Learning to Associate: HybridBoosted Multi-Target Tracker for Crowded Scene

1. Learning to Associate: HybridBoosted Multi-Target Tracker for Crowded Scene Yuan Li, Chang Huang and Ram Nevatia

2. Yuan Li

3. outline • Instruction • Related work • MAP formulation • Affinity model • Results • Conclusion

6. overview

7. Introduction • learning-based hierarchical approach of multi-target tracking • HybridBoost algorithm-hybrid loss function • association of tracklet is formulated as a joint problem of ranking and classification

8. ranking • the ranking part aims to rank correct tracklet associations higher than other alternatives

9. classification • the classification part is responsible to reject wrong associations when no further association should be done

10. HybridBoost • combines the merits of the RankBoost algorithm and the AdaBoost algorithm .

11. RankBoost • learning to rank as a problem of binary classification on instance pairs • trains one weak ranker at each round of iteration • //re-weighted: it decreases the weight of correctly ranked pairs and increases the weight of wrongly ranked pairs.??

12. adaboost • http://www.cmlab.csie.ntu.edu.tw/~cyy/learning/tutorials/AdaBoostBinary.pdf

13. Related work • the earliest works look at a longer period of time in contrast to frame-by-frame tracking. • To overcome this, a category of DataAssociation based Tracking algorithm • there has been no use of machine learning algorithmin building the affinity model.

14. MAP formulation • Robust Object Tracking by Hierarchical Association of Detection Responses • ours

15. MAP formulation v1 • R = {ri} the set of all detection responses

16. MAP formulation v1(cont.) • tracklet association

17. MAP formulation v1(cont.)

18. MAP formulation v2

19. MAP formulation v2(cont.) • Inner cost • Transition cost

20. MAP formulation v2(cont.) • With these ,we can rewrite it

21. Affinity model • Hybridboostalgorithm • Feature pool and weak learner • Training process

22. Hybridboostalgorithm • Ie.

23. Hybridboostalgorithm(cont.)

24. Loos function • initial

25. Hybridboostalgorithm

26. Feature pool and weak learner

27. Training process • T:tracklet set from the previous stage • G:groundtruth track set

28. Training process_conti • For each Ti ∈ T, if • connecting Ti’stail to the head of some other tracklet • connecting Ti’s head to the tail of some other tracklet before Ti which is also matched to G

29. Ranking sample set

30. Binary sample set

31. Training process(cont.) • use thegroundtruthG and the tracklet set Tk−1 obtained from stagek − 1 to generate ranking and binary classification samples • learn a strong ranking classifier Hkby the HybridBoost algorithm • UsingHk as the affinity model to perform association on Tk−1and generate Tk

32. Experimental results • Implementation details • Evaluation metrics • Analysis of the training process • Tracking performance

33. Implementation details • dual-threshold strategy to generate short but reliable tracklets • four stages of association • maximum allowed frame gap 16, 32, 64 and 128 • a strong ranking classifier H with 100 weak ranking classifiers • Β=0.75 • ζ = 0

34. Evaluation metrics

35. track fragments &ID switches • Traditional ID switch:“two tracks exchanging their ids”. • ID switch : a tracked trajectory changing its matched GT ID • track fragments:more strict

36. compare

37. Best features • Motion smoothness (feature type 13 or 14) • color histogram similarity (feature 4) • number of miss detected frames in the gap between the two trackelts (feature 7 or 9).

38. Strong ranking classifier output

39. Choice of β

40. Tracking performance

41. Conclusion and future work

42. problem • tracklet ?affinity model?圓圈?路徑? • automatically selectamong various features andcorresponding non-parametric models? Rankboost ? Adaboost?