diff --git a/src/main.rs b/src/main.rs
index ce3d988..a7663ab 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,60 +1,10 @@
-const GRADIENT_LEN: usize = 1 << 16;
-const TABLE_SIZE: usize = 128;
-const RES_X: usize = 2048;
-const RES_Y: usize = 1556;
+mod test_image;
+
+use test_image::{RES_X, RES_Y};
 
 fn main() {
     // Build the test image.
-    let pixels = {
-        let mut pixels = vec![[0.0f32; 3]; RES_X * RES_Y];
-        assert!(((GRADIENT_LEN * 4) + (TABLE_SIZE * TABLE_SIZE * TABLE_SIZE)) <= pixels.len());
-
-        // Keep track of which pixel we're at.
-        let mut pi = 0;
-
-        // Gray gradient.
-        for i in 0..GRADIENT_LEN {
-            let v = i as f32 / (GRADIENT_LEN - 1) as f32;
-            pixels[pi] = [v, v, v];
-            pi += 1;
-        }
-
-        // Red gradient.
-        for i in 0..GRADIENT_LEN {
-            let v = i as f32 / (GRADIENT_LEN - 1) as f32;
-            pixels[pi][0] = v;
-            pi += 1;
-        }
-
-        // Green gradient.
-        for i in 0..GRADIENT_LEN {
-            let v = i as f32 / (GRADIENT_LEN - 1) as f32;
-            pixels[pi][1] = v;
-            pi += 1;
-        }
-
-        // Blue gradient.
-        for i in 0..GRADIENT_LEN {
-            let v = i as f32 / (GRADIENT_LEN - 1) as f32;
-            pixels[pi][2] = v;
-            pi += 1;
-        }
-
-        // 3D RGB table.
-        for r in 0..TABLE_SIZE {
-            let rn = r as f32 / (TABLE_SIZE - 1) as f32;
-            for g in 0..TABLE_SIZE {
-                let gn = g as f32 / (TABLE_SIZE - 1) as f32;
-                for b in 0..TABLE_SIZE {
-                    let bn = b as f32 / (TABLE_SIZE - 1) as f32;
-                    pixels[pi] = [rn, gn, bn];
-                    pi += 1;
-                }
-            }
-        }
-
-        pixels
-    };
+    let pixels = test_image::build();
 
     // Write the test image.
     use exr::{
@@ -63,7 +13,7 @@ fn main() {
         prelude::WritableImage,
     };
     Image::from_layer(Layer::new(
-        (1920, 1080),
+        (RES_X, RES_Y),
         LayerAttributes::named(""),
         Encoding::SMALL_LOSSLESS,
         SpecificChannels::rgb(|co: exr::math::Vec2<usize>| {
@@ -72,6 +22,6 @@ fn main() {
         }),
     ))
     .write()
-    .to_file("lut_extractor_2048x1556.exr")
+    .to_file(format!("lut_extractor_{}x{}.exr", RES_X, RES_Y))
     .unwrap();
 }
diff --git a/src/test_image.rs b/src/test_image.rs
new file mode 100644
index 0000000..fcd6035
--- /dev/null
+++ b/src/test_image.rs
@@ -0,0 +1,95 @@
+pub const GRADIENT_LEN: usize = 1 << 17;
+pub const TABLE_SIZE: usize = 144;
+pub const RES_X: usize = 2560;
+pub const RES_Y: usize = 1440;
+
+// Compile time assert.
+const _: () = {
+    assert!(((GRADIENT_LEN * 4) + (TABLE_SIZE * TABLE_SIZE * TABLE_SIZE)) <= (RES_X * RES_Y));
+};
+
+/// Creates the test image, as a Vec of RGB triples.
+pub fn build() -> Vec<[f32; 3]> {
+    let mut pixels = vec![[0.0f32; 3]; RES_X * RES_Y];
+
+    // Keep track of which pixel we're at.
+    let mut pi = 0;
+
+    // Gray gradient.
+    for i in 0..GRADIENT_LEN {
+        let v = i as f32 / (GRADIENT_LEN - 1) as f32;
+        pixels[pi] = [v, v, v];
+        pi += 1;
+    }
+
+    // Red gradient.
+    for i in 0..GRADIENT_LEN {
+        let v = i as f32 / (GRADIENT_LEN - 1) as f32;
+        pixels[pi][0] = v;
+        pi += 1;
+    }
+
+    // Green gradient.
+    for i in 0..GRADIENT_LEN {
+        let v = i as f32 / (GRADIENT_LEN - 1) as f32;
+        pixels[pi][1] = v;
+        pi += 1;
+    }
+
+    // Blue gradient.
+    for i in 0..GRADIENT_LEN {
+        let v = i as f32 / (GRADIENT_LEN - 1) as f32;
+        pixels[pi][2] = v;
+        pi += 1;
+    }
+
+    // 3D RGB table.
+    for r in 0..TABLE_SIZE {
+        let rn = r as f32 / (TABLE_SIZE - 1) as f32;
+        for g in 0..TABLE_SIZE {
+            let gn = g as f32 / (TABLE_SIZE - 1) as f32;
+            for b in 0..TABLE_SIZE {
+                let bn = b as f32 / (TABLE_SIZE - 1) as f32;
+                pixels[pi] = [rn, gn, bn];
+                pi += 1;
+            }
+        }
+    }
+
+    pixels
+}
+
+/// Gives the index in the test image Vec of the given
+/// gray-gradient index.
+#[inline(always)]
+pub fn gray_idx(idx: usize) -> usize {
+    idx
+}
+
+/// Gives the index in the test image Vec of the given
+/// red-gradient index.
+#[inline(always)]
+pub fn red_idx(idx: usize) -> usize {
+    GRADIENT_LEN + idx
+}
+
+/// Gives the index in the test image Vec of the given
+/// green-gradient index.
+#[inline(always)]
+pub fn green_idx(idx: usize) -> usize {
+    GRADIENT_LEN * 2 + idx
+}
+
+/// Gives the index in the test image Vec of the given
+/// blue-gradient index.
+#[inline(always)]
+pub fn blue_idx(idx: usize) -> usize {
+    GRADIENT_LEN * 3 + idx
+}
+
+/// Gives the index in the test image Vec of the given
+/// rgb table indices.
+#[inline(always)]
+pub fn rgb_idx(r_idx: usize, g_idx: usize, b_idx: usize) -> usize {
+    (GRADIENT_LEN * 4) + (r_idx * TABLE_SIZE * TABLE_SIZE) + (g_idx * TABLE_SIZE) + b_idx
+}