pixelator.rb

require 'chunky_png'

module Pixelator
  extend self

  # Go go go!
  def pixelize!(image)
    for_each_block_of image do |x, y|
      color = average_of all_colors_from block: [x, y], of: image
      fill block: [x, y], with: color, of: image
    end

    image
  end

  # Iterates through each block of an image
  def for_each_block_of(image, &blk)
    (0..image.width/ten).each do |x|
      (0..image.height/ten).each { |y| yield x, y }
    end
  end

  # Fill a block with a color
  def fill(options)
    x, y  = options[:block]
    color = options[:with]
    image = options[:of]

    image.rect x*ten, y*ten, x*ten+ten, y*ten+ten, color, color  if color
  end

  # Returns all colors in a given block range
  def all_colors_from(options)
    x, y  = options[:block]
    image = options[:of]

    (0...ten * ten).map do |i|
      _x, _y = (x * ten + i/ten), (y * ten + i%ten)
      image[_x, _y]  if image.include_xy?(_x, _y)
    end.compact
  end

  # Adds a color to a hash-color
  def add_color(hash, color)
    channels.each { |chan|
      hash[chan] ||= 0
      hash[chan] += ChunkyPNG::Color.send(chan, color)
    }
    hash
  end

  # Divides a hash-color by a divisor
  def divide_color(hash, divisor)
    channels.each { |chan| hash[chan] /= divisor }
    hash
  end

  # Averages a list of colors
  def average_of(array)
    if array.length > 0
      h = array.inject({}) { |h, color| add_color(h, color) }
      h = divide_color(h, array.length)
      ChunkyPNG::Color.rgba(h[:r], h[:g], h[:b], h[:a])
    end
  end

  # Color channels
  def channels() [:r, :g, :b, :a]; end

  # Block size
  def ten() 10; end
end

image = Pixelator.pixelize! ChunkyPNG::Image.from_file('input.png')
image.save('output.png')