Colored image blob detection

bassie.png

bassie_detected.png

colored_blob_detection.rb

require 'chunky_png'

class ChunkyPNG::Image
  def neighbors(x,y)
    [[x, y-1], [x+1, y], [x, y+1], [x-1, y]].select do |xy|
      include_xy?(*xy)
    end
  end
end

def label_recursively(image, areas, label, x, y)
  image[x,y] = label
  (areas[label] ||= []) << [x,y]

  image.neighbors(x,y).each do |xy|
    if image[*xy] == -1
      areas[label] << xy
      label_recursively(image, areas, label, *xy)
    end
  end
end

image = ChunkyPNG::Image.from_file('bassie.png')
working_image = image.dup

working_image.pixels.map! do |pixel|
  redness = ChunkyPNG::Color.r(pixel) - (ChunkyPNG::Color.g(pixel) + ChunkyPNG::Color.b(pixel))
  redness > 100 ? -1 : 0
end

areas, label = {}, 0

working_image.height.times do |y|
  working_image.row(y).each_with_index do |pixel, x|
    label_recursively(working_image, areas, label += 1, x, y) if pixel == -1
  end
end

area = areas.values.max { |result, area| result.length <=> area.length }
x, y = area.map{ |xy| xy[0] }, area.map{ |xy| xy[1] }

image.rect(x.min, y.min, x.max, y.max, ChunkyPNG::Color.rgb(0,255,0))
image.save('bassie_detected.png')