ruby-hough-hack

gist-1.rb

# Authors: Robert Jackson, Jonathan Jackson
# the formatting of this file has been altered in
# order to fit on this website. Check out
# https://gist.github.com/1233581 if you care

require 'chunky_png' #or 'oily_png'
class Hough
  def initialize(image_path, options={})
    @image = ChunkyPNG::Image.from_file(image_path)
    @image_path = image_path
    @angles ||= {}
  end
  def is_dark?(color)
    ChunkyPNG::Color.r(color) +
    ChunkyPNG::Color.g(color) +
    ChunkyPNG::Color.b(color) < 40
  end
  def is_light?(color)
    ChunkyPNG::Color.r(color) +
    ChunkyPNG::Color.g(color) +
    ChunkyPNG::Color.b(color) > 600
  end
  def angles(theta)
    @angles[theta] ||= {
      :cos => Math.cos(theta),
      :sin => Math.sin(theta)
    }
  end
  def get_hough_matrix
    hough = Hash.new(0)

    # iterate over every point of the image 'Hooray Chunky Png'
    @image.height.times do |y|
      @image.width.times do |x|

        # run the point through hough transform only if the
        # sum of the points' rgb values are less than 40 (are black)
        # and the point directly below's( y+1 ) rgb values
        # are greater than 600 (are white)
        if is_dark?(@image[x,y]) && is_light?(@image[x,y + 1])

          # run r = xcos(theta) + ysin(theta) from 0 to 20
          # stepping 0.2 at a time
          (0..20).step(0.2).each do |theta|

            # http://en.wikipedia.org/wiki/Hough_transform"
            distance = (
                        x * angles(theta)[:cos] +
                        y * angles(theta)[:sin]
                      ).to_i

            # populate [theta, distance] as key to hough and increment
            # the point's score
            hough[[theta, distance]] += 1 if distance >= 0
          end
        end
      end
    end
    return hough
  end

  def average_theta
    # sort by score, grab top twenty, sum (inject) and divide by length to
    # get the average. (after #sort_by hough looks like
    # [[theta, distance] score]) so v[0][0] is just score
    get_hough_matrix.sort_by {|k,v| v }.take(20).inject(0.0) { |sum,v|
      sum + v[0][0]
     } / 20
  end
end