I wan tto use fft to filter a large 2d image (~1000x1000). I want to filter the image several times each time with a different kernel (~21x21).
To benefit from the using the fft i can calculate the image fft once then only calculate each kernel's fft multiply the two and invFFT..
the problem is that the image is much larger than the kernel and zero padding the kernel to the image size looks to be very wasteful, is there a fft implementation that takes advantge of the zeros and computes the larger fft but withou the external zero padding?
Thnak you in advance,