下载图片然后傅立叶变换
展示频谱
计算灰度级平均值
使用高斯低通滤波器，可以指定size,m*n，高斯函数的中心位置。
用例图做高斯低通滤波。((a)Download Fig. 4.41(a) from the book web site and compute its (centered) Fourier spectrum.
(b) Display the spectrum.
(c) Use your result in (a) to compute the average value of the image.
(d) Implement the Gaussian lowpass filter in Eq. (4.8-7). You must be able to specify the size, M x N, of the resulting 2D function. In addition, you must be able to specify the location of the center of the Gaussian function.
(e) Download Fig. 4.41(a) from the book web site and lowpass filter it to duplicate the results in Fig. 4.48.)