Lecture 18: Recent work in recognition(slides adapted from Dan Huttenlocher, Mark Everingham, and James Hays)CS6670: Computer VisionNoah SnavelyAnnouncements• Project 3: Eigenfaces– due Wednesday, November 11 at 11:59pmObject recognition• Category recognition has been the focus of extensive research in the past decade• Extensive use and development of machine learning techniques, better features• Moderate-scale datasets derived from the Web– PASCAL VOC: 20 object categories, > 10K images, > 25K instances, hand-labeled ground truth, annual competitions• Twenty object categories (aeroplane to TV/monitor) • Three challenges:– Classification challenge (is there an X in this image?)– Detection challenge (draw a box around every X)– Segmentation challengeisis there a cat?Chance essentially 0Best localization methods• Sliding window-style classifiers – SVM, Adaboost– Flexible spatial template: “star model”• Separate classifiers by viewpoint• Use of context in classifiers• Local features– HoG, SIFT, local histograms of gradient orientationsHoG features• Image partitioned into 8x8 blocks• In each block, compute histogram of gradient orientationsFlexible Spatial Template (UofC-TTI)• Hierarchical model [Felzenszwalb et al 2008]– Coarse template for finding the root part– Fine-scale templates connected by springs– Learning automatically from labeled bounding boxes• Separate models per viewpointSix-component car modelroot filters (coarse)part filters (fine) deformation modelsside viewfrontal viewSix-component person modelGIST descriptors• Global descriptor computed from entire image [Oliva and Torralba 2001]GIST DescriptorHays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Criminisi, Perez, and Toyama. Region filling and object removal by exemplar-based inpainting. IEEE Transactions on Image Processing. 2004.Hays and Efros, SIGGRAPH 2007Criminisi et al. resultHays and Efros, SIGGRAPH 2007Criminisi et al. resultHays and Efros, SIGGRAPH 2007Scene Completion AlgorithmInput image Scene DescriptorImage Collection200 matches20 completionsContext matching+ blending……Hays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Hays and Efros, SIGGRAPH 2007Projective geometryReadings• Mundy, J.L. and Zisserman, A., Geometric Invariance in Computer Vision, Appendix: Projective Geometry for Machine Vision, MIT Press, Cambridge, MA, 1992, (read 23.1 - 23.5, 23.10)– available online: http://www.cs.cmu.edu/~ph/869/papers/zisser-mundy.pdfAmes
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