| 1. |
- Lindeberg, Tony, 1964-, et al.
(författare)
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Analysis of brain activation patterns using a 3-D scale-space primal sketch
- 1999
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Ingår i: Human Brain Mapping. - 1065-9471 .- 1097-0193. ; 7:3, s. 166-94
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Tidskriftsartikel (refereegranskat)abstract
- A fundamental problem in brain imaging concerns how to define functional areas consisting of neurons that are activated together as populations. We propose that this issue can be ideally addressed by a computer vision tool referred to as the scale-space primal sketch. This concept has the attractive properties that it allows for automatic and simultaneous extraction of the spatial extent and the significance of regions with locally high activity. In addition, a hierarchical nested tree structure of activated regions and subregions is obtained. The subject in this article is to show how the scale-space primal sketch can be used for automatic determination of the spatial extent and the significance of rCBF changes. Experiments show the result of applying this approach to functional PET data, including a preliminary comparison with two more traditional clustering techniques. Compared to previous approaches, the method overcomes the limitations of performing the analysis at a single scale or assuming specific models of the data.
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| 2. |
- Eriksson, Patric, et al.
(författare)
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A role for 'sensor simulation' and 'pre-emptive learning' in computer aided robotics
- 1995
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Ingår i: 26th International Symposium on Industrial Robots, Symposium Proceedings. - : Mechanical Engineering Publ.. - 1860580009 ; , s. 135-140
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Konferensbidrag (refereegranskat)abstract
- Sensor simulation in Computer Aided Robotics (CAR) can enhance the capabilities of such systems to enable off-line generation of programmes for sensor driven robots. However, such sensor simulation is not commonly supported in current computer aided robotic environments. A generic sensor object model for the simulation of sensors in graphical environments is described in this paper. Such a model can be used to simulate a variety of sensors, for example photoelectric, proximity and ultrasonic sensors. Tests results presented here show that this generic sensor model can be customised to emulate the characteristics of the real sensors. The preliminary findings from the first off-line trained mobile robot are presented. The results indicate that sensor simulation within CARs can be used to train robots to adapt to changing environments.
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| 3. |
- Lindeberg, Tony, 1964-, et al.
(författare)
-
Scale-space with causal time direction
- 1996
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Konferensbidrag (refereegranskat)abstract
- This article presents a theory for multi-scale representation of temporal data. Assuming that a real-time vision system should represent the incoming data at different time scales, an additional causality constraint arises compared to traditional scale-space theory—we can only use what has occurred in the past for computing representations at coarser time scales. Based on a previously developed scale-space theory in terms of noncreation of local maxima with increasing scale, a complete classification is given of the scale-space kernels that satisfy this property of non-creation of structure and respect the time direction as causal. It is shown that the cases of continuous and discrete time are inherently different.
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| 4. |
- Bretzner, Lars, et al.
(författare)
-
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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| 5. |
- Bretzner, Lars, et al.
(författare)
-
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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| 6. |
- Lindeberg, Tony, 1964-, et al.
(författare)
-
Förfarande och anordning för överföring av information genom rörelsedetektering, samt användning av anordningen : [Method and arrangement for controlling means for three-dimensional transfer of information by motion detection]
- 1998
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Patent (populärvet., debatt m.m.)abstract
- The invention concerns a method and an arrangement for controlling means (24, 26), themselves controlled by processors, for three-dimensional transfer of information by motion detection using an image capturing device (20). Features of an object (10) are detected and transferred to line and point correspondences, which are used for controlling means (22, 26) to perform rotational and translational motion.
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| 7. |
- Bretzner, Lars, et al.
(författare)
-
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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| 8. |
- 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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| 9. |
- Lindeberg, Tony, 1964-, et al.
(författare)
-
Automatic generation of break points for MDL based curve classification
- 1995
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Ingår i: Scandinavian Conference on Image Analysis. ; , s. 767-776
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Konferensbidrag (refereegranskat)abstract
- This article presents a method for segmenting and classifying edges using minimum description length (MDL) approximation with automatically generated break points. A scheme is proposed where junction candidates are first detected in a multi-scale pre-processing step, which generates junction candidates with associated regions of interest. These junction features are matched to edges based on spatial coincidence. For each matched pair, a tentative break point is introduced at the edge point closest to the junction. Finally, these feature combinations serve as input for an MDL approximation method which tests the validity of the break point hypotheses and classifies the resulting edge segments as either ``straight'' or ``curved''. Experiments on real world image data demonstrate the viability of the approach.
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| 10. |
- Lindeberg, Tony, 1964-
(författare)
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Direct estimation of affine image deformations using visual front-end operations with automatic scale selection
- 1995
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Ingår i: Proc. 5th International Conference on Computer Vision. - : IEEE Computer Society. ; , s. 134-141
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Konferensbidrag (refereegranskat)abstract
- This article deals with the problem of estimating deformations of brightness patterns using visual front-end operations. Estimating such deformations constitutes an important subtask in several computer vision problems relating to image correspondence and shape estimation. The following subjects are treated: The problem of decomposing affine flow fields into simpler components is analysed in detail. A canonical parametrization is presented based on singular value decomposition, which naturally separates the rotationally invariant components of the flow field from the rotationally variant ones. A novel mechanism is presented for automatic selection of scale levels when estimating local affine deformations. This mechanism is expressed within a multi-scale framework where disparity estimates are computed in a hierarchical coarse-to-fine manner and corrected using iterative techniques. Then, deformation estimates are selected from the scales that minimize a certain normalized residual over scales. Finally, the descriptors so obtained serve as initial data for computing refined estimates of the local deformations.
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