Publications of Wolfgang Effelsberg

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Martin Mauve, Hannes Hartenstein, Holger Füßler, Jörg Widmer und Wolfgang Effelsberg. 2002 Positionsbasiertes Routing für die Kommunikation zwischen Fahrzeugen Informationstechnik und technische Informatik : it + ti, 44, 2, 278-286
In the near future communication between vehicles by means of wireless technology will enhance both safety and comfort of the passengers. One main challenge in realizing this communication will be the routing of messages from one sender to one or more receivers. In this paper we propose a position-based ad-hoc routing protocol which solves this problem. In this protocol all vehicles work together, thus no pre-established infrastructure is required. As a consequence, the resulting network is inexpensive and robust. In order to prove the viability of the approach, a simulation study was performed using the ns-2 network simulator. As a basis for this study realistic car movement patterns were used. The study shows that even over large distances requiring message forwarding by multiple vehicles, high success rates for the delivery of messages are achieved.

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Dirk Farin, Wolfgang Effelsberg und Peter H. N. de With. IEEE Press, 2002 Robust Clustering-Based Video-Summarization with Integration of Domain-Knowledge . Washington, DCClustering techniques have been widely used in automatic video-summarization applications to group shots with comparable content. We enhance the popular k-means clustering algorithm to integrate user-supplied domain-knowledge into the cluster generation step. This provides a convenient way to exclude scenes from the summary which are a-priori known to be irrelevant. Furthermore, we added an additional, time-constrained clustering step preceding the scene clustering step to exclude short ranges with transitional content. This makes the algorithm robust to fading and wipe-effects in the input without requiring explicit cut detection.
Dirk Farin, Michael Käsemann, Peter H. N. de With und Wolfgang Effelsberg. Werkgemeenschap voor Informatie- en Communicatietheorie, 2002 Rate-Distortion Optimal Adaptive Quantization and Coefficient Thresholding for MPEG Coding . EnschedeThis paper presents an MPEG-2 compatible adaptive quantization algorithm that leads to the optimal encoding of I-frames in the sense of maximizing PSNR. It integrates three key features into a single Lagrangian optimization model: adaptive quantization including quantizer-change overhead consideration, coefficient thresholding, and a new coefficient amplitude reduction technique. Our results show that I-frames generated by the TM5 reference encoder are about 1.5-2.0 dB below the theoretical optimum.
Thomas Haenselmann und Wolfgang Effelsberg. SPIE Press, 2002 Texture Resynthesis Using Principle Component Analysis Proceedings of SPIE. Bellingham, Wash.Today's lossless image compression algorithms are not well optimized for high frequency components. These occure especially in textured regions of and image and make image compression ineffective. On the other hand the high demand of storage is not justified since the human visual system perceives texture with regard to it's general structure while omitting specific details. Rather than storing textured parts of an image we present a method for analyzing (in the source image) and resynthesizing (in the decompressed target image) textured regions with regard to it's structural appearance. First we define image blocks in a way that they cover regions with homogenious texture in the source image. These blocks are transformed each in turn. For the transform we use the Karhunen-Loève transform. After the transform into the new domain we statistically analyze the resulting coefficients. For resynthesizing new texture we generate random numbers that exactly meet these statistics. Using the inverse KL-transform the random coefficients are finally transformed back into the spatial domain. The visual appearance of the resulting artificial texture matches the original to a very high degree.
Thomas Haenselmann und Wolfgang Effelsberg. SPIE, 2002 Wavelet-based Semi-automatic Live-wire Segmentation Proceedings of SPIE. Bellingham, Wash.The live-wire approach is a well-known algorithm based on a graph search to locate boundaries for image segmentation. We will extend the original cost function, which is solely based on finding strong edges, so that the approach can take a large variety of boundaries into account. The cost function adapts to the local characteristics of a boundary by analyzing a user-defined sample using a continuous wavelet decomposition. We will finally extend the approach into 3D in order to segment objects in volumetric data, e. g., from medical CT and MR scans.
Gerald Kühne, Joachim Weickert, Markus Beier und Wolfgang Effelsberg. Springer, 2002 Fast Implicit Active Contour Models Lecture Notes in Computer Science. Heidelberg [u.a.]Implicit active contour models are widely used in image processing and computer vision tasks. Most implementations, however, are based on explicit updating schemes and are therefore of limited computational efficiency. In this paper, we present fast algorithms based on the semi-implicit additive operator splitting (AOS) scheme for both the geometric and the geodesic active contour model. Our experimental results with synthetic and real-world images demonstrate that AOS-based implementations clearly outperform their explicit counterparts.
Martin Mauve, Nicolai Scheele, Werner Geyer und Wolfgang Effelsberg. Optimization Software, 2002 Ubiquitous Computing in Education . New York, NY [u.a.]
Claudia Schremmer, Wolfgang Effelsberg, Jean-Claude Grattarola und Edoardo Berera. net4net [u.a.], 2002 A Novel Student Cooperation Across Country Borders . Berne [u.a.]In the winter term 2001/02, the universities of Mannheim/Germany and Nice/France have invented a new form of student cooperation on a tele-seminar basis. Our international tele-seminar on e-commerce encompassed a joint introductory week in Nice, cooperative student work in bi-national teams during the winter term, and a concluding joint week in Mannheim with a presentation of the groups' results. Twelve students of each university were selected to participate at this seminar. Since it could not be expected from neither side to master the other's language, the common language was defined to be English. In this paper we describe the set-up of the tele-seminar and its technical, peda-gogic, and cultural issues for the students and their teachers.

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Nicolai Scheele, Martin Mauve, Wolfgang Effelsberg, Anja Wessels und Stefan Fries. , Technical report. 2002 The Interactive Lecture: A new Teaching Paradigm based on Ubiquitous Computing Mannheim, . 02-006
In this paper we present a new teaching paradigm based on ubiquitous computing, which we call the Interactive Lecture. It specifically supports situations where the interactivity between students and lecturer is usually limited, such as lectures with a large number of students, or teleteaching scenarios. In an Interactive Lecture each student is equipped with a handheld computer. These computers connect to the computer of the lecturer via wireless communication. Interactivity between students and lecturer is then increased by a number of services. Examples for these services are: online-feedback which enables students to give immediate feedback about the lecture (e.g., about its speed and difficulty), or online-quizzes were all students participate in solving problems described by the lecturer. We have developed a first prototype of the software and performed a thorough evaluation during a graduate course. The results of this evaluation indicate that interactivity was increased significantly and that the students were very enthusiastic about participating in Interactive Lectures in the future.

Publications of Wolfgang Effelsberg

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