包含巴特沃斯低通滤波器去噪，图像平滑 阶数M=3 截断频率D0=40，指数低通滤波器 阶数N=3 截断频率d0=40，理想低通滤波器 梯形低通滤波器 截断半径35-50-Butterworth low-pass filter with de-noising, image smoothing order of M = 3 truncation frequency D0 = 40, index of low-pass filter order of N = 3 truncation frequency d0 = 40, the ideal low-pass filter low-pass filter ladder truncation radius of 35-50