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Comparative Evaluation of Random Forest and Fern Classifiers for Real-Time Feature Matching

This paper presents a comparative evaluation of Random Forest and Fern classifiers for real-time feature matching in mixed/augmented reality applications. The study explores parameters such as scale, size of the training set, number of classes, and training time. The results and conclusions are discussed, along with potential future research questions.

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Comparative Evaluation of Random Forest and Fern Classifiers for Real-Time Feature Matching

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  1. Comparative Evaluation of Random Forest and Fern classifiers for Real-Time Feature Matching I. Barandiaran1, C.Cottez1, C.Paloc1 , M.Graña2 1Departamento de Aplicaciones Biomédicas Asociación VICOMTech, San Sebastián, {ibarandiaran,ccottez,cpaloc}@vicomtech.org 2University of Basque Country Computer Science School, Pº. Manuel de Lardizabal, 1 20009, San Sebastián, Spain ccpgrrom@si.ehu.es VISUAL INTERACTION AND COMMUNICATIONS TECHNOLOGIES WSCG2008, Plzen, 04-07, Febrary 2008

  2. Summary • Introduction. • Random Forest, FERNS • Mixed/Augmented Reality Application. • Conclusions/Questions.

  3. Introduction • Motivation and objectives • Motivated by the work of Vincent LePetit (CVLab). • Real-Time Augmented Reality. • Camera Pose Estimation. • Markerless tracking. • Model-based tracking. • Tracking by detection. • Test and compare different parameters. • Scale. • Size of the Training Set. • Number of Classes. • Training Time. 3

  4. Introduction • Augmented Reality Features: • Mix Virtual and Real Objects.. • Real-Time. • Portable Devices (Head Mounted Display,Tablet PC, PDA Device, Movil Phone..)

  5. Introduction • Problems: • Rendering. • Real-Time(Delay). • Registration/Pose Estimation.

  6. Introduction • Model Based Tracking • Some a priori knowledge is available. • May not depend on the past. • Frame by Frame estimation. • Robust against partial object occlusion. • Automatic tracking initialization. 6 • Non model-based Tracking • No a priori knowledge of the object to be tracked. • Updates/Propagates an estimation over time. • Partial object occlusions. • Tend to tracking reinitialization.

  7. Summary Introduction Random Forest, FERNS Mixed/Augmented Reality Conclusions/Questions

  8. Random Forest, FERNS • Tracking of Planar Surfaces. • The Classifiers are applied for interest point (feature) matching. • Matched Points are used during camera pose estimation Process.

  9. Random Forest, FERNS • Building the training set. • Frontal view of the object to be detected. • Feature Point extraction FAST (Rosten06) and YAPE (CvLab). • Sub-images (patches) are generated for each class. Classes to Be recognized by the Classifier

  10. Random Forest, FERNS Training Set (examples) Random Affine transformations ….. 10 • Building the training set. • Generate Random Affine transformations. • Generate new examples of each Class.

  11. RandomForest • Multiclassifier based on Randomized Trees. • Firstly introduced in 1997 handwritten recognition (Amit, Y.,German, D.) • Developed by Leo Breiman (Medical Data Analisys). • Recently Applied to tracking by detection (LePetit06). • Main Features • Fast Training Step, and execution. • Good Precision. • Random selection of the independent variables (features). • Random selection of Examples. • Easy to Implement and paralelizable.

  12. RandomForest • Classifier Training. • N Binary-Trees are Grown. • Pixel intensity tests are executed in any non-terminal node. • Pixels can be selected at Random. • Posterior Distributions P(Y=c |T=Tk,n)are stored in leave nodes.

  13. RandomForest • Example Classification. • Every example is dropped down the trees. • The Example traverse the tree towards the leaf nodes. Pixels to be tested

  14. Random Forest T1 Tn T2 Random Forest • Combine Results • The example labeling is obtained as a combination of partial results obtained by every tree in the forest.

  15. FERNS Introduced in 2007 (Mustafa Özuysal). Multiclassifier. Applied to 3D keypoint recognition. Successfully applied to image recognition/retrieval (Zisserman07). • Main Features • Non hierarchical structure. • Semi Naive-Bayes Combination Strategy. • Random selection of the independent variables (features). • Random selection of Examples. • Easy to Implement and paralelizable. 15

  16. FERNS Semi-Naive Bayes Combination. 16

  17. Posterior Distributions (Look-up Tables) Possible Outputs 7 0 FERNS • Classifier Training . . . 17

  18. 6 2 0 3 FERNS Classifier Training Posterior Distributions (Look-up Tables) . . . . Class 1 Fern 1 Class 2 . . . Class 1 Fern 2 Class 2 . . . . . . . Fern n 18

  19. Posterior Distributions (Look-up Tables) 2 6 1 FERNS Example Classification. Fern 3 Fern 1 Fern 2 19

  20. Random Forest vs FERNS 20 • Rotation Range • 20 Trees, 15 Depth. • 225 Different Clases. • 400 Images per class.

  21. Random Forest vs FERNS • Scale Range • 20 Trees, 15 Depth. • 225 Different Clases. • 400 Images per class.

  22. Random Forest vs FERNS • Size of the training Set • 20 Trees, 15 Depth. • 225 Different Classes. • [0.5-1.5] Scale Range.

  23. Random Forest vs FERNS • Number of different Classes. • 20 Trees, 15 Depth. • [0.8-1.2] Scale Range. • 1500 Training images per class.

  24. Random Forest vs FERNS • Training time. • 20 Trees, 15 Depth. • 225 Different Classes. • [0.5-1.5] Scale Range. 24

  25. Pose Estimation Homography Estimation • Robust Estimation (RANSAC). • Non-Linear Minimization (Levenberg-Marquardt).

  26. Summary Introduction. Random Forest, FERNS. Mixed/Augmented Reality Application. Conclusions/Questions.

  27. Augmented Reality Application • European Project IMPROVE (Improving Display and Rendering Technology for Virtual Environments) • Develop of new interaction metaphors. • Develop of new Displays. • Photo Realistic Rendering. • Development of Markerless Tracking Techniques. 27

  28. Augmented Reality Application ArchitecturalScenario AutomotiveScenario 28

  29. Marker-Less tracking (InDoor Scenario) Augmented Reality Application Textured plane Image Augmentation Feature Points Tracking 29

  30. Marker-Less tracking (OutDoor Scenario) Augmented Reality Application Image Acquisition Image Augmentation Feature points Tracking 30

  31. Augmented Reality Application • Performance • 20 Trees. • Full Rotation Range and [0.8-1.2] Scale Range. • 1000 images per Class. • 250 Different Classes.

  32. Summary Introduction. Random Forest, FERNS. Mixed/Augmented Reality Application. Conclusions/Questions. 32

  33. Conclusions • Both Approaches are very Similar. • The classifier is more sensitive to variations in scale. • The classifier is robust against variations in object orientation. • When the classifier converges, increase the number of trees does not improve accuracy. • The node test can be selected at random. • FERNS Requires more Memmory Than Random Forest. • Training and classification Time is Higher in FERNS than in Random Forest. • Random Forest are Faster than FERNS (without heuristics) • FERNS Supports more classes than Random Forest. • The Output of both classifiers must be filtered. • The higher the classification accuracy, the better the performance of the tracking.

  34. ThanksForListening Iñigo Barandiaran Martirena (ibarandiaran@vicomtech.org) Researcher, VICOMTech Paseo Mikeletegi 57 20009 San Sebastián Tfno: +34 943 30 92 30 Fax : +34 943 30 93 93

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