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https://github.com/mapbox/pixelmatch

The smallest, simplest and fastest JavaScript pixel-level image comparison library
https://github.com/mapbox/pixelmatch

diff image-comparison testing-tools

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The smallest, simplest and fastest JavaScript pixel-level image comparison library

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README 

        
# pixelmatch



[![Node](https://github.com/mapbox/pixelmatch/actions/workflows/node.yml/badge.svg)](https://github.com/mapbox/pixelmatch/actions/workflows/node.yml)

[![](https://img.shields.io/badge/simply-awesome-brightgreen.svg)](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 |

| --- | --- | --- |

| ![](test/fixtures/4a.png) | ![](test/fixtures/4b.png) | ![1diff](test/fixtures/4diff.png) |

| ![](test/fixtures/3a.png) | ![](test/fixtures/3b.png) | ![1diff](test/fixtures/3diff.png) |

| ![](test/fixtures/6a.png) | ![](test/fixtures/6b.png) | ![1diff](test/fixtures/6diff.png) |



## 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

import fs from 'fs';

import {PNG} from 'pngjs';

import pixelmatch from '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

```



Or use in the browser from a CDN:



```html



	import pixelmatch from 'https://esm.run/pixelmatch';

```



## [Changelog](https://github.com/mapbox/pixelmatch/releases)