Image Diff Comparer
Compare two images pixel by pixel to find what changed, with a difference heatmap, a tolerance threshold, and the percentage of pixels that differ.
Last reviewed by the Radiatus Cloud team
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The eye is bad at spotting small changes
Comparing two screenshots by looking at them finds large differences and misses the ones that matter: a control shifted by two pixels, a colour that changed by a shade, an element that lost a border. Those are exactly the regressions that reach production, because they survive review. A pixel comparison finds all of them, and finds them in a fraction of a second across the whole image.
Tolerance is what makes it usable
An exact comparison flags differences nobody can see, because text rendering, image compression and GPU rasterisation all vary slightly between runs and machines. Without a tolerance, every comparison of two screenshots from different sessions reports thousands of differing pixels and tells you nothing. A threshold of a few units per channel removes that noise and leaves the changes a person would notice.
Anti-aliasing produces most false positives
A shape moved by a fraction of a pixel changes the anti-aliased edge along its whole boundary, so an element that appears identical produces a thin outline of differences. Because these pixels form a line rather than an area, counting how much of the difference sits on edges separates a genuine change from a rendering variation. That distinction is the difference between a comparison you can act on and one you learn to ignore.
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Frequently Asked Questions
Why do identical-looking screenshots differ?
Text rendering, image compression, GPU rasterisation and font hinting all vary slightly between runs and machines. An exact comparison reports thousands of differing pixels for two images nobody could tell apart, which is why a tolerance is essential.
What tolerance should I use?
A few units per channel removes rendering noise while keeping real changes. Higher than about 20 starts hiding genuine differences such as a changed shade or a slightly different border.
Why does a moved element show as an outline?
Because moving a shape by a fraction of a pixel changes its anti-aliased edge along the whole boundary. The interior matches and only the outline differs, which is why edge-heavy differences usually mean a shift rather than a change.
What if the images are different sizes?
They cannot be compared pixel by pixel without scaling one, which introduces resampling differences of its own. The tool reports the mismatch rather than scaling silently, since a scaled comparison answers a different question.
Is this the same as visual regression testing?
It is the core of it. A full setup adds capturing the screenshots consistently, storing baselines and deciding what counts as a failure. The comparison itself is this.
Privacy & Security
Everything runs in your browser; nothing is uploaded.
How to Use
Upload two images to see exactly which pixels differ between them.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.
Related Tools
EXIF Viewer
ImageExtract hidden EXIF data (Camera, GPS, Settings) from images.
Favicon Generator
ImageGenerate favicons and app icons at every required size from one source image, with the exact HTML to reference them.
Placeholder Image Generator
ImageGenerate placeholder images at any size with custom colours and label text. Produced in your browser as downloadable files, no external hotlinking.