gistfile1.rb

# Paperclip attachment, with sorting and special convert options
class PageAsset < ActiveRecord::Base
  acts_as_list :scope => :page
  has_attached_file :asset,
                    :styles => {
                                  :small    => "110x82#",
                                  :thumb    => "150x90#",
                                  :large    => "460x345>",
                                  :original => "1600x1200>"
                                },
                    :convert_options => { 
                        :large => '-background white -gravity center -extent 460x345' 
                        } # 460x350, keeping ratio, filling extra margin with blank
  validates_attachment_presence :asset, :message => "Image requise."
  validates_attachment_content_type :asset, 
    :content_type => ['image/pjpeg', 'image/jpeg', 'image/png'],
    :message => "doit être une image JPEG ou PNG"
  validates_attachment_size :asset, :less_than => 4.megabytes,
    :message => "doit être comprise entre :min et :max octets"
end