Introduction - If you have any usage issues, please Google them yourself
The original image in the horizontal direction and vertical direction and two filters (low pass, high pass) with convolution, you can get the original image area of 4 1/4 graph, respectively, horizontal and vertical direction low frequency ( HH), horizontal and vertical high-frequency low-frequency (HG), horizontal and vertical high-frequency low-frequency (GH), horizontal and vertical high-frequency high-frequency (GG).