傅立叶变换是数字图像处理中应用最广的一种变换，其中图像增强、图像复原和图像分析与描述等，每一类处理方法都要用到图像变换，尤其是图像的傅立叶变换。常用的图像增强技术可分为基于空域和基于变换域的两类方法。最常用的变换域是频域空间。在频域空间，图像的信息表现为不同频率分量的组合。如果能让某个范围内的分量或某些频率的分量受到抑制而让其他分量不受影响，就可以改变输出图像的频率分布，达到不同的增强目的。



4、高通滤波- 锐化



-Fourier transform in digital image processing is a transformation, which is the most widely used,　including image enhancement, image restoration and image analysis and descr iption. Each　method is used for image processing, especially the image transform. This paper describes the digital image transform and gives the MATLAB program. Then, using FFT, realizes the image smoothing by using the low-pass filter and images sharpening by using the high-pass filter.