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https://github.com/lawmurray/jekyll-responsive-magick

A Jekyll plugin for responsive images using ImageMagick. Works with Jekyll 4.
https://github.com/lawmurray/jekyll-responsive-magick

imagemagick jekyll-plugin ruby-gem

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A Jekyll plugin for responsive images using ImageMagick. Works with Jekyll 4.

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README 

        
# Responsive Images for Jekyll Sites



`jekyll-responsive-magick` is a Jekyll plugin for responsive images. It adds filters for setting the `srcset`, `width` and `height` attributes of `img` elements, while automatically generating image variants of configured sizes using the ImageMagick command-line tools. Resized images are cached to minimize build times, regenerated only when the original source image changes.



The plugin has no dependencies besides the ImageMagick command line tools. This is by design, to make it easy to deploy on services such as Cloudflare Pages. For an example of its use, see [indii.org](https://indii.org). For a walkthrough of the implementation, see [Responsive Images with Jekyll and ImageMagick](https://indii.org/blog/responsive-images-with-jekyll-and-imagemagick/).



## License



`jekyll-responsive-magick` is open source software. It is licensed under the Apache License, Version 2.0 (the "License"); you may not use it except in compliance with the License. You may obtain a copy of the License at

.



## Getting started



The plugin requires ImageMagick. It is standard in Linux distributions and available through Homebrew on macOS. If you happen to be hosting with [CloudFlare Pages](https://pages.cloudflare.com/), it is already installed.



1. **Install the plugin** If you are using a `Gemfile`, add the following:

  ```ruby

  group :jekyll_plugins do

    gem 'jekyll-responsive-magick', '~> 1.2'

  ```

  then `bundle install`. Alternatively, `gem install jekyll-responsive-magick` or simply copy the `lib/jekyll-responsive-magick.rb` file into your site's `_plugins` directory.



2. **Enable the plugin** Add the following to your site's `_config.yml` file:

  ```yaml

  plugins: 

  - jekyll-responsive-magick

  ```



## Usage



The plugin provides three filters: `srcset`, `width` and `height`. Each consumes an absolute path to an image (as it would appear in `src`) and generates a value for the corresponding attribute. The intended usage is:

```html



```

`src` **must be** an absolute path, i.e. beginning with `/`, such as `/assets/example.jpg`. This is necessary for the plugin to find the right file in your project.



With the plugin installed and one or more uses of the `srcset`, `width` or `height` filters, you can build your site as normal, now with responsive images.



There may be cases where you cannot use responsive images but still want to resize to an explicit width, for example in a `background-image` style property. A fourth filter, `size`, can be used for this purpose:

```html

...


```



## Configuration



You can configure the size variants and quality of resized images by adding configuration options such as the following to your `_config.yml`:



```yaml

responsive:

  widths: [400,500,700,900]

  quality: 30

  format: webp

  verbose: true

```



The choice of `widths` should cover the typical sizes of images as they appear on your site. The choice of `quality` (between 0 and 100) is a trade-off between file size (lower at lower quality) and clarity (higher at higher quality). It could be tuned by eye. Low quality can be satisfactory with the prevalence of high definition displays.



The `format` option can be used to specify the output format of the resized images. The default is the original format but you can force conversion to `webp`, for example, which is a modern format with good compression. Simply omit the option to preserve the original format of each image.



Set `verbose` to `true` for debugging purposes. It will echo the commands being executed under the hood. Simply omit the option if not debugging.



## Performance



The `srcset`, `width` and `height` filters call ImageMagick's `convert` and `identity` on demand, rather than for all image assets in a project. Caching is used to call `identity` at most once per image per build, and `convert` once per image per width, storing resized images in a subdirectory `_responsive/` for reuse in subsequent builds. Resized images in `_responsive/` are updated only if their original source image changes (detected using last modified times on files).



If you experience any issues with outdated images, or simply wish to clean up, remove the whole `_responsive/` directory and rebuild. You may also wish to do this if you change the `widths` option in `_config.yml`.



When using `width` and `height`, expect additional build time of about one second per 100 images due to the overhead of launching `identity` processes.



When using `srcset` for the first time, expect additional build time on the order of minutes as resized images are generated with `convert`. Performance will improve drastically on subsequent builds because of the `_responsive/` subdirectory.



## Further reading



For a walkthrough of the implementation, see [Responsive Images with Jekyll and ImageMagick](https://indii.org/blog/responsive-images-with-jekyll-and-imagemagick/).



## Building the Gem (developers only)



To build and install, update the version number in `jekyll-responsive-magick.gemspec`, then:

```bash

gem build jekyll-responsive-magick.gemspec

gem install --user-install jekyll-responsive-magick-VERSION.gem

```



To release a new version to [RubyGems](https://rubygems.org):

```bash

gem signin

gem push jekyll-responsive-magick-VERSION.gem

```



For development and testing purposes, it is often easier to copy the `lib/jekyll-responsive-magick.rb` file into a site's `_plugins` directory and make modifications there.