An unopinionated Jekyll plugin for generating and using responsive images
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README.md

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.

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Installation

This plugin can be installed in three steps:

1. Install the gem

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.

2. Create an image template file

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.

3. Configure the plugin

You must have a responsive_image block in your _config.yml for this plugin to work. The minimum required configuration is a template path:

responsive_image:
  template: _includes/responsive-image.html

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

Usage

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..." %}

Liquid variables as attributes

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 %}

Templates

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

Template Variables

The following variables are available in the template:

Variable Type Description
path String The path of the unmodified image. This is always the same as the path attribute passed to the tag.
resized Array An array of all the resized images. Each image is an Image Object.
original Object An Image Object containing information about the original image.
* String Any other attributes will be passed to the template verbatim as strings (see below).

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

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

Variable Type Description
path String The path to the image.
width Integer The width of the image.
height Integer The height of the image.
basename String Basename of the file (assets/some-file.jpg => some-file.jpg).
dirname String Directory of the file relative to base_path (assets/sub/dir/some-file.jpg => sub/dir).
filename String Basename without the extension (assets/some-file.jpg => some-file).
extension String Extension of the file (assets/some-file.jpg => jpg).

All configuration options

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}

Caching

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:
    - ...