module ChunkyPNG::Canvas::PNGDecoding

def decode_png_scanline_average(bytes, previous_bytes, pixelsize = 3)
  bytes.each_with_index do |byte, i|
    a = (i >= pixelsize) ? bytes[i - pixelsize] : 0
    b = previous_bytes[i]
    bytes[i] = (byte + (a + b / 2).floor) % 256
  end
  bytes
end