'Calculate a minimal bounding box in the form ``((ymin, ymax),
(xmin, xmax))``.  Note these are pixel locations, not slice
indices.  For ``mode=\'partial\'``, the bounding box indices are
for the valid (non-filled) cutout values.'

@staticmethod
def _calc_bbox(slices):

    return ((slices[0].start, (slices[0].stop - 1)), (slices[1].start, (slices[1].stop - 1)))
