HasImage is a plugin/gem that allows Ruby on Rails applications to have attached images. It is very small and lightweight: it only requires one column (“has_image_file”) in your model to store the uploaded image’s file name.

It is, by design, very simplistic: It only supports using a filesystem for storage, and only supports MiniMagick as an image processor. However, its code is very small, clean and hackable, so adding support for other backends or processors should be fairly easy.

HasImage works best for sites that want to show image galleries with fixed-size thumbnails. It uses ImageMagick’s crop and center gravity functions to produce thumbnails that generally look acceptable, unless the image is a panorama, or the subject matter is close to one of the margins, etc. For most sites where people upload pictures of themselves or their pets the generated thumbnails will look good almost all the time.

It’s pretty easy to change the image processing / resizing code; you can just override HasImage::Processor#resize_image to do what you wish:

 
  module HasImage::
    class Processor
      def resize_image(size)
        @image.combine_options do |commands|
          commands.my_custom_resizing_goes_here
        end
      end
    end
  end

Another image attachment library? Why?

Attachment_fu is too large and general for some of the places I want to use images. I sometimes found myself writing more code to hack attachment_fu than it took to create this gem. In fact, most of the code here has been plucked from my various projects that use attachment_fu.

The other image attachment libraries I found fell short of my needs for various other reasons, so I decided to roll my own.

Examples

Point-and-drool use case:

It’s probably not what you want, but it may be useful for bootstrapping.

  class Member < ActiveRecord::Base
    has_image
  end

Single image, no thumbnails, with some size limits:

  class Picture < ActiveRecord::Base
    has_image :resize_to => "200x200",
      :max_size => 3.megabytes,
      :min_size => 4.kilobytes
  end

Image with some thumbnails:

  class Photo < ActiveRecord::Base
    has_image :resize_to => "640x480",
      :thumbnails => {
        :square => "200x200",
        :medium => "320x240" 
      },
      :max_size => 3.megabytes,
      :min_size => 4.kilobytes
  end

HasImage also provides a view helper to make displaying the images extremely simple:

<%= image_tag_for(@photo, :thumb => :square) %>

Getting it

Has image can be installed as a gem, or as a Rails plugin. Gem installation is easiest, and recommended:

gem install norman-has_image—source http://gems.github.com

and add

to your environment.rb file.

Alternatively, you can install it as a Rails plugin:

./script plugin install git://github.com/norman/has_image.git

Rails versions before 2.1 do not support plugin installation using Git, so if you’re on 2.0 (or earlier), then please install the gem rather than the plugin.

Then, make sure the model has a column named “has_image_file.”

Git repository:

git://github.com/norman/has_image.git

Hacking it

Don’t like the way it makes images? Want to pipe the images through some crazy fast seam carving library written in OCaml, or watermark them with your corporate logo? Happiness is just a monkey-patch away:

  module HasImage
    class Processor
      def resize_image(size)
        # your new-and-improved thumbnailer code goes here.
      end
    end
  end

HasImage follows a philosophy of “skinny model, fat plugin.” This means that it tries to pollute your ActiveRecord model with as little functionality as possible, so that in a sense, the model is acts like a “controller” and the plugin like a “model” as regards the image handling functionality. This makes it easier to test, hack, and reuse, because the storage and processing functionality is largely independent of your model, and of Rails.

My goal for HasImage is to keep it very small. If you need a lot of functionality that’s not here, instead of patching this code, you will likely be better off using attachment_fu, which is much more powerful, but also more complex.

Bugs

Please report them on Lighthouse.

At the time of writing (July 2008), HasImage is in its infancy. Your patches, bug reports and withering criticism are more than welcome.