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Unsupervised Learning of Categorical Segments in Image Collections *California Institute of Technology **Technion Marco Andreetto*, Lihi Zelnik-Manor**, Pietro Perona* The Sixth IEEE Computer Society Workshop on Perceptual Organization in Computer Vision (POCV 2008)
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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Motivation
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Normalized cuts: Shi and Malik PAMI 2000
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Motivation
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Categorical segments: from human segmentation
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Motivation
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Related works Russell et al. CVPR 2006 Cao and Fei-Fei ICCV 2007 Wang and Grimson NIPS 2007 Andreetto et al. ICCV 2007
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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An image as a set of segments
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K = 2 N
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An image as a set of segments K = 2 Segment probability N
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An image as a set of segments K = 2 Segment probability fkfk K Segment density N
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Image formation K = 2 c Segment probability Label fkfk K x Segment density N
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What we’re looking forObserved Probabilistic model for clustering c fkfk KN x Likelihood of x to be in cluster k
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Non-parametric densities Sum of local kernels
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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N Learning categorical segments c fkfk K x w gkgk K Segment appearance Joint for all images Segment shape/color Specific per image M
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Visual words Filter Bank VQ w1w1 w2w2 w3w3 wNwN Filter bank: 17 outputs 256 visual words Winn et al. ICCV 2005 … …
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Inference N c fkfk K x w gkgk K M
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Gibbs sampling
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Prior term: Number of pixels in image m assigned to segment k
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Gibbs sampling Prior term: Visual words term: Number of pixels in image m assigned to segment k Number of visual word h assigned to segments k
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Gibbs sampling Prior term: Visual words term: Segment term: Number of pixels in image m assigned to segment k Number of visual word h assigned to segments k Non-parametric density Estimate for segment k Affinity between observations i and j
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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Experimental results (MSRC)
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Classification results (MSRC) Class NameWang and GrimsonOur model DetectionFalse Al.DetectionFalse Al. Cow0.56620.03340.48890.0823 GrassN/A 0.63890.0337 Cars0.68380.24370.33130.1732 SkyN/A 0.99540.0096 FoliageN/A 0.47350.1122 SeaN/A 0.61990.0174 Bikes0.56610.37140.54360.0646 Faces0.69730.42170.61610.0429 Running time: 18.75 sec. per image
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Experimental results (Labelme)
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Categorical segments (Labelme) Segment 1: FoliageSegment 2: Buildings Segment 1: SkySegment 3: Street pavement
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Categorical segments (scenes)
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Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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Conclusions We presented a model for unsupervised learning of categorical segments We describe an inference method based on Gibbs sampling We show some experimental results on a standard dataset MSRC v1.
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Future work Faster inference method (variational approximation) Automatic inference of the number of segments Learning geometric relationships between segments
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Thank You
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