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|

    images.last[x,y] = rgb(
      r(pixel) + r(images.last[x,y]) - 2 * [r(pixel), r(images.last[x,y])].min,
      g(pixel) + g(images.last[x,y]) - 2 * [g(pixel), g(images.last[x,y])].min,
      b(pixel) + b(images.last[x,y]) - 2 * [b(pixel), b(images.last[x,y])].min
    )
  end

end

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