What Is an Image Pixel Diff Tool?
An image comparison tool aligns two browser-decodable images on a common canvas and reveals visual changes. Overlay mode uses a draggable divider for before-and-after inspection. Pixel-diff mode compares RGBA channel values against an adjustable threshold, reports the changed pixel count and percentage, finds the smallest bounding box around changes, and creates a downloadable PNG.
How to Compare Two Images
- 1Upload the first and second image. Images are centered on a canvas sized to the larger width and height, with transparent space around a smaller source.
- 2Use the overlay slider to reveal more or less of the second image and inspect layout, crop, color, or rendering changes.
- 3Switch to pixel diff and adjust the threshold. A pixel changes when any red, green, blue, or alpha channel differs by more than that value.
- 4Review the changed count, percentage, and bounding box, then download the generated diff PNG.
Common Image Comparison Uses
Visual regression review
Compare baseline and current UI screenshots to quantify rendering changes before accepting a test result.
Design and export verification
Inspect two mockups, image exports, maps, charts, or generated assets for subtle pixel-level differences.
Before-and-after inspection
Use the overlay divider to evaluate retouching, compression, cleanup, annotation, or processing results.
Frequently asked questions
Are the compared images uploaded?
No. Image decoding, canvas normalization, pixel comparison, statistics, and PNG export all run in your browser.
How are different image sizes compared?
The tool creates a canvas using the larger width and height, centers each image without scaling, and leaves transparent padding around the smaller image.
What does the threshold control?
It is the maximum tolerated channel difference from 0 to 255. Higher values ignore larger color or alpha variations; zero flags every non-identical pixel.