code: def _ycbcr2l(self, mode):
          
          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
docs: Convert from YCbCr to L.