Compare two images pixel by pixel

Compare is a pixel diff for two images: it counts every pixel whose red, green, blue or alpha channel differs, and reports the result as a count, a percentage and a downloadable difference map. The comparison runs at full resolution rather than on a preview, so a single changed pixel is still found. A threshold slider decides how far a channel has to move before a pixel counts as changed, and three views — side by side, difference, and an onion skin that fades B over A — show where the changes are.

How it works

  1. Load image A Drop a file onto the A slot, or drop two files at once to fill A and B together. A paste from the clipboard goes into the first empty slot.
  2. Load image B Fill the second slot the same way. If the two images are different sizes, the tool says so and offers to scale B to A's dimensions before comparing.
  3. Set the threshold Zero counts every difference. Raise the slider, up to 64, and a channel then has to differ by more than that value before the pixel is counted as changed.
  4. Pick a view Side by side shows both images unchanged, Difference marks the changed pixels in the accent colour over a flattened grey copy of A, and Onion skin fades B over A at an opacity you set.
  5. Save the difference map Download difference map writes the marked image as a PNG named after image A. Swap A and B, or clear both, from the same panel.

Questions

Do both images have to be the same size?
Yes. A pixel comparison needs both images at the same dimensions, and file4edit refuses to compare a mismatched pair until you choose to scale image B to A's size. That scaling resamples B, which invents small differences of its own, so a low count after scaling should be read with suspicion.
Does it count changes in transparency?
Yes. A pixel counts as changed when any one of its four channels differs by more than the threshold, alpha included. An image that changed only its transparency is reported as changed rather than treated as identical.
Are the two images uploaded to compare them?
No. Both images are decoded and compared inside your own browser tab, at full resolution. There is no server and no account, and the tool keeps working offline after the first visit.

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