Resizing images made easy - thanks to ImageMagick.

This plugin requires Grunt ^0.4.5 and ImageMagick.

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

npm install grunt-image-resize --save-dev

One the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:

grunt.loadNpmTasks('grunt-image-resize');

Make sure ImageMagick is installed on your system and properly set up in your PATH.

Ubuntu:

$ apt-get install imagemagick

Mac OS X (using Homebrew):

$ brew install imagemagick

Windows & others:

http://www.imagemagick.org/script/binary-releases.php

Confirm that ImageMagick is properly set up by executing convert -help in a terminal.

In your project's Gruntfile, add a section named image_resize to the data object passed into grunt.initConfig().

grunt.initConfig({
  image_resize: {
    options: {
      width: 100,
      height: 100,
      overwrite: true
    },
    your_target: {
      // Target-specific file lists and/or options go here.
    },
  },
})

Type: Number

A number value that is passed as pixel or percentage value to imagemagick. If not defined, the resized image will keep the aspect ratio.

Type: Number

A number value that is passed as pixel or percentage value to imagemagick. If not defined, the resized image will keep the aspect ratio.

Type: Boolean Default value: true

Determines whether file that already exist under this destination will be overwritten.

Type: Boolean Default value: false

Determines whether images will be upscaled. If set to false (default), image will be copied instead of resized if it would be upscaled by resizing.

Type: Boolean Default value: false

Determines whether images will be cropped after resizing to exactly match options.width and options.height.

Type: String Default value: Center Possible values: NorthWest, North, NorthEast, West, Center, East, SouthWest, South, SouthEast

When cropping images this sets the image gravity. Doesn't have any effect, if options.crop is false.

Type: Number Default value: Number of CPUs

Determines how many resize operations are executed in parallel.

Type: Number Default value: 1

Determines the output quality of the resized image. Ranges from 0 (really bad) to 1 (almost lossless). Only applies to jpg images.

Type: Boolean Default value: false

Determines if resized image will be rotated according to EXIF information. Only applies to jpg images.

In this example, the default options are used to resize an image to 100px width. So if the test/fixtures/wikipedia.png file has a width of 500px, the generated result would be a 100px wide tmp/wikipedia.png.

grunt.initConfig({
  image_resize: {
    resize: {
      options: {
        width: 100
      },
      files: {
        'tmp/wikipedia.png': 'test/fixtures/wikipedia.png'
      }
    }
  }
})

In this example, we prevent the destination file from being overwritten if it already exists. It the file tmp/wikipedia.png already exists, for example because we just ran the task configuration above, this would not overwrite tmp/wikipedia.png. The file tmp/wikipedia.png would still be 100px wide.

grunt.initConfig({
  image_resize: {
    no_overwrite: {
      options: {
        width: 50,
        overwrite: false
      },
      files: {
        'tmp/wikipedia.png': 'test/fixtures/wikipedia.png'
      }
    }
  }
})

By default, the task does not resize images which would be upscaled. It only allows downscaling. You can allow upscaling by setting the upscale option to true. Otherwise images will copied instead of resized when they would be upscaled by resizing.

grunt.initConfig({
  image_resize: {
    no_overwrite: {
      options: {
        width: 600,
        upscale: true
      },
      files: {
        'tmp/wikipedia.png': 'test/fixtures/wikipedia.png'
      }
    }
  }
})

grunt.initConfig({
  image_resize: {
    resize: {
      options: {
        width: 100,
      },
      src: 'src/*.JPG',
      dest: 'dest/'
    }
  }
})

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