[PD] Motion Tracking etc

[Jonathan Goodwin]

Hi,

Have tried searching this one, but no results - maybe I'm looking for the
wrong things!

I'm looking for some pointers on motion tracking preferably in PD, but maybe
in another app if it's more suited. Please forgive these broad queries about
dev techniques...I'm still new to this game, and although now somewhat
capable at picking apart other people's examples and learning that way, I'm
not great yet at figuring out ways to start things from scratch!

Basically, I'm looking to use a webcam (i-sight f.wire) to capture the
actions of people in front of a projector screen, basically simulating
shadows/representations. I want these 'shadows' to remain on the screen for
longer depending on how long they stand there. Also, when they move, I want
a shadow to follow them on the screen like a trail. I.e. A fainter shadow
for passing motion that will disappear quickly, but a more intense shadow
that stays for longer if the person stands still.

I thought a way I could do this would be to constantly capture images of
people, say every 5 secs, and overlay these images onto the screen for a set
amount of time. Therefore, if a person stood still for longer then more
layers of these images would build up, therefore taking longer to disappear.
But I would need some kind of tracking system to only image the movement,
otherwise I would be constantly photographing the background and/or the
empty room!

What things/considerations should I be at looking at to achieve something
like this if it is possible? Can PD or GEM etc grab stills from a webcam?

Apologies for long mail, hope all is understood!

Cheers
Jonathan

P.S. I've been looking at alternative systems using the new Flash 8 and
Processing. But I'd prefer a PD based solution if poss, as I'm (currently!)
no programmer!