2,404 research outputs found
Finding Temporally Consistent Occlusion Boundaries in Videos using Geometric Context
We present an algorithm for finding temporally consistent occlusion
boundaries in videos to support segmentation of dynamic scenes. We learn
occlusion boundaries in a pairwise Markov random field (MRF) framework. We
first estimate the probability of an spatio-temporal edge being an occlusion
boundary by using appearance, flow, and geometric features. Next, we enforce
occlusion boundary continuity in a MRF model by learning pairwise occlusion
probabilities using a random forest. Then, we temporally smooth boundaries to
remove temporal inconsistencies in occlusion boundary estimation. Our proposed
framework provides an efficient approach for finding temporally consistent
occlusion boundaries in video by utilizing causality, redundancy in videos, and
semantic layout of the scene. We have developed a dataset with fully annotated
ground-truth occlusion boundaries of over 30 videos ($5000 frames). This
dataset is used to evaluate temporal occlusion boundaries and provides a much
needed baseline for future studies. We perform experiments to demonstrate the
role of scene layout, and temporal information for occlusion reasoning in
dynamic scenes.Comment: Applications of Computer Vision (WACV), 2015 IEEE Winter Conference
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Lifting GIS Maps into Strong Geometric Context for Scene Understanding
Contextual information can have a substantial impact on the performance of
visual tasks such as semantic segmentation, object detection, and geometric
estimation. Data stored in Geographic Information Systems (GIS) offers a rich
source of contextual information that has been largely untapped by computer
vision. We propose to leverage such information for scene understanding by
combining GIS resources with large sets of unorganized photographs using
Structure from Motion (SfM) techniques. We present a pipeline to quickly
generate strong 3D geometric priors from 2D GIS data using SfM models aligned
with minimal user input. Given an image resectioned against this model, we
generate robust predictions of depth, surface normals, and semantic labels. We
show that the precision of the predicted geometry is substantially more
accurate other single-image depth estimation methods. We then demonstrate the
utility of these contextual constraints for re-scoring pedestrian detections,
and use these GIS contextual features alongside object detection score maps to
improve a CRF-based semantic segmentation framework, boosting accuracy over
baseline models
On the Sobolev quotient of three-dimensional CR manifolds
We exhibit examples of compact three-dimensional CR manifolds of positive
Webster class, {\em Rossi spheres}, for which the pseudo-hermitian mass as
defined in \cite{CMY17} is negative, and for which the infimum of the
CR-Sobolev quotient is not attained. To our knowledge, this is the first
geometric context on smooth closed manifolds where this phenomenon arises, in
striking contrast to the Riemannian case.Comment: 36 pages, 2 figure
The large scale geometry of some metabelian groups
We study the large scale geometry of the upper triangular subgroup of
PSL(2,Z[1/n]), which arises naturally in a geometric context. We prove a
quasi-isometry classification theorem and show that these groups are
quasi-isometrically rigid with infinite dimensional quasi-isometry group. We
generalize our results to a larger class of groups which are metabelian and are
higher dimensional analogues of the solvable Baumslag-Solitar groups BS(1,n)
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