Bipolarization.cs

using System.Collections.Generic;
using System.Drawing;
using System.Linq;
using System.Text.RegularExpressions;

namespace Bipolarization
{
    class Program
    {
        static void Main(string[] args)
        {
            args.ToList().ForEach(a => Bipolarize(Image.FromFile(a)).Save(NewName(a)));
        }

        private static Image Bipolarize(Image i)
        {
            var b = new Bitmap(i);
            Map(b).ToList().ForEach(_ => Bipolarize(b, _));
            return b;
        }

        private static IEnumerable<Point> Map(Image i)
        {
            return from x in Enumerable.Range(0, i.Width)
                   from y in Enumerable.Range(0, i.Height)
                   select new Point(x, y);
        }

        private static void Bipolarize(Bitmap b, Point p)
        {
            b.SetPixel(p.X, p.Y, Bipolarization(b.GetPixel(p.X, p.Y)));
        }

        private static Color Bipolarization(Color c)
        {
            return Average(c) < 30 ? Color.Black : Color.White;
        }

        private static double Average(Color c)
        {
            return new int[] { c.R, c.G, c.B }.Average();
        }

        private static string NewName(string n)
        {
            return Regex.Replace(n, @"\.([^\.]+)$", @".new.$1");
        }
    }
}

bipolarization.rb

#coding:utf-8

require 'System.Drawing'
include System::Drawing

def bipolarize(i)
  b = Bitmap.new(i)
  (0...b.width).each do |x|
    (0...b.height).each do |y|
      b.set_pixel(x, y, bipolarization(b.get_pixel(x, y)))
    end
  end
  b
end

def bipolarization(c)
  average(c) < 30 ? Color.Black : Color.White
end

def average(c)
  [c.r, c.g, c.b].inject{|s, c| s += c} / 3
end

def new_name(n)
  n.sub(/\.([^\.]+)$/, ".new.\\1")
end

ARGV.each{|a| bipolarize(Image.from_file(a)).save(new_name(a))}