[PD] pix_multiblob and tracking multiple objects

Antoine Villeret antoine.villeret at gmail.com
Thu Apr 18 15:39:52 CEST 2013

morphological filters affect the shape
they mostly work on binary images
the most common are erode, dilate, close and open algorithm
with which you can make a "pepper or salt removing filter" to remove black
or white isolated pixels

concerning background subtraction, if you use a fixed background (you make
a snapshot at startup and subtract it to the video stream) you will have
defects due to light change,
some background part could be interpreted as a foreground feature
adaptive background technique use a dynamic image reference, which could be
made with a low-pass filter, this image is then subtracted to the video
this makes a high-pass filter

do it yourself

2013/4/18 Ska Frenz <skafrenz at gmail.com>

> 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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