[PD] Motion Detection Strategies - Gem

IOhannes m zmoelnig zmoelnig at iem.at
Sat Oct 7 19:15:40 CEST 2006

David Powers 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.

so you want to do color tracking?
simplest thing is to just use the specified color-channel for [pix_blob]
(e.g. [pix_blob 1] should just track the Red channel of an RGB signal
(check the help-patch)).
this only works in trivial cases (red, green, blue, white); for a more
general approach convert the image's colorspace into hsv (with
[pix_rgb2hsv] and mask out all colours you don't want on the
colour-circle (e.g with [pix_curve]) and then track this.

once you only have the pixel of the desired colour, you can of couse
also do motion tracking on the color-filtered image.

i thought i had some example of colortracking added to the gem-examples
(but i might be wrong).


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