def zoom_cen(im, bb):
    """
    Cut out a square box from the image center with half-box size bb.
    :param im: image from which box will be taken
    :param bb: half-box size
    :return:
    """
    x = int(im.shape[1]/2)
    y = int(im.shape[0]/2)
    return im[int(y-bb):int(y+bb), int(x-bb):int(x+bb)]