Bidirectional Hough Transformation with ChunkyPNG

hough.rb

require 'mathn'
require 'chunky_png'

def hough_transformation(img, cutoff=185, steps=1)
  mx, my = img.width*0.5, img.height*0.5
  to_rad = Math::PI / 180.0
  hough  = Hash.new(0)
  img.width.times do |x|
    #puts "#{x} of #{img.width}"
    img.height.times do |y|
      next if ChunkyPNG::Color.to_grayscale_bytes(img[x,y]).first < cutoff
      (0...180).step(steps).each do |a|
        rad = a * to_rad
        d   = (x-mx) * Math.cos(rad) + (y-my) * Math.sin(rad)
        hough[[a.to_i, d.to_i]] += 1
      end
    end
  end
  hough
end

def display_hough_transformation(hough, heatmap='heatmap.png', outname='hough.png')
  heat  = (ChunkyPNG::Image.from_file(heatmap) rescue nil)
  max   = hough.values.max
  max_d = hough.max_by{|k,v| k[1].abs}[0][1].abs
  out   = ChunkyPNG::Image.new(180, max_d*2+1, ChunkyPNG::Color::BLACK) #TRANSPARENT
  hough.each_pair do |k,v|
    a, d = k
    c = ((v / max) * 255).to_i
    out[a, max_d + d] = heat ? heat[c, 0] : ChunkyPNG::Color.rgb(c,c,c)
  end
  out.save(outname)
end

#http://community.topcoder.com/tc?module=Static&d1=tutorials&d2=geometry2
def draw_hough_lines(hough, img)
  mx, my  = img.width*0.5, img.height*0.5
  max     = hough.values.max
  to_rad  = Math::PI / 180.0
  cutoff  = max - (max / 2)
  objects = hough.select{|k,v| v > cutoff}
  p objects
  img[mx,my] = ChunkyPNG::Color.rgb(0,255,0)
  objects.each do |k,v|
    a, d = k
    a = a * to_rad
    (-mx..mx).step(0.01).each do |x|
      begin
        y = ((1 / Math.sin(a)) * (d - x * Math.cos(a)))
        img[(mx+x).to_i,(my+y).to_i] = ChunkyPNG::Color.rgb(255,0,0)
      rescue
      end
    end
    #img.circle(mx, my, d.abs, ChunkyPNG::Color.rgb(255,0,0))
  end
  img.save('reverse_hough.png')
end


img = ChunkyPNG::Image.from_file('test.png')
puts "calculating hough transformation"
hough = hough_transformation(img)
puts "creating hough space image"
display_hough_transformation(hough, nil)
puts "creating reverse hough transformation image"
draw_hough_lines(hough, img)