fix(plugin-color): compute sepia output channels from the original pixel

packages/jimp/src/__snapshots__/callbacks.test.ts.snap

@@ -269,13 +269,13 @@ AA-8E-1Cᵃᵃ 39-55-C6ᵃᵃ
 exports[`Callbacks > with sepia 1`] = `
 Visualization:
 
-▥◇5
-4□◆
-6▥◇
+268
+▰▰◆
+▾▪▰
 
 Data:
 
-64-22-2Dᶠᶠ C4-F3-B7ᶠᶠ 30-3B-4Eᶠᶠ
-FF-FF-E5ᶠᶠ F4-FF-FFᶠᶠ 94-5E-7Cᶠᶠ
-64-22-2D⁷ᶠ C4-F3-B7⁷ᶠ 30-3B-4E⁷ᶠ
+64-58-45ᶠᶠ C4-AE-88ᶠᶠ 30-2A-21ᶠᶠ
+FF-FF-CDᶠᶠ F4-D9-A9ᶠᶠ 94-83-66ᶠᶠ
+64-58-45⁷ᶠ C4-AE-88⁷ᶠ 30-2A-21⁷ᶠ
 `;

plugins/plugin-color/src/index.ts

@@ -510,13 +510,13 @@ export const methods = {
    */
   sepia<I extends JimpClass>(image: I) {
     image.scan((_, __, idx) => {
-      let red = image.bitmap.data[idx]!;
-      let green = image.bitmap.data[idx + 1]!;
-      let blue = image.bitmap.data[idx + 2]!;
+      const r = image.bitmap.data[idx]!;
+      const g = image.bitmap.data[idx + 1]!;
+      const b = image.bitmap.data[idx + 2]!;
 
-      red = red * 0.393 + green * 0.769 + blue * 0.189;
-      green = red * 0.349 + green * 0.686 + blue * 0.168;
-      blue = red * 0.272 + green * 0.534 + blue * 0.131;
+      const red = r * 0.393 + g * 0.769 + b * 0.189;
+      const green = r * 0.349 + g * 0.686 + b * 0.168;
+      const blue = r * 0.272 + g * 0.534 + b * 0.131;
 
       image.bitmap.data[idx] = red < 255 ? red : 255;
       image.bitmap.data[idx + 1] = green < 255 ? green : 255;

plugins/plugin-color/src/sepia.node.test.ts

@@ -0,0 +1,25 @@
+import { expect, test, describe } from "vitest";
+
+import { methods as color } from "./index.js";
+
+function scanImage(data: number[]) {
+  return {
+    bitmap: { data: Uint8Array.from(data), width: data.length / 4, height: 1 },
+    scan(cb: (x: number, y: number, idx: number) => void) {
+      for (let idx = 0; idx < this.bitmap.data.length; idx += 4) {
+        cb(idx / 4, 0, idx);
+      }
+      return this;
+    },
+  };
+}
+
+describe("sepia", () => {
+  test("computes each output channel from the original pixel", () => {
+    const image = scanImage([255, 0, 0, 255]);
+
+    color.sepia(image as any);
+
+    expect(Array.from(image.bitmap.data)).toEqual([100, 88, 69, 255]);
+  });
+});