GitHub Pixel Diff by illusionist nemo

GitHub and GitLab both show you two versions of an image. Neither shows you what changed between them.

Pixel Diff adds a fourth mode next to 2-up, Swipe and Onion Skin — in GitHub's image viewer and in GitLab's merge requests. It compares the two images pixel by pixel, paints every difference red, and crops the result to the area that actually changed — so a three-pixel shift in a long screenshot is a three-pixel shift you can see, not a picture you have to hunt through.

• A threshold slider: raise it to ignore compression noise, lower it to catch everything.
• Before / after / diff, and all three side by side, sharing one scale and one crop.
• Images that changed size are aligned and compared anyway.
• SVG and other vector images are rasterised before comparison.
• Works on the images the site has already loaded — nothing is uploaded anywhere.
• A GitLab of your own: add its address on the settings page, grant access, and the mode appears in that instance too.
• No merge request at hand? Two images of your own compare the same way at https://nemo-illusionist.github.io/gh-pixel-diff/

The comparison runs in your browser, in a background thread. The extension has no server, collects nothing, and sends nothing.

Open source: https://github.com/Nemo-Illusionist/gh-pixel-diff