N-dimensional Fourier interpolation

Performs N-D FFT interpolation with upsampling, downsampling, or mixed up- and downsampling

Description

Performs N-D FFT interpolation on any data for which fftn works. Will upsample by zero-filling, downsample by truncating high frequencies, or combine both up- and downsampling by dimension to allow arbitrary reshaping.

• MATLAB release: MATLAB 7 (R14)

[Matthias Schabel]

This code is needed as well (append on to end of fftInterpolate.m file): 
 
function subData = subRange(data,rng) 
 
if (isempty(rng))  
    subData = data;  
    return;  
end; 
 
sz = size(data); 
dim = length(sz); 
 
lo = rng(:,1)'; 
hi = rng(:,2)'; 
 
if (length(lo) ~= dim || length(hi) ~= dim) 
    error('subRange :: dimension mismatch'); 
end; 
 
% replace zeros with lower/upper limit  
for i=1:dim 
    if (lo(i) == 0) lo(i) = 1; end; 
    if (hi(i) == 0) hi(i) = sz(i); end; 
end; 
 
if (any(lo<1) | any(hi > sz)) 
    error('subRange :: sub-range out of bounds'); 
end; 
 
switch (dim) 
    case 1, subData = data(lo(1):hi(1));  
    case 2, subData = data(lo(1):hi(1),... 
                    lo(2):hi(2));  
    case 3, subData = data(lo(1):hi(1),... 
                    lo(2):hi(2),... 
                    lo(3):hi(3));  
    case 4, subData = data(lo(1):hi(1),... 
                    lo(2):hi(2),... 
                    lo(3):hi(3),... 
                    lo(4):hi(4));  
    case 5, subData = data(lo(1):hi(1),... 
                    lo(2):hi(2),...[] 
                    lo(3):hi(3),... 
                    lo(4):hi(4),... 
                    lo(5):hi(5));  
    otherwise, 
            % generate string and use eval 
            str = 'subData = data('; 
            for i=1:dim 
                str = [str 'lo(' num2str(i) '):hi(' num2str(i) ')']; 
                if (i~=dim) 
                    str = [str ',']; 
                else 
                    str = [str ');']; 
                end; 
            end; 
            eval(str); 
end; 
         
return; 
 
 
 

[Benjamin]

Matthias, I cannot get this to work. The example image posted seems to interpolate the peaks dataset by a factor of two. But when I run the following code, I don't get the same result: 
>>> figure; subplot(1,2,1); imagesc(peaks); 
>>> subplot(1,2,2); imagesc(fftInterpolate(peaks,2)); 
what's going on?