Test that two images are identical for the Seam Carving algorithm. (trekhleb#694)

* Test that two images are identical for the Seam Carving algorithm. * Tune the Seam Carving tests. * Tune the Seam Carving tests. * Tune the Seam Carving tests. * Tune the Seam Carving tests.

Author: trekhleb

.husky/pre-commit

@@ -1,5 +1,6 @@
 #!/bin/sh
 ."$(dirname "$0")/_/husky.sh"
 
+# @TODO: Implement the pre-commit checks.
 # npm run lint
 # npm run test

src/algorithms/image-processing/seam-carving/__tests__/resizeImageWidth.test.js

@@ -4,6 +4,40 @@ import resizeImageWidth from '../resizeImageWidth'
 consttestImageBeforePath='./src/algorithms/image-processing/seam-carving/__tests__/test-image-before.jpg';
 consttestImageAfterPath='./src/algorithms/image-processing/seam-carving/__tests__/test-image-after.jpg';
 
+/**
+ * Compares two images and finds the number of different pixels.
+ *
+ * @param{ImageData} imgA - ImageData for the first image.
+ * @param{ImageData} imgB - ImageData for the second image.
+ * @param{number} threshold - Color difference threshold [0..255]. Smaller - stricter.
+ * @returns{number} - Number of different pixels.
+ */
+functionpixelsDiff(imgA,imgB,threshold=0){
+if(imgA.width!==imgB.width||imgA.height!==imgB.height){
+thrownewError('Images must have the same size');
+}
+
+letdifferentPixels=0;
+constnumColorParams=4;// RGBA
+
+for(letpixelIndex=0;pixelIndex<imgA.data.length;pixelIndex+=numColorParams){
+// Get pixel's color for each image.
+const[aR,aG,aB]=imgA.data.subarray(pixelIndex,pixelIndex+numColorParams);
+const[bR,bG,bB]=imgB.data.subarray(pixelIndex,pixelIndex+numColorParams);
+
+// Get average pixel's color for each image (make them greyscale).
+constaAvgColor=Math.floor((aR+aG+aB)/3);
+constbAvgColor=Math.floor((bR+bG+bB)/3);
+
+// Compare pixel colors.
+if(Math.abs(aAvgColor-bAvgColor)>threshold){
+differentPixels+=1;
+}
+}
+
+returndifferentPixels;
+}
+
 describe('resizeImageWidth',()=>{
 it('should perform content-aware image width reduction',()=>{
 // @see: https://jestjs.io/docs/asynchronous
@@ -21,6 +55,7 @@ describe('resizeImageWidth', () =>{
 constcanvasAfter=createCanvas(imgAfter.width,imgAfter.height);
 constctxAfter=canvasAfter.getContext('2d');
 ctxAfter.drawImage(imgAfter,0,0,imgAfter.width,imgAfter.height);
+constimgDataAfter=ctxAfter.getImageData(0,0,imgAfter.width,imgAfter.height);
 
 consttoWidth=Math.floor(imgBefore.width/2);
 
@@ -44,8 +79,13 @@ describe('resizeImageWidth', () =>{
 expect(imgDataTest.width).toBe(imgAfter.width);
 expect(imgDataTest.height).toBe(imgAfter.height);
 
-// @TODO: Check that images are identical.
-// expect(canvasTest.toDataURL()).toEqual(canvasAfter.toDataURL());
+constcolorThreshold=50;
+constdifferentPixels=pixelsDiff(imgDataTest,imgDataAfter,colorThreshold);
+
+// Allow 10% of pixels to be different
+constpixelsThreshold=Math.floor((imgAfter.width*imgAfter.height)/10);
+
+expect(differentPixels).toBeLessThanOrEqual(pixelsThreshold);
 });
 });
 });