Using libdevil to thumbnail and watermark

d.rb

# Gem: http://rubygems.org/gems/devil
# Library: http://openil.sourceforge.net/
# Images for use with this: http://dl.dropbox.com/u/363740/images.zip

# To install on snow leopard with homebrew:
#   1. brew install devil
#   2. gem install devil
#   3. ???
#   4. Profit!

require 'rubygems'
require 'devil'

# Set the image to be centered when enlarging the canvas
Devil.set_options(:placement => Devil::CENTER)

# Set the background to be black when enlarging the canvas ([r,g,b,a])
Devil.set_options(:clear_color => [0,0,0,255])

# Memory automatically freed after blocks are done running

def thumbnail1(input, output)
  # Make a square thumbnail with black padding to maintain aspect ratio
  Devil.load_image(input) do |image|
    # Make the image square (black borders added) with the image centered
    longest_side = [image.width,image.height].max
    image.enlarge_canvas(longest_side, longest_side)

    # Thumbnail the image (applying a blur to keep it from looking crappy)
    image.thumbnail2(200)

    # Save to a new file
    image.save(output)
  end
end

def thumbnail2(input, output)
  Devil.load_image(input) do |image|
    if image.width == image.height
      image.thumbnail2(200) # Just do normal thumbnailing if it's already square
    elsif image.width > image.height
      new_width = (image.width / image.height.to_f) * 200
      image.resize2(new_width, 200)
      x_offset = (new_width - 200) / 2.0
      image.crop(x_offset, 0, 200, 200)
    else
      new_height = (image.height / image.width.to_f) * 200
      image.resize2(200, new_height)
      y_offset = (new_height - 200) / 2.0
      image.crop(0, y_offset, 200, 200)
    end

    # Save to a new file
    image.save(output)
  end
end

def thumbnail_with_watermark(input, output, watermark)
  thumbnail2(input, output)

  i = Devil.load_image(output)
  w = Devil.load_image(watermark)

  if w.width > (i.width / 2.0) || w.height > (i.height / 2.0)
    new_width  = w.width
    new_height = w.height

    if w.width > (i.width / 2.0)
      old_width = new_width
      new_width = i.width / 2.0
      new_height = (new_height / old_width.to_f) * new_width
    end

    if w.height > (i.height / 2.0)
      old_height = new_height
      new_height = i.height / 2.0
      new_width = (new_width / old_height.to_f) * new_height
    end

    w.resize2(new_width, new_height)
    i.blit(w, i.width - w.width - 10, i.height - w.height - 10)
  else
    i.blit(w, i.width - w.width - 10, i.height - w.height - 10)
  end

  i.save(output)

  i.free
  w.free
end

thumbnail1('square.jpg', 'square1.jpg')
thumbnail1('wider.jpg',  'wider1.jpg')
thumbnail1('taller.jpg', 'taller1.jpg')

thumbnail2('square.jpg', 'square2.jpg')
thumbnail2('wider.jpg',  'wider2.jpg')
thumbnail2('taller.jpg', 'taller2.jpg')

thumbnail_with_watermark('square.jpg', 'square-wide-watermarked.jpg', 'wider.jpg')
thumbnail_with_watermark('wider.jpg',  'wider-wide-watermarked.jpg',  'wider.jpg')
thumbnail_with_watermark('taller.jpg', 'taller-wide-watermarked.jpg', 'wider.jpg')

thumbnail_with_watermark('square.jpg', 'square-tall-watermarked.jpg', 'taller.jpg')
thumbnail_with_watermark('wider.jpg',  'wider-tall-watermarked.jpg',  'taller.jpg')
thumbnail_with_watermark('taller.jpg', 'taller-tall-watermarked.jpg', 'taller.jpg')