def _ycbcr2l(self, mode):
        """Convert from YCbCr to L.
        """
        self._check_modes(("YCbCr", "YCbCrA"))

        self.channels = [self.channels[0]] + self.channels[3:]
        if self.fill_value is not None:
            self.fill_value = [self.fill_value[0]] + self.fill_value[3:]
        self.mode = mode
Convert from YCbCr to L.