Publications of Wolfgang Effelsberg

Sorted by Year

[2018] [2017] [2016] [2015] [2014] [2013] [2012] [2011] [2010] [2009] [2008] [2007] [2006] [2005] 2004 [2003] [2002] [2001] [2000] [1999] [1998] [1997] [1996] [1995] [1994] [1993] [1992] [1991] [1990] [1988] [1987] [1986] [1985] [1984] [1983] [1981] [1980] [1979]

Artikel

  • Martin Mauve, Jürgen Vogel, Volker Hilt und Wolfgang Effelsberg. 2004 Local-lag and Timewarp : Providing Consistency for Replicated Continuous Applications IEEE Transactions on Multimedia, 6, 2, 47-57
    In this paper we investigate how consistency can be established for replicated applications changing their state in reaction to user-initiated operations as well as the passing of time. Typical examples of these applications are networked computer games and distributed virtual environments. We give a formal definition of the terms consistency and correctness for this application class. Based on these definitions, it is shown that an important tradeoff relationship exists between the responsiveness of the application and the appearance of short-term inconsistencies. We propose to exploit the knowledge of this tradeoff by voluntarily decreasing the responsiveness of the application in order to eliminate short-term inconsistencies. This concept is called local-lag. Furthermore, a timewarp scheme is presented that complements local-lag by guaranteeing consistency and correctness for replicated continuous applications. The computational complexity of the timewarp algorithm is determined in theory and practice by examining a simple networked computer game. The timewarp scheme is then compared to the well-known dead-reckoning approach. It is shown that the choice between both schemes is application-dependent.
  • Roy Pea, Michael Mills, Joseph Rosen, Kenneth Dauber, Wolfgang Effelsberg und Eric Hoffert. 2004 The DIVER Project : Interactive Digital Video Repurposing IEEE MultiMedia, 11, 2, 54-61

Konferenz Beitrag

  • Dirk Farin, Susanne Krabbe, Wolfgang Effelsberg und Peter H. N. de With. SPIE, 2004 Robust Camera Calibration for Sport Videos using Court Models Proceedings of SPIE. Bellingham, WAWe propose an automatic camera calibration algorithm for court sports. The obtained camera calibration parameters are required for applications that need to convert positions in the video frame to real-world coordinates or vice versa. Our algorithm uses a model of the arrangement of court lines for calibration. Since the court model can be specified by the user, the algorithm can be applied to a variety of different sports. The algorithm starts with a model initialization step which locates the court in the image without any user assistance or a-priori knowledge about the most probable position. Image pixels are classified as court line pixels if they pass several tests, including color and local texture constraints. A Hough transform is applied to extract line elements, forming a set of court line candidates. The subsequent combinatorial search establishes correspondences between lines in the input image and lines from the court model. For the succeeding input frames, an abbreviated calibration algorithm is used that predicts the camera parameters for the new image and optimizes them using a gradient-descent algorithm. We have conducted experiments on a variety of sport videos (tennis, volleyball, and goal area sequences of soccer games). Video scenes with considerable difficulties were selected to test the robustness of the algorithm. Results show that the algorithm is very robust to occlusions, partial court views, bad lighting conditions, or shadows.
  • Dirk Farin, Peter H. N. de With und Wolfgang Effelsberg. SPIE, 2004 Minimizing MPEG-4 Sprite Coding-Cost Using Multi-Sprites . San Jose, Calif.Object-oriented coding in the MPEG-4 standard enables the separate processing of foreground objects and the scene background (sprite). Since the background sprite only has to be sent once, transmission bandwidth can be saved. This paper shows that the concept of merging several views of a non-changing scene background into a single background sprite is usually not the most efficient way to transmit the background image. We have found that the counter-intuitive approach of splitting the background into several independent parts can reduce the overall amount of data. For this reason, we propose an algorithm that provides an optimal partitioning of a video sequence into independent background sprites (a multi-sprite), resulting in a significant reduction of the involved coding cost. Additionally, our algorithm results in background sprites of better quality by ensuring that the sprite resolution has at least the final display resolution throughout the sequence. Even though our sprite generation algorithm creates multiple sprites instead of a single background sprite, it is fully compatible with the existing MPEG-4 standard. The algorithm has been evaluated with several test-sequences, including the well-known Table-tennis and Stefan sequences. We were able to reduce the total coding cost by factors of about 2.7 or even higher.
  • Holger Füßler, Hannes Hartenstein, Jörg Widmer und Wolfgang Effelsberg. TUHH, 2004 Contention-Based Forwarding for Street Scenarios . Hamburg
  • Stephan Kopf, Thomas Haenselmann, Dirk Farin und Wolfgang Effelsberg. SPIE, 2004 Automatic Generation of Summaries for the Web Proceedings of SPIE. Bellingham, Wash.Many TV broadcasters and film archives are planning to make their collections available on the Web. However, a major problem with large film archives is the fact that it is difficult to search the content visually. A video summary is a sequence of video clips extracted from a longer video. Much shorter than the original, the summary preserves its essential messages. Hence, video summaries may speed up the search significantly. Videos that have full horizontal and vertical resolution will usually not be accepted on the Web, since the bandwidth required to transfer the video is generally very high. If the resolution of a video is reduced in an intelligent way, its content can still be understood. We introduce a new algorithm that reduces the resolution while preserving as much of the semantics as possible. In the MoCA (movie content analysis) project at the University of Mannheim we developed the video summarization component and tested it on a large collection of films. In this paper we discuss the particular challenges which the reduction of the video length poses, and report empirical results from the use of our summarization tool.
  • Stephan Kopf, Thomas Haenselmann, Dirk Farin und Wolfgang Effelsberg. IEEE Operations Center, 2004 Automatic generation of video summaries for historical films . Piscataway, NJA video summary is a sequence of video clips extracted from a longer video. Much shorter than the original, the summary preserves its essential messages. In the ECHO (European Chronicles On-line) project, a system was developed to store and manage large collections of historical films for the preservation of cultural heritage. At the University of Mannheim, we have developed the video summarization component of the ECHO system. We discuss the particular challenges the historical film material poses, and how we have designed new video processing algorithms and modified existing ones to cope with noisy black-and-white films.
  • Ralf Schmitz, Hannes Hartenstein, Telemaco Melia, Xavier Perez-Costa und Wolfgang Effelsberg. Ges. für Informatik, 2004 Der Einfluss von Schwankungen der Übertragungsweite auf die Leistungsfähigkeit von Ad Hoc Netzwerken GI-Edition : Lecture Notes in Informatics. Proceedings. BonnDie Leistungsfähigkeit eines drahtlosen, mobilen Ad-Hoc Netzwerkes wird im wesentlichen durch die Fähigkeit der Protokolle bestimmt, auf Änderungen der Netzwerktopologie effektiv zu reagieren. Die für diese Netzwerke charakteristische Eigenschaft der Dynamik in der Netztopologie basiert im wesentlichen auf der Mobilität der Knoten und auf Schwankungen der Funkreichweite. Während der Mobilitätsaspekt bereits umfassend untersucht wurde, werden die Eigenschaften des drahtlosen Mediums in Modellen meist idealisiert mittels konstantem Funkradius evaluiert. Solche Ergebnisse werden den tatsächlichen Begebenheiten, wie Erfahrungen in Feldtests belegen, nicht gerecht. In dieser Arbeit untersuchen wir den Einfluss von Mobilität, von zeitabhängigen Schwankungen der Übertragungsreichweite und der Kombination beider Faktoren auf die Netzwerk-Leistungsmerkmale Topologieänderungsrate (Topological Change Rate, TCR) und Linkstabilität. Die temporären Fluktuationen des Funkradius werden mittels eines Gauss-Markov Prozesses erster Ordnung modelliert, während die Auswirkungen der Mobilität basierend auf dem Random Waypoint Mobilitätsmodell untersucht werden. Die Ergebnisse unserer vergleichenden Simulationsstudie zeigen, dass Fluktuationen der Übertragungsreichweite zusätzlich zur Mobilität die Leistungsmetriken eines Ad-Hoc Netzwerkes erheblich beeinflussen. Daher empfehlen wir, Fluktuationen der Radiowellenausbreitung bei dem Entwurf von Ad-Hoc Protokollen und Ad-Hoc Modellierung nicht zu vernachlässigen.
  • Matthias Transier, Holger Füßler, Thomas Butter und Wolfgang Effelsberg. Ges. für Informatik, 2004 Implementation of the SPBM Routing Protocol for the Linux Kernel . Bonn

Forschungs Papier

  • Stephan Kopf, Thomas Haenselmann und Wolfgang Effelsberg. , . 2004 Automatic Generation of Video Summaries for Historical Films , .
    A video summary is a sequence of video clips extracted from a longer video. Much shorter than the original, the summary preserves its essential messages. In the project ECHO (European Chronicles On-line) a system was developed to store and manage large collections of historical films for the preservation of cultural heritage. At the University of Mannheim we have developed the video summarization component of the ECHO system. In this paper we discuss the particular challenges the historical film material poses, and how we have designed new video processing algorithms and modified existing ones to cope with noisy black-and-white films. We also report empirical results from the use of our summarization tool at the four major European national video archives.
  • Matthias Transier, Holger Füßler, Jörg Widmer, Martin Mauve und Wolfgang Effelsberg. , Technical Reports. 2004 A Hierarchical Approach to Position-Based Multicast for Mobile Ad-hoc Networks Mannheim, . 04-002
    In this paper we present Scalable Position-Based Multicast (SPBM), a multicast routing protocol for ad-hoc networks. SPBM uses the geographic position of nodes to provide a highly scalable group membership scheme and to forward data packets in a way that is very robust to changes in the topology of the network. SPBM bases the forwarding decision on whether there are group members located in a given direction or not, allowing for a hierarchical aggregation of membership information: the further away a region is from an intermediate node the higher the level of aggregation should be for this region. Because of aggregation, the overhead for group membership management scales logarithmically with the number of nodes and is independent of the number of multicast senders for a given multicast group. Furthermore, we show that group management overhead is bounded by a constant if the frequency of membership updates is scaled down with the aggregation level. This scaling of the update frequency is reasonable since the higher the level of aggregation the lower the number of membership changes for the aggregate. The performance of SPBM is investigated by means of simulation, including a comparison with ODMRP, and through mathematical analysis. We also describe an open source kernel implementation of SPBM that has been successfully deployed on hand-held computers.
[2018] [2017] [2016] [2015] [2014] [2013] [2012] [2011] [2010] [2009] [2008] [2007] [2006] [2005] 2004 [2003] [2002] [2001] [2000] [1999] [1998] [1997] [1996] [1995] [1994] [1993] [1992] [1991] [1990] [1988] [1987] [1986] [1985] [1984] [1983] [1981] [1980] [1979]