Return an |_SofMarker| instance for the SOFn marker at *offset* in
        stream.

def from_stream(cls, stream, marker_code, offset):
        """
        Return an |_SofMarker| instance for the SOFn marker at *offset* in
        stream.
        """
        # field                 off  type   notes
        # ------------------  ---  -----  ----------------------------
        # segment length       0   short
        # Data precision       2   byte
        # Vertical lines       3   short  px_height
        # Horizontal lines     5   short  px_width
        # ------------------  ---  -----  ----------------------------
        segment_length = stream.read_short(offset)
        px_height = stream.read_short(offset, 3)
        px_width = stream.read_short(offset, 5)
        return cls(marker_code, offset, segment_length, px_width, px_height)