Paperclip processor to convert PDF to JPG to go around problems with the old versions of imagemagick and ghostscript available on Heroku. This file is located in [APP_ROOT]/lib/paperclip_processors/ghostscript.rb

content.rb

# Model using the ghostscript processor
class Content < ActiveRecord::Base
  
  has_attached_file :resource,
                    :styles => { :preview => ["725x1200>", :jpg], :thumb => ["100x140>", :jpg] },
                    :processors => [:ghostscript, :thumbnail],
                    :convert_options => { :all => '-colorspace RGB -flatten -density 300 -quality 100' }, 
                    :path => ":page_path/:class/:id/:resource_token/:style/:filename"
end

ghostscript.rb

module Paperclip
  class Ghostscript < Processor

    attr_accessor :current_geometry, :target_geometry, :format, :whiny, :convert_options, :source_file_options

    def initialize file, options = {}, attachment = nil
      super
      @file                = file
      @format              = options[:format]

      @current_format      = File.extname(@file.path)
      @basename            = File.basename(@file.path, @current_format)
    end

    def make
      src = @file
      dst = Tempfile.new([@basename, @format ? ".#{@format}" : ''])
      dst.binmode

      begin
        parameters = []
        parameters << "-dNOPAUSE -dBATCH -sDEVICE=jpeg -r144 -dUseCIEColor -dFirstPage=1 -dLastPage=1"
        parameters << "-sOutputFile=:dest"
        parameters << ":source"

        parameters = parameters.flatten.compact.join(" ").strip.squeeze(" ")
        
        success = Paperclip.run("gs", parameters, :source => "#{File.expand_path(src.path)}", :dest => File.expand_path(dst.path))
      rescue PaperclipCommandLineError => e
        raise PaperclipError, "There was an error processing the thumbnail for #{@basename}" if @whiny
      end
      dst
    end
  end
end