Codebrawl entry

README.md

Pixelizer entry for Codebrawl

This example needs Ruby 1.9.

Two ways to run this:

$ ./pixelizer.rb infile.png > outfile.png
$ ./pixelizer.rb - > outfile.png < infile.png

output.png

pixelizer.rb

#!/usr/bin/env ruby

require 'chunky_png'

class Pixelizer
  include ChunkyPNG

  # The ChunkyPNG::Image instance.
  attr_reader :png

  # The pixelizer accepts an IO object, like a file handle or $stdin.
  def initialize(io)
    @png = Image.from_io io
  end

  # Pixelizes using a very simple algorithm. Every block of 10x10 pixels
  # is evaluated, and replaced by one single color closest to the set of
  # colors within that block. You can overwrite the 10x10 pixels by setting
  # the first argument.
  def pixelize!(block_size = 10)
    dimension = @png.dimension
    @block_point = Point.new 0, 0

    while @block_point.within_bounds? dimension
      y_delta = dimension.height - @block_point.y
      @block_height = y_delta < block_size ? y_delta : block_size

      while @block_point.within_bounds? dimension
        x_delta = dimension.width - @block_point.x
        @block_width = x_delta < block_size ? x_delta : block_size

        pixelize_block!

        @block_point.x += block_size
      end

      @block_point.x = 0
      @block_point.y += block_size
    end
  end

  protected

  # Replaces the block with a single color.
  def pixelize_block!
    new_color = blur_color

    for block_y in 0...@block_height
      for block_x in 0...@block_width
        @png[@block_point.x + block_x, @block_point.y + block_y] = new_color
      end
    end
  end

  # Calculates the new color for a block based on surrounding colors.
  # Completely transparent pixels don't count of course.
  def blur_color
    colors = {r: [], g: [], b: [], a: []}

    for block_y in  0...@block_height
      for block_x in 0...@block_width
        color = @png[@block_point.x + block_x, @block_point.y + block_y]
        unless Color.fully_transparent? color
          colors.keys.each do |channel|
            colors[channel] << Color.send(channel, color)
          end
        end
      end
    end

    return Color::TRANSPARENT if colors[:r].empty?

    Color.rgba *(colors.map do |chan, set|
                   set.inject(:+) / set.length
                 end)
  end
end

unless ARGV[0]
  $stderr.puts "Usage: #{$0} [input.png | -] > output.png"
  exit 1
end

begin
  io = ARGV[0] == '-' ? $stdin : File.open(ARGV[0], 'rb')
  pix = Pixelizer.new io
  pix.pixelize!
  pix.png.write $stdout
rescue
  $stderr.puts "Sorry, something went wrong.\n#{$!}"
  exit 1
end