# File lib/HGR.rb, line 9
        def raw_bytes
                bytes=""
                bytes<< [137, 80, 78, 71, 13, 10, 26, 10].pack("C*") # PNG signature
                bytes<< PNG.chunk('IHDR',
                        [ @height, @width, @bits, 6, 0, 0, 0 ].pack("N2C5"))
                # 0 == filter type code "none"
                data = @data.map { |row| [0] + row.map { |p| p.values } }.flatten
                bytes<< PNG.chunk('IDAT', Zlib::Deflate.deflate(data.pack("C*"), 9))
                bytes<< PNG.chunk('IEND', '')
                bytes
        end