numpy.clip(a, a_min, a_max, out=None)
Clip (limit) the values in an array. Given an interval, values outside the interval are clipped to the interval edges. For example, if an interval of [0, 1] is specified, values smaller than 0 become 0, and values larger than 1 become 1.
即整个数组的值限制在指定值a_min,与a_max之间，对比a_min小的和比a_max大的值就重置为a_min,和a_max。
