Save resized copies of retina images at regular size.

resize_mobile_images.rb

require 'rmagick'

source = ARGV[0]

Dir.glob('images/' + source + '/*.*').each do |retina_path|
  mobile_path = retina_path.sub(/retina/, 'normal')

  retina_file = File.new(retina_path)
  mobile_file = File.new(mobile_path) if File.exist?(mobile_path)

  if !File.exist?(mobile_path) || retina_file.mtime > mobile_file.mtime
    puts '  Retina image has changed! Shrinking: ' + retina_path
    GC.start

    image = Magick::Image::read(retina_path).first
    image.resize!(image.columns / 2, image.rows / 2, Magick::GaussianFilter, 0.2)
    image.write mobile_path

    image.destroy!
  end
end