#! usr/bin/env ruby
require 'chunky_png'

class ChunkyPNG::Image
  # s: Integer (pixel size)
  def pixelize s = 10
    temp = Array.new((height*1.0/s).ceil) {Array.new((width*1.0/s).ceil) {Array.new(3) {0}}}
    height.times {|j| width.times {|i| ChunkyPNG::Color.to_truecolor_bytes(get_pixel(i,j)).each.with_index {|e,k| temp[j/s][i/s][k] += e}}}
    png = ChunkyPNG::Image.new width, height
    sq = s**2
    height.times {|j| width.times {|i| png.set_pixel(i,j, ChunkyPNG::Color.parse(ChunkyPNG::Color.rgb(*temp[j/s][i/s].map {|e| e/sq})))}}
    png
  end
end

image = ChunkyPNG::Image.from_file('input.png')
image.pixelize.save('output_average.png')