diff --git a/src/main/java/eu/jonahbauer/raytracing/Main.java b/src/main/java/eu/jonahbauer/raytracing/Main.java
index 8111102..699743a 100644
--- a/src/main/java/eu/jonahbauer/raytracing/Main.java
+++ b/src/main/java/eu/jonahbauer/raytracing/Main.java
@@ -13,6 +13,8 @@ import java.nio.file.Path;
 import java.util.function.IntFunction;
 
 public class Main {
+    public static final boolean DEBUG = false;
+
     public static void main(String[] args) throws IOException {
         var config = Config.parse(args);
         var example = config.example;
diff --git a/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java b/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
index a0b728a..7870fc5 100644
--- a/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
+++ b/src/main/java/eu/jonahbauer/raytracing/math/Vec3.java
@@ -178,4 +178,9 @@ public record Vec3(double x, double y, double z) {
     public @NotNull Vec3 withZ(double z) {
         return new Vec3(x, y, z);
     }
+
+    @Override
+    public @NotNull String toString() {
+        return "(" + x + "," + y + "," + z + ")";
+    }
 }
diff --git a/src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java b/src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java
index 54dc744..e3c6a1e 100644
--- a/src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java
+++ b/src/main/java/eu/jonahbauer/raytracing/render/renderer/SimpleRenderer.java
@@ -16,6 +16,8 @@ import java.util.SplittableRandom;
 import java.util.random.RandomGenerator;
 import java.util.stream.IntStream;
 
+import static eu.jonahbauer.raytracing.Main.DEBUG;
+
 public final class SimpleRenderer implements Renderer {
     private final int sqrtSamplesPerPixel;
     private final int maxDepth;
@@ -104,6 +106,9 @@ public final class SimpleRenderer implements Renderer {
                 for (int sj = 0; sj < sqrtSamplesPerPixel; sj++) {
                     for (int si = 0; si < sqrtSamplesPerPixel; si++) {
                         var ray = camera.cast(x, y, si, sj, sqrtSamplesPerPixel, random);
+                        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);
                     }
@@ -127,36 +132,75 @@ public final class SimpleRenderer implements Renderer {
         while (depth-- > 0) {
             var optional = scene.hit(ray, new Range(0.001, Double.POSITIVE_INFINITY));
             if (optional.isEmpty()) {
-                color = Color.add(color, Color.multiply(attenuation, scene.getBackgroundColor(ray)));
+                var background = scene.getBackgroundColor(ray);
+                color = Color.add(color, Color.multiply(attenuation, background));
+                if (DEBUG) {
+                    System.out.println("  Hit background: " + background);
+                }
                 break;
             }
 
             var hit = optional.get();
+            if (DEBUG) {
+                System.out.println("  Hit " + hit.target() + " at t=" + hit.t() + " (" + hit.position() + ")");
+            }
             var material = hit.material();
             var emitted = material.emitted(hit);
+            if (DEBUG && !Color.BLACK.equals(emitted)) {
+                System.out.println("  Emitted: " + emitted);
+            }
+
             var result = material.scatter(ray, hit, random);
             color = Color.add(color, Color.multiply(attenuation, emitted));
 
-            if (result.isEmpty()) break;
+            if (result.isEmpty()) {
+                if (DEBUG) {
+                    System.out.println("  Absorbed");
+                }
+                break;
+            }
 
             switch (result.get()) {
                 case Material.SpecularScatterResult(var a, var scattered) -> {
                     attenuation = Color.multiply(attenuation, a);
                     ray = scattered;
+
+                    if (DEBUG) {
+                        System.out.println("  Specular scattering with albedo " + a);
+                    }
                 }
                 case Material.PdfScatterResult(var a, var pdf) -> {
                     if (scene.getLights() == null) {
                         attenuation = Color.multiply(attenuation, a);
                         ray = new Ray(hit.position(), pdf.generate(random));
+
+                        if (DEBUG) {
+                            System.out.println("  Pdf scattering with albedo " + a);
+                        }
                     } else {
-                        var mixed = new MixtureProbabilityDensityFunction(new TargetingProbabilityDensityFunction(hit.position(), scene.getLights()), pdf);
+                        var mixed = new MixtureProbabilityDensityFunction(new TargetingProbabilityDensityFunction(hit.position(), scene.getLights()), pdf, 0.5);
                         var direction = mixed.generate(random);
                         var factor = pdf.value(direction) / mixed.value(direction);
                         attenuation = Color.multiply(attenuation, Color.multiply(a, factor));
                         ray = new Ray(hit.position(), direction);
+
+                        if (DEBUG) {
+                            System.out.println("  Pdf scattering with albedo " + a + " and factor " + factor);
+                        }
                     }
+
                 }
             }
+
+            if (DEBUG) {
+                System.out.println("  Combined color is " + color);
+                System.out.println("  Combined attenuation is " + attenuation);
+                System.out.println("  New ray is " + ray);
+            }
+        }
+
+        if (DEBUG) {
+            System.out.println("  Final color is " + color);
         }
 
         return color;
diff --git a/src/main/java/eu/jonahbauer/raytracing/render/texture/Color.java b/src/main/java/eu/jonahbauer/raytracing/render/texture/Color.java
index 991badf..511d72f 100644
--- a/src/main/java/eu/jonahbauer/raytracing/render/texture/Color.java
+++ b/src/main/java/eu/jonahbauer/raytracing/render/texture/Color.java
@@ -5,6 +5,8 @@ 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 {
     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);
@@ -82,6 +84,17 @@ public record Color(double r, double g, double b) implements Texture {
         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);
     }
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java b/src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java
index 1483782..cf21baf 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/HitResult.java
@@ -7,7 +7,7 @@ import org.jetbrains.annotations.NotNull;
 import java.util.Objects;
 
 public record HitResult(
-        double t, @NotNull Vec3 position, @NotNull Vec3 normal,
+        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 {
@@ -16,7 +16,7 @@ public record HitResult(
     }
 
     public @NotNull HitResult withPositionAndNormal(@NotNull Vec3 position, @NotNull Vec3 normal) {
-        return new HitResult(t, position, normal, material, u, v, isFrontFace);
+        return new HitResult(t, position, normal, target, material, u, v, isFrontFace);
     }
 
     @Override
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/hittable2d/Hittable2D.java b/src/main/java/eu/jonahbauer/raytracing/scene/hittable2d/Hittable2D.java
index 74bb50a..23282b6 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/hittable2d/Hittable2D.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/hittable2d/Hittable2D.java
@@ -52,10 +52,15 @@ public abstract class Hittable2D implements Hittable {
 
         var frontFace = denominator < 0;
         return Optional.of(new HitResult(
-                t, position, frontFace ? normal : normal.neg(),
+                t, position, frontFace ? normal : normal.neg(), this,
                 material, alpha, beta, frontFace
         ));
     }
 
     protected abstract boolean isInterior(double alpha, double beta);
+
+    @Override
+    public @NotNull String toString() {
+        return this.getClass().getSimpleName() + "(origin=" + origin + ", u=" + u + ", v=" + v + ")";
+    }
 }
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Box.java b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Box.java
index 14169af..8df9f0d 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Box.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Box.java
@@ -110,7 +110,7 @@ public final class Box implements Hittable, Target {
         var uv = material.texture().isUVRequired();
         var u = uv ? side.getTextureU(box, position) : Double.NaN;
         var v = uv ? side.getTextureV(box, position) : Double.NaN;
-        return Optional.of(new HitResult(t, position, normal, material, u, v, frontFace));
+        return Optional.of(new HitResult(t, position, normal, this, material, u, v, frontFace));
     }
 
     @Override
@@ -173,6 +173,11 @@ public final class Box implements Hittable, Target {
                && box.min().z() < point.z() && point.z() < box.max().z();
     }
 
+    @Override
+    public @NotNull String toString() {
+        return "Box(min=" + box.min() + ", max=" + box.max() + ")";
+    }
+
     private enum Side {
         NEG_X(Vec3.UNIT_X.neg()),
         NEG_Y(Vec3.UNIT_Y.neg()),
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java
index bf104a4..eb0613e 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/ConstantMedium.java
@@ -32,7 +32,7 @@ public record ConstantMedium(@NotNull Hittable boundary, double density, @NotNul
         if (hitDistance > distance) return Optional.empty();
 
         var t = tmin + hitDistance / length;
-        return Optional.of(new HitResult(t, ray.at(t), Vec3.UNIT_X, material, 0, 0, true)); // arbitrary normal, u, v and isFrontFace
+        return Optional.of(new HitResult(t, ray.at(t), Vec3.UNIT_X, this, material, 0, 0, true)); // arbitrary normal, u, v and isFrontFace
     }
 
     @Override
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Sphere.java b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Sphere.java
index c1d0ecf..1802dd6 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Sphere.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/hittable3d/Sphere.java
@@ -67,7 +67,7 @@ public final class Sphere implements Hittable, Target {
         }
 
         return Optional.of(new HitResult(
-                t, position, frontFace ? normal : normal.neg(),
+                t, position, frontFace ? normal : normal.neg(), this,
                 material, u, v, frontFace
         ));
     }
@@ -97,4 +97,9 @@ public final class Sphere implements Hittable, Target {
 
         return target.times(radius).plus(center).minus(origin);
     }
+
+    @Override
+    public @NotNull String toString() {
+        return "Sphere(center=" + center + ", radius=" + radius + ")";
+    }
 }
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/transform/RotateY.java b/src/main/java/eu/jonahbauer/raytracing/scene/transform/RotateY.java
index 0084202..b250185 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/transform/RotateY.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/transform/RotateY.java
@@ -89,6 +89,11 @@ public sealed class RotateY extends Transform {
         return bbox;
     }
 
+    @Override
+    public @NotNull String toString() {
+        return object + " rotated by " + Math.toDegrees(Math.atan2(sin, cos)) + "° around the y axis";
+    }
+
     private static final class RotateYTarget extends RotateY implements Target {
 
         private RotateYTarget(@NotNull Hittable object, double angle) {
diff --git a/src/main/java/eu/jonahbauer/raytracing/scene/transform/Translate.java b/src/main/java/eu/jonahbauer/raytracing/scene/transform/Translate.java
index 8eb2cb7..db8a805 100644
--- a/src/main/java/eu/jonahbauer/raytracing/scene/transform/Translate.java
+++ b/src/main/java/eu/jonahbauer/raytracing/scene/transform/Translate.java
@@ -48,6 +48,11 @@ public sealed class Translate extends Transform {
         return bbox;
     }
 
+    @Override
+    public @NotNull String toString() {
+        return object + " translated by " + offset;
+    }
+
     private static final class TranslateTarget extends Translate implements Target {
         private TranslateTarget(@NotNull Hittable object, @NotNull Vec3 offset) {
             super(object, offset);