How is the image comparison performed?
Pixelmatch compares pixel colours with an anti-aliasing-aware perceptual difference method. Select matching-size images, or explicitly resize the second to the first. The latter changes pixel positions and is less useful for exact regression tests.
Visual regression and everyday uses
Spot altered graphics, website layout regressions, lost design details and image changes. The changed-pixel percentage is based on the resolution compared, not an objective measure of image quality.
Privacy and limitations
The files never leave your browser. Images larger than 16 million pixels are rejected to control memory use. JPEG artifacts, scaling and compression can create differences even when photographs look alike. Download the PNG difference map and a JSON statistics report.
Are my files uploaded?
No. The comparison runs with JavaScript and WebAssembly running in your browser tab. Your files are read from your device and the results are created on your device; nothing is sent to gratistools.be or anyone else, which is also why there are no queues, daily limits or watermarks. See the privacy page.
Frequently asked questions
Is this tool free?
Yes. The core tool is free to use in your browser.