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)
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
Motivation
Normalized cuts: Shi and Malik PAMI 2000
Motivation
Categorical segments: from human segmentation
Motivation
Related works Russell et al. CVPR 2006 Cao and Fei-Fei ICCV 2007 Wang and Grimson NIPS 2007 Andreetto et al. ICCV 2007
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
An image as a set of segments
K = 2 N
An image as a set of segments K = 2 Segment probability N
An image as a set of segments K = 2 Segment probability fkfk K Segment density N
Image formation K = 2 c Segment probability Label fkfk K x Segment density N
What we’re looking forObserved Probabilistic model for clustering c fkfk KN x Likelihood of x to be in cluster k
Non-parametric densities Sum of local kernels
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
N Learning categorical segments c fkfk K x w gkgk K Segment appearance Joint for all images Segment shape/color Specific per image M
Visual words Filter Bank VQ w1w1 w2w2 w3w3 wNwN Filter bank: 17 outputs 256 visual words Winn et al. ICCV 2005 … …
Inference N c fkfk K x w gkgk K M
Gibbs sampling
Prior term: Number of pixels in image m assigned to segment k
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
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
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
Experimental results (MSRC)
Classification results (MSRC) Class NameWang and GrimsonOur model DetectionFalse Al.DetectionFalse Al. Cow GrassN/A Cars SkyN/A FoliageN/A SeaN/A Bikes Faces Running time: sec. per image
Experimental results (Labelme)
Categorical segments (Labelme) Segment 1: FoliageSegment 2: Buildings Segment 1: SkySegment 3: Street pavement
Categorical segments (scenes)
Outline Motivation and related work A probabilistic model for single image segmentation Unsupervised learning of categorical segments Experimental results Conclusions and future works
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.
Future work Faster inference method (variational approximation) Automatic inference of the number of segments Learning geometric relationships between segments
Thank You