gistfile1.rb

# Hook for storing the dimensions of uploaded images.
# 
# Use like this:
# 
#   class MyModel
#     has_attached_file :image, :styles => { :thumb  => '72x72#' }
#   
#     stores_dimensions :image
#   end
# 
# You can now access the width and height using MyModel#image_width and MyModel#image_height.

module Paperclip
  module ClassMethods
    def stores_dimensions name
      property "#{name}_width".to_sym, Integer
      property "#{name}_height".to_sym, Integer
      
      define_method "#{name}_image?" do
        !!self.send("#{name}_content_type").match('^image/')
      end
      
      before :save do
        if self.send("#{name}?") and self.send("#{name}_image?")
          attachment = self.send(name)
          
          attribute_set("#{name}_width".to_sym, attachment.width)
          attribute_set("#{name}_height".to_sym, attachment.height)
        end
      end
    end
  end

  class Attachment
    def width(style = default_style)
      Paperclip::Geometry.from_file(to_file(style)).width
    end
 
    def height(style = default_style)
      Paperclip::Geometry.from_file(to_file(style)).height
    end
  end
end