1. An Information Fusion Approach for Multiview Feature Tracking Esra Ataer-Cansizoglu (ataer@ece.neu.edu) and Margrit Betke (betke@cs.bu.edu ) Image and Video Computing Group, Computer Science Department, Boston University Introduction Where is the object/feature point? time Robust tracking is important for  Human Computer Interaction  Video-based Surveillance  Remote Sensing  Video Indexing Problem: Failure in tracking, especially due to occlusion Solution: Automatic Recovery Idea: Use multiple cameras http://www.cs.bu.edu/faculty/betke/research/jordan-bubble.jpg Conclusion  System detects tracking failures with high accuracy  Promising results on automatic feature re-initialization  Correlation based term is strong to predict reliability  Proposed RM is inexpensive to compute Feature Extensions:  Use of particle filters or other trackers on 3D  Extend RM using geometric constraints about the motion of the object  Use of multiple points considering constraints about shape Proposed Method Idea: Construct a Reliability Measure (RM) for each view to detect tracking failures Observation: Prefer the view in which object is most visible. Which parameter is most informative for tracking in a view? Wikipedia, Epipolar Geometry, http://en.wikipedia.org/wiki/Epipolar_geometry F: Fundamental Matrix Right Camera Left Camera  Normalized Correlation Coefficient (NCC) I: Image T: Template N: number of pixels  Epipolar distance (EPD)  Estimate of the 3D Position  Geometric constraints about the shape/motion of the object  Term 1  Term 2  Term 3  Term 4 z: 2D tracks, : Reconstructed 3D Trajectory, y: Projection of estimated 3D position and Term 2 Term 3 Term 4 Term 1 where Proposed System:  Independent 2D trackers in each view utilize pyramidal implementation of optical flow algorithm  Stereoscopic reconstruction of 3D trajectories (simple linear method)  Predicting 3D Position with ‘Constant Velocity Assumption’  Automatic recovery using projection of estimated 3D position Experiments & Results Left-view RM (top) and right-view RM’ (bottom) for the video of subject A and direction of subject’s movements where for all and High correlation b/w values of term 1 and term 2 DROP TERM 2! RMs with do not have succinct peaks. Weigh term 1 more! Values of pairs and triplets of RM terms with weights set equally. RMs with final weights for subject A. Final Weights DATASET  Cameras 20 inches apart, 120 o between optical axis  Training Set: 8 subjects, ~450 frames each Subjects rotating head center to right and then left and up, down.  Test Set: 26 subjects, 2 sequences per subject, ~1200 frames in each sequence. Recording data from left and right cameras, while subject is using a mouse-replacement interface from frontal camera RESULTS  The feature was lost in both views 9 times, but was declared as lost in only one of the views.  53 false alarms, but in all cases the feature was reinitialized to a location at most 3 pixels from the actual location, hence the false alarm rate is negligible.  For 254 correctly detected tracking failures, the system was able to recover 181 times (71.3%). 304 feature loss events in one view = 254 detected in correct view + 25 detected in the other view + 25 not detected True positive rate 83.5% Feature Loss Problem with Camera Mouse:  Camera Mouse is a mouse-replacement interface for people with disabilities.  Automatic re-initialization would enable the subject to use Camera Mouse freely without the intervention of a caregiver. Adjusting Weights References [1] Camera Mouse, http://www.cameramouse.org/, accessed August 2010. [2] C. Connor, E. Yu, J. Magee, E. Cansizoglu, S. Epstein, and M. Betke, "Movement and Recovery Analysis of a Mouse-Replacement Interface for Users with Severe Disabilities," 13th Int. Conference on Human-Computer Interaction, 10 pp., San Diego, USA, July 2009. [3] Y. Tong, Y. Wang, Z. Zhu, and Q. Ji, “Robust Facial Feature Tracking under Varying Face Pose and Facial Expression,” Pattern Recognition, 40(11):3195-3208, November 2007. [4] C. Fagiani, M. Betke, and J. Gips, “Evaluation of tracking methods for human-computer interaction,” IEEE Workshop on Applications in Computer Vision (WACV 2002), pp. 121-126, Orlando, USA, December 2002.