Image Diff
Compare two images pixel by pixel and see every changed pixel highlighted in red, with the percentage that differs and a tolerance for compression noise.
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Input
Compare two images pixel by pixel
Output
Choose two images
Changed pixels are painted red over a faded copy of the first image, the same idea visual regression tools such as Playwright's toHaveScreenshot use. Screenshots taken on different machines differ in font antialiasing even when nothing changed, which is what the tolerance is for.
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About this tool
Method, assumptions, practical next steps, and limits.
Visual regression by hand
Before and after screenshots of a page change, two exports of a design, a chart rendered by two library versions: a pixel diff shows exactly what moved. Automated suites such as Playwright's toHaveScreenshot and pixelmatch use the same principle with a threshold.
Tolerance matters
Screenshots from different machines differ in font antialiasing and GPU rendering even when nothing changed, and JPEG compression changes pixels slightly. A small tolerance ignores that noise; zero shows every difference.