Addon to CarrierWave to process GIF files.

gif_processes.rb

# lib/addons/carrierwave/gif_processes.rb
#
# Addons to CarrierWave to process GIF files with RMagick.
#
# Example:
#
#   class AvatarUploader < CarrierWave::Uploader::Base
#     include CarrierWave::GifProcesses
#
#     version :medium do
#       process :optimize_animation
#       process resize_to_fill: [200, 200]
#     end
#
#     version :thumb do
#       process :remove_animation
#       process resize_to_fill: [32, 32]
#     end
#   end

module CarrierWave
  module GifProcesses

    # Remove the GIF animation
    #   process :remove_animation
    def remove_animation
      manipulate! do |img, index|
        index == 0 ? img : nil
      end
    end

    # Re-optimize the animation. This can help lower the file size with GIFs.
    # Without this resizing GIF files can result in very large image formats.
    def optimize_animation
      list = ::Magick::ImageList.new.from_blob file.read
      if list.size > 1
        list = list.coalesce
        list.optimize_layers(Magick::OptimizeLayer)
        list.remap
        File.open(current_path, 'wb') { |f| f.write list.to_blob }
      end
    end

  end
end