how to fix broad band in fft?

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Rabih Sokhen 2022-2-9

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https://ww2.mathworks.cn/matlabcentral/answers/1646435-how-to-fix-broad-band-in-fft

评论： Rabih Sokhen 2022-2-10

Hy guys.

I'm trying to obtain the fft of a array. however the result are coming out to be braod band, i expected to get bands with a width of 1 pixel.

any suggestion for this problem.

Thanks and Regards

code:

clear all
clc
z=50;
a=ones(z,z);
for i=1:z
    for j=2:z
        a(i,j)=a(i,j-1)+1;
    end
end
a = a.'*a;
subplot(121)
img(abs(a))
subplot(122)
img(abs(log(fftshift(fft2(a)))))

% this is a small example what is happening in my results

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Catalytic 2022-2-9

编辑：Catalytic 2022-2-9

"i expected that's the band will not be broad , only 1 pixel as width , because the analytique equation should fit my band at 100% to extract to amplitude and the phase"

I don't really understand that part. The fft2 and ifft2 form an invertible 1-1 pair. Because a=ones(50) produces a 1-pixel wide spectrum, no other a can do so. Otherwise fft2 would not be invertible.

Rabih Sokhen 2022-2-10