def parse(cls, fptr, offset, length):
        """Parse JPEG 2000 signature box.

        Parameters
        ----------
        fptr : file
            Open file object.
        offset : int
            Start position of box in bytes.
        length : int
            Length of the box in bytes.

        Returns
        -------
        JPEG2000SignatureBox
            Instance of the current JPEG2000 signature box.
        """
        read_buffer = fptr.read(4)
        signature = struct.unpack('>BBBB', read_buffer)

        return cls(signature=signature, length=length, offset=offset)