> AFAIK, most of the bigger commercial packages use FT to process data for a lot
> of the filters.   I could be wrong, but reading and videos on FFT suggest
> exactly that.
>
> I'm thinking that 1D, 2D and 3D FFT would be useful for:
>
> general smoothing, sharpening, edge-detection

If your filter is fixed, it's often faster to convert your 
frequency-domain filter into a time-domain filter and optimise it (a 
one-off cost), rather than doing an FFT and iFFT on the entire dataset.

> feature and color analysis of images

I came up with the idea (at work) of using FFT for measuring the speed 
of jets of ink from a camera image. We implant a small vibration on the 
fluid at a known temporal frequency (usually about 100 kHz, and we know 
this frequency very accurately), then use FFT on the captured image to 
get out the spatial frequency of the vibration (the jet diameter has a 
slight sine wave on it). With these two bits of information you can 
calculate the speed of the jet to a high accuracy even with quite bad 
image quality.

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