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A Ruby gem for on-the-fly processing - suitable for image uploading in Rails, Sinatra and much more!


Dragonfly is a Rack framework for on-the-fly processing and encoding. It includes an extension for Ruby on Rails to enable easy image handling.

For the lazy rails user

To use simply for image thumbnails etc. in Rails...


config.gem 'rmagick',    :lib => 'RMagick'
config.gem 'rack-cache', :lib => 'rack/cache'
config.gem 'dragonfly',  :lib => 'dragonfly/rails/images', :source => ''


add_column :albums, :cover_image_uid, :string


class Album < ActiveRecord::Base
  image_accessor :cover_image            # Defines reader/writer for cover_image
  # ...

View (for uploading via a file field):

<% form_for @album, :html => {:multipart => true} do |f| %>
  <%= f.file_field :cover_image %>
<% end %>

View (to display):

<%= image_tag @album.cover_image.url(:gif) %>
<%= image_tag @album.cover_image.url('400x200') %>
<%= image_tag @album.cover_image.url('100x100!', :png) %>
<%= image_tag @album.cover_image.url('100x100#') %>
<%= image_tag @album.cover_image.url('50x50+30+30sw', :tiff) %>
<%= image_tag @album.cover_image.url(:rotate, 15) %>

Using outside of rails, custom storage/processing/encoding/analysis, and more...

Dragonfly is primarily a Rack app, the Rails part of it being nothing more than a separate layer on top of the main code, which means you can use it as a standalone app, or with Sinatra, Merb, etc.

It is intended to be highly customizable, and is not limited to images, but any data type that could suit on-the-fly processing/encoding.

For more info, consult the DOCUMENTATION


Please use the github issue tracker if you have any issues.


Google group dragonfly-users



Copyright (c) 2009 Mark Evans. See LICENSE for details.

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