reverse_animation_gif.rb

# -*- coding: utf-8 -*-
require 'rubygems'
require 'RMagick'

filename = ARGV.first

unless filename
  warn "usage: #{$0} <ANIMATION GIF FILE>"
  exit 1
end

source = Magick::ImageList.new(filename)

dest = Magick::ImageList.new

source.coalesce.reverse.each{ |frame|
  dest.push frame
}
dest.delay = source.delay
dest.iterations = 0

dest.optimize_layers(Magick::OptimizeTransLayer).deconstruct.write("out.gif")