在傅立叶变换域，变换系数反映了图像的某些特征。频谱的直流低频分量对应于图像的平滑区域，而外界叠加噪声对应于频谱中频率较高的部分等。

构造一个低通滤波器，使低频分量顺利通过而有效地阻止高频分量，即可滤除频域中高频部分的噪声，再经逆变换就可以得到平滑图像。-In the Fourier transform domain, the transform coefficients reflect some characteristics of the image. DC low frequency spectrum corresponding to the image of the smooth area, and superimposed noise outside the frequency corresponding to the higher part of the spectrum and so on. Construct a low-pass filter, the low frequency components and effectively prevent the smooth passage of high frequency components, you can filter out high frequency noise in the frequency domain, and then the inverse transform to get a smooth image.