Resemble.js

Analyse and compare images with Javascript and HTML5. More info & Resemble.js Demo. Compatible with Node.js.

Get it

npm install resemblejs

bower install resemblejs

Example

Retrieve basic analysis on an image:

var api = resemble(fileData).onComplete(function(data){
	console.log(data);
	/*
	{
	  red: 255,
	  green: 255,
	  blue: 255,
	  brightness: 255
	}
	*/
});

Use resemble to compare two images:

var diff = resemble(file).compareTo(file2).ignoreColors().onComplete(function(data){
	console.log(data);
	/*
	{
	  misMatchPercentage : 100, // %
	  isSameDimensions: true, // or false
	  dimensionDifference: { width: 0, height: -1 }, // defined if dimensions are not the same
	  getImageDataUrl: function(){}
	}
	*/
});

Scale second image to dimensions of the first one:

//diff.useOriginalSize();
diff.scaleToSameSize();

You can also change the comparison method after the first analysis:

// diff.ignoreNothing();
// diff.ignoreColors();
// diff.ignoreAlpha();
diff.ignoreAntialiasing();

And change the output display style:

resemble.outputSettings({
  errorColor: {
    red: 255,
    green: 0,
    blue: 255
  },
  errorType: 'movement',
  transparency: 0.3,
  largeImageThreshold: 1200,
  useCrossOrigin: false,
  outputDiff: true
})
// .repaint();

It is possible to narrow down the area of comparison, by specifying a bounding box measured in pixels from the top left:

resemble.outputSettings({
  boundingBox: {
    left: 100,
    top: 200,
    right: 200,
    bottom: 600
  }
})
// .repaint();

You can also exclude part of the image from comparison, by specifying the excluded area in pixels from the top left:

resemble.outputSettings({
  ignoredBox: {
    left: 100,
    top: 200,
    right: 200,
    bottom: 600
  }
})
// .repaint();

By default, the comparison algorithm skips pixels when the image width or height is larger than 1200 pixels. This is there to mitigate performance issues.

You can modify this behaviour by setting the largeImageThreshold option to a different value. Set it to 0 to switch it off completely.

useCrossOrigin is true by default, you might need to set it to false if you're using Data URIs.

Single callback api

The resemble.compare API provides a convenience function that is used as follows:

const compare = require('resemblejs').compare;

function getDiff(){

const options = {
  output: {
    errorColor: {
      red: 255,
      green: 0,
      blue: 255
    },
    errorType: 'movement',
    transparency: 0.3,
    largeImageThreshold: 1200,
    useCrossOrigin: false,
    outputDiff: true
  },
  scaleToSameSize: true,
  ignore: ['nothing', 'less', 'antialiasing', 'colors', 'alpha'],
};
// The parameters can be Node Buffers
// data is the same as usual with an additional getBuffer() function
compare(image1, image2, options, function (err, data) {
	if (err) {
		console.log('An error!')
	} else {
		console.log(data);
		/*
		{
		  misMatchPercentage : 100, // %
		  isSameDimensions: true, // or false
		  dimensionDifference: { width: 0, height: -1 }, // defined if dimensions are not the same
		  getImageDataUrl: function(){}
		}
		*/

	}
});

Node.js

Installation

On Node, Resemble uses the canvas package instead of the native canvas support in the browser. To prevent browser users from being forced into installing Canvas, it's included as a peer dependency which means you have to install it alongside Resemble.

Canvas relies on some native image manipulation libraries to be install on the system. Please read the Canvas installation instructions for OSX/Windows/Linux.

Example commands for installation on OSX

npm install resemblejs
brew install pkg-config cairo libpng jpeg giflib
npm install canvas

Usage

The API under Node is the same as on the resemble.compare but promise based:

const compareImages = require('resemblejs/compareImages');
const fs = require("mz/fs");

async function getDiff(){

const options = {
  output: {
    errorColor: {
      red: 255,
      green: 0,
      blue: 255
    },
    errorType: 'movement',
    transparency: 0.3,
    largeImageThreshold: 1200,
    useCrossOrigin: false,
    outputDiff: true
  },
  scaleToSameSize: true,
  ignore: ['nothing', 'less', 'antialiasing', 'colors', 'alpha'],
};
// The parameters can be Node Buffers
// data is the same as usual with an additional getBuffer() function
const data = await compareImages(
	await fs.readFile('./demoassets/People.jpg'),
	await fs.readFile('./demoassets/People2.jpg'),
	options,
);

await fs.writeFile('./output.png', data.getBuffer());

}

getDiff();

Tests

To run the tests on Node (using Jest), type:

npm run test

Dockerfile

For convenience I've added a simple Dockerfile to run the NodeJS tests in an Ubuntu container

docker build -t huddle/resemble .
docker run huddle/resemble

---

Created by James Cryer and the Huddle development team.