Image Diff

What does Image Diff do?

It finds the differences between two images, like a spot-the-difference puzzle solved by the computer. Every pixel of image A is compared with the same pixel of image B. Pixels whose color differs by more than the threshold are marked, nearby marked pixels are grouped and boxed, and the number of differences is shown.

Use it to check a design before and after a change, catch visual regressions in screenshots, compare two exports of the same photo, or find what was edited in an image.

How to use

1. Drop the first image on A and the second on B, or click each area to choose a file. You can also drop two files at once, or paste an image with Ctrl+V (Cmd+V on a Mac); a pasted image goes into the empty slot, or replaces B.
2. Choose a view:
   • Side by side: A and B next to each other. When zoomed in, both scroll together.
   • Slider: drag across the image to reveal A on the left and B on the right.
   • Blink: A and B take turns in the same place, so changes stand out. Pause it to switch by hand.
   • Diff: A in faded gray with the different pixels in red.
3. Use ◀ ▶ to step through the differences. When zoomed in, the view scrolls to each one.
4. Raise the Threshold to ignore small color changes such as JPEG noise or slightly different anti-aliasing. At 0, any change counts.
5. Click Download diff PNG to save the diff image (with the boxes, if they are shown).

Images of different sizes

• Stretch B to A resizes B to the size of A. Use it when the same picture was saved at a different resolution.
• Align top-left places both images at the top-left corner without resizing. The area covered by only one image counts as different. Use it for screenshots that grew or shrank.

How the difference is measured

Colors are compared in the YIQ color space, which weighs brightness more than hue, close to how people see. Transparent pixels are compared as if they were on white, so a change in transparency is also found. The threshold is a percentage of the largest possible difference; the default of 10 ignores changes that are hard to see.

Marked pixels within about 8 pixels of each other form one difference. Up to 300 of the largest differences are boxed.

FAQ

Are my images uploaded?

No. Both images are decoded and compared in your browser. They are saved in this browser's storage with the tool (up to 20 MB in total), so they're still there after a reload. If you share the tool with a link, they're included in the link. To not keep them, turn off Keep files in the tool's settings.

Which formats are supported?

Any image your browser can open: PNG, JPEG, WebP, GIF (the first frame), AVIF, BMP, SVG and more. HEIC works only in browsers that support it, such as Safari.

Why does it find differences everywhere in two photos that look the same?

JPEG compression and resizing change pixels slightly. Raise the threshold until only the real changes remain. Photos taken separately are never aligned to the pixel, so this tool works best on images made from the same source, such as screenshots and exports.

Is there a size limit?

Images larger than about 16 megapixels (4096 × 4096) are reduced before comparing.