fix(ssim-cie94): increase SSIM window radius (#19343)

While migrating Playwright tests from pixelmatch comparator to the
ssim-cie94 comparator, we noticed a rendering artifact that happens
on playwright screenshot tests on WebKit Linux.

This PR adds a set of cropped-down examples and tunes the ssim-cie94
comparator to accept these rendering artifacts.

packages/playwright-core/src/image_tools/compare.ts

@@ -18,7 +18,7 @@ import { blendWithWhite, colorDeltaE94, rgb2gray } from './colorUtils';
 import { ImageChannel } from './imageChannel';
 import { ssim, FastStats } from './stats';
 
-const SSIM_WINDOW_RADIUS = 5;
+const SSIM_WINDOW_RADIUS = 15;
 const VARIANCE_WINDOW_RADIUS = 1;
 
 function drawPixel(width: number, data: Buffer, x: number, y: number, r: number, g: number, b: number) {

tests/image_tools/fixtures/should-match/webkit-rendering-artifacts/README.md

@@ -0,0 +1,2 @@
+A set of examples with rendering artifacts that happen when running Playwright
+screenshot tests on WebKit linux.