| 1. |
- Ardö, Håkan, et al.
(författare)
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Bayesian Formulation of Image Patch Matching Using Cross-correlation
- 2009
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Ingår i: 2009 Third ACM/IEEE International Conference on Distributed Smart Cameras (ICDSC). - 9781424446209 ; , s. 92-99
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Konferensbidrag (refereegranskat)abstract
- A classical solution for matching two image patches is to use the cross-correlation coefficient. This works well if there is a lot of structure within the patches, but not so well if the patches are close to uniform. This means that some patches are matched with more confidence than others. By estimating this uncertainty more weight can be put on the confident matches than those that are more uncertain. In this paper we present a system that can learn the distribution of the correlation coefficient from a video sequence of an empty scene. No manual annotation of the video is needed. Two distributions functions are learned for two different cases: i) the correlation between an estimated background image and the current frame showing that background and ii) the correlation between an estimated background image and an unrelated patch. Using these two distributions the patch matching problem is formulated as a binary classification problem and the probability of two patches matching is derived. The model depends on the signal to noise ratio. The noise level is reasonably invariant over time, while the signal level, represented by the amount of structure in the patch or it's spatial variance, has to be measured for every frame. A common application where this is useful is feature point matching between different images. Another application is background/foreground segmentation. In this paper it is shown how the theory can be used to implement a very fast background/foreground segmentation by transforming the calculations to the DCT-domain and processing a motion JPEG stream without uncompressing it. This allows the algorithm to be embedded on a 150MHz ARM based network camera. It is also suggested to use recursive quantile estimation to estimate the background model. This gives very accurate background models even if there is a lot of foreground present during the initialisation of the model.
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| 2. |
- Ardö, Håkan, et al.
(författare)
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Foreground Estimation and Hidden Markov Models for Tracking
- 2005
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- We will give a short introduction to foreground/background estimation and Hidden Markov fortracking. More information about the topics can be found in the papers listed at the end.
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| 3. |
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| 4. |
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| 5. |
- Ardö, Håkan, et al.
(författare)
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Real time viterbi optimization of hidden Markov Models for multi target tracking
- 2007
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Ingår i: 2007 IEEE Workshop on Motion and Video Computing (WMVC'07). - 0769527930
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Konferensbidrag (refereegranskat)abstract
- In this paper the problem of tracking multiple objects in image sequences is studied. A Hidden Markov Model describing the movements of multiple objects is presented. Previously similar models have been used, but in real time system the standard dynamic programming Viterbi algorithm is typically not used to find the global optimum state sequence, as it requires that all past and future observations are available. In this paper we present an extension to the Viterbi algorithm that allows it to operate on infinite time sequences and produce the optimum with only a finite delay. This makes it possible to use the Viterbi algorithm in real time applications. Also, to handle the large state spaces of these models another extension is proposed. The global optimum is found by iteratively running an approximative algorithm with higher and higher precision. The algorithm can determine when the global optimum is found by maintaining an upper bound on all state sequences not evaluated. For real time performance some approximations are needed and two such approximations are suggested. The theory has been tested on three real data experiments, all with promising results.
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| 6. |
- Block, Daniel Jerome, et al.
(författare)
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The Reaction Wheel Pendulum
- 2007
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Bok (övrigt vetenskapligt/konstnärligt)abstract
- "This monograph describes the Reaction Wheel Pendulum, the newest inverted-pendulum-like device for control education and research. We discuss the history and background of the reaction wheel pendulum and other similar experimental devices. We develop mathematical models of the reaction wheel pendulum in depth, including linear and nonlinear models, and models of the sensors and actuators that are used for feedback control. We treat various aspects of the control problem, from linear control of the motor, to stabilization of the pendulum about an equilibrium configuration using linear control, to the nonlinear control problem of swingup control. This monograph can be used as a supplement for courses in feedback control at the undergraduate level, courses in mechatronics, or courses in linear and nonlinear state space control at the graduate level. It can also be used as a laboratory manual and as a reference for research in nonlinear control."
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| 7. |
- Burgner, Chris, et al.
(författare)
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Digital Control of Tunneling Accelerometer
- 2009
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Ingår i: 2009 IEEE Sensors. ; , s. 1824-1827
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Konferensbidrag (refereegranskat)abstract
- A controller for a tunneling accelerometer has two tasks: to establish tunneling and to maintain tunneling during acceleration. This paper describes the design and implementation of a digital controller that accomplishes these tasks and provides the appropriate gain switching. The control law is based on a standard configuration of an observer and state feedback. A digital controller is implemented because the controller parameters can be easily adjusted, thereby allowing for rapid prototyping. The design methodology presented here can be used as a general plug-and-play controller platform for a range of MEMS sensors. The performance of the digital controller is illustrated experimentally using metrics such as tracking response, drift, noise floor and response linearity.
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| 8. |
- Byröd, Martin, et al.
(författare)
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A Column-Pivoting Based Strategy for Monomial Ordering in Numerical Gröbner Basis Calculations
- 2008
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Ingår i: Lecture Notes in Computer Science. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 1611-3349 .- 0302-9743. ; 5305, s. 130-143
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Konferensbidrag (refereegranskat)abstract
- This paper presents a new fast approach to improving stability in polynomial equation solving. Gröbner basis techniques for equation solving have been applied successfully to several geometric computer vision problems. However, in many cases these methods are plagued by numerical problems. An interesting approach to stabilising the computations is to study basis selection for the quotient space C[x]/I . In this paper, the exact matrix computations involved in the solution procedure are clarified and using this knowledge we propose a new fast basis selection scheme based on QR-factorization with column pivoting. We also propose an adaptive scheme for truncation of the Gröbner basis to further improve stability. The new basis selection strategy is studied on some of the latest reported uses of Gröbner basis methods in computer vision and we demonstrate a fourfold increase in speed and nearly as good overall precision as the previous SVD-based method. Moreover, we get typically get similar or better reduction of the largest errors.
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| 9. |
- Byröd, Martin, et al.
(författare)
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Bundle Adjustment using Conjugate Gradients with Multiscale Preconditioning
- 2009
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Ingår i: British Machine Vision Conference.
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Konferensbidrag (refereegranskat)abstract
- Bundle adjustment is a key component of almost any feature based 3D reconstruction system, used to compute accurate estimates of calibration parameters and structure and motion configurations. These problems tend to be very large, often involving thousands of variables. Thus, efficient optimization methods are crucial. The traditional Levenberg Marquardt algorithm with a direct sparse solver can be efficiently adapted to the special structure of the problem and works well for small to medium size setups. However, for larger scale configurations the cubic computational complexity makes this approach pro- hibitively expensive. The natural step here is to turn to iterative methods for solving the normal equations such as conjugate gradients. So far, there has been little progress in this direction. This is probably due to the lack of suitable pre-conditioners, which are con- sidered essential for the success of any iterative linear solver. In this paper, we show how multi scale representations, derived from the underlying geometric layout of the problem, can be used to dramatically increase the power of straight forward preconditioners such as Gauss-Seidel.
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| 10. |
- Byröd, Martin, et al.
(författare)
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Fast and Robust Numerical Solutions to Minimal Problems for Cameras with Radial Distortion
- 2008
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Ingår i: [Host publication title missing]. ; , s. 2586-2593
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Konferensbidrag (refereegranskat)abstract
- A number of minimal problems of structure from motion for cameras with radial distortion have recently been studied and solved in some cases. These problems are known to be numerically very challenging and in several cases there exist no known practical algorithm yielding solutions in floating point arithmetic. We make some crucial observations concerning the floating point implementation of Gröbner basis computations and use these new insights to formulate fast and stable algorithms for two minimal problems with radial distortion previously solved in exact rational arithmetic only: (i) simultaneous estimation of essential matrix and a common radial distortion parameter for two partially calibrated views and six image point correspondences and (ii) estimation of fundamental matrix and two different radial distortion parameters for two uncalibrated views and nine image point correspondences. We demonstrate on simulated and real experiments that these two problems can be efficiently solved in floating point arithmetic.
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