[PD] Motion Detection Strategies - Gem

Kyle Klipowicz kyleklip at gmail.com
Fri Oct 6 21:17:51 CEST 2006

Hi David~

Smoothing control signals can be done by using a line object.

[inlet jittery_signal]
[pack f 100] (100 ms linear smoother)
[outlet smooth_signal]

You can also easily experiment with different forms of interpolation
if you scale your control range over the interval [0, 1].  A quartic
interpolation would simply be like this:

[inlet scaled_line]
[expr pow($f1, 4)]
[outlet quartic_envelope]

For averaging, I believe that .hc has made some nice ones for his HID
library that would suit your purposes.  Or, you could use a list of
however many "control samples" you'd want to average, and then operate
on them with fbar's list-abs.  Or, you could do something like this
with iemmatrix too.  There are even some control rate objects like
lowpass filters and such.  There's a ton of possibilities!


On 10/6/06, David Powers <cyborgk at gmail.com> wrote:
> Hi everyone,
> I bought a cheap Logitech webcam to try motion detection with PD+Gem.
> I'm considering, among others things, using this as part of a digital
> instrument design.
> First of all, the cheap webcam is of course rather noisy. But, the
> motion detection doing:
> [pix_movement 0.3]
> l
> [alpha]
> l
> [pix_blob]
> definitely does seem to work okay.
> I did a test using the X and Y to control FM synthesis however, and it
> mostly worked but tended to produce a lot of noise when something was
> moving. What is the recommended way to smooth out the signal a bit?
> Also, best way to find the average speed of motion?
> Finally, are there more advanced motion detection strategies? Like,
> say, could I somehow put a bright red dot on my index finger, and just
> detect where my index finger is? I'd love to hear what people have
> done.
> I also wonder, how the hell I would set it up for a real performance -
> Experimental music concerts here tend to be in small alternative sorts
> of venues, with not much space.
> ~David
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