How can I use fft2 and ifft2 to calculate the cross correlation of two images

I have two images and their sizes are different. How can I use fft2 and ifft2 to calculate the cross correlation of these images?

Answer 1

[Sreeram]

Hi Wayne,

Before computing the cross-correlation, both images need to be zero-padded to the same size. This ensures that the frequency-domain multiplication is valid and that the result captures the full cross-correlation.

Once the images are appropriately padded, you can compute the cross-correlation using:

c = ifft2(fft2(X) .* conj(fft2(Y)));

where X and Y are the zero-padded versions of the original images.

I have used the approach described in this article for one of my own projects and found it very effective for template matching:

http://werner.yellowcouch.org/Papers/subimg/

I think you'll find it helpful as well.