Ruby script to resize pictures

require 'rmagick'

dir = File.dirname(__FILE__)

Dir.glob "#{dir}/**/*.jpg" do |filename|
  image = Magick::Image.read(filename)[0]

  # note: there is another useful method which you can use to resize and crop square
  # image.resize_to_fill(200)

  # You can set size here. The original resolution should be kept.
  [[720,540,"large"],[240,180,"thumbnail"]].each do |size|
    w_scale = image.columns / (1.0 * size[0])
    h_scale = image.rows / (1.0 * size[1])

    scale = w_scale >= h_scale ? w_scale : h_scale
    scale = 1.0 / scale

    small_image = image.resize(scale)
    small_image.write File.dirname(filename) + "/" + File.basename(filename, ".jpg") + "_#{size[2]}.jpg"
    small_image.destroy!
  end

  image.destroy!
end