'Set the image mode for any subsequent images which will be sent
to the clients. The modes may currently be either \'full\' or \'diff\'.
Note: diff images may not contain transparency, therefore upon
draw this mode may be changed if the resulting image has any
transparent component.'

def set_image_mode(self, mode):

    if (mode not in [u'full', u'diff']):
        raise ValueError(u'image    mode    must    be    either    full    or    diff.')
    if (self._current_image_mode != mode):
        self._current_image_mode = mode
        self.handle_send_image_mode(None)
