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| 2. |
- Bretzner, Lars, et al.
(författare)
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Feature tracking with automatic selection of spatial scales
- 1998
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- When observing a dynamic world, the size of image structures may vary over nada. This article emphasizes the need for including explicit mechanisms for automatic scale selection in feature tracking algorithms in order to: (i) adapt the local scale of processing to the local image structure, and (ii) adapt to the size variations that may occur over time. The problems of corner detection and blob detection are treated in detail, and a combined framework for feature tracking is presented in which the image features at every time moment are detected at locally determined and automatically selected nadaes. A useful property of the scale selection method is that the scale levels selected in the feature detection step reflect the spatial extent of the image structures. Thereby, the integrated tracking algorithm has the ability to adapt to spatial as well as temporal size variations, and can in this way overcome some of the inherent limitations of exposing fixed-scale tracking methods to image sequences in which the size variations are large. In the composed tracking procedure, the scale information is used for two additional major purposes: (i) for defining local regions of interest for searching for matching candidates as well as setting the window size for correlation when evaluating matching candidates, and (ii) stability over time of the scale and significance descriptors produced by the scale selection procedure are used for formulating a multi-cue similarity measure for matching. Experiments on real-world sequences are presented showing the performance of the algorithm when applied to (individual) tracking of corners and blobs. Specifically, comparisons with fixed-scale tracking methods are included as well as illustrations of the increase in performance obtained by using multiple cues in the feature matching step.
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| 3. |
- Bretzner, Lars, et al.
(författare)
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Feature Tracking with Automatic Selection of Spatial Scales
- 1998
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Ingår i: Computer Vision and Image Understanding. - : Elsevier BV. - 1077-3142 .- 1090-235X. ; 71:3, s. 385-393
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Tidskriftsartikel (refereegranskat)abstract
- When observing a dynamic world, the size of image structures may vary over time. This article emphasizes the need for including explicit mechanisms for automatic scale selection in feature tracking algorithms in order to: (i) adapt the local scale of processing to the local image structure, and (ii) adapt to the size variations that may occur over time. The problems of corner detection and blob detection are treated in detail, and a combined framework for feature tracking is presented. The integrated tracking algorithm overcomes some of the inherent limitations of exposing fixed-scale tracking methods to image sequences in which the size variations are large. It is also shown how the stability over time of scale descriptors can be used as a part of a multi-cue similarity measure for matching. Experiments on real-world sequences are presented showing the performance of the algorithm when applied to (individual) tracking of corners and blobs.
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| 4. |
- Bretzner, Lars, et al.
(författare)
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Hand-gesture recognition using multi-scale colour features, hierarchical features and particle filtering
- 2002
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Ingår i: Fifth IEEE International Conference on Automatic Face and Gesture Recognition, 2002. Proceedings. - : IEEE conference proceedings. ; , s. 63-74
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Konferensbidrag (refereegranskat)abstract
- This paper presents algorithms and a prototype systemfor hand tracking and hand posture recognition. Hand posturesare represented in terms of hierarchies of multi-scalecolour image features at different scales, with qualitativeinter-relations in terms of scale, position and orientation. Ineach image, detection of multi-scale colour features is performed.Hand states are then simultaneously detected andtracked using particle filtering, with an extension of layeredsampling referred to as hierarchical layered sampling. Experimentsare presented showing that the performance ofthe system is substantially improved by performing featuredetection in colour space and including a prior with respectto skin colour. These components have been integrated intoa real-time prototype system, applied to a test problem ofcontrolling consumer electronics using hand gestures. In asimplified demo scenario, this system has been successfullytested by participants at two fairs during 2001.
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| 5. |
- Bretzner, Lars
(författare)
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Multi-scale feature tracking and motion estimation
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis studies the problems of feature tracking and motion estimation and presents an application of these concepts to human-computer interaction. The presentation is divided into three parts. The first part addresses feature tracking in a multi-scale context. Features in an image appear at different scales, and these scales can be expected to change over time due to the size variations that occur when objects move relative to the camera. A scheme for feature tracking is presented, which incorporates a mechanism for automatic scale selection and it is argued that such a mechanism is necessary to handle size variations over time. Experiments demonstrate how the proposed scheme is robust to size variations in situations where a traditional fixed scale tracker fails. This leads to extended feature trajectories, which are valuable for motion and structure estimation. It is also shown how an object representation suitable for tracking can be built in a conceptually simple way as a multi-scale feature hierarchy with qualitative relations between features at different scales. Experiments illustrate the capability of the proposed hierarchy to handle occlusions and semirigid objects. The second part of the thesis develops a geometric framework for computing estimates of 3D structure and motion from sparse feature correspondences in monocular sequences. A tool is presented, called the centered affine trifocal tensor, for motion estimation from three affine views. Moreover, a factorization approach is developed which simultaneously handles point and line correspondences in multiple affine views. Experiments show the influence of several factors on the accuracy of the structure and motion estimates, including noise in the feature localization, perspective effects and the number of feature correspondences. This motion estimation framework is also applied to feature correspondences obtained from the abovementioned feature tracker. The last part integrates the functionalities from the first two parts into a pre-prototype system which explores new principles for human-computer interaction. The idea is to transfer 3D orientation to a computer using no other equipment than the operator’s hand.
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| 6. |
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| 7. |
- Bretzner, Lars, et al.
(författare)
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Qualitative multi-scale feature hierarchies for object tracking
- 1999
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Ingår i: Proc Scale-Space Theories in Computer Vision Med. - : Elsevier. - 354066498X ; , s. 117-128
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Konferensbidrag (refereegranskat)abstract
- This paper shows how the performance of feature trackers can be improved by building a view-based object representation consisting of qualitative relations between image structures at different scales. The idea is to track all image features individually, and to use the qualitative feature relations for resolving ambiguous matches and for introducing feature hypotheses whenever image features are mismatched or lost. Compared to more traditional work on view-based object tracking, this methodology has the ability to handle semi-rigid objects and partial occlusions. Compared to trackers based on three-dimensional object models, this approach is much simpler and of a more generic nature. A hands-on example is presented showing how an integrated application system can be constructed from conceptually very simple operations.
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| 8. |
- Bretzner, Lars, et al.
(författare)
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Qualitative Multi-Scale Feature Hierarchies for Object Tracking
- 2000
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Ingår i: Journal of Visual Communication and Image Representation. - : Elsevier. - 1047-3203 .- 1095-9076. ; 11, s. 115-129
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows how the performance of feature trackers can be improved by building a view-based object representation consisting of qualitative relations between image structures at different scales. The idea is to track all image features individually, and to use the qualitative feature relations for resolving ambiguous matches and for introducing feature hypotheses whenever image features are mismatched or lost. Compared to more traditional work on view-based object tracking, this methodology has the ability to handle semi-rigid objects and partial occlusions. Compared to trackers based on three-dimensional object models, this approach is much simpler and of a more generic nature. A hands-on example is presented showing how an integrated application system can be constructed from conceptually very simple operations.
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| 9. |
- Bretzner, Lars, et al.
(författare)
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Structure and Motion Estimation using Sparse Point and Line Correspondences in Multiple Affine Views
- 1999
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This paper addresses the problem of computing three-dimen\-sional structure and motion from an unknown rigid configuration of points and lines viewed by an affine projection model. An algebraic structure, analogous to the trilinear tensor for three perspective cameras, is defined for configurations of three centered affine cameras. This centered affine trifocal tensor contains 12 non-zero coefficients and involves linear relations between point correspondences and trilinear relations between line correspondences. It is shown how the affine trifocal tensor relates to the perspective trilinear tensor, and how three-dimensional motion can be computed from this tensor in a straightforward manner. A factorization approach is developed to handle point features and line features simultaneously in image sequences, and degenerate feature configurations are analysed. This theory is applied to a specific problem in human-computer interaction of capturing three-dimensional rotations from gestures of a human hand. This application to quantitative gesture analyses illustrates the usefulness of the affine trifocal tensor in a situation where sufficient information is not available to compute the perspective trilinear tensor, while the geometry requires point correspondences as well as line correspondences over at least three views.
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| 10. |
- Bretzner, Lars, et al.
(författare)
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Use your hand as a 3-D mouse or relative orientation from extended sequences of sparse point and line correspondances using the affine trifocal tensor
- 1998
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Ingår i: Computer Vision — ECCV'98. - : Springer Berlin/Heidelberg. ; , s. 141-157
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Konferensbidrag (refereegranskat)abstract
- This paper addresses the problem of computing three-dimensional structure and motion from an unknown rigid configuration of point and lines viewed by an affine projection model. An algebraic structure, analogous to the trilinear tensor for three perspective cameras, is defined for configurations of three centered affine cameras. This centered affine trifocal tensor contains 12 coefficients and involves linear relations between point correspondences and trilinear relations between line correspondences It is shown how the affine trifocal tensor relates to the perspective trilinear tensor, and how three-dimensional motion can be computed from this tensor in a straightforward manner. A factorization approach is also developed to handle point features and line features simultaneously in image sequences.This theory is applied to a specific problem of human-computer interaction of capturing three-dimensional rotations from gestures of a human hand. A qualitative model is presented, in which three fingers are represented by their position and orientation, and it is shown how three point correspondences (blobs at the finger tips) and three line correspondences (ridge features at the fingers) allow the affine trifocal tensor to be determined, from which the rotation is computed. Besides the obvious application, this test problem illustrates the usefulness of the affine trifocal tensor in a situation where sufficient information is not available to compute the perspective trilinear tensor, while the geometry requires point correspondences as well as line correspondences over at least three views.
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