Pixelizing images with ChunkyPNG

output.png

pixelize.rb

require 'chunky_png'

module ChunkyPNG::Color
  def self.average(pixels)
    pixel_rgbs = pixels.map{|p| to_truecolor_bytes(p)}
    averaged_rgb = [0,0,0].zip(*pixel_rgbs).map{|colors| colors.inject(&:+) / pixels.size}
    rgb(*averaged_rgb)
  end
end

module Pixelizeable
  def pixilize!(pixel_width, pixel_height = pixel_width)
    collect_block!(pixel_height, pixel_width) do |block|
      new_color = ChunkyPNG::Color.average(block.pixels)
      new_pixels = (0...(block.width * block.height)).collect{new_color}
      ChunkyPNG::Canvas.new(block.width, block.height, new_pixels)
    end
  end
  
  def collect_block!(pixel_width, pixel_height)
    image_block_width = (width.to_f / pixel_width.to_f).ceil
    image_block_height = (height.to_f / pixel_height.to_f).ceil
    x_offsets = (0...image_block_width).map{|x| x * pixel_width}
    y_offsets = (0...image_block_height).map{|x| x * pixel_height}
    xy_offsets = x_offsets.product(y_offsets)
    
    xy_offsets.each do |x_offset, y_offset|
      block_width = [pixel_width, width - x_offset].min
      block_height = [pixel_height, height - y_offset].min
      new_block = yield crop(x_offset, y_offset, block_width, block_height)
      replace!(new_block, x_offset, y_offset)
    end
  end
end
ChunkyPNG::Image.send :include, Pixelizeable

image = ChunkyPNG::Image.from_file('input.png')
image.pixilize!(10)
image.save('output.png')