LOCAL IMAGE COMPARISON
Image Diff Tool
Compare two image files you select locally. View side-by-side, overlay and difference modes with exact threshold semantics. Mismatched dimensions are shown explicitly; images are never silently rescaled.
SELECT TWO IMAGES
Baseline and candidate images
Each file must be a PNG or JPEG under 5 MB, no side longer than 8,192 pixels, and no more than 4,194,304 pixels (for example, 2048 × 2048). Files are read locally and never uploaded.
No file selected
No file selected
Saved projects for this tool store only the view mode and threshold. You must reselect the image files after reopening a project.
DIFF RESULTS
Image comparison
Diff view
Choose a view mode and adjust the threshold.
Baseline
Candidate
Difference (magenta = above threshold)
Drag slider to blend baseline and candidate
How comparison works
Both images are decoded in your browser with an HTMLImageElement and then drawn to a canvas. Pixels are compared only where both images have data. If the widths and heights differ, the tool reports the mismatch visibly and compares the overlapping top-left region; it does not rescale either image.
For each pixel, the tool takes the largest absolute difference across its R, G, B and A channels. A pixel is counted as different only when that value is greater than the selected threshold. At threshold 0, any changed channel counts; at 255, no pixel can exceed the threshold. Pixels outside a mismatched image’s overlapping top-left area are not counted.
Bounds and limitations
- Only image files you select locally are read. The tool cannot capture remote URLs or screenshots.
- Only PNG and JPEG are accepted. File size is limited to 5 MB, either side to 8,192 pixels, and decoded pixels to 4,194,304 per image.
- Images with mismatched dimensions are compared over their overlapping region only.
- Color-space and metadata differences are not compared; only decoded pixel values are used.
- The diff report is a deterministic summary of pixel differences; it does not judge visual acceptability.