Image Difference Checker
What Image Difference Checker actually does
A threshold can tell you that no change is large enough to matter, but it cannot make two different images identical. This comparison workbench keeps those answers separate. It measures exact visible-pixel changes and above-threshold changes, localizes them with an inclusive bounding box, and provides a transparent heatmap and versioned JSON report.
How to use it
- Choose a reference image and candidate image; strict mode refuses silent dimension changes.
- Set the maximum tolerated sRGB channel delta and the background used to compare transparency.
- Inspect swipe, overlay, heatmap, or side-by-side views, then download the heatmap and metrics.
Useful for
- Review a before-and-after edit without losing small changes in a visual slider.
- Check a visual regression screenshot and locate the region that changed.
- Measure whether a re-export or compression pass changed any visible pixels.
Limits worth knowing
- This is deterministic pixel comparison, not perceptual similarity or a quality score.
- Images are not automatically aligned, cropped, rotated, or color-profile normalized.
- Animated frames, HDR content, and comparisons above 24 million output pixels are not supported.
Questions people ask
Are images uploaded?
No. Decoding, compositing, pixel measurement, preview, and downloads all happen in this browser tab.
Why can a result be within threshold but not identical?
Exact identity means every visible channel is equal. Within threshold means differences exist, but none is larger than the tolerance you selected.
What happens when dimensions differ?
Strict mode stops and explains the mismatch. You can explicitly choose Resize B to A, after which the report records both original dimensions and the resize.