对原始图像在水平方向和垂直方向与2个滤波器(低通、高通)相卷积，可以得到4块面积为原图像1/4的子图，分别为水平方向低频和垂直方向低频(HH)、水平方向低频和垂直方向高频(HG)、水平方向高频和垂直方向低频(GH)、水平方向高频和垂直方向高频(GG)。-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).