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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]);