1阶巴特沃兹低通滤波器 将原定义在图像空间的图像转换的频域空间，利用频域空间的特有性质进行加工，最后再转换到图像空间-An order Butterworth low-pass filter the original definition of the image of the image space into the frequency domain, frequency domain-specific nature of processing, and finally converted