Creating thumbnails of PDFs with attachment_fu

We needed to create some thumbnails from uploading PDF files for a new site feature – We’re using attachment_fu which doesn’t support that (yet?), but we’re using RMagick as our processor and it understands PDF files.

I came up with the hack below (warning, first draft, only briefly tested) which works without having to modify the attachment_fu plugin itself. One day I’ll loop back and figure out a cleaner way to do this and see which of attachment_fu’s other image processors can even support pdfs.

There are three methods to override to make a go of this:

  1. self.image? : consider pdf files as an image so thumbnail process will happen
  2. thumbnail_name_for : change the extension of the saved thumbnail filename to png
  3. resize_image: override to change format via block passed to to_blob

Apologies for the crappy source formatting, I have to install a plugin to do that well one of these days

###Hacks to allow creation of png thumbnails for pdf uploads - depends on RMagic being the configured processor
## likely very fragile

def self.image?(content_type)
(content_types +  ['application/pdf']).include?(content_type)

alias_method :original_thumbnail_name_for, :thumbnail_name_for
def thumbnail_name_for(thumbnail=nil)
return original_thumbnail_name_for(thumbnail) unless (content_type == 'application/pdf' && !thumbnail.blank?)
basename = filename.gsub /.w+$/ do |s|
ext = s; ''
#copied from rmagick_processor with change in last few lines
def resize_image(img, size)
size = size.first if size.is_a?(Array) && size.length == 1 && !size.first.is_a?(Fixnum)
if size.is_a?(Fixnum) || (size.is_a?(Array) && size.first.is_a?(Fixnum))
size = [size, size] if size.is_a?(Fixnum)
img.change_geometry(size.to_s) { |cols, rows, image| image.resize!(cols<1 ? 1 : cols, rows<1 ? 1 : rows) }
img.strip! unless attachment_options[:keep_profile]
if content_type == 'application/pdf' # here force the output format to PNG if its a pdf
self.temp_path = write_to_temp_file(img.to_blob {self.format = 'PNG'})
self.temp_path = write_to_temp_file(img.to_blob)