updownsample

up/down sample an input matrix using the fourier domain.

Description

Up/down sample an image/matrix/vector (can be of complex numbers) using the frequency domain.
The matrix/vector should be continuous of a high degree (has continuous derivatives) in order to obtain a reasonable up/down sampling

Speed-up can be achieved if the user up-samples to a near power of 2. no optimization is done inside this code for efficient fft usage.

Documentation is found inside the *.m file.

type "updownsample" for the example

Acknowledgements

The author wishes to acknowledge the following in the creation of this submission:
fft_upsample

• MATLAB release: MATLAB 6.1 (R12.1)

[Aaron Clarke]

Nice function. Works great.

[Ahmed Zakzouk]

nice work

[David Felguera]

Problems with circular convolutions ...

Just try:

in_m = ones(10,10);
in_m = [zeros(10,10);in_m;zeros(10,10)];
in_m = [in_m,zeros(30,10)];
figure(100);
imagesc(in_m);
out_x_sz = 320;
out_y_sz = 320;
out_m = updownsample( in_m,out_x_sz,out_y_sz,0,1);
figure(200);
imagesc(out_m);

I dont know exactly if its a circular convolution but it seems to. (could be some kind of aliasing too, when processing some kind of images)

[Jeroen Corthout]