image-diff

Create image differential between two images

This was created as part of a visual regression project.

Getting Started

Requirements

image-diff depends on ImageMagick.

Please install this before continuing.

Setup

Install the module with: npm install image-diff

var imageDiff = require('image-diff');
imageDiff({
  actualImage: 'checkerboard.png',
  expectedImage: 'white.png',
  diffImage: 'difference.png',
}, function (err, imagesAreSame) {
  // error will be any errors that occurred
  // imagesAreSame is a boolean whether the images were the same or not
  // diffImage will have an image which highlights differences
});

Documentation

image-diff exposes the function imageDiff as its export.

imageDiff(options, cb)

Create an differential image between multiple images

• options Object
  • options.actualImage String - Path to actual image file
    • options.actualImage must exist
  • options.expectedImage String - Path to expected image file
    • If options.expectedImage does not exist, a transparent image with the same height/width will be created.
  • options.diffImage String - Optional path to output differential image
  • options.shadow Boolean - Optional flag to indicate if we should draw a shadow of the unchanged parts of the images
    • For example, if an image is + and we diff with -, then the image will have | be red but also contain a faded -
    • By default, this options is false meaning a shadow will not be drawn
• cb Function - Error-first function to handle diff result
  • cb should have the signature function (err, imagesAreSame)
  • err Error|null - If there was an error in diffing, this will be it
  • imagesAreSame Boolean - Indicates that images are same or not

imageDiff.getFullResult(options, cb)

Same as imageDiff but yields a fuller result

• options Object - See imageDiff#options
• cb Function - Error-first function to handle diff result
  • cb should have the signature function (err, result)
  • err Error|null - If there was an error in diffing, this will be it
  • result Object
    • total Float - Root mean square pixel difference across all pixels
      • Value can range from 0 (no difference) to 655535 (every pixel is different)
    • percentage Float - Normalized total difference
      • Value can range from 0.00 (no difference) to 1.00 (every pixel is different)
    • More info here: http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17284

Example:

var imageDiff = require('image-diff');
imageDiff.getFullResult({
  actualImage: 'checkerboard.png',
  expectedImage: 'white.png',
  diffImage: 'difference.png',
}, function (err, result) {
  // result = {total: 46340.2, difference: 0.707107}
});

imageDiff.getRawResult(options, cb)

Same as imageDiff but yields raw CLI result

• options Object - See imageDiff#options
• cb Function - Error-first function to handle diff result
  • cb should have the signature function (err, result)
  • err Error|null - If there was an error in diffing, this will be it
  • result String - Result from ImageMagick's compare command
    • Example output can be found here: http://www.imagemagick.org/discourse-server/viewtopic.php?f=1&t=17284

CLI usage

We offer an image-diff executable to diff from the CLI. When images match, its exit code will be 0. When they don't match, then it will be non-zero (e.g. 1).

$ image-diff --help

  Usage: image-diff [options] <actual-image> <expected-image> [diff-image]

  Options:

    -h, --help     output usage information
    -V, --version  output the version number
    --shadow       Draw a shadow of unchanges parts on diff image

Example usage:

# Images don't match
image-diff checkerboard.png white.png diff.png
echo $?
# 1
# We can look at `diff.png` for the diff result

# Images do match
image-diff checkerboard.png white.png
echo $?
# 0

Contributing

In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint via grunt and test via npm test.

Attribution

The font used for the example image is Arial 30pt bold and Courier New 38pt.

License

Copyright (c) 2013 Uber

Licensed under the MIT license.