jekyll-responsive-image

A Jekyll plugin for automatically resizing images. Fully configurable and unopinionated, jekyll-responsive-image allows you to display responsive images however you like: using <img srcset>, <picture>, or Imager.js.

This plugin can be installed in three steps:

Either add jekyll-responsive-image to your Gemfile, or run the following command to install the gem:

$ gem install jekyll-responsive-image

Then you can either add jekyll-responsive-image to the plugins section of your _config.yml:

plugins:
  - jekyll-responsive-image

Note: If you are using a Jekyll version less than 3.5.0, use the gems key instead of plugins.

Or you can copy the contents of responsive_image.rb into your _plugins directory.

You will need to create a template in order to use the responsive_image and responsive_image_block tags. Normally the template lives in your _includes/ directory. Not sure where to start? Take a look at the sample templates.

For more advanced templates, see the Templates section below.

You must have a responsive_image block in your _config.yml for this plugin to work. At a minimum, your responsive_image configuration should have a template path and a list of sizes.

responsive_image:
  template: _includes/responsive-image.html
  sizes:
    - width: 320
    - width: 480
    - width: 800

For a list of all the available configuration options, see the All configuration options section below.

Replace your images with the responsive_image tag, specifying the path to the image in the path attribute.

{% responsive_image path: assets/my-file.jpg %}

You can override the template on a per-image basis by specifying the template attribute.

{% responsive_image path: assets/my-file.jpg template: _includes/another-template.html %}

Any extra attributes will be passed straight to the template as variables.

{% responsive_image path: assets/image.jpg alt: "Lorem ipsum..." title: "Lorem ipsum..." %}

You can use Liquid variables as attributes with the responsive_image_block tag. This tag works in exactly the same way as the responsive_image tag, but is implemented as a block tag to allow for more complex logic.

Important! The attributes in the responsive_image_block tag are parsed as YAML, so whitespace and indentation are significant!

{% assign path = 'assets/test.png' %}
{% assign alt = 'Lorem ipsum...' %}

{% responsive_image_block %}
  path: {{ path }}
  alt: {{ alt }}
  {% if title %}
  title: {{ title }}
  {% endif %}
{% endresponsive_image_block %}

It's easy to build your own custom templates to render images however you want using the template variables provided by jekyll-responsive-image.

The following variables are available in the template:

Any other attributes that are given to the responsive_image or responsive_image_block tags will be available in the template. For example the following tag will provide an {{ alt }} variable to the template:

{% responsive_image path: assets/my-file.jpg alt: "A description of the image" %}

Image objects (like original and each object in resized) contain the following properties:

A full list of all of the available configuration options is below.

responsive_image:
  # [Required]
  # Path to the image template.
  template: _includes/responsive-image.html

  # [Optional, Default: 85]
  # Quality to use when resizing images.
  default_quality: 90

  # [Optional, Default: []]
  # An array of resize configuration objects. Each object must contain at least
  # a `width` value.
  sizes:
    - width: 480  # [Required] How wide the resized image will be.
      quality: 80 # [Optional] Overrides default_quality for this size.
    - width: 800
    - width: 1400
      quality: 90

  # [Optional, Default: false]
  # Rotate resized images depending on their EXIF rotation attribute. Useful for
  # working with JPGs directly from digital cameras and smartphones
  auto_rotate: false

  # [Optional, Default: false]
  # Strip EXIF and other JPEG profiles. Helps to minimize JPEG size and win friends
  # at Google PageSpeed.
  strip: false

  # [Optional, Default: assets]
  # The base directory where assets are stored. This is used to determine the
  # `dirname` value in `output_path_format` below.
  base_path: assets

  # [Optional, Default: assets/resized/%{filename}-%{width}x%{height}.%{extension}]
  # The template used when generating filenames for resized images. Must be a
  # relative path.
  #
  # Parameters available are:
  #   %{dirname}     Directory of the file relative to `base_path` (assets/sub/dir/some-file.jpg => sub/dir)
  #   %{basename}    Basename of the file (assets/some-file.jpg => some-file.jpg)
  #   %{filename}    Basename without the extension (assets/some-file.jpg => some-file)
  #   %{extension}   Extension of the file (assets/some-file.jpg => jpg)
  #   %{width}       Width of the resized image
  #   %{height}      Height of the resized image
  #
  output_path_format: assets/resized/%{width}/%{basename}

  # [Optional, Default: true]
  # Whether or not to save the generated assets into the source folder.
  save_to_source: false

  # [Optional, Default: false]
  # Cache the result of {% responsive_image %} and {% responsive_image_block %}
  # tags. See the "Caching" section of the README for more information.
  cache: false

  # [Optional, Default: []]
  # By default, only images referenced by the responsive_image and responsive_image_block
  # tags are resized. Here you can set a list of paths or path globs to resize other
  # images. This is useful for resizing images which will be referenced from stylesheets.
  extra_images:
    - assets/foo/bar.png
    - assets/bgs/*.png
    - assets/avatars/*.{jpeg,jpg}

jekyll-responsive-image uses rmagick which is currently incompatible with ImageMagick 7. If you get an error like:

Can't install RMagick 2.16.0. Can't find MagickWand.h

Then you will need to install ImageMagick 6. If you are using Homebrew on Mac OS, this can be done with the following commands:

$ brew uninstall imagemagick
$ brew install imagemagick@6 && brew link imagemagick@6 --force

You may be able to speed up the build of large sites by enabling render caching. This is usually only effective when the same image is used many times, for example a header image that is rendered in every post.

The recommended way to enable caching is on an image-by-image basis, by adding cache: true to the tag:

{% responsive_image path: 'assets/my-file.jpg' cache: true %}

{% responsive_image_block %}
    path: assets/my-file.jpg
    cache: true
{% endresponsive_image_block %}

You can also enable it for all images by adding cache: true to your _config.yml:

responsive_image:
  cache: true
  template: _includes/responsive-image.html
  sizes:
    - ...

If you'd like to contribute to this repository, here's how you can set it up for development:

1. Fork this repository
2. Clone the fork to your local machine
3. Install ImageMagick (if you haven't already)
4. Run bundle install
5. Run the tests like this: cucumber

If you'd like your Jekyll project to use your local fork directly, you can add the :path parameter to your gem command in the project's Gemfile:

gem 'jekyll-responsive-image', :path => "/your/local/path/to/jekyll-responsive-image"

If you'd like your changes to be considered for the original repository, simply submit a pull request after you've made your changes. Please make sure all tests pass.