Add new option for ignored regions

index.js

@@ -9,7 +9,9 @@ const defaultOptions = {
     aaColor: [255, 255, 0], // color of anti-aliased pixels in diff output
     diffColor: [255, 0, 0], // color of different pixels in diff output
     diffColorAlt: null,     // whether to detect dark on light differences between img1 and img2 and set an alternative color to differentiate between the two
-    diffMask: false         // draw the diff over a transparent background (a mask)
+    diffMask: false,        // draw the diff over a transparent background (a mask)
+    ignoredRegions: null,   // array of {x1,y1,x2,y2} objects representing image regions to ignore from checking
+    ignoredColor: null,     // color of ignored region
 };
 
 function pixelmatch(img1, img2, output, width, height, options) {
@@ -50,9 +52,45 @@ function pixelmatch(img1, img2, output, width, height, options) {
         for (let x = 0; x < width; x++) {
 
             const pos = (y * width + x) * 4;
+            if (isPixelIgnored(x, y, options.ignoredRegions)) {
+                if (output && !options.diffMask) {
+
+                    if (options.ignoredColor) {
+                        drawPixel(output, pos, ...options.ignoredColor);
+                    } else {
+                        drawGrayPixel(img1, pos, options.alpha, output);
+                    }
+                }
+                continue;
+            }
 
             // squared YUV distance between colors at this pixel position, negative if the img2 pixel is darker
-            const delta = colorDelta(img1, img2, pos, pos);
+            let delta = colorDelta(img1, img2, pos, pos);
+            if ((delta > maxDelta || delta < -1 * maxDelta) && (options.horizontalShiftPixels > 0 || options.verticalShiftPixels > 0)) {
+                let minAbsDelta = 9999;
+                let minOtherDelta = 9999;
+                for (let hShift = -1 * options.horizontalShiftPixels; hShift <= options.horizontalShiftPixels; ++hShift) {
+                    for (let vShift = -1 * options.verticalShiftPixels; vShift <= options.verticalShiftPixels; ++vShift) {
+                        if (x + hShift < 0 || x + hShift > width || y + vShift < 0 || y + vShift > height) {
+                            //Ignore shifts of pixels outside the image
+                            continue;
+                        }
+                        const currDelta = colorDelta(img1, img2, pos, pos + ((width * vShift) + hShift) * 4);
+                        if (Math.abs(currDelta) < Math.abs(minAbsDelta)) {
+                            minAbsDelta = currDelta;
+                        }
+                        const otherDelta = colorDelta(img1, img2, pos + ((width * vShift) + hShift) * 4, pos);
+                        if (Math.abs(otherDelta) < Math.abs(minOtherDelta)) {
+                            minOtherDelta = otherDelta;
+                        }
+                    }
+                }
+                if (Math.abs(minAbsDelta) > Math.abs(minOtherDelta)) {
+                    delta = minAbsDelta;
+                } else {
+                    delta = minOtherDelta;
+                }
+            }
 
             // the color difference is above the threshold
             if (Math.abs(delta) > maxDelta) {
@@ -234,3 +272,23 @@ function drawGrayPixel(img, i, alpha, output) {
     const val = blend(rgb2y(r, g, b), alpha * img[i + 3] / 255);
     drawPixel(output, i, val, val, val);
 }
+
+function isPixelIgnored(x, y, ignoredRegions) {
+    if (ignoredRegions == null) {
+        return false;
+    }
+    for (const region of ignoredRegions) {
+        if (isPixelInRegion(x, y, region)) {
+            return true;
+        }
+    }
+    return false;
+}
+
+function isPixelInRegion(x, y, region) {
+    const {x1, y1, x2, y2} = region;
+    if (isNaN(x1) || isNaN(y1) || isNaN(x2) || isNaN(y2)) {
+        return false;
+    }
+    return x1 <= x && x <= x2 && y1 <= y && y <= y2;
+}

test/test.js

@@ -17,6 +17,24 @@ diffTest('2a', '2b', '2diff', {
     aaColor: [0, 192, 0],
     diffColor: [255, 0, 255]
 }, 12437);
+diffTest('2a', '2b', '2diff_ignored_regions', {
+    threshold: 0.05,
+    ignoredRegions: [
+        {
+            x1: 128,
+            y1: 0,
+            x2: 256,
+            y2: 128,
+        },
+        {
+            x1: 0,
+            y1: 128,
+            x2: 128,
+            y2: 256
+        }
+    ],
+    ignoredColor: [0, 255, 255]
+}, 2229);
 diffTest('3a', '3b', '3diff', options, 212);
 diffTest('4a', '4b', '4diff', options, 36049);
 diffTest('5a', '5b', '5diff', options, 0);