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Unified Crowd Segmentation

Unified Crowd Segmentation. P . Tu , T. Sebastian, G. Doreto , N. Krahnstoever , J. Rittscher , T. Yu ECCV 2008. Presenter: Ramin Mehran. Goal: Segmentation. Crowd Analysis Conventional Approach Segmentation Object Detection Tracking Analysis. Ideas: a Robust Algorithm. Approaches.

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Unified Crowd Segmentation

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  1. Unified Crowd Segmentation P. Tu, T. Sebastian, G. Doreto, N. Krahnstoever, J. Rittscher, T. Yu ECCV 2008 Presenter: RaminMehran

  2. Goal: Segmentation • Crowd Analysis • Conventional Approach • Segmentation • Object Detection • Tracking • Analysis CV Lab @ UCF - Presenter: RaminMehran

  3. Ideas: a Robust Algorithm CV Lab @ UCF - Presenter: RaminMehran

  4. Approaches • Bottom up • Low level feature grouping • Whole body classifiers • Top down • Background segmentation • BOTH! CV Lab @ UCF - Presenter: Ramin Mehran

  5. Algorithm Overview CV Lab @ UCF - Presenter: Ramin Mehran

  6. Affinity of Patches to Hypotheses • Head-Shoulder Detection • Grouping Patches • Assigning Patches to Heads Ck gk(zi) zi zj gk(zi, zj) • Top Down  Head/Shoulder Detection • Bottom up  Patch Affinities CV Lab @ UCF - Presenter: Ramin Mehran

  7. Maximum Likelihood How likely is the assignment a patch to a head E-M Steps Is it likely near the head? Is it like neighboring patches? Assignment indicator Consistency Affinity CV Lab @ UCF - Presenter: Ramin Mehran

  8. E-Step k Increase the expectations i CV Lab @ UCF - Presenter: Ramin Mehran

  9. E-Step affect CV Lab @ UCF - Presenter: Ramin Mehran

  10. M-Step • Enforce Consistency • Where is the head? • Contiguous patches • Path from Patches to the Head • Dynamic Programming • Shortest low cost path Ck Cm • Inconsistent patches • No Contribution to V (assignment) CV Lab @ UCF - Presenter: Ramin Mehran

  11. Head/Shoulder Body Detection Strong Classifier out of Weak Classifiers Strong Classifier (SC(s,z)) Orientation Orientation Orientation Orientation Aggregation of weak Classifiers CV Lab @ UCF - Presenter: Ramin Mehran

  12. Weak Classifier R Ck Needs Camera Calibration zi • Weak Classifier • Ratio of the intersection of patch and the region • Sobel Orientation CV Lab @ UCF - Presenter: Ramin Mehran

  13. What’s the Affinity? patch Head and body bounding box Patch to Head/Shoulder Affinity • Patch to Patch Affinity • Histogram matching of colors • Motion matching of flow CV Lab @ UCF - Presenter: Ramin Mehran

  14. Patch Size • Camera Calibration • Width of the average pedestrian • Large Patches • Occlusion Handling • Small Patches • Discrimination of correct and incorrect assigments CV Lab @ UCF - Presenter: Ramin Mehran

  15. Sample Results CV Lab @ UCF - Presenter: Ramin Mehran

  16. Results Compared to Histogram of Oriented Gradient method Superior mostly because of handling occlusions CV Lab @ UCF - Presenter: Ramin Mehran

  17. Thank you! CV Lab @ UCF - Presenter: Ramin Mehran

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