require 'chunky_png'
require 'zbar'

#Turns Colour PNG into 8bit BW Y800 string.
# @param image [ChunckyPNG::Image]
# @return [String] Y800 image, as a string
def png_to_y800(image)
  y800 = ""
  (0...image.width).each do |w|
    (0...image.height).each do |h|
      v = image[h,w]
      y800 << (((ChunkyPNG::Color::r(v) * 0.21  +
                ChunkyPNG::Color::g(v) * 0.72 +
                ChunkyPNG::Color::b(v) * 0.07).round ) & 0xFF ).chr
    end
  end
  return y800
end

png_image = ChunkyPNG::Image.from_file(IMG)
y800_image = png_to_y800(png_image)
zbar_image = ZBar::Image.new
zbar_image.set_data(ZBar::Format::Y800, y800_image, png_image.width, png_image.height)
puts zbar_image.process[0].data