def to_blob
      str = StringIO.new
      str.set_encoding("ASCII-8BIT")
      write(str)
      str.string
    end
def to_blob
      str = StringIO.new
      str.set_encoding("ASCII-8BIT")
      write(str)
      str.string
    end
Encodes this datastream into a string.
 @return [String] The encoded PNG datastream.