Jekyll thumbnail generator

A generator plugin for Jekyll that generated thumbnails of images related to each post. Also includes Liquid templates showing these thumbnails in a page.

Tested with Jekyll 3.1.2.

Dependencies

1. rmagick. Tested with version 2.16.0
2. Jekyll asset path plugin. Works also without, but the image paths are assumed to use the asset path plugin structure.

Usage

Creating image gallery thumbnails

Images to process into thumbnails are read from Jekyll front matter. The format is the following:

gallery:
  - file: first-image.jpg
    title: First image file
  - file: second-image.jpg
    title: Second image file

Paths are relative to asset path plugin's asset path. That is, for posts the gallery directory is assets/posts/<post-title>/ and for pages assets/<page-title>/.

Thumbnails are generated in directory thumbnails in the asset path. Thumbnails are resized to fit dimensions of 200×120 pixels, or as specified in _config.yml option thumbnail_size:

thumbnail_gallery:
  width:  300
  height: 180

Generated thumbnails are included in the page as normal assets. You can use gallery.html in _includes directory as a starting point for a gallery implementation.

For styling the thumbnail gallery, you can use _gallery.scss in directory _sass as a starting point. It can be referenced from main.css, which must define sass variables thumbnail-gallery-width and thumbnail-gallery-height in Liquid like this:

$thumbnail-gallery-width:
    {% if site.thumbnail_gallery.width == nil %}
        200px
    {% else %}
        {{ site.thumbnail_gallery.width}}px
     {% endif %}
;
$thumbnail-gallery-height:
    {% if site.thumbnail_gallery.height == nil %}
        120px
    {% else %}
        {{ site.thumbnail_gallery.height}}px
     {% endif %}
;

Creating cover photo thumbnail

Also, a shrank copy for post cover image can be made. The photo to resize is by default cover.jpg. This can be overridden in front matter:

cover: other-image.png

Thumbnail dimensions are by default 400×240 pixels. These can be overridden in _config.yml:

thumbnail_cover:
  width:  200
  height: 120

Cover photo thumbnail is included in pages as normal assets. See includes post_summary.html and post_summary_content.html in _includes directory for example.

Bugs

1. Changing something that regerates a thumbnail leads to page being regenerated twice. The reason is that thumbnails are included in Jekyll's watch, so regenerated thumbnail itself is detected.