Addon to CarrierWave to process GIF files.

gif_processes.rb

# frozen_string_literal: true

require "rmagick"

# Addons to CarrierWave to process GIF files.
#
# Example:
#
#   class AvatarUploader < CarrierWave::Uploader::Base
#     include CarrierWave::GifProcesses
#
#     version :medium do
#       process :coalesce_animation
#       process resize_to_fill: [200, 200]
#       process :optimize_animation
#     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!(&:collapse!) if file.content_type == "image/gif"
    end

    # Remove animation optimizations. Makes the file size larger but allows
    # later manipulations to work better with optimized gifs. Be sure to call
    # optimize_animation after resizing the image.
    #
    #     process :coalesce_animation
    def coalesce_animation
      manipulate!(&:coalesce) if file.content_type == "image/gif"
    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.
    #
    #     process :optimize_animation
    def optimize_animation
      return unless file.content_type == "image/gif"

      list = ::Magick::ImageList.new.from_blob(file.read)
      return unless list.size > 1

      list = list.coalesce
      list.optimize_layers(Magick::OptimizeLayer)
      list.remap
      File.open(current_path, "wb") do |f|
        f.write list.to_blob
      end
    end
  end
end

Gist updated to work with MiniMagick. It still requires RMagick for the ImageList layers optimizations, though.