Image diff checker
Choose the first and the second picture. The tool compares them pixel by pixel, marks the changes in red on a faded copy of the first picture or on a black and white mask and tells you how many pixels differ. Both files stay on your device.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose the first image, then the second.
- Move the Tolerance slider until only real changes stay marked.
- Pick the map style and press Download difference map if you want to keep it.
How it works
Both pictures are drawn on canvases of the same size and their red, green, blue and alpha values are read for every pixel. The largest of the four differences decides: above the tolerance, the pixel is changed. The tool counts changed pixels and finds the smallest box around all of them.
Example
Two pictures of 100 × 100 pixels where a 10 × 10 logo changed: 100 of 10 000 pixels differ, which is 1% of the picture, and the box is 10 × 10 pixels. At tolerance 0 compression noise could add many more pixels, so raise the tolerance for photos.
Tips
- Compare lossless files (PNG) where you can: they show only real changes.
- For screenshots of the same page, use the same window size so both pictures have the same dimensions.
Frequently asked questions
What does the tolerance do?
A pixel counts as changed when any of its red, green, blue or alpha values differs by more than the tolerance (0 to 255). With 0, even a one-step difference counts. A small value such as 10 ignores the invisible noise that JPG compression adds.
Why do two almost identical photos show many differences?
Saving as JPG again, resizing or a different colour profile changes many pixel values by a few steps. Raise the tolerance until only the real changes remain.
What happens when the pictures have different sizes?
They are placed at the top-left corner of a canvas as large as the bigger one. Pixels covered by only one of them count as different. If you want to compare scaled versions, resize one of them to the same size first.
Are my images uploaded?
No. Both are decoded and compared by your browser, and the map is created on your device.