[PD] pix_multiblob and tracking multiple objects

John Harrison john.harrison at alum.mit.edu
Thu Apr 18 15:15:12 CEST 2013

I'm not totally clear on the big picture here but it could be you might
save yourself a lot of time and effort doing your blob tracking with
Community Core Vision (CCV) then sending the blob data to Pd through OSC.
After initially doing my blob tracking in Pd only (which did work), I
switched to this CCV --> Pd approach and got better results because of all
of the built-in filtering etc. that is provided with that open-source
cross-platform software.


On Thu, Apr 18, 2013 at 5:22 AM, Ska Frenz <skafrenz at gmail.com> wrote:

> Hi, thank you for the suggestions, I'll check openCv. Can you explain how
> to use "morphological filters" to clear up the noise in the image? Are
> there examples around? Also, could you please explain me better what do you
> mean with "adaptive background subtraction method"?
> Thank you for your time :)
> francesco
> 2013/4/17 Antoine Villeret <antoine.villeret at gmail.com>
>> hi,
>> the segmentation method (how you extract what is your interest from the
>> rest of the image) is very critical in video tracking
>> background subtraction is a basic way to extract blob and it works only
>> in certain conditions of light (if you want to track something outdoor, you
>> should use an adaptive background subtraction method)
>> moreover, there is no general method to do video tracking, it depends on
>> what you want to track and how it is filmed
>> so, the first thing is to have a good image, with not too much lighting
>> changes, good contrast between background and features to track
>> then you can start thinking about segmentation, and the
>> segmentation accuracy depends on the quality of the video
>> you may need to do something more than just background subtraction, for
>> example, you could apply some morphological filter to remove noise
>> after that, you can start tracking
>> you could also apply a threshold on the blob size to not track very small
>> blob
>> blob of interest are often surrounded by very small blobs due to
>> segmentation noise
>> but you can have a look at pix_opencv objects,
>> there is [pix_opencv_blobtrack] which implements a whole processing
>> chain, including foreground extractor, blob detector, blob tracker and
>> follower
>> I'm not sure it's included in pd-extended, but you can find some binaries
>> on build server
>> hope this help
>> antoine
>> --
>> do it yourself
>> http://antoine.villeret.free.fr
>> 2013/4/17 Ska Frenz <skafrenz at gmail.com>
>>>  Hi everyone, this is my first time on the pd-list so I hope I won't do
>>> anything wrong.
>>> I'm writing here to get some help about pd tracking objects
>>> (pix_blob..). I'm using the background subtraction method, to track objects
>>> and I need help to understand how I can track multiple objects with
>>> multiples different blobs. I'm trying the pix_multiblob and yes, it show 2
>>> blobs..but they track the same object. Then basically I do not understand
>>> how can I make the first blob to follow just one object for all the time
>>> that specific object is inside the webcam rectangle, and the second blob to
>>> track another separate object. I cannot find any material that clearly
>>> talks about this.I attached the patch I'm working on. I'd love to see some
>>> well-explained examples if you know where to get them.
>>> Thank you very much for your help :)
>>> Francesco
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