code: def parse(cls, fptr, offset, length):
          
          num_bytes = offset + length - fptr.tell()
          read_buffer = fptr.read(num_bytes)
  
          lst = struct.unpack_from('>BBB', read_buffer, offset=0)
          method, precedence, approximation = lst
  
          if method == 1:
              # enumerated colour space
              colorspace, = struct.unpack_from('>I', read_buffer, offset=3)
              if colorspace not in _COLORSPACE_MAP_DISPLAY.keys():
                  msg = "Unrecognized colorspace ({colorspace})."
                  msg = msg.format(colorspace=colorspace)
                  warnings.warn(msg, UserWarning)
              icc_profile = None
  
          else:
              # ICC profile
              colorspace = None
              if (num_bytes - 3) < 128:
                  msg = ("ICC profile header is corrupt, length is "
                         "only {length} when it should be at least 128.")
                  warnings.warn(msg.format(length=num_bytes - 3), UserWarning)
                  icc_profile = None
              else:
                  profile = _ICCProfile(read_buffer[3:])
                  icc_profile = profile.header
  
          return cls(method=method,
                     precedence=precedence,
                     approximation=approximation,
                     colorspace=colorspace,
                     icc_profile=icc_profile,
                     length=length,
                     offset=offset)
docs: Parse JPEG 2000 color specification box.
  
          Parameters
          ----------
          fptr : file
              Open file object.
          offset : int
              Start position of box in bytes.
          length : int
              Length of the box in bytes.
  
          Returns
          -------
          ColourSpecificationBox
              Instance of the current colour specification box.