[WM]: Zero padding the FFT to resize

[Joseph O'Ruanaidh <joruanaidh@genuone.com>]

> 
> Please help me as my case is time critical.
>  
> I am implementing the Image Resizing algorithm.
> I read the letter below.
> Implemented the same but all in vein.Please tell me where i am wrong.
>   

X 1000 !!!! :-(




By popular demand, here is example code of how to enlarge an image using an FFT:

% Copyright: Joseph O'Ruanaidh 2003, All Rights Reserved
% Disclaimer: not to be used for air traffic control

function y=fftResize(x, l)

ff=fft2(x);
[m,n]=size(ff);

ml = floor((l-1)*m/2)*2
mm = m + 2*ml
nl = floor((l-1)*n/2)*2
nn = n + 2*nl

% what will soon be the new transform
qq = zeros(mm, nn);

% The following indices copy from the original FFT to the new FFT if mod(m, 2)==0
    xr =  [1:m/2 ml+m/2+1 2*ml+((m/2+2):m)]
else
    xr = [1:((m+1)/2) 2*ml+(((m+3)/2):m)]
end
if mod(n, 2)==0
    yr = [1:n/2 nl+n/2+1 2*nl+((n/2+2):n)]
else
    yr = [1:((n+1)/2)  2*nl+(((n+3)/2):n)]
end

% Do the copying and rescale the indices
qq(xr, yr) = ff*(mm*nn)/(m*n);

% And don't forget the most important part
y=ifft2(qq);



The results are not perfect due to Gibbs and his pesky phenomenon.

Now please let me live in peace, I beg of you.

Joe





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