def _image_send_graphics_data(self, m, fn, data):
header = self._int_low_high(len(data) + <NUM_LIT:2>, <NUM_LIT:2>)<EOL>self._raw(GS + b'<STR_LIT>' + header + m + fn + data)<EOL>
Wrapper for GS ( L, to calculate and send correct data length.

:param m: Modifier//variant for function. Usually '0'
:param fn: Function number to use, as byte
:param data: Data to send