https://blog.youkuaiyun.com/lxlclzy1130/article/details/50816967 https://blog.youkuaiyun.com/lxlclzy1130/article/details/52510795 此文章对于梯度方向直方图的计算过程有着详细的说明https://blog.youkuaiyun.com/passball/article/details/82254256