Compare two images

How images are compared

• Only pixels covered by both images are compared. The difference for a pixel is the largest of the alpha-weighted red, green and blue differences and the alpha difference (0–255).
• “What counts as different” sets where a difference starts. “Any difference” marks pixels with a difference of 1 or more, “Ignore small differences” 11 or more, and “Large differences only” 41 or more.
• Two fully transparent pixels count as the same, even if their colour values differ.
• Different pixels close to each other (neighbouring 16-pixel cells) are grouped into one area, shown with a numbered bounding box. The list shows the first 100 areas.

When the sizes differ

The tool does not align the images on its own. Choose “Align top left”, “Align centres” or “Resize right to match left”.

• Areas only one image covers are counted separately as “pixels in one image only” and shown with diagonal stripes.
• “Resize right to match left” scales the right image, which changes pixel values, so more differences may appear. If the aspect ratios differ, the image is stretched.

Views

• Side by side: the two images next to each other. When zoomed in, scrolling is linked.
• Overlay: the right image on top of the left one, with adjustable opacity.
• Slider: the left image on the left of the divider and the right image on the right. Drag the divider or use the arrow keys on the slider.
• Highlight differences: different pixels in magenta, areas only one image covers in grey stripes, matching pixels in light grey, with numbered boxes around each area. You can save this image as a PNG.

Notes

• Simply saving a JPEG again can change pixel values without changing how it looks. In that case, choose “Ignore small differences”.
• This is not for comparing the content of photos taken from different positions or angles, and it does not detect whether an image has been edited.
• Photos with orientation data (EXIF) are rotated as they appear before comparing. Colours are treated as sRGB; colour profiles are not compared.

Limits

Up to 50 MB and 50 million pixels per image. If the aligned size exceeds about 16.77 million pixels (equivalent to 4,096 × 4,096), the images are not compared. They are not scaled down, because that would change the pixel differences.