文章和代码以及样例图片等相干资源，曾经归档至【Github仓库：digital-image-processing-matlab】或者公众号【AIShareLab】回复 数字图像处理 也可获取。
26.edge
性能：辨认强度图像中的边界。
语法：
BW = edge(I,'sobel')BW = edge(I,'sobel',thresh)BW = edge(I,'sobel',thresh,direction) [BW,thresh] = edge(I,'sobel',...)BW = edge(I,'prewitt')BW = edge(I,'prewitt',thresh)BW = edge(I,'prewitt',thresh,direction) [BW,thresh] = edge(I,'prewitt',...)BW = edge(I,'roberts')BW = edge(I,'roberts',thresh) [BW,thresh] = edge(I,'roberts',...) BW = edge(I,'log')BW = edge(I,'log',thresh)BW = edge(I,'log',thresh,sigma) [BW,threshold] = edge(I,'log',...) BW = edge(I,'zerocross',thresh,h) [BW,thresh] = edge(I,'zerocross',...) BW = edge(I,'canny')BW = edge(I,'canny',thresh)BW = edge(I,'canny',thresh,sigma) [BW,threshold] = edge(I,'canny',...) 举例
I = imread('rice.tif');BW1 = edge(I,'prewitt'); BW2 = edge(I,'canny'); imshow(BW1);figure, imshow(BW2)27.erode
性能：弱化二进制图像的边界。
语法：
BW2 = erode(BW1,SE)BW2 = erode(BW1,SE,alg) BW2 = erode(BW1,SE,...,n)举例
BW1 = imread('text.tif'); SE = ones(3,1);BW2 = erode(BW1,SE);imshow(BW1)figure, imshow(BW2) 相干命令： bwmorph, dilate
28.fft2
性能：进行二维疾速傅里叶变换。
语法：
B = fft2(A)B = fft2(A,m,n)举例
load imdemos saturn2 imshow(saturn2)B = fftshift(fft2(saturn2));imshow(log(abs(B)),[]), colormap(jet(64)), colorbar相干命令：
dct2, fftshift, idct2, ifft2
29.fftn
性能：进行n 维疾速傅里叶变换。
语法：
B = fftn(A)B = fftn(A,siz) 相干命令： fft2, ifftn30.fftshift
性能：把疾速傅里叶变换的DC 组件移到光谱核心。
语法：
B = fftshift(A)举例
B = fftn(A);C = fftshift(B);相干命令：
fft2, fftn, ifftshift
31.filter2
性能：进行二维线性过滤操作。
语法：
B = filter2(h,A)B = filter2(h,A,shape)举例
A = magic(6) A =35 1 6 26 19 243 32 7 21 23 2531 9 2 22 27 208 28 33 17 10 1530 5 34 12 14 164 36 29 13 18 11h = fspecial('sobel') h =1 2 10 0 0–1 –2 –1B = filter2(h,A,'valid') B =–8 4 4 –8–23 –44 –5 40–23 –50 1 40–8 4 4 –8相干命令：
conv2, roifilt2
32.freqspace
性能：确定二维频率响应的频率空间。
语法：
[f1,f2] = freqspace(n) [f1,f2] = freqspace([m n])[x1,y1] = freqspace(...,'meshgrid') f = freqspace(N)f = freqspace(N,'whole')相干命令：
fsamp2, fwind1, fwind2
33.freqz2
性能：计算二维频率响应。
语法：
[H,f1,f2] = freqz2(h,n1,n2)[H,f1,f2] = freqz2(h,[n2 n1])[H,f1,f2] = freqz2(h,f1,f2)[H,f1,f2] = freqz2(h)[...] = freqz2(h,...,[dx dy])[...] = freqz2(h,...,dx) freqz2(...)举例
Hd = zeros(16,16); Hd(5:12,5:12) = 1;Hd(7:10,7:10) = 0;h = fwind1(Hd,bartlett(16)); colormap(jet(64))freqz2(h,[32 32]); axis ([–1 1 –1 1 0 1])34.fsamp2
性能：用频率采样法设计二维FIR 过滤器。
语法：
h = fsamp2(Hd)h = fsamp2(f1,f2,Hd,[m n])举例
[f1,f2] = freqspace(21,'meshgrid'); Hd = ones(21);r = sqrt(f1.^2 + f2.^2); Hd((r<0.1)|(r>0.5)) = 0;colormap(jet(64)) mesh(f1,f2,Hd)相干命令：
conv2, filter2, freqspace, ftrans2, fwind1, fwind2
35.fspecial
性能：创立预约义过滤器。
语法：
h = fspecial(type)h = fspecial(type,parameters)举例
I = imread('saturn.tif');h = fspecial('unsharp',0.5); I2 = filter2(h,I)/255; imshow(I)figure, imshow(I2)相干命令：
conv2, edge, filter2, fsamp2, fwind1, fwind2
36.ftrans2
性能：通过频率转换设计二维FIR 过滤器。
语法：
h = ftrans2(b,t) h = ftrans2(b) 举例
colormap(jet(64))b = remez(10,[0 0.05 0.15 0.55 0.65 1],[0 0 1 1 0 0]);[H,w] = freqz(b,1,128,'whole'); plot(w/pi–1,fftshift(abs(H)))相干命令：
conv2, filter2, fsamp2, fwind1, fwind2
参考文献：
[1] Rafael C. Gonzalez, Richard E. Woods, and Steven L. Eddins. 2003. Digital Image Processing Using MATLAB. Prentice-Hall, Inc., USA.
[2] [阮秋琦. 数字图像处理（MATLAB版）[M]. 北京：电子工业出版社, 2014.](https://github.com/timerring/digital-image-processing-matlab/blob/main/reference/Digital_Image_Processing_(MATLAB_version).pdf)
[3] [冈萨雷斯. 数字图像处理（第三版）[M]. 北京：电子工业出版社, 2011.](https://github.com/timerring/digital-image-processing-matlab/blob/main/reference/Digital_Image_Processing_(Third_Edition).pdf)