file_uploader.rb

class FileUploader < CarrierWave::Uploader::Base
  require 'carrierwave/processing/mini_magick'

  include CarrierWave::MiniMagick

  storage :fog

  version :thumb do
    process :resize_first_page
    process :convert => :jpg
    process :set_content_type
  end

  private
  def resize_first_page
    manipulate! do |pdff|
      first_page = Magick::ImageList.new("#{current_path}[0]").first
      thumb = first_page.resize_to_fill!(220,155)
      thumb
    end
  end

  def set_content_type(*args)
    self.file.instance_variable_set(:@content_type, "image/jpg")
  end

end

Even 3 years old this seems to be a valid way to convert a PDF cover page. However, Magick::ImageList.new results in the error uninitialized constant Magick::ImageList. Are you aware if anything has changed with MiniMagick that makes this method no longer available? Thanks!

@atstockland I'm getting a maybe it is not an image? error when it enters manipulate!, did you experience this at all?

+1 @sighmin did you find a workaround ?

ImageList in MiniMagick was removed. It was in beta and the developer concluded that it wasted too much memory to be included sadly :/