说明：  利用傅里叶变换，在频域上对两幅图像配准，是一种比较配准的新方法，但是对弹性配准的效果不是很好 需要进一步的研究。
(Registers two images (2-D rigid translation) within a fraction of a pixel specified by the user. Instead of computing a zero-padded FFT (fast Fourier transform), this code uses selective upsampling by a matrix-multiply DFT (discrete FT) to dramatically reduce computation time and memory without sacrificing accuracy)