -2,10 +2,8 @@ package eu.jonahbauer.raytracing.scene.transform;
 
 import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
-import eu.jonahbauer.raytracing.math.Vec3;
 import eu.jonahbauer.raytracing.scene.HitResult;
 import eu.jonahbauer.raytracing.scene.Hittable;
-import eu.jonahbauer.raytracing.scene.Target;
 import org.jetbrains.annotations.NotNull;
 
 import java.util.Objects;
@@ -24,7 +22,7 @@ public abstract class Transform implements Hittable {
     protected abstract @NotNull HitResult transform(@NotNull HitResult result);
 
     @Override
-    public final @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public final @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @NotNull RandomGenerator random) {
-        return object.hit(transform(ray), range).map(this::transform);
+        return object.hit(transform(ray), range, random).map(this::transform);
     }
 }

src/main/java/eu/jonahbauer/raytracing/scene/transform/Translate.java

@@ -35,7 +35,7 @@ public sealed class Translate extends Transform {
 
     @Override
     protected final @NotNull Ray transform(@NotNull Ray ray) {
-        return new Ray(ray.origin().minus(offset), ray.direction());
+        return new Ray(ray.origin().minus(offset), ray.direction(), ray.lambda());
     }
 
     @Override

src/main/java/eu/jonahbauer/raytracing/scene/util/HittableBinaryTree.java

@@ -8,6 +8,7 @@ import org.jetbrains.annotations.Nullable;
 
 import java.util.Comparator;
 import java.util.List;
+import java.util.random.RandomGenerator;
 
 public final class HittableBinaryTree extends HittableCollection {
     private final @Nullable Hittable left;
@@ -46,17 +47,17 @@ public final class HittableBinaryTree extends HittableCollection {
     }
 
     @Override
-    public void hit(@NotNull Ray ray, @NotNull State state) {
+    public void hit(@NotNull Ray ray, @NotNull State state, @NotNull RandomGenerator random) {
         if (!bbox.hit(ray, state.getRange())) return;
         if (left instanceof HittableCollection coll) {
-            coll.hit(ray, state);
+            coll.hit(ray, state, random);
         } else if (left != null) {
-            hit(state, ray, left);
+            hit(state, ray, left, random);
         }
         if (right instanceof HittableCollection coll) {
-            coll.hit(ray, state);
+            coll.hit(ray, state, random);
         } else if (right != null) {
-            hit(state, ray, right);
+            hit(state, ray, right, random);
         }
     }
 

src/main/java/eu/jonahbauer/raytracing/scene/util/HittableCollection.java

@@ -8,20 +8,21 @@ import org.jetbrains.annotations.NotNull;
 
 import java.util.Objects;
 import java.util.Optional;
+import java.util.random.RandomGenerator;
 
 public abstract class HittableCollection implements Hittable {
 
     @Override
-    public final @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range) {
+    public final @NotNull Optional<HitResult> hit(@NotNull Ray ray, @NotNull Range range, @NotNull RandomGenerator random) {
         var state = new State(range);
-        hit(ray, state);
+        hit(ray, state, random);
         return state.getResult();
     }
 
-    public abstract void hit(@NotNull Ray ray, @NotNull State state);
+    public abstract void hit(@NotNull Ray ray, @NotNull State state, @NotNull RandomGenerator random);
 
-    protected static boolean hit(@NotNull State state, @NotNull Ray ray, @NotNull Hittable object) {
+    protected static boolean hit(@NotNull State state, @NotNull Ray ray, @NotNull Hittable object, @NotNull RandomGenerator random) {
-        var r = object.hit(ray, state.range);
+        var r = object.hit(ray, state.range, random);
         if (r.isPresent()) {
             if (state.range.surrounds(r.get().t())){
                 state.result = r.get();

src/main/java/eu/jonahbauer/raytracing/scene/util/HittableList.java

@@ -7,6 +7,7 @@ import org.jetbrains.annotations.NotNull;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.random.RandomGenerator;
 
 public final class HittableList extends HittableCollection {
     private final @NotNull List<Hittable> objects;
@@ -22,8 +23,8 @@ public final class HittableList extends HittableCollection {
     }
 
     @Override
-    public void hit(@NotNull Ray ray, @NotNull State state) {
+    public void hit(@NotNull Ray ray, @NotNull State state, @NotNull RandomGenerator random) {
-        objects.forEach(object -> hit(state, ray, object));
+        objects.forEach(object -> hit(state, ray, object, random));
     }
 
     @Override

src/main/java/eu/jonahbauer/raytracing/scene/util/PdfUtil.java

@@ -13,7 +13,7 @@ public final class PdfUtil {
      * must be unit vectors.
      */
     public static double getSolidAngle(@NotNull Vec3 a, @NotNull Vec3 b, @NotNull Vec3 c) {
-        var angle = 2 * Math.atan(Math.abs(Vec3.tripleProduct(a, b, c)) / (1 + a.times(b) + b.times(c) + c.times(a)));
+        var angle = 2 * Math.atan(Math.abs(Vec3.tripleProduct(a, b, c)) / (1 + a.dot(b) + b.dot(c) + c.dot(a)));
         return angle < 0 ? 2 * Math.PI + angle : angle;
     }
 }

src/main/resources/eu/jonahbauer/raytracing/spectrum/CIE_std_illum_D50.csv

@@ -0,0 +1,531 @@
+300,0.01922
+301,0.222348
+302,0.425476
+303,0.628604
+304,0.831732
+305,1.03486
+306,1.23799
+307,1.44112
+308,1.64424
+309,1.84737
+310,2.0505
+311,2.62329
+312,3.19608
+313,3.76887
+314,4.34166
+315,4.91445
+316,5.48724
+317,6.06003
+318,6.63282
+319,7.20561
+320,7.7784
+321,8.47531
+322,9.17222
+323,9.86913
+324,10.566
+325,11.263
+326,11.9599
+327,12.6568
+328,13.3537
+329,14.0506
+330,14.7475
+331,15.0676
+332,15.3876
+333,15.7076
+334,16.0277
+335,16.3478
+336,16.6678
+337,16.9878
+338,17.3079
+339,17.628
+340,17.948
+341,18.2542
+342,18.5603
+343,18.8665
+344,19.1727
+345,19.4788
+346,19.785
+347,20.0912
+348,20.3974
+349,20.7035
+350,21.0097
+351,21.3029
+352,21.5961
+353,21.8894
+354,22.1826
+355,22.4758
+356,22.769
+357,23.0622
+358,23.3555
+359,23.6487
+360,23.9419
+361,24.2438
+362,24.5457
+363,24.8475
+364,25.1494
+365,25.4513
+366,25.7532
+367,26.0551
+368,26.3569
+369,26.6588
+370,26.9607
+371,26.7134
+372,26.4661
+373,26.2187
+374,25.9714
+375,25.7241
+376,25.4768
+377,25.2295
+378,24.9821
+379,24.7348
+380,24.4875
+381,25.0258
+382,25.5641
+383,26.1024
+384,26.6407
+385,27.179
+386,27.7174
+387,28.2557
+388,28.794
+389,29.3323
+390,29.8706
+391,31.8144
+392,33.7581
+393,35.7018
+394,37.6456
+395,39.5894
+396,41.5331
+397,43.4768
+398,45.4206
+399,47.3644
+400,49.3081
+401,50.0286
+402,50.749
+403,51.4695
+404,52.19
+405,52.9104
+406,53.6309
+407,54.3514
+408,55.0719
+409,55.7923
+410,56.5128
+411,56.8649
+412,57.217
+413,57.5691
+414,57.9212
+415,58.2733
+416,58.6254
+417,58.9775
+418,59.3296
+419,59.6817
+420,60.0338
+421,59.8122
+422,59.5905
+423,59.3689
+424,59.1473
+425,58.9256
+426,58.704
+427,58.4824
+428,58.2608
+429,58.0391
+430,57.8175
+431,59.5182
+432,61.219
+433,62.9197
+434,64.6205
+435,66.3212
+436,68.0219
+437,69.7227
+438,71.4234
+439,73.1242
+440,74.8249
+441,76.0671
+442,77.3094
+443,78.5516
+444,79.7938
+445,81.036
+446,82.2783
+447,83.5205
+448,84.7627
+449,86.005
+450,87.2472
+451,87.5837
+452,87.9202
+453,88.2567
+454,88.5932
+455,88.9297
+456,89.2662
+457,89.6027
+458,89.9392
+459,90.2757
+460,90.6122
+461,90.6878
+462,90.7634
+463,90.839
+464,90.9146
+465,90.9902
+466,91.0657
+467,91.1413
+468,91.2169
+469,91.2925
+470,91.3681
+471,91.7421
+472,92.1162
+473,92.4902
+474,92.8643
+475,93.2383
+476,93.6123
+477,93.9864
+478,94.3604
+479,94.7345
+480,95.1085
+481,94.7939
+482,94.4793
+483,94.1648
+484,93.8502
+485,93.5356
+486,93.221
+487,92.9064
+488,92.5919
+489,92.2773
+490,91.9627
+491,92.3388
+492,92.7149
+493,93.091
+494,93.4671
+495,93.8432
+496,94.2193
+497,94.5954
+498,94.9715
+499,95.3476
+500,95.7237
+501,95.8127
+502,95.9016
+503,95.9906
+504,96.0795
+505,96.1685
+506,96.2575
+507,96.3464
+508,96.4354
+509,96.5243
+510,96.6133
+511,96.6649
+512,96.7164
+513,96.768
+514,96.8196
+515,96.8712
+516,96.9227
+517,96.9743
+518,97.0259
+519,97.0774
+520,97.129
+521,97.626
+522,98.123
+523,98.62
+524,99.117
+525,99.614
+526,100.111
+527,100.608
+528,101.105
+529,101.602
+530,102.099
+531,101.965
+532,101.83
+533,101.696
+534,101.561
+535,101.427
+536,101.292
+537,101.158
+538,101.024
+539,100.889
+540,100.755
+541,100.911
+542,101.067
+543,101.223
+544,101.38
+545,101.536
+546,101.692
+547,101.848
+548,102.005
+549,102.161
+550,102.317
+551,102.085
+552,101.854
+553,101.622
+554,101.39
+555,101.158
+556,100.927
+557,100.695
+558,100.463
+559,100.232
+560,100
+561,99.7735
+562,99.547
+563,99.3205
+564,99.094
+565,98.8675
+566,98.641
+567,98.4145
+568,98.188
+569,97.9615
+570,97.735
+571,97.8533
+572,97.9716
+573,98.0899
+574,98.2082
+575,98.3265
+576,98.4448
+577,98.5631
+578,98.6814
+579,98.7997
+580,98.918
+581,98.3761
+582,97.8342
+583,97.2922
+584,96.7503
+585,96.2084
+586,95.6665
+587,95.1246
+588,94.5826
+589,94.0407
+590,93.4988
+591,93.9177
+592,94.3366
+593,94.7555
+594,95.1744
+595,95.5933
+596,96.0122
+597,96.4311
+598,96.85
+599,97.2689
+600,97.6878
+601,97.8459
+602,98.0041
+603,98.1622
+604,98.3203
+605,98.4784
+606,98.6366
+607,98.7947
+608,98.9528
+609,99.111
+610,99.2691
+611,99.2463
+612,99.2236
+613,99.2008
+614,99.1781
+615,99.1553
+616,99.1325
+617,99.1098
+618,99.087
+619,99.0643
+620,99.0415
+621,98.7095
+622,98.3776
+623,98.0456
+624,97.7136
+625,97.3816
+626,97.0497
+627,96.7177
+628,96.3857
+629,96.0538
+630,95.7218
+631,96.0353
+632,96.3489
+633,96.6624
+634,96.976
+635,97.2895
+636,97.603
+637,97.9166
+638,98.2301
+639,98.5437
+640,98.8572
+641,98.5382
+642,98.2192
+643,97.9002
+644,97.5812
+645,97.2622
+646,96.9432
+647,96.6242
+648,96.3052
+649,95.9862
+650,95.6672
+651,95.9195
+652,96.1717
+653,96.424
+654,96.6762
+655,96.9285
+656,97.1808
+657,97.433
+658,97.6853
+659,97.9375
+660,98.1898
+661,98.6712
+662,99.1525
+663,99.6339
+664,100.115
+665,100.597
+666,101.078
+667,101.559
+668,102.041
+669,102.522
+670,103.003
+671,102.616
+672,102.229
+673,101.842
+674,101.455
+675,101.068
+676,100.681
+677,100.294
+678,99.9071
+679,99.52
+680,99.133
+681,97.9578
+682,96.7826
+683,95.6074
+684,94.4322
+685,93.257
+686,92.0817
+687,90.9065
+688,89.7313
+689,88.5561
+690,87.3809
+691,87.8032
+692,88.2254
+693,88.6477
+694,89.0699
+695,89.4922
+696,89.9145
+697,90.3367
+698,90.759
+699,91.1812
+700,91.6035
+701,91.732
+702,91.8605
+703,91.989
+704,92.1175
+705,92.246
+706,92.3746
+707,92.5031
+708,92.6316
+709,92.7601
+710,92.8886
+711,91.2852
+712,89.6818
+713,88.0783
+714,86.4749
+715,84.8715
+716,83.2681
+717,81.6647
+718,80.0612
+719,78.4578
+720,76.8544
+721,77.8201
+722,78.7858
+723,79.7514
+724,80.7171
+725,81.6828
+726,82.6485
+727,83.6142
+728,84.5798
+729,85.5455
+730,86.5112
+731,87.1181
+732,87.7249
+733,88.3318
+734,88.9386
+735,89.5455
+736,90.1524
+737,90.7592
+738,91.3661
+739,91.9729
+740,92.5798
+741,91.1448
+742,89.7098
+743,88.2748
+744,86.8398
+745,85.4048
+746,83.9699
+747,82.5349
+748,81.0999
+749,79.6649
+750,78.2299
+751,76.1761
+752,74.1223
+753,72.0685
+754,70.0147
+755,67.9608
+756,65.907
+757,63.8532
+758,61.7994
+759,59.7456
+760,57.6918
+761,60.2149
+762,62.738
+763,65.2612
+764,67.7843
+765,70.3074
+766,72.8305
+767,75.3536
+768,77.8768
+769,80.3999
+770,82.923
+771,82.4581
+772,81.9932
+773,81.5283
+774,81.0634
+775,80.5985
+776,80.1336
+777,79.6687
+778,79.2038
+779,78.7389
+780,78.274
+781,78.402
+782,78.5301
+783,78.6581
+784,78.7862
+785,78.9142
+786,79.0422
+787,79.1703
+788,79.2983
+789,79.4264
+790,79.5544
+791,78.9391
+792,78.3238
+793,77.7085
+794,77.0932
+795,76.478
+796,75.8627
+797,75.2474
+798,74.6321
+799,74.0168
+800,73.4015
+801,72.4534
+802,71.5052
+803,70.5571
+804,69.609
+805,68.6608
+806,67.7127
+807,66.7646
+808,65.8165
+809,64.8683
+810,63.9202
+811,64.6059
+812,65.2916
+813,65.9772
+814,66.6629
+815,67.3486
+816,68.0343
+817,68.72
+818,69.4056
+819,70.0913
+820,70.777
+821,71.1435
+822,71.5099
+823,71.8764
+824,72.2429
+825,72.6094
+826,72.9758
+827,73.3423
+828,73.7088
+829,74.0752
+830,74.4417

src/main/resources/eu/jonahbauer/raytracing/spectrum/CIE_std_illum_D65.csv

@@ -0,0 +1,531 @@
+300,0.0341
+301,0.36014
+302,0.68618
+303,1.01222
+304,1.33826
+305,1.6643
+306,1.99034
+307,2.31638
+308,2.64242
+309,2.96846
+310,3.2945
+311,4.98865
+312,6.6828
+313,8.37695
+314,10.0711
+315,11.7652
+316,13.4594
+317,15.1535
+318,16.8477
+319,18.5418
+320,20.236
+321,21.9177
+322,23.5995
+323,25.2812
+324,26.963
+325,28.6447
+326,30.3265
+327,32.0082
+328,33.69
+329,35.3717
+330,37.0535
+331,37.343
+332,37.6326
+333,37.9221
+334,38.2116
+335,38.5011
+336,38.7907
+337,39.0802
+338,39.3697
+339,39.6593
+340,39.9488
+341,40.4451
+342,40.9414
+343,41.4377
+344,41.934
+345,42.4302
+346,42.9265
+347,43.4228
+348,43.9191
+349,44.4154
+350,44.9117
+351,45.0844
+352,45.257
+353,45.4297
+354,45.6023
+355,45.775
+356,45.9477
+357,46.1203
+358,46.293
+359,46.4656
+360,46.6383
+361,47.1834
+362,47.7285
+363,48.2735
+364,48.8186
+365,49.3637
+366,49.9088
+367,50.4539
+368,50.9989
+369,51.544
+370,52.0891
+371,51.8777
+372,51.6664
+373,51.455
+374,51.2437
+375,51.0323
+376,50.8209
+377,50.6096
+378,50.3982
+379,50.1869
+380,49.9755
+381,50.4428
+382,50.91
+383,51.3773
+384,51.8446
+385,52.3118
+386,52.7791
+387,53.2464
+388,53.7137
+389,54.1809
+390,54.6482
+391,57.4589
+392,60.2695
+393,63.0802
+394,65.8909
+395,68.7015
+396,71.5122
+397,74.3229
+398,77.1336
+399,79.9442
+400,82.7549
+401,83.628
+402,84.5011
+403,85.3742
+404,86.2473
+405,87.1204
+406,87.9936
+407,88.8667
+408,89.7398
+409,90.6129
+410,91.486
+411,91.6806
+412,91.8752
+413,92.0697
+414,92.2643
+415,92.4589
+416,92.6535
+417,92.8481
+418,93.0426
+419,93.2372
+420,93.4318
+421,92.7568
+422,92.0819
+423,91.4069
+424,90.732
+425,90.057
+426,89.3821
+427,88.7071
+428,88.0322
+429,87.3572
+430,86.6823
+431,88.5006
+432,90.3188
+433,92.1371
+434,93.9554
+435,95.7736
+436,97.5919
+437,99.4102
+438,101.228
+439,103.047
+440,104.865
+441,106.079
+442,107.294
+443,108.508
+444,109.722
+445,110.936
+446,112.151
+447,113.365
+448,114.579
+449,115.794
+450,117.008
+451,117.088
+452,117.169
+453,117.249
+454,117.33
+455,117.41
+456,117.49
+457,117.571
+458,117.651
+459,117.732
+460,117.812
+461,117.517
+462,117.222
+463,116.927
+464,116.632
+465,116.336
+466,116.041
+467,115.746
+468,115.451
+469,115.156
+470,114.861
+471,114.967
+472,115.073
+473,115.18
+474,115.286
+475,115.392
+476,115.498
+477,115.604
+478,115.711
+479,115.817
+480,115.923
+481,115.212
+482,114.501
+483,113.789
+484,113.078
+485,112.367
+486,111.656
+487,110.945
+488,110.233
+489,109.522
+490,108.811
+491,108.865
+492,108.92
+493,108.974
+494,109.028
+495,109.082
+496,109.137
+497,109.191
+498,109.245
+499,109.3
+500,109.354
+501,109.199
+502,109.044
+503,108.888
+504,108.733
+505,108.578
+506,108.423
+507,108.268
+508,108.112
+509,107.957
+510,107.802
+511,107.501
+512,107.2
+513,106.898
+514,106.597
+515,106.296
+516,105.995
+517,105.694
+518,105.392
+519,105.091
+520,104.79
+521,105.08
+522,105.37
+523,105.66
+524,105.95
+525,106.239
+526,106.529
+527,106.819
+528,107.109
+529,107.399
+530,107.689
+531,107.361
+532,107.032
+533,106.704
+534,106.375
+535,106.047
+536,105.719
+537,105.39
+538,105.062
+539,104.733
+540,104.405
+541,104.369
+542,104.333
+543,104.297
+544,104.261
+545,104.225
+546,104.19
+547,104.154
+548,104.118
+549,104.082
+550,104.046
+551,103.641
+552,103.237
+553,102.832
+554,102.428
+555,102.023
+556,101.618
+557,101.214
+558,100.809
+559,100.405
+560,100
+561,99.6334
+562,99.2668
+563,98.9003
+564,98.5337
+565,98.1671
+566,97.8005
+567,97.4339
+568,97.0674
+569,96.7008
+570,96.3342
+571,96.2796
+572,96.225
+573,96.1703
+574,96.1157
+575,96.0611
+576,96.0065
+577,95.9519
+578,95.8972
+579,95.8426
+580,95.788
+581,95.0778
+582,94.3675
+583,93.6573
+584,92.947
+585,92.2368
+586,91.5266
+587,90.8163
+588,90.1061
+589,89.3958
+590,88.6856
+591,88.8177
+592,88.9497
+593,89.0818
+594,89.2138
+595,89.3459
+596,89.478
+597,89.61
+598,89.7421
+599,89.8741
+600,90.0062
+601,89.9655
+602,89.9248
+603,89.8841
+604,89.8434
+605,89.8026
+606,89.7619
+607,89.7212
+608,89.6805
+609,89.6398
+610,89.5991
+611,89.4091
+612,89.219
+613,89.029
+614,88.8389
+615,88.6489
+616,88.4589
+617,88.2688
+618,88.0788
+619,87.8887
+620,87.6987
+621,87.2577
+622,86.8167
+623,86.3757
+624,85.9347
+625,85.4936
+626,85.0526
+627,84.6116
+628,84.1706
+629,83.7296
+630,83.2886
+631,83.3297
+632,83.3707
+633,83.4118
+634,83.4528
+635,83.4939
+636,83.535
+637,83.576
+638,83.6171
+639,83.6581
+640,83.6992
+641,83.332
+642,82.9647
+643,82.5975
+644,82.2302
+645,81.863
+646,81.4958
+647,81.1285
+648,80.7613
+649,80.394
+650,80.0268
+651,80.0456
+652,80.0644
+653,80.0831
+654,80.1019
+655,80.1207
+656,80.1395
+657,80.1583
+658,80.177
+659,80.1958
+660,80.2146
+661,80.4209
+662,80.6272
+663,80.8336
+664,81.0399
+665,81.2462
+666,81.4525
+667,81.6588
+668,81.8652
+669,82.0715
+670,82.2778
+671,81.8784
+672,81.4791
+673,81.0797
+674,80.6804
+675,80.281
+676,79.8816
+677,79.4823
+678,79.0829
+679,78.6836
+680,78.2842
+681,77.4279
+682,76.5716
+683,75.7153
+684,74.859
+685,74.0027
+686,73.1465
+687,72.2902
+688,71.4339
+689,70.5776
+690,69.7213
+691,69.9101
+692,70.0989
+693,70.2876
+694,70.4764
+695,70.6652
+696,70.854
+697,71.0428
+698,71.2315
+699,71.4203
+700,71.6091
+701,71.8831
+702,72.1571
+703,72.4311
+704,72.7051
+705,72.979
+706,73.253
+707,73.527
+708,73.801
+709,74.075
+710,74.349
+711,73.0745
+712,71.8
+713,70.5255
+714,69.251
+715,67.9765
+716,66.702
+717,65.4275
+718,64.153
+719,62.8785
+720,61.604
+721,62.4322
+722,63.2603
+723,64.0885
+724,64.9166
+725,65.7448
+726,66.573
+727,67.4011
+728,68.2293
+729,69.0574
+730,69.8856
+731,70.4057
+732,70.9259
+733,71.446
+734,71.9662
+735,72.4863
+736,73.0064
+737,73.5266
+738,74.0467
+739,74.5669
+740,75.087
+741,73.9376
+742,72.7881
+743,71.6387
+744,70.4893
+745,69.3398
+746,68.1904
+747,67.041
+748,65.8916
+749,64.7421
+750,63.5927
+751,61.8752
+752,60.1578
+753,58.4403
+754,56.7229
+755,55.0054
+756,53.288
+757,51.5705
+758,49.8531
+759,48.1356
+760,46.4182
+761,48.4569
+762,50.4956
+763,52.5344
+764,54.5731
+765,56.6118
+766,58.6505
+767,60.6892
+768,62.728
+769,64.7667
+770,66.8054
+771,66.4631
+772,66.1209
+773,65.7786
+774,65.4364
+775,65.0941
+776,64.7518
+777,64.4096
+778,64.0673
+779,63.7251
+780,63.3828
+781,63.4749
+782,63.567
+783,63.6592
+784,63.7513
+785,63.8434
+786,63.9355
+787,64.0276
+788,64.1198
+789,64.2119
+790,64.304
+791,63.8188
+792,63.3336
+793,62.8484
+794,62.3632
+795,61.8779
+796,61.3927
+797,60.9075
+798,60.4223
+799,59.9371
+800,59.4519
+801,58.7026
+802,57.9533
+803,57.204
+804,56.4547
+805,55.7054
+806,54.9562
+807,54.2069
+808,53.4576
+809,52.7083
+810,51.959
+811,52.5072
+812,53.0553
+813,53.6035
+814,54.1516
+815,54.6998
+816,55.248
+817,55.7961
+818,56.3443
+819,56.8924
+820,57.4406
+821,57.7278
+822,58.015
+823,58.3022
+824,58.5894
+825,58.8765
+826,59.1637
+827,59.4509
+828,59.7381
+829,60.0253
+830,60.3125

src/test/java/eu/jonahbauer/raytracing/math/Vec3Test.java

@@ -21,10 +21,10 @@ class Vec3Test {
     }
 
     @Test
-    void timesVec() {
+    void dotVec() {
         var a = new Vec3(1, 2, 3);
         var b = new Vec3(-1, 1, -2);
-        assertEquals(-5, a.times(b));
+        assertEquals(-5, a.dot(b));
     }
 
     @Test

src/test/java/eu/jonahbauer/raytracing/render/canvas/RGBCanvasTest.java

@@ -1,6 +1,6 @@
 package eu.jonahbauer.raytracing.render.canvas;
 
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
 import eu.jonahbauer.raytracing.render.ImageFormat;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
@@ -13,11 +13,11 @@ import java.util.Objects;
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 
-class ImageTest {
+class RGBCanvasTest {
 
     @Test
     void test(@TempDir Path dir) throws IOException {
-        var image = new Image(256, 256);
+        var image = new RGBCanvas(256, 256);
 
         for (var y = 0; y < image.getHeight(); y++) {
             for (var x = 0; x < image.getWidth(); x++) {
@@ -25,7 +25,7 @@ class ImageTest {
                 var g = (double) y / (image.getHeight() - 1);
                 var b = 0;
 
-                image.set(x, y, new Color(r, g, b));
+                image.set(x, y, new ColorRGB(r, g, b));
             }
         }
 
@@ -35,7 +35,7 @@ class ImageTest {
         String expected;
         String actual;
 
-        try (var in = Objects.requireNonNull(ImageTest.class.getResourceAsStream("simple_image.ppm"))) {
+        try (var in = Objects.requireNonNull(RGBCanvasTest.class.getResourceAsStream("simple_image.ppm"))) {
             expected = new String(in.readAllBytes(), StandardCharsets.US_ASCII);
         }
 

src/test/java/eu/jonahbauer/raytracing/scene/hittable3d/SphereTest.java

@@ -3,7 +3,7 @@ package eu.jonahbauer.raytracing.scene.hittable3d;
 import eu.jonahbauer.raytracing.math.Range;
 import eu.jonahbauer.raytracing.math.Ray;
 import eu.jonahbauer.raytracing.math.Vec3;
-import eu.jonahbauer.raytracing.render.texture.Color;
+import eu.jonahbauer.raytracing.render.color.ColorRGB;
 import eu.jonahbauer.raytracing.render.material.LambertianMaterial;
 import org.junit.jupiter.api.Test;
 
@@ -15,7 +15,7 @@ class SphereTest {
     void hit() {
         var center = new Vec3(1, 2, 3);
         var radius = 5;
-        var sphere = new Sphere(center, radius, new LambertianMaterial(Color.WHITE));
+        var sphere = new Sphere(center, radius, new LambertianMaterial(ColorRGB.WHITE));
 
         var origin = new Vec3(6, 7, 8);
         var direction = new Vec3(-1, -1, -1);