用频率域中的滤波器进行图像处理，包括理想高通滤波器和低通滤波器，butterworth高通滤波器和低通滤波器，高斯高通滤波器和低通滤波器。不调用相关函数，纯数学写。-With frequency domain filter for image processing, including the ideal high-pass filter and low pass filter, butterworth high-pass filter and low pass filters, high pass filter and Gaussian low-pass filter. Correlation function does not call, write pure mathematics.