Resemble.js/README.md

<h1 align="center"><img src="https://raw.github.com/HuddleEng/Resemble.js/master/demoassets/resemble.png" alt="Resemble.js" width="256"/></h1>

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<p align="center">
  Analyse and compare images with Javascript and HTML5. <a href="http://huddleeng.github.io/Resemble.js/">More info & Resemble.js Demo</a>. Compatible with Node.js.
</p>

<hr />

### Get it

`npm install resemblejs`

`bower install resemblejs`

### Example

Retrieve basic analysis on an image:

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

Use resemble to compare two images:

```javascript
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:

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

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

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

And change the output display style:

```javascript
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:

```javascript
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:

```javascript
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.

Resemble.js also supports Data URIs as strings

```javascript
resemble.outputSettings({ useCrossOrigin: false });
var diff = resemble("data:image/jpeg;base64,/9j/4AAQSkZJRgAB...").compareTo(
    "data:image/jpeg;base64,/9j/,/9j/4AAQSkZJRg..."
);
```

`useCrossOrigin` is true by default, you might need to set it to false if you're using [Data URIs](https://developer.mozilla.org/en-US/docs/Web/HTTP/Basics_of_HTTP/Data_URIs).

### Single callback api

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

```js
const compare = require("resemblejs").compare;

function getDiff() {
    const options = {};
    // 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

#### Usage

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

```js
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: "antialiasing"
    };

    // 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:

```bash
npm run test
```

There are also some in-browser tests. To run these install and run a http-server such as [http-server](https://github.com/indexzero/http-server) from the root of the project. Then in the browser, navigate to `localhost:8080/chai-tests/test.html`, open up the developer console to see the results.

#### Dockerfile

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

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

#### Reference to academic papers

As people have asked in the past, Resemble.js hasn't knowingly implemented any published ideas. RGBA colour comparison is simple and straightforward when working with the Canvas API. The antialiasing algorithim was developed at Huddle over several days of trial-and-error using various false-positive results from PhantomCSS tests.

---

Created by [James Cryer](http://github.com/jamescryer) and the Huddle development team.