def __extract_bbox(arr, bb_old):
    "Extracts the bounding box of an binary objects hole (assuming only one in existence)."
    hole = ndimage.binary_fill_holes(arr)- arr
    bb_list = ndimage.find_objects(ndimage.binary_dilation(hole, iterations = 1))
    if 0 == len(bb_list): return bb_old
    else: bb = bb_list[0]
    
    if not bb_old: return list(bb)
    
    for i in range(len(bb_old)):
        bb_old[i] = slice(min(bb_old[i].start, bb[i].start),
                          max(bb_old[i].stop, bb[i].stop))
    return bb_old
Extracts the bounding box of an binary objects hole (assuming only one in existence).