scott <sco### [at] scottcom> wrote:
> > 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.

I'm still exploring the world of FT and what can be done with it.
It may take me some time to learn enough where what you just said will be
meaningful and I will understand _why_.

> 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.

That sounds pretty cool.  Trying to visualize that and what the FT would look
like - if your jet is vertical in the image, then the result would be an
additional horizontal streak (due to the vibration) in the 2D FFT?

I'm just getting ready to run some test images through my code to see what the
output is, and if it makes sense intuitively, and is numerically correct.
I think I'd like to edit it so that "DC" is at the center of the 2D FFT so that
I can make more direct comparisons with most of what I see online.

What software package and FT library do you use?

Any assistance in understanding this all and creating some experiments and
demonstrations in SDL would be a huge help.

Thanks!

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