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N-dimensional Fourier interpolation

version 1.5 (2.35 KB) by

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

Updated

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.

Sandra Ortega

Michael Hawks

Michael Hawks (view profile)

Kevin - I think the following one-line function (added to the bottom of the code) should do the trick.

function i = odd(x)
i = (floor(x/2)~=(x/2));

Kevin Sharp

Kevin Sharp (view profile)

This fails with ...

??? Undefined function or method 'odd' for input arguments of type 'double'.

Error in ==> fftInterpolate at 61
centeru = floor(newsz/2)+1+odd(newsz);

Matthias

Matthias (view profile)

Dear author

rng = [ceil(newsz/2)-ceil(sz/2)+1;ceil(newsz/2)-ceil(sz/2)+sz]';

and replace it with
rng = [ceil(newsz/2)-floor(sz/2)+1;ceil(newsz/2)-floor(sz/2)+sz]';

then the code also works with odd dimesions.

Matthias Wurm

Matthias

Matthias (view profile)

code works excellent for data with even dimensions. In case of odd dimensions the code fails.

Benjamin

Benjamin (view profile)

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?

Matthias Schabel

Matthias Schabel (view profile)

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;