| 291. |
- Lindström, Johan, et al.
(författare)
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Background and Foreground Modeling Using an Online EM Algorithm
- 2006
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Ingår i: IEEE International Workshop on Visual Surveillance. ; VS2006, s. 9-16
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Konferensbidrag (refereegranskat)abstract
- A novel approach to background/foreground segmentation using an online EM algorithm is presented. The method models each layer as a Gaussian mixture, with local, per pixel, parameters for the background layer and global parameters for the foreground layer, utilising information from the entire scene when estimating the foreground. Additionally, the online EM algorithm uses a progressive learning rate where the relative update speed of each Gaussian component depends on how often the component has been observed. It is shown that the progressive learning rate follows naturally from introduction of a forgetting factor in the log-likelihood. To reduce the number of mixture components similar foreground components are merged using a method based on the Kullback-Leibler distance. A bias is introduced in the variance estimates to avoid the known problem of singularities in the log-likelihood of Gaussian mixtures when the variance tends to zero. To allow a decoupling of the learning rate of the Gaussian components and the speed at which stationary objects are incorporated into the background a CUSUM detector is used instead of the prevailing method that uses the ratio of prior probability to standard deviation. The algorithm is scale invariant and its properties on gray-scale and RGB videos, as well as on output from an edge detector, is compared to that of another algorithm. Especially for the edge detector video performance increases dramatically.
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| 292. |
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| 293. |
- Lomsky, Milan, 1948, et al.
(författare)
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A new automated method for analysis of gated-SPECT images based on a three-dimensional heart shaped model
- 2005
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Ingår i: Clin Physiol Funct Imaging. - 1475-0961. ; 25:4, s. 234-40
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Tidskriftsartikel (refereegranskat)abstract
- A new automated method for quantification of left ventricular function from gated-single photon emission computed tomography (SPECT) images has been developed. The method for quantification of cardiac function (CAFU) is based on a heart shaped model and the active shape algorithm. The model contains statistical information of the variability of left ventricular shape. CAFU was adjusted based on the results from the analysis of five simulated gated-SPECT studies with well defined volumes of the left ventricle. The digital phantom NURBS-based Cardiac-Torso (NCAT) and the Monte-Carlo method SIMIND were used to simulate the studies. Finally CAFU was validated on ten rest studies from patients referred for routine stress/rest myocardial perfusion scintigraphy and compared with Cedar-Sinai quantitative gated-SPECT (QGS), a commercially available program for quantification of gated-SPECT images. The maximal differences between the CAFU estimations and the true left ventricular volumes of the digital phantoms were 11 ml for the end-diastolic volume (EDV), 3 ml for the end-systolic volume (ESV) and 3% for the ejection fraction (EF). The largest differences were seen in the smallest heart. In the patient group the EDV calculated using QGS and CAFU showed good agreement for large hearts and higher CAFU values compared with QGS for the smaller hearts. In the larger hearts, ESV was much larger for QGS than for CAFU both in the phantom and patient studies. In the smallest hearts there was good agreement between QGS and CAFU. The findings of this study indicate that our new automated method for quantification of gated-SPECT images can accurately measure left ventricular volumes and EF.
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| 294. |
- Lundh, Michael, et al.
(författare)
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Automatic Initialization of a Robust Self-Tuning Controller
- 1994
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Ingår i: Automatica. - : Elsevier BV. - 0005-1098. ; 30:11, s. 1649-1662
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes a method for automatically initializing a self-tuning controller. The procedure can be used for systems that are adequately described by models of at most third-order with time delay. For this class of systems it gives a self-tuner that can be initialized simply by pushing a button.
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| 295. |
- Lundh, Magnus, et al.
(författare)
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Model optimization for autotuners in industrial control systems
- 2021
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Ingår i: Proceedings of the 26th International Conference on Emerging Technologies and Factory Automation (ETFA). - 9781728129891 ; , s. 1-4
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Konferensbidrag (refereegranskat)abstract
- Automatic tuning of PID controllers using relay feedback experiments has received attention on and off since it was first proposed and industrially implemented in a control system in the 1980s. While optimal experiment design and modern system identification easily outperform the original automatic tuner, they rely on computational resources that are not always available in industrial control systems. Here we present a combination of experiment and subsequent output-error identification of continuoustime first-order time-delayed (FOTD) system models, that requires very little in terms of computations and memory. The method has been extensively evaluated in simulation, and a prototype has been implemented for the ABB AC 800M controller family.
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| 296. |
- Lunsjö, Karl, et al.
(författare)
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A new radiographic method for evaluating the degree of sliding in devices used in hip-fracture surgery
- 1997
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Ingår i: Acta Radiologica. - 0284-1851. ; 38:6, s. 1057-1062
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To find a practical method for estimating the degree of sliding that occurs in screw-plate devices used in hip-fracture surgery. Greater understanding of the sliding mechanisms in different fracture types should improve surgical technique and reduce the failure rate. Methods and Results: In dynamic screw-plate devices, the lag screw slides inside the barrel of the plate. A recent innovation allows the barrel-plate to slide inside a side-plate, thus making possible a combined fracture compression along the neck and the shaft of femur. The lengths of the different parts and the angle of a device in vivo, measured on a radiograph, depend on the position of the femur relative to the photographic film and the roentgen source. We obtained these measurements with a ruler and a protractor from sequential a.p. radiographs of the hip and implemented them in a special computerized program that used the principles of the scaled orthographic and the central projection models. These calculations provided the correct amount of sliding by the lag screw and by the barrel-plate within the side-plate. Conclusion: The method presented here can establish the real degree of sliding in screw-plate devices from standard a.p. radiographs independently of the position of the hip.
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| 297. |
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| 298. |
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