# Image Pixel Diff

> Compare two images pixel by pixel: diff highlight, blend, swipe, onion skin and blink, with changed-pixel counts and bounding boxes. Files never uploaded.

- URL: https://bytescope.dev/en/image-diff/
- Locale: en · Also: [ja](https://bytescope.dev/ja/image-diff.md) · [zh-Hant](https://bytescope.dev/zh-Hant/image-diff.md)
- Runs: Your files never leave your browser — all processing is local.
- Requires: Any modern browser (Chrome, Edge, Firefox, Safari), desktop and mobile.
- Updated: 2026-09-08

## What it does

This is an image diff online tool for anyone who needs to compare two images pixel by pixel — designers checking a redline against a build, developers verifying a screenshot regression, or photographers spotting edits. Drop or paste image A and image B and the tool highlights exactly what changed, backed by a mature pixel-comparison engine with anti-aliasing detection so lossy-compression noise doesn't drown out real differences. A tolerance slider, per-channel difference amplification and automatic bounding boxes turn "these look different" into precise, measurable numbers.

Existing tools in this niche are surprisingly weak — most upload your files and give you a single, fixed comparison view. This one does five comparison modes locally in your browser (diff highlight, difference blend, swipe, onion skin and blink), never uploads a thing, and reports the changed-pixel count, percentage, maximum channel delta and the number of changed regions. It's the fast, private way to find the difference between images — mismatched sizes are handled too, by padding or scaling before the comparison runs.

## Limits

Does not compare PDFs, text or folders; it compares exactly two raster images of the same size.

## FAQ

### What comparison modes does this image diff tool offer?

Five, and you can switch between them instantly on the same pair: Diff highlight paints changed pixels in orange over a dimmed base; Difference blend shows the amplified |A−B| value image; Swipe drags a divider between the two images; Onion skin cross-fades B over A with an opacity slider; and Blink alternates A and B about twice a second. Most online tools give you one mode — comparing two images pixel by pixel is easier when you can flip between all five.

### How do I compare two images that have different dimensions?

When the two images aren't the same size the tool warns you and offers two ways to reconcile them before diffing: 'Align top-left' pads the smaller image with transparency so both share a canvas, and 'Scale B to A' resamples the second image to the first image's dimensions. Pick whichever matches what you're checking.

### What does the tolerance slider do?

Tolerance (0–255) sets how different two pixels must be before they count as a change. Raise it to ignore the tiny color shifts that lossy JPEG or WebP compression introduces, so you only see real differences. The tool also detects anti-aliased edges and can ignore them, which further cuts false positives when you want to find the difference between images that were re-encoded.

### Are my images uploaded to a server?

No. All decoding and comparison run entirely in your browser inside a Web Worker — your images never leave your device, there is no upload step and no file-size limit beyond your machine's memory. You can even use the page offline once it has loaded.

### Can I see where the changes are and export the result?

Yes. The stats panel reports the number and percentage of different pixels, the maximum per-channel delta, and how many separate regions changed. Turn on 'outline changed regions' to draw bounding boxes over the differences, and use 'Download diff.png' to save the current view as a PNG.

### What's the difference between diff highlight and difference blend?

Diff highlight is a yes/no view: each pixel is either changed (orange) or not, controlled by the tolerance threshold. Difference blend is a continuous view: it shows |A−B| per channel multiplied by a gain factor, so faint, sub-threshold differences (gradients, compression artifacts, watermarks) become visible when you turn the gain up.

## Related tools

- [Image Inspector](https://bytescope.dev/en/image-inspector.md) — Pick colors and read pixel coordinates with a magnifying loupe.
- [Image Format Converter](https://bytescope.dev/en/image-convert.md) — Batch convert between PNG, JPEG, WebP and GIF with live size feedback.
- [Image ↔ Base64 Converter](https://bytescope.dev/en/image-base64.md) — Convert images to Base64 data URIs and back, in batches.