[PD] Live motion tracking using pd / gem

Max Neupert max at revolwear.com
Sun Mar 14 02:50:43 CET 2004

am 12.03.2004 22:03 Uhr schrieb chris clepper unter cgc at humboldtblvd.com:
> On Mar 12, 2004, at 7:29 PM, Max Neupert wrote:
>> 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
>> RGB
>> 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
> 30fps.

Oh, wow, franz hidgen helped me to install the CVS version of GEM and it was
definitely worth it, it does what you said. Thank you.

 >> 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.

Thank you a lot.

Even better than comparing the sequencing frames to each other would be for
my purpose to let the camera grab a frame of the empty stage to later
compare those to the ones with spectators. Somebody out there who has done


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