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README.md
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# pixelmatch
[](https://travis-ci.com/mapbox/pixelmatch)
[](https://github.com/mourner/projects)
The smallest, simplest and fastest JavaScript pixel-level image comparison library,
originally created to compare screenshots in tests.
Features accurate **anti-aliased pixels detection**
and **perceptual color difference metrics**.
Inspired by [Resemble.js](https://github.com/Huddle/Resemble.js)
and [Blink-diff](https://github.com/yahoo/blink-diff).
Unlike these libraries, pixelmatch is around **150 lines of code**,
has **no dependencies**, and works on **raw typed arrays** of image data,
so it's **blazing fast** and can be used in **any environment** (Node or browsers).
```js
const numDiffPixels = pixelmatch(img1, img2, diff, 800, 600, {threshold: 0.1});
```
Implements ideas from the following papers:
- [Measuring perceived color difference using YIQ NTSC transmission color space in mobile applications](http://www.progmat.uaem.mx:8080/artVol2Num2/Articulo3Vol2Num2.pdf) (2010, Yuriy Kotsarenko, Fernando Ramos)
- [Anti-aliased pixel and intensity slope detector](https://www.researchgate.net/publication/234126755_Anti-aliased_Pixel_and_Intensity_Slope_Detector) (2009, Vytautas Vyšniauskas)
## [Demo](https://observablehq.com/@mourner/pixelmatch-demo)
## Example output
| expected | actual | diff |
| --- | --- | --- |
|  |  |  |
|  |  |  |
|  |  |  |
## API
### pixelmatch(img1, img2, output, width, height[, options])
- `img1`, `img2` — Image data of the images to compare (`Buffer`, `Uint8Array` or `Uint8ClampedArray`). **Note:** image dimensions must be equal.
- `output` — Image data to write the diff to, or `null` if don't need a diff image.
- `width`, `height` — Width and height of the images. Note that _all three images_ need to have the same dimensions.
`options` is an object literal with the following properties:
- `threshold` — Matching threshold, ranges from `0` to `1`. Smaller values make the comparison more sensitive. `0.1` by default.
- `includeAA` — If `true`, disables detecting and ignoring anti-aliased pixels. `false` by default.
- `alpha` — Blending factor of unchanged pixels in the diff output. Ranges from `0` for pure white to `1` for original brightness. `0.1` by default.
- `aaColor` — The color of anti-aliased pixels in the diff output in `[R, G, B]` format. `[255, 255, 0]` by default.
- `diffColor` — The color of differing pixels in the diff output in `[R, G, B]` format. `[255, 0, 0]` by default.
- `diffColorAlt` — An alternative color to use for dark on light differences to differentiate between "added" and "removed" parts. If not provided, all differing pixels use the color specified by `diffColor`. `null` by default.
- `diffMask` — Draw the diff over a transparent background (a mask), rather than over the original image. Will not draw anti-aliased pixels (if detected).
Compares two images, writes the output diff and returns the number of mismatched pixels.
## Command line
Pixelmatch comes with a binary that works with PNG images:
```bash
pixelmatch image1.png image2.png output.png 0.1
```
## Example usage
### Node.js
```js
const fs = require('fs');
const PNG = require('pngjs').PNG;
const pixelmatch = require('pixelmatch');
const img1 = PNG.sync.read(fs.readFileSync('img1.png'));
const img2 = PNG.sync.read(fs.readFileSync('img2.png'));
const {width, height} = img1;
const diff = new PNG({width, height});
pixelmatch(img1.data, img2.data, diff.data, width, height, {threshold: 0.1});
fs.writeFileSync('diff.png', PNG.sync.write(diff));
```
### Browsers
```js
const img1 = img1Context.getImageData(0, 0, width, height);
const img2 = img2Context.getImageData(0, 0, width, height);
const diff = diffContext.createImageData(width, height);
pixelmatch(img1.data, img2.data, diff.data, width, height, {threshold: 0.1});
diffContext.putImageData(diff, 0, 0);
```
## Install
Install with NPM:
```bash
npm install pixelmatch
```
Use in the browser from a CDN:
```html
<script src="https://cdn.jsdelivr.net/npm/pixelmatch@5.3.0"></script>
```
## [Changelog](https://github.com/mapbox/pixelmatch/releases)