Detecting merging blobs ofxCV

Dana_Avesar · April 4, 2016, 7:58pm

Is there any code already out there that can detect one two blobs or labels have merged? I am trying to detect when one object touches the other.

Hennio · April 5, 2016, 1:55pm

Maybe check if the new blob (5) has an area similar to those blobs which have dissapeared (0 and 1)?

stephanschulz · April 6, 2016, 1:18pm

you could try using ofxCv::RectTracker which allows you to know when a blob/label is not existing anymore, but it is still alive (can still be queried) until it’s persistence time runs out.

label 1 and 0 would still return a position but that position does not change anymore.
label 5 would return a very young age, so you know it’s new.
label 5’s position would be close to the middle of position 1 and 0.

		bool existsCurrent(unsigned int label) const;
		bool existsPrevious(unsigned int label) const;
		int getAge(unsigned int label) const;
		int getLastSeen(unsigned int label) const;

github.com

kylemcdonald/ofxCv/blob/master/libs/ofxCv/include/ofxCv/Tracker.h#L148


		const std::vector<unsigned int>& getPreviousLabels() const;
		const std::vector<unsigned int>& getNewLabels() const;
		const std::vector<unsigned int>& getDeadLabels() const;
		unsigned int getLabelFromIndex(unsigned int i) const;
		
		// organized by label
		int getIndexFromLabel(unsigned int label) const;
		const T& getPrevious(unsigned int label) const;
		const T& getCurrent(unsigned int label) const;
		bool existsCurrent(unsigned int label) const;
		bool existsPrevious(unsigned int label) const;
		int getAge(unsigned int label) const;
		int getLastSeen(unsigned int label) const;
	};
	
	template <class T>
	void Tracker<T>::setPersistence(unsigned int persistence) {
		this->persistence = persistence;
	}
	
	template <class T>

Dana_Avesar · April 6, 2016, 3:59pm

Thanks for the help! The area solution is working well. However the merged blob is not always a “new label”, sometimes it is a label that existed previously, has died, and just re-emerges. I’m using RectTracker, and the getNewLabels() only gives me labels that have never existed previously. How can I detect these labels that are new but have existed previously?