[PD] Live motion tracking using pd / gem / GridFlow / PiDiP

chris clepper cgc at humboldtblvd.com
Sat Mar 13 04:03:01 CET 2004

On Mar 12, 2004, at 7:29 PM, Max Neupert wrote:

> Hi list,
> I am working on a project where I want to confront the observer with a
> projection that changes according to his/her position, thus 
> eliminating the
> effects of perspective.
> So I tried that, the problem is that the object just understands the 
> colorspace, converting the YUV camera stream first seems quite a 
> processing
> task for the computer.

Actually, pix_movement does work with YUV - get the CVS version of GEM. 
   I wrote an Altivec version of it for PPC.  The object is quite fast 
and uses well under 10% CPU on a 1Ghz G4 running 720x480 video at 

> I succeded in creating a gem patch according to the tutorial patch 
> which
> does something, but there is no working tracking
> (see attached patch)

The only problem I see is that you haven't given pix_movement a 
threshold argument.  Send something like 0.1 to the right inlet to make 
it do it's thing.  The only way I've been able to get decent tracking 
out of movement + blob is to use some sort of data smoothing object 
like hyperspasm's smooth object or even a plain old GEM average object. 
  Without this the output is too erratic.  Also, slow movement works a 
whole lot better than fast for these objects.

I'm in the process of writing a new luma based tracking object that 
might get finished beta testing at some point in the near future.  It 
will spit out a grid of 1 and 0 based on the comparing the luma in each 
grid coordinate to the luma value you are looking for.  The output is a 
generic pd list for you to use in whatever way you see fit.

I've attached a simplified version of your patch.

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