This image pixel compare reads two local images and walks every decoded pixel. The widths must match and the heights must match. If they do not, the page says the images do not have the same pixel size and it does not scale, crop, or letterbox. Tolerance defaults to 0 and may be a whole number up to 16. At 0, all four RGBA channels must be equal. A pixel is outside tolerance when any channel’s absolute difference is greater than that integer. The percent is the outside count divided by the compared count, times 100, to one decimal, half up.
The diff PNG paints an outside pixel as opaque red, 255,0,0,255, and a within pixel as 0,0,0,0. Download that PNG after a successful compare. There is no SSIM, no perceptual hash, and no quality headline. JPEG and WebP pixels are whatever this browser decoded. Two files can differ after decode even when they look alike. PNG versus PNG in the same browser is the strict case.
If the error is a size mismatch and you actually wanted a new size, the Image Resizer is the separate tool. This page will not grow a resize button, because a hidden scale would make unequal screenshots look comparable.
Both files stay local. A refused type or an over-cap file clears the result. There is no partial compare.
Two identical 2 by 1 buffers report 2 within, 0 outside, and 0.0 percent. Change one channel by 3 and tolerance 0 reports 1 outside. The diff byte for that pixel is red and opaque, and the matching pixel is transparent. Tolerance 3 accepts the delta of 3. Tolerance 2 still rejects it. One mismatch out of three pixels prints 33.3 percent. A 2 by 2 file against a 2 by 1 file is an error, even if the top row matches.
Alpha is a channel. A pixel that matches in RGB and differs only in alpha is outside tolerance 0. Raising tolerance can accept that alpha gap when the difference is within the integer. The page does not ignore alpha to make screenshots look closer. A failed file on either side, including a type the sniffer refuses, clears the previous counts and the previous diff.
Use this for a screenshot revision or two exports you expected to match. Do not use it to decide that a photograph is good. A red overlay shows where channels disagreed under the rule you set. It does not say which file is the original, and it does not merge them.
Both images must decode to the same width and height. This page does not resize, crop, or letterbox. Tolerance 0 requires all four RGBA channels to match. A pixel is outside tolerance when any channel differs by more than that integer, up to 16. The diff PNG paints mismatches red and matches transparent. This is not SSIM and not a quality score. JPEG decode can differ by browser. Limits: 8 MB, 8,000 px, and 16 megapixels on each file.
No. Different decoded width or height is an error. The previous diff is cleared. Resize elsewhere if you meant to change a size.
All four channels. A pixel is outside tolerance when any channel differs by more than the integer you set, up to 16.
No. It is the mismatch count divided by the pixel count, to one decimal. It is not SSIM and not a visual grade.
The compare uses pixels this browser decoded. It does not claim the files are the same bytes, and it does not promise the same JPEG pixels in every browser.