Generate all colors of RGB in a png file

color_palette.rb

require 'chunky_png'

png = ChunkyPNG::Image.new(4096, 4096)

(0..255).each do |b|
  (0..255).each do |g|
    (0..255).each do |r|
      x = b/16*256 + r
      y = b%16*256 + g
      png[x,y] = ChunkyPNG::Color.rgb(r, g, b)
    end
  end
end

png.save('color_palette.png')