How to use the image difference checker
- Choose picture A and picture B.
- Set the threshold from 0 to 255. A pixel counts as different when its red, green or blue value changes by more than the threshold.
- Choose what to show: differences in red over a faded picture A, differences only, picture A or picture B.
- Read the number and share of pixels that differ and the area that changed, then download the current view as a PNG.
How the comparison works
Both pictures are drawn at the same size and compared pixel by pixel. For each pixel the tool finds the largest difference among red, green and blue. If it is above the threshold, the pixel counts as different. The share is the number of different pixels over the total, and the box shows the smallest rectangle that holds all of them.
A threshold of 0 flags any change at all, including the tiny differences that come from saving a picture as a JPG. A higher threshold ignores small color noise and shows only clear changes. The 16 in the form is an example value, and you can change it to suit your pictures.
Pictures of different sizes
If B is not the same size as A, B is stretched to A's size before comparing, and the page says so. If the shapes also differ, many pixels will be flagged. Work at the same size when you can. Large pictures are reduced to 1,600 pixels on the long side so the comparison stays fast, and the page shows the size used.
Typical uses are checking a design against its build, spotting what changed between two screenshots, and testing whether an edit or a compression step changed a picture more than expected. For text differences use the diff checker, and to compare lists see compare two lists. The image compressor and image converter are useful before and after.
Privacy
Both pictures are read and compared in your browser. Nothing is uploaded, and each picture can be up to 25 MB.
Assumptions and limits
- A pixel differs when its largest red, green or blue change is above the threshold.
- Pictures are compared at the size of picture A, up to 1,600 pixels on the long side.
- Transparent areas are drawn over white.
- The default threshold of 16 is an example value.
Frequently asked questions
How do I compare two images for differences?
Choose both pictures and the page highlights the differing pixels in red and tells you how many there are. You can raise the threshold to ignore tiny changes.
Why do identical looking pictures show differences?
Saving as JPG changes colors slightly. With a threshold of 0 those small changes are flagged. Raise the threshold to ignore them.
What if the pictures are different sizes?
Picture B is stretched to the size of picture A, and the page tells you. Results are most meaningful when the pictures have the same size and shape.
Are my pictures uploaded?
No. They are compared in your browser.