This paper addresses the problem of computing the fundamental matrix which describes a geometric ... more This paper addresses the problem of computing the fundamental matrix which describes a geometric relationship between a pair of stereo images : the epipolar geometry. In the uncalibrated case, epipolar geometry captures all the 3D information available from the scene. It is of a central importance for problems such as 3D reconstruction, self-calibration and feature tracking. Hence, the computation of the fundamental matrix is of great interest. The existing methods 10] uses two steps : a linear step followed by a non linear one. But the linear step gives rarely a close form solution for the fundamental matrix resulting in more iterations for the non linear step which is not guaranteed to converge to the correct solution. In this paper, a novel method based on virtual parallax is proposed. The problem is formulated di erently, instead of computing directely the 3 3 fundamental matrix, we compute a homography with one epipole position, and show that this is equivalent to compute the fundamental matrix. Simple equations are derived by reducing the number of parameters to estimate. As a consequence, we obtain an accurate fundamental matrix of rank 2 with a stable linear computation. Experiments with simulated and real images validate our method and clearly show the improvement over the existing methods.
Storage and Retrieval for Image and Video Databases, 1994
The aim of this paper is to show how image points can be extracted accurately. We will restrict o... more The aim of this paper is to show how image points can be extracted accurately. We will restrict our search to specific points identified by corners, which are stable given a sequence. Our approach makes us of a model-based corner detector. It matches a part of the image containing a corner against a predefined corner model. Once the fitting is
: This paper presents a matching method which is based on invariantsof the luminance function. Th... more : This paper presents a matching method which is based on invariantsof the luminance function. This makes matching possible in the case ofimportant geometric transformations between images. The method is robustto occlusion, as local properties of the image signal are used. We proposeto use differential measures invariant to rotations in a multi-scale framework.Promising results are obtained which might be used
This paper describes an original approach for automatically building a navigation tool within a v... more This paper describes an original approach for automatically building a navigation tool within a video. It aims at determining efficient representations of a video, in the context of contentbased video browsing, relying on the creation of hyper-links between elementary shots of a video.
This overview summarizes the goals of the European projects Cumuli, Panorama ,a ndVanguard and re... more This overview summarizes the goals of the European projects Cumuli, Panorama ,a ndVanguard and references the various contri- butions in this volume. There are several overlaps between the projects which all evolve around the geometric analysis of scenes from multiple images. All projects attempt to reconstruct the geometry and visual ap- pearance of complex 3D scenes that may be static or dynamic. While Cumuli and Vanguard deal with images from uncalibrated cam- eras and unrestricted camera position for general scenes, Panorama focusses on a highly calibrated setup used to capture 3D person mod- els. Cumuli and Vanguard developed techniques for handling multi- view relations, object tracking and camera calibration, image and geom- etry based view synthesis, and D model generation. Interaction with the modeled scene and mixing of virtual and real objects leads to Vir- tual/Augmented Reality applications in Vanguard and Cumuli, while the Panorama approach is tuned to fully automatic ...
Proceedings Fourth IEEE Workshop on Applications of Computer Vision. WACV'98 (Cat. No.98EX201), 1998
This paper presents the first version of our platform for automatically building the structure of... more This paper presents the first version of our platform for automatically building the structure of a video sequence. The first application uses semi-automatic tools based only on image analysis for building interactive videos: decomposing the video into shots, extracting and tracking objects within each shot and linking occurrences of similar objects among the shots. The second application provides the end user with a powerful browser to navigate through any preprocessed hypervideo.
Sixth International Conference on Computer Vision (IEEE Cat. No.98CH36271), 1998
... We have used two different planar scenes for our experimentation : Van Gogh” and “Asterix” . ... more ... We have used two different planar scenes for our experimentation : Van Gogh” and “Asterix” . The “Van Gogh” scene is the L'sower” painting shown in figure 1. The “Asterix” scene can be seen in figure 3. The two scenes are very different. ...
This paper describes an original approach for automatically building a navigation toolwithin a vi... more This paper describes an original approach for automatically building a navigation toolwithin a video. It aims at determining efficient representations of a video, in the context of contentbasedvideo browsing, relying on the creation of hyper-links between elementary shots of a video.
Proceedings of the IEEE Workshop on Visual Motion, 1991
The D reconstruction from projections and feature correspondence between projections are two majo... more The D reconstruction from projections and feature correspondence between projections are two major problems in structure from motion. The authors show a geometric method on how a 3D affine shape is obtained from two parallel projections through general 4 reference points, or from two central projections when additional vanishing points are available. And they show also that correspondences can be established through reference points; the reference points configuration for central projections should contain at least a set of 4 coplanar points. The method is developed both for point and line segment features. Apart from that the correspondence of the necessary reference points should be known in advance, one needs neither to calibrate cameras nor to have any knowledge of its position and displacement. Projective geometry and affine geometry invariants are manipulated to perform both reconstruction and correspondence
Storage and Retrieval for Image and Video Databases, 1994
The use of correlation as a measure of similarity between two signals is a well known technique. ... more The use of correlation as a measure of similarity between two signals is a well known technique. Correlationis commonly used in stereo vision to solve the correspondence problem. In this context the aim is to find theposition of a point in one of the two images of a weakly calibrated stereo pair which corresponds to a point inthe other image.
ABSTRACT We are addressing the problem of matching images of scene or of objects when a large col... more ABSTRACT We are addressing the problem of matching images of scene or of objects when a large collection of reference objects is considered. The paper addresses also the issue of dealing with illumination change and camera position changes. Our approach is firstly based on the use of invariants. Invariants have to be computed locally so that the resulting values will not affected by partial occlusion or accidental highlights. In- variants proved to be a very discriminant piece of information and stored in a hash table they allow efficient indexing of visual shape. Final recognition can be performed using simply a robust voting technique or can be improved using Bayesian decision.
It is possible to recover the three-dimensional structure of a scene using only correspondences b... more It is possible to recover the three-dimensional structure of a scene using only correspondences between images taken with uncalibrated cameras (faugeras 1992). The reconstruction obtained this way is only defined up to a projective transformation of the 3D space. However, this kind of structure allows some spatial reasoning such as finding a path. In order to perform more specific reasoning, or to perform work with a robot moving in Euclidean space, Euclidean or affine constraints have to be added to the camera observations. Such constraints arise from the knowledge of the scene: location of points, geometrical constraints on lines, etc. First, this paper presents a reconstruction method for the scene, then it discusses how the framework of projective geometry allows symbolic or numerical information about positions to be derived, and how knowledge about the scene can be used for computing symbolic or numerical relationships. Implementation issues and experimental results are discussed. 1 . 0004-3702/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOOO4-3702(95)00035-6 214 R. Mohr et trl. /Artificial Intelligence 78 (1995) 213-238 R. Mohr et al./ArtiJicial Inielligence 78 (1995) 213-238 R. Mohr et ul./Ariijiiciul Intelligence 78 (1995) 213-238
International Conference on Pattern Recognition, 1990
The strengths and the drawbacks of active contour models are described, and the absolute necessit... more The strengths and the drawbacks of active contour models are described, and the absolute necessity of a criterion for assessing the solutions is pointed out. A method called snake growing, based on successive lengthenings of the snake, is proposed. The strength of this approach is that, at each stage, good convergence conditions are realized and initialization problems can be eliminated
Using a novel cell design the authors have achieved a 13.7% conversion efficiency with amorphous ... more Using a novel cell design the authors have achieved a 13.7% conversion efficiency with amorphous silicon and amorphous silicon-germanium alloys in a three-cell stacked-junction configuration. 13.0% conversion efficiency was achieved in the tandem configuration. The efficiency value was measured using a triple-source solar simulator adjusted for global AM1.5 test conditions. This device has a structure of stainless steel/textured silver/zinc oxide/ni1p/ni2p/ni3p/ITO/grid.
This paper addresses the problem of computing the fundamental matrix which describes a geometric ... more This paper addresses the problem of computing the fundamental matrix which describes a geometric relationship between a pair of stereo images : the epipolar geometry. In the uncalibrated case, epipolar geometry captures all the 3D information available from the scene. It is of a central importance for problems such as 3D reconstruction, self-calibration and feature tracking. Hence, the computation of the fundamental matrix is of great interest. The existing methods 10] uses two steps : a linear step followed by a non linear one. But the linear step gives rarely a close form solution for the fundamental matrix resulting in more iterations for the non linear step which is not guaranteed to converge to the correct solution. In this paper, a novel method based on virtual parallax is proposed. The problem is formulated di erently, instead of computing directely the 3 3 fundamental matrix, we compute a homography with one epipole position, and show that this is equivalent to compute the fundamental matrix. Simple equations are derived by reducing the number of parameters to estimate. As a consequence, we obtain an accurate fundamental matrix of rank 2 with a stable linear computation. Experiments with simulated and real images validate our method and clearly show the improvement over the existing methods.
Storage and Retrieval for Image and Video Databases, 1994
The aim of this paper is to show how image points can be extracted accurately. We will restrict o... more The aim of this paper is to show how image points can be extracted accurately. We will restrict our search to specific points identified by corners, which are stable given a sequence. Our approach makes us of a model-based corner detector. It matches a part of the image containing a corner against a predefined corner model. Once the fitting is
: This paper presents a matching method which is based on invariantsof the luminance function. Th... more : This paper presents a matching method which is based on invariantsof the luminance function. This makes matching possible in the case ofimportant geometric transformations between images. The method is robustto occlusion, as local properties of the image signal are used. We proposeto use differential measures invariant to rotations in a multi-scale framework.Promising results are obtained which might be used
This paper describes an original approach for automatically building a navigation tool within a v... more This paper describes an original approach for automatically building a navigation tool within a video. It aims at determining efficient representations of a video, in the context of contentbased video browsing, relying on the creation of hyper-links between elementary shots of a video.
This overview summarizes the goals of the European projects Cumuli, Panorama ,a ndVanguard and re... more This overview summarizes the goals of the European projects Cumuli, Panorama ,a ndVanguard and references the various contri- butions in this volume. There are several overlaps between the projects which all evolve around the geometric analysis of scenes from multiple images. All projects attempt to reconstruct the geometry and visual ap- pearance of complex 3D scenes that may be static or dynamic. While Cumuli and Vanguard deal with images from uncalibrated cam- eras and unrestricted camera position for general scenes, Panorama focusses on a highly calibrated setup used to capture 3D person mod- els. Cumuli and Vanguard developed techniques for handling multi- view relations, object tracking and camera calibration, image and geom- etry based view synthesis, and D model generation. Interaction with the modeled scene and mixing of virtual and real objects leads to Vir- tual/Augmented Reality applications in Vanguard and Cumuli, while the Panorama approach is tuned to fully automatic ...
Proceedings Fourth IEEE Workshop on Applications of Computer Vision. WACV'98 (Cat. No.98EX201), 1998
This paper presents the first version of our platform for automatically building the structure of... more This paper presents the first version of our platform for automatically building the structure of a video sequence. The first application uses semi-automatic tools based only on image analysis for building interactive videos: decomposing the video into shots, extracting and tracking objects within each shot and linking occurrences of similar objects among the shots. The second application provides the end user with a powerful browser to navigate through any preprocessed hypervideo.
Sixth International Conference on Computer Vision (IEEE Cat. No.98CH36271), 1998
... We have used two different planar scenes for our experimentation : Van Gogh” and “Asterix” . ... more ... We have used two different planar scenes for our experimentation : Van Gogh” and “Asterix” . The “Van Gogh” scene is the L'sower” painting shown in figure 1. The “Asterix” scene can be seen in figure 3. The two scenes are very different. ...
This paper describes an original approach for automatically building a navigation toolwithin a vi... more This paper describes an original approach for automatically building a navigation toolwithin a video. It aims at determining efficient representations of a video, in the context of contentbasedvideo browsing, relying on the creation of hyper-links between elementary shots of a video.
Proceedings of the IEEE Workshop on Visual Motion, 1991
The D reconstruction from projections and feature correspondence between projections are two majo... more The D reconstruction from projections and feature correspondence between projections are two major problems in structure from motion. The authors show a geometric method on how a 3D affine shape is obtained from two parallel projections through general 4 reference points, or from two central projections when additional vanishing points are available. And they show also that correspondences can be established through reference points; the reference points configuration for central projections should contain at least a set of 4 coplanar points. The method is developed both for point and line segment features. Apart from that the correspondence of the necessary reference points should be known in advance, one needs neither to calibrate cameras nor to have any knowledge of its position and displacement. Projective geometry and affine geometry invariants are manipulated to perform both reconstruction and correspondence
Storage and Retrieval for Image and Video Databases, 1994
The use of correlation as a measure of similarity between two signals is a well known technique. ... more The use of correlation as a measure of similarity between two signals is a well known technique. Correlationis commonly used in stereo vision to solve the correspondence problem. In this context the aim is to find theposition of a point in one of the two images of a weakly calibrated stereo pair which corresponds to a point inthe other image.
ABSTRACT We are addressing the problem of matching images of scene or of objects when a large col... more ABSTRACT We are addressing the problem of matching images of scene or of objects when a large collection of reference objects is considered. The paper addresses also the issue of dealing with illumination change and camera position changes. Our approach is firstly based on the use of invariants. Invariants have to be computed locally so that the resulting values will not affected by partial occlusion or accidental highlights. In- variants proved to be a very discriminant piece of information and stored in a hash table they allow efficient indexing of visual shape. Final recognition can be performed using simply a robust voting technique or can be improved using Bayesian decision.
It is possible to recover the three-dimensional structure of a scene using only correspondences b... more It is possible to recover the three-dimensional structure of a scene using only correspondences between images taken with uncalibrated cameras (faugeras 1992). The reconstruction obtained this way is only defined up to a projective transformation of the 3D space. However, this kind of structure allows some spatial reasoning such as finding a path. In order to perform more specific reasoning, or to perform work with a robot moving in Euclidean space, Euclidean or affine constraints have to be added to the camera observations. Such constraints arise from the knowledge of the scene: location of points, geometrical constraints on lines, etc. First, this paper presents a reconstruction method for the scene, then it discusses how the framework of projective geometry allows symbolic or numerical information about positions to be derived, and how knowledge about the scene can be used for computing symbolic or numerical relationships. Implementation issues and experimental results are discussed. 1 . 0004-3702/95/$09.50 0 1995 Elsevier Science B.V. All rights reserved SSDIOOO4-3702(95)00035-6 214 R. Mohr et trl. /Artificial Intelligence 78 (1995) 213-238 R. Mohr et al./ArtiJicial Inielligence 78 (1995) 213-238 R. Mohr et ul./Ariijiiciul Intelligence 78 (1995) 213-238
International Conference on Pattern Recognition, 1990
The strengths and the drawbacks of active contour models are described, and the absolute necessit... more The strengths and the drawbacks of active contour models are described, and the absolute necessity of a criterion for assessing the solutions is pointed out. A method called snake growing, based on successive lengthenings of the snake, is proposed. The strength of this approach is that, at each stage, good convergence conditions are realized and initialization problems can be eliminated
Using a novel cell design the authors have achieved a 13.7% conversion efficiency with amorphous ... more Using a novel cell design the authors have achieved a 13.7% conversion efficiency with amorphous silicon and amorphous silicon-germanium alloys in a three-cell stacked-junction configuration. 13.0% conversion efficiency was achieved in the tandem configuration. The efficiency value was measured using a triple-source solar simulator adjusted for global AM1.5 test conditions. This device has a structure of stainless steel/textured silver/zinc oxide/ni1p/ni2p/ni3p/ITO/grid.
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Papers by Roger Mohr