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International Conference on computer Vision (ICCV)

作者： Simakov Frolova Basri Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

We present a method for shape reconstruction from several images of a moving object. The reconstruction is dense (up to image resolution). The method assumes that the motion is known, e.g., by tracking a small number of feature points on the object. The object is assumed Lambertian (completely matte), light sources should not be very close to the object but otherwise arbitrary, and no knowledge of lighting conditions is required. An object changes its appearance significantly when it changes its orientation relative to light sources, causing violation of the common brightness constancy assumption. While a lot of effort is devoted to deal with this violation, we demonstrate how to exploit it to recover 3D structure from 2D images. We propose a new correspondence measure that enables point matching across views of a moving object. The method has been tested both on computer simulated examples and on a real object.

关键词： Shape Image reconstruction Brightness Light sources Stereo vision Information resources Cameras Calibration computer science Image resolution

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Degeneracies, dependencies and their implications in multi-body and multi-sequence factorizations

Degeneracies, dependencies and their implications in multi-b...

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Conference on computer Vision and Pattern Recognition (CVPR)

作者： L. Zelnik-Manor M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

The body of work on multi-body factorization separates between objects whose motions are independent. In this work we show that in many cases objects moving with different 3D motions will be captured as a single object using these approaches. We analyze what causes these degeneracies between objects and suggest an approach for overcoming some of them. We further show that in the case of multiple sequences linear dependencies can supply information for temporal synchronization of sequences and for spatial matching of points across sequences.

关键词： Layout Character generation Cameras Shape Bismuth computer science Subspace constraints Video sequences Stacking

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A step towards sequence-to-sequence alignment

A step towards sequence-to-sequence alignment

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Conference on computer Vision and Pattern Recognition (CVPR)

作者： Y. Caspi M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

The paper presents an approach for establishing correspondences in time and in space between two different video sequences of the same dynamic scene, recorded by stationary uncalibrated video cameras. The method simultaneously estimates both spatial alignment as well as temporal synchronization (temporal alignment) between the two sequences, using all available spatio-temporal information. Temporal variations between image frames (such as moving objects or changes in scene illumination) are powerful cues for alignment, which cannot be exploited by standard image-to-image alignment techniques. We show that by folding spatial and temporal cues into a single alignment framework, situations which are inherently ambiguous for traditional image-to-image alignment methods, are often uniquely resolved by sequence-to-sequence alignment. We also present a "direct" method for sequence-to-sequence alignment. The algorithm simultaneously estimates spatial and temporal alignment parameters directly from measurable sequence quantities, without requiring prior estimation of point correspondences, frame correspondences, or moving object detection. Results are shown on real image sequences taken by multiple video cameras.

关键词： Layout Cameras Video sequences Electrical capacitance tomography Lighting Spatial resolution Pixel computer science Space stations Image resolution

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Space-time video completion

Space-time video completion

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Conference on computer Vision and Pattern Recognition (CVPR)

作者： Y. Wexler E. Shechtman M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

We present a method for space-time completion of large space-time "holes" in video sequences of complex dynamic scenes. The missing portions are filled-in by sampling spatio-temporal patches from the available parts of the video, while enforcing global spatio-temporal consistency between all patches in and around the hole. This is obtained by posing the task of video completion and synthesis as a global optimization problem with a well-defined objective function. The consistent completion of static scene parts simultaneously with dynamic behaviors leads to realistic looking video sequences. Space-time video completion is useful for a variety of tasks, including, but not limited to: (i) Sophisticated video removal (of undesired static or dynamic objects) by completing the appropriate static or dynamic background information, (ii) Correction of missing/corrupted video frames in old movies, and (iii) Synthesis of new video frames to add a visual story, modify it, or generate a new one. Some examples of these are shown in the paper.

关键词： Video sequences Layout Sampling methods computer science Motion pictures Laboratories Constraint optimization Image texture Filling Heuristic algorithms

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Foundations of e-Democracy

arXiv

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arXiv 2017年

作者： Shapiro, Ehud Department of Computer Science & Applied Math Weizmann Institute of Science Rehovot Israel

The Internet revolution of democracy, which will transform earthly representative democracies by employing the communication and collaboration capabilities of the Internet, has yet to come. Here, we enlist the wisdom of our forefathers to lead the way. By consulting the 1789 Declaration of the Rights of Man and of the Citizen, we distill core values of democracy and derive from them requirements for the foundations of e-democracy. Building these foundations can usher the urgently-needed revolution of democracy. Copyright © 2017, The Authors. All rights reserved.

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Event-based analysis of video

Event-based analysis of video

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Conference on computer Vision and Pattern Recognition (CVPR)

作者： L. Zelnik-Manor M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

ISBN: (纸本)0769512720

Dynamic events can be regarded as long-term temporal objects, which are characterized by spatio-temporal features at multiple temporal scales. Based on this, we design a simple statistical distance measure between video sequences (possibly of different lengths) based on their behavioral content. This measure is non-parametric and can thus handle a wide range of dynamic events. We use this measure for isolating and clustering events within long continuous video sequences. This is done without prior knowledge of the types of events, their models, or their temporal extent. An outcome of such a clustering process is a temporal segmentation of long video sequences into event-consistent sub-sequences, and their grouping into event-consistent clusters. Our event representation and associated distance measure can also be used for event-based indexing into long video sequences, even when only one short example-clip is available. However, when multiple example-clips of the same event are available (either as a result of the clustering process, or given manually), these can be used to refine the event representation, the associated distance measure, and accordingly the quality of the detection and clustering process.

关键词： Video sequences Motion pictures Length measurement Dynamic range Indexing Information analysis Parametric statistics Stochastic processes computer science Event detection

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Alignment of non-overlapping sequences

Alignment of non-overlapping sequences

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International Conference on computer Vision (ICCV)

作者： Y. Caspi M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

ISBN: (纸本)0769511430

This paper shows how two image sequences that have no spatial overlap between their fields of view can be aligned both in time and in space. Such alignment is possible when the two cameras are attached closely together and are moved jointly in space. The common motion induces "similar" changes over time within the two sequences. This correlated temporal behavior is used to recover the spatial and temporal transformations between the two sequences. The requirement of "coherent appearance" in standard image alignment techniques is therefore replaced by "coherent temporal behavior", which is often easier to satisfy. This approach to alignment can be used not only for aligning nan-overlapping sequences, but also for handling other cases that are inherently difficult for standard image alignment techniques. We demonstrate applications of this approach to three real-world problems: (i) alignment of non-overlapping sequences for generating wide-screen movies, (ii) alignment of images (sequences) obtained at significantly different zooms, for surveillance applications, and (iii) multi-sensor image alignment for multi-sensor fusion.

关键词： Cameras Image sequences Layout Robot vision systems computer science Motion pictures Surveillance Hardware

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Multi-view subspace constraints on homographies

Multi-view subspace constraints on homographies

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International Conference on computer Vision (ICCV)

作者： L. Zelnik-Manor M. Irani Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

The motion of a planar surface between two camera views induces a homography. The homography depends on the camera intrinsic and extrinsic parameters, as well as on the 3D plane parameters. While camera parameters vary across different views, the plane geometry remains the same. Based on this fact, the paper derives linear subspace constraints on the relative motion of multiple (/spl ges/2) planes across multiple views. The paper has three main contributions. It shows that the collection of all relative homographies of a pair of planes (homologies) across multiple views, spans a 4-dimensional linear subspace. It shows how this constraint can be extended to the case of multiple planes across multiple views. It suggests two potential application areas which can benefit from these constraints: the accuracy of homography estimation can be improved by enforcing the multi-view subspace constraints; and violations of these multi-view constraints can be used as a cue for moving object detection. All the results derived in this paper are true for uncalibrated cameras.

关键词： Subspace constraints Cameras Layout Geometry Object detection Transmission line matrix methods computer science Calibration Algorithm design and analysis

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Stereoscopic families of permutations, and their applications

Stereoscopic families of permutations, and their application...

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Israel Symposium on the Theory of Computing and Systems

作者： U. Feige R. Krauthgamer Department of Applied Math and Computer Science Weizmann Institute of Science Rehovot Israel

A stereoscopic family of permutations maps an m-dimensional mesh into several 1-dimensional lines, in a way that jointly preserves distance information. Specifically, consider any two points and denote their distance on the m-dimensional mesh by d. Then the distance between their images, on the line on which these images are closest together is O(d/sup m/). We initiate a systematic study of stereoscopic families of permutations. We show a construction of these families that involves the use of m+1 images. We also show that under some additional restrictions (namely adjacent points on the image lines originate at points which are not too far away on the mesh), three images are necessary in order to construct such a family for the 2-dimensional mesh. We present two applications for stereoscopic families of permutations. One application is an algorithm for routing on the mesh that guarantees delivery of each packet within a number of steps that depends upon the distance between this packet's source and destination, but is independent of the size of the mesh. Our algorithm is exceptionally simple, involves no queues, and can be used in dynamic settings in which packets are continuously generated. Another application is an extension of the construction of nonexpansive hash functions of Linial and Sasson (STOC 96) from the case of one dimensional metrics to arbitrary dimensions.

关键词： computer science Career development Upper bound Optical network units Wavelength routing

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A Two-Frame Theory of Motion, Lighting and Shape

A Two-Frame Theory of Motion, Lighting and Shape

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26th IEEE Conference on computer Vision and Pattern Recognition (CVPR 2008), vol.10

作者： Ronen Basri Darya Frolova Department of Computer Science and Applied Math Weizmann Institute of Science Rehovot Israel

This paper explores how shape, motion, and lighting interact in the case of a two-frame motion sequence. We consider a rigid object with Lambertian reflectance properties undergoing small motion with respect to both a camera and a stationary point light source. Assuming orthographic projection, we derive a single, first order quasilinear partial differential equation that relates shape, motion, and lighting, while eliminating out the albedo. We show how this equation can be solved, when the motion and lighting parameters are known, to produce a 3D reconstruction of the object. A solution is obtained using the method of characteristics and can be refined by adding regularization. We further show that both smooth bounding contours as well as surface markings can be used to derive Dirichlet boundary conditions. Experimental results demonstrate the quality of this reconstruction.

关键词： Shape Image reconstruction Brightness Cameras Boundary conditions Reflectivity Light sources Partial differential equations Surface reconstruction Photometry

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