Image Diff

What this tool does

Compare two images pixel by pixel in your browser. Load an image into slot A and slot B — by click, drag-and-drop, or paste — and the tool paints a result image that marks exactly which pixels changed. Nothing is uploaded to a server.

Tolerance and transparency

• Tolerance sets how large a per-channel color change is allowed before a pixel counts as different (0 = any change, 255 = almost nothing counts). A small tolerance like 8 hides JPEG noise and antialiasing while keeping real edits visible.
• Ignore transparency compares RGB only, so two images that differ only in their alpha channel count as identical.

Size mismatch handling

When the two images have different dimensions, both are centered on the larger canvas: the bigger image is cropped around its center, the smaller one is padded with the canvas background. The compared area is shown above the result so the comparison stays honest — no silent stretching. Areas outside the overlap are excluded from the statistics automatically.

View modes

• Highlight differences dims unchanged pixels and paints every differing pixel red, which makes the changed regions pop immediately.
• Difference heatmap colors each differing pixel on a cold-to-hot ramp according to how far its channels moved, so small tweaks and big changes are distinguishable at a glance.
• Align assist overlays both images as red and cyan with a difference blend: wherever the two match the canvas turns black, and misaligned edges light up. Drag the canvas (or focus it and use the arrow keys; Shift+arrow moves 10 px at a time, double-click resets) to slide image B until the view goes as dark as possible, then switch back to the diff modes — the comparison now uses your alignment.
• Image A / Image B shows either source image at the same zoom for a direct visual check.

Overlap-only statistics

Pixels where one of the two images shows only background — the edges revealed by sliding B during alignment, or the padding around different sizes — are painted flat gray and excluded from the statistics. The reported numbers always describe the region where both images actually have content; a badge above the result shows how many pixels were excluded.

Statistics

The stats bar reports the total compared pixels, identical and different counts, the percentage of differing pixels, and the maximum and mean per-channel delta over differing pixels. Export the currently displayed result as PNG at any time.

Performance and privacy

Comparison runs in a Web Worker when available, with a main-thread fallback. Images are decoded and diffed entirely on your device.