Matlab图像处理库的二维傅立叶变换，时域和频域的尺寸相同，这导致傅立叶变换运算低效，这里是一个优化后的算法的代码。-Many image processing applications require an extensive usage

of FFT2 routine (or, in the most general case, a N-dimensional

FFT) of matrices having the same dimensions. In these cases Matlab

FFT2 can result extremely inefficient.