code: def _validate_channel_definition(self, jp2h, colr):
          
          cdef_lst = [j for (j, box) in enumerate(jp2h.box)
                      if box.box_id == 'cdef']
          if len(cdef_lst) > 1:
              msg = ("Only one channel definition box is allowed in the "
                     "JP2 header.")
              raise IOError(msg)
          elif len(cdef_lst) == 1:
              cdef = jp2h.box[cdef_lst[0]]
              if colr.colorspace == core.SRGB:
                  if any([chan + 1 not in cdef.association or
                          cdef.channel_type[chan] != 0 for chan in [0, 1, 2]]):
                      msg = ("All color channels must be defined in the "
                             "channel definition box.")
                      raise IOError(msg)
              elif colr.colorspace == core.GREYSCALE:
                  if 0 not in cdef.channel_type:
                      msg = ("All color channels must be defined in the "
                             "channel definition box.")
                      raise IOError(msg)
docs: Validate the channel definition box.