Low-pass filtering on an image with FFT

I know that I want to isolate the low frequency values in the Fourier transform of the image before performing an inverse Fourier transform. Problem is, I've never actually used and don't know how to use the FFT and IFFT functions in SmileBASIC. Particularly because it involves imaginary numbers?? I can't wrap my head around those.

For a low pass filter you should use BIQUAD instead. (you can use FFT/IFFT but it's less efficient) I don't actually know how BIQUAD works though lol Anyway first you have to split the colors into RGB channels, then use BIQUAD to blur each row of the image, then blur each column