Image difference blend

1.png

2.png

diff.png

difference_blend.rb

require 'chunky_png'
include ChunkyPNG::Color

images = [
  ChunkyPNG::Image.from_file('1.png'),
  ChunkyPNG::Image.from_file('2.png')
]

images.first.height.times do |y|
  images.first.row(y).each_with_index do |pixel, x|

    channels = [
      [r(pixel), r(images.last[x,y])],
      [g(pixel), g(images.last[x,y])],
      [b(pixel), b(images.last[x,y])]
    ]

    images.last[x,y] = rgb(
      *channels.map do |channel|
        channel.first + channel.last - 2 * channel.min
      end
    )
  end

end

images.last.save('diff.png')