Resizing retina images with rmagick

Guardfile

guard 'process', :name => 'shrink-images', :command => 'ruby resize-mobile-images.rb' do
  watch /^images\/mobileretina\/.+.png/
end

resize-mobile-images.rb

require 'rmagick'

Dir.glob('images/mobileretina/*.png').each do |image_path|

  GC.start

  image = Magick::Image::read(image_path).first
  image.scale!(0.5)
  new_path = image_path.sub(/retina/, 'normal')
  image.write new_path

  image.destroy!

end