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%---------------------------------------------------------------------------- 
% exa030903, for example 3.9.3 
% to obtain the  DTFT of 2-D Hamming windows;  
%---------------------------------------------------------------------------- 
clear; 
 
% 生成二维hamming窗 
n=64; 
x=0:1:n-1; 
y=x; 
s=2*pi/n; 
[X,Y]=meshgrid(x,y); 
f1=.54-.46*cos(s*X); 
f2=.54-.46*cos(s*Y); 
z=f1.*f2; 
figure(1) 
surf(x,y,z); 
colormap([1 1 0]); 
 
% 计算二维DTFT  
x=-n/2:1:n/2-1; 
y=x; 
[X,Y]=meshgrid(x,y); 
z1=fft2(z); 
z1=abs(z1); 
 
% 将原点移至图的中心  
m=n/2; 
  for k=1:m; 
   for l=1:m; 
      a(k,l)=z1(k,l); 
      b(k,l)=z1(k,l+m); 
      c(k,l)=z1(k+m,l); 
      d(k,l)=z1(k+m,l+m); 
   end 
   end 
   for k=1:m; 
      for l=1:m; 
         z1(k,l)=d(k,l); 
         z1(k+m,l+m)=a(k,l); 
         z1(k,l+m)=c(k,l); 
         z1(k+m,l)=b(k,l); 
      end 
   end 
 
% 频域用对数表示 
   z1=20*log10(z1); 
   figure(2) 
   surf(X,Y,z1); 
   colormap([1 1 0]);