grunt-image-resize

Resizing images made easy - thanks to ImageMagick.

Getting Started

This plugin requires Grunt ^0.4.5 and ImageMagick.

Grunt

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');

ImageMagick

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.

The "image_resize" task

Overview

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.
    },
  },
})

Options

options.width

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.

options.height

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.

options.overwrite

Type: Boolean Default value: true

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

options.upscale

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.

options.crop

Type: Boolean Default value: false

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

options.gravity

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.

options.concurrency

Type: Number Default value: Number of CPUs

Determines how many resize operations are executed in parallel.

options.quality

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.

options.autoOrient

Type: Boolean Default value: false

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

Usage Examples

Default Options

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'
      }
    }
  }
})

Prevent overwriting

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'
      }
    }
  }
})

Allow upscaling

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'
      }
    }
  }
})

Resize all the images in a directory

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

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 and test your code using Grunt.