'Calculate the center position.  The center position will be
fractional for even-sized arrays.  For ``mode=\'partial\'``, the
central position is calculated for the valid (non-filled) cutout
values.'

@staticmethod
def _calc_center(slices):

    return tuple(((0.5 * ((slices[i].start + slices[i].stop) - 1)) for i in [1, 0]))
