Add commands 3

Author: timerring

13_common_image_processing_commands_in_Matlab_(3).md

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+# Matlab常用图像处理命令108例（三）
+
+## 26.edge
+
+功能：识别强度图像中的边界。
+
+语法： 
+
+```matlab
+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 
+
+```matlab
+I = imread('rice.tif');
+BW1 = edge(I,'prewitt'); 
+BW2 = edge(I,'canny'); 
+imshow(BW1);
+figure, imshow(BW2)
+```
+
+![](https://raw.githubusercontent.com/timerring/scratchpad2023/main/2023/03/11-22-16-12-1678544168.png)
+
+## 27.erode
+
+功能：弱化二进制图像的边界。
+
+语法：
+
+```matlab
+BW2 = erode(BW1,SE)
+BW2 = erode(BW1,SE,alg) 
+BW2 = erode(BW1,SE,...,n)
+```
+
+举例 
+
+```matlab
+BW1 = imread('text.tif'); 
+SE = ones(3,1);
+BW2 = erode(BW1,SE);
+imshow(BW1)
+figure, imshow(BW2) 
+```
+
+相关命令： bwmorph, dilate
+
+## 28.fft2
+
+功能：进行二维快速傅里叶变换。
+
+语法： 
+
+```matlab
+B = fft2(A)
+B = fft2(A,m,n)
+```
+
+举例 
+
+```matlab
+load imdemos saturn2 
+imshow(saturn2)
+```
+
+![](https://raw.githubusercontent.com/timerring/scratchpad2023/main/2023/03/11-22-16-56-1678544214.png)
+
+```matlab
+B = fftshift(fft2(saturn2));
+imshow(log(abs(B)),[]), colormap(jet(64)), colorbar
+```
+
+![](https://raw.githubusercontent.com/timerring/scratchpad2023/main/2023/03/11-22-17-25-1678544244.png)
+
+相关命令： 
+dct2, fftshift, idct2, ifft2
+
+## 29.fftn
+
+功能：进行n 维快速傅里叶变换。
+语法： 
+
+```matlab
+B = fftn(A)
+B = fftn(A,siz) 相关命令： fft2, ifftn
+```
+
+## 30.fftshift
+
+功能：把快速傅里叶变换的DC 组件移到光谱中心。
+语法：
+
+```matlab
+B = fftshift(A)
+```
+
+举例 
+
+```matlab
+B = fftn(A);
+C = fftshift(B);
+```
+
+相关命令： 
+fft2, fftn, ifftshift
+
+## 31.filter2
+
+功能：进行二维线性过滤操作。
+语法：
+
+```matlab
+B = filter2(h,A)
+B = filter2(h,A,shape)
+```
+
+举例 
+
+```matlab
+A = magic(6) 
+A =
+35 1 6 26 19 24
+3 32 7 21 23 25
+31 9 2 22 27 20
+8 28 33 17 10 15
+30 5 34 12 14 16
+4 36 29 13 18 11
+h = fspecial('sobel') 
+h =
+1 2 1
+0 0 0
+–1 –2 –1
+B = filter2(h,A,'valid') 
+B =
+–8 4 4 –8
+–23 –44 –5 40
+–23 –50 1 40
+–8 4 4 –8
+```
+
+相关命令： 
+conv2, roifilt2
+
+## 32.freqspace
+
+功能：确定二维频率响应的频率空间。
+语法： 
+
+```matlab
+[f1,f2] = freqspace(n) 
+[f1,f2] = freqspace([m n])
+[x1,y1] = freqspace(...,'meshgrid') 
+f = freqspace(N)
+f = freqspace(N,'whole')
+```
+
+相关命令： 
+fsamp2, fwind1, fwind2
+
+## 33.freqz2
+
+功能：计算二维频率响应。
+语法： 
+
+```matlab
+[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 
+
+```matlab
+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])
+```
+
+![](https://raw.githubusercontent.com/timerring/scratchpad2023/main/2023/03/11-22-20-26-1678544423.png)
+
+## 34.fsamp2
+
+功能：用频率采样法设计二维FIR 过滤器。
+语法： 
+
+```matlab
+h = fsamp2(Hd)
+h = fsamp2(f1,f2,Hd,[m n])
+```
+
+举例
+
+```matlab
+[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)
+```
+
+相关命令： 
+conv2, filter2, freqspace, ftrans2, fwind1, fwind2
+
+## 35.fspecial
+
+功能：创建预定义过滤器。
+语法： 
+
+```matlab
+h = fspecial(type)
+h = fspecial(type,parameters)
+```
+
+举例 
+
+```matlab
+I = imread('saturn.tif');
+h = fspecial('unsharp',0.5); 
+I2 = filter2(h,I)/255; 
+imshow(I)
+figure, imshow(I2)
+```
+
+![](https://raw.githubusercontent.com/timerring/scratchpad2023/main/2023/03/11-22-21-26-1678544485.png)
+
+相关命令： 
+conv2, edge, filter2, fsamp2, fwind1, fwind2
+
+## 36.ftrans2
+
+功能：通过频率转换设计二维FIR 过滤器。
+
+语法：
+
+```matlab
+h = ftrans2(b,t) h = ftrans2(b) 
+```
+
+举例 
+
+```matlab
+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)))
+```
+
+相关命令：
+
+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.](https://github.com/timerring/digital-image-processing-matlab/blob/main/reference/Digital_Image_Processing_Using_Matlab.pdf)
+
+[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)
+
+
+
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