def _setup_shrink_factors(scale: int=1):
    """Setup the smoothing sigmas array for registration"""
    shrink_factors = [1]
    if scale > 1:
        for idx in range(1, scale, 1):
            shrink_factors.insert(0, 2 ** idx)
        print('No smoothing sigmas given, setting to {}'.format(shrink_factors)
            )
    return shrink_factors
