Stephan Kopf

Titel: PD Dr. rer. nat.

Office: B 220

Office hours: Tuesdays, 12:00 - 13:00 p.m. in room A5, B220

Phone: +49 621 181-2613, Fax: +49 621 181-2601

Email: kopf@pi4.informatik.uni-mannheim.de

Interests

  • Video content analysis
  • Computer vision
  • Computer graphics
  • Multimedia applications

 Specific research areas

  • Video retargeting
  • Digital watermarking for multimedia content
  • High dynamic range videos
  • Object recognition
  • New learning technologies

Curriculum vitae

Dr. Stephan Kopf received the M.Sc. degree in business informatics (2000) and the Ph.D. degree in computer science (2007) both from the University of Mannheim (Germany). He finished his 'habilitation' (postdoctoral lecture qualification) on 'Algorithms for Image and Video Processing' in 2012 and is currently working as senior researcher and lecturer at the multimedia department at the University of Mannheim. His research interests focus on multimedia content analysis, media retargeting, high dynamic range videos, shape-based object recognition, and digital watermarking for videos. He has published over 50 refereed journal and conference papers in these fields. Dr. Kopf is initiator and co-editor of the ACM SIG Multimedia Records and the ACM SIGMM eNewsletter. He serves on the program committee of several conferences and workshops, and is initiator and co-chair of several workshops.

Publications

2016

  • Daniel Schön, Melanie Klinger, Stephan Kopf and Wolfgang Effelsberg. SCITEPRESS, 2016 Customized teaching scenarios for smartphones in university lecture settings : experiences with several teaching scenarios using the MobileQuiz2 . Setubal, PortugalMany teachers use Audience Response Systems (ARS) in lectures to re-activate their listeners and to get an insight in students’ knowledge of the current lecture contents. Plenty of such applications have been developed in recent years, they provide a high variety of different teaching scenarios with the use of the students’ smartphones, including quizzes, lecture feedback and dynamic message boards. We developed a novel application based on an abstract model to enable this variety of customizable teaching scenarios within one application. After presenting the application to the first charge of lecturers, the responses were quite good, and several new teaching scenarios were created and used. This paper presents first experiences when using a variety of customizable teaching scenarios, the special opportunities and challenges as well as the opinions of lecturers and students, which we collected with a survey at the end of the semester.
  • Daniel Schön, Melanie Klinger, Stephan Kopf, Thilo Weigold and Wolfgang Effelsberg. Springer, 2016 Customizable learning scenarios for students’ mobile devices in large university lectures : a next generation audience response system Communications in computer and information science. Cham
  • Stefan Wilk, Stephan Kopf and Wolfgang Effelsberg. 2016 Collaborative annotation of videos relying on weak consistency ACM transactions on multimedia computing, communications, and applications : TOMCCAP, 12, 9, Article 45
  • Mariia Zrianina and Stephan Kopf. , Technical reports. 2016 Classification of iconic images Mannheim, . 16-001
    Iconic images represent an abstract topic and use a presentation that is intuitively understood within a certain cultural context. For example, the abstract topic “global warming” may be represented by a polar bear standing alone on an ice floe. Such images are widely used in media and their automatic classification can help to identify high-level semantic concepts. This paper presents a system for the classification of iconic images. It uses a variation of the Bag of Visual Words approach with enhanced feature descriptors. Our novel color pyramids feature incorporates color information into the classification scheme. It improves the average F1 measure of the classification by 0:117. The performance of our system is further evaluated under a variety of parameters.

2015

  • Simone Paolo Ponzetto, Hartmut Wessler, Lydia Weiland, Stephan Kopf, Wolfgang Effelsberg and Heiner Stuckenschmidt. Peter Lang Edition, 2015 Automatic classification of iconic images based on a multimodal model : an interdisciplinary project Sprache - Medien - Innovationen. Frankfurt am Main ; Bern; Wien
  • Philipp Schaber, Sally Dong, Benjamin Guthier, Stephan Kopf and Wolfgang Effelsberg. ACM, 2015 Modeling temporal effects in re-captured video . New York, NYThe re-capturing of video content poses significant challenges to algorithms in the fields of video forensics, watermarking, and near-duplicate detection. Using a camera to record a video from a display introduces a variety of artifacts, such as geometric distortions, luminance transformations, and temporal aliasing. A deep understanding of the causes and effects of such phenomena is required for their simulation, and for making the affected algorithms more robust. In this paper, we provide a detailed model of the temporal effects in re-captured video. Such effects typically result in the re-captured frames being a blend of the original video's source frames, where the specific blend ratios are difficult to predict. Our proposed parametric model captures the temporal artifacts introduced by interactions between the video renderer, display device, and camera. The validity of our model is demonstrated through experiments with real re-captured videos containing specially marked frames.
  • Philipp Schaber, Stephan Kopf, Sina Wetzel, Tyler Ballast, Christoph Wesch and Wolfgang Effelsberg. 2015 CamMark: Analyzing, Modeling, and Simulating Artifacts in Camcorder Copies ACM transactions on multimedia computing, communications, and applications : TOMM, 11, 10, Article 42, 1-23
    To support the development of any system that includes the generation and evaluation of camcorder copies, as well as to provide a common benchmark for robustness against camcorder copies, we present a tool to simulate digital video re-acquisition using a digital video camera. By resampling each video frame, we simulate the typical artifacts occurring in a camcorder copy: geometric modifications (aspect ratio changes, cropping, perspective and lens distortion), temporal sampling artifacts (due to different frame rates, shutter speeds, rolling shutters, or playback), spatial and color subsampling (rescaling, filtering, Bayer color filter array), and processing steps (automatic gain control, automatic white balance). We also support the simulation of camera movement (e.g., a hand-held camera) and background insertion. Furthermore, we allow for an easy setup and calibration of all the simulated artifacts, using sample/reference pairs of images and videos. Specifically temporal subsampling effects are analyzed in detail to create realistic frame blending artifacts in the simulated copies. We carefully evaluated our entire camcorder simulation system and found that the models we developed describe and match the real artifacts quite well.
  • Daniel Schön, Melanie Klinger, Stephan Kopf and Wolfgang Effelsberg. SCITEPRESS, Science and Technology Publications, 2015 A model for customized in-class learning scenarios - an approach to enhance audience response systems with customized logic and interactivity . [Setúbal]
  • Daniel Schön, Licheng Yang, Melanie Klinger, Stephan Kopf and Wolfgang Effelsberg. Assoc. for the Advancement of Computing in Education , Universität Mannheim 2015 On the effects of different parameters in classroom interactivity systems on students . Waynesville, NCClassroom Response Systems (CRS) are often used in higher education lectures. They help to activate students and to get a deeper insight on the students' knowledge base and on their opinion on currently discussed topics. Many different systems were created, offering a similar amount of functionality. We thus investigate what the important parameters of such systems are, and how they influence the students’ behavior. Therefore, we consider classic response systems as well as systems with a higher amount of interactivity. In a first step, we have defined eight possible parameters, like the usage of pictures or a progress bar. We did a field study in thirty six lectures comparing the impact of the different parameters. As expected, the overall satisfaction with CRS is very high but we have obtained surprising results with particular parameters. We present the most interesting results and give a suggestion on which parameters are useful for an investigation in greater depth.
  • Stefan Wilk, Stephan Kopf and Wolfgang Effelsberg. ACM, 2015 Video composition by the crowd : a system to compose user-generated videos in near real-time . New York, NY

2014

  • Benjamin Guthier, Stephan Kopf, Matthias Wichtlhuber and Wolfgang Effelsberg. 2014 Parallel Implementation of a Real-Time High Dynamic Range Video System Integrated Computer-Aided Engineering : ICAE, 21, 63, 189-202
  • Johannes Kiess, Daniel Gritzner, Benjamin Guthier, Stephan Kopf and Wolfgang Effelsberg. ACM, 2014 GPU Video Retargeting with Parallelized SeamCrop . New York, NY
  • Max Lehn, Tonio Triebel, Robert Rehner, Benjamin Guthier, Stephan Kopf, Alejandro Buchmann and Wolfgang Effelsberg. 2014 On Synthetic Workloads for Multiplayer Online Games: A Methodology for Generating Representative Shooter Game Workloads Multimedia Systems, 20, 52, 609-620
  • Philipp Schaber, Stephan Kopf, Christoph Wesch and Wolfgang Effelsberg. ACM, 2014 CamMark : a camcorder copy simulation as watermarking benchmark for digital video . New York, NYIn 1998, Petitcolas et al. proposed StirMark as a benchmark for image watermarking schemes. The main idea was to introduce a re-sampling process that mimics the analog process of printing and scanning a watermarked image. For digital video, the corresponding concept is a camcorder copy, where a video displayed on a screen is (digitally) recorded using a video camera. As most commercial video streaming systems (VOD, IPTV) and offline distribution (Blu-ray, HDDs for cinemas) are strongly protected by means of DRM, filming a display is actually a relevant use case and a requirement for robust video watermarking systems to survive. We therefore present a tool to simulate content re-acquisition with a camcorder. Our goal is to support watermark development by enabling automated test cases for such camcorder copy attacks, as well as to provide a benchmark for robust video watermarking. Manually creating camcorder copies is a cumbersome process, and even more problematic, it is hardly reproducible with the same setup. By re-sampling each video frame, we simulate the typical artifacts of a camcorder copy: geometric modifications (aspect ratio changes, cropping, perspective and lens distortion), temporal modifications (unsynchronized frame rates and the resulting frame blending), sub-sampling (rescaling, filtering, Bayer color array filter), and histogram changes (AGC, AWB). We also support simulating camera movement (e.g., a hand-held camera) and background insertion.
  • Daniel Schön, Philip Mildner, Stephan Kopf and Wolfgang Effelsberg. Gesellschaft für Informatik, 2014 SMASH: Ein generisches System für interaktive Szenarien in der Vorlesung GI-Edition / Proceedings. Freiburg, Br.
  • Daniel Schön, Steffen Sikora, Stephan Kopf and Wolfgang Effelsberg. RWTH, 2014 GLA: A Generic Analytics Tool for e-Learning CEUR workshop proceedings. AachenSeveral software applications are used at the University of Mannheim for learning and teaching purposes. The majority of them, like lecture feedback, quizzes, forums, and wikis, are hosted within our learning management system ILIAS. In addition, we run several prototypes of serious games and mobile feedback systems. While the data generated by students and teachers is mainly used for current courses, it could be further used for Learning Analytics if it was stored in an adequate format. Considering the variable and fast-moving nature of our learning applications, we invented a concept for a generic database structure, that can handle analyses on a variety of original tools. This paper presents the prototype application GLA (Generic Learning Analytics), which tries to provide a step in the right direction. Data from wikis, forums, quizzes and serious games transformed into one homogeneous format that can be used to do comparable analyzes. Beside comparing several semesters and courses of one application, we can also match related data sets e. g. user behavior between a wiki and a file upload.

2013

  • Torben Dittrich, Stephan Kopf, Philipp Schaber, Benjamin Guthier and Wolfgang Effelsberg. ACM, 2013 Saliency Detection for Stereoscopic Video . New York, NY
  • Benjamin Guthier, Kalun Ho, Stephan Kopf and Wolfgang Effelsberg. ACM, 2013 Determining Exposure Values from HDR Histograms for Smartphone Photography . [New York, NY]
  • Benjamin Guthier, Johannes Kiess, Stephan Kopf and Wolfgang Effelsberg. , Technical reports. 2013 Stereoscopic Seam Carving With Temporal Consistency Mannheim, . 13-002
    In this paper, we present a novel technique for seam carving of stereoscopic video. It removes seams of pixels in areas that are most likely not noticed by the viewer. When applying seam carving to stereoscopic video rather than monoscopic still images, new challenges arise. The detected seams must be consistent between the left and the right view, so that no depth information is destroyed. When removing seams in two consecutive frames, temporal consistency between the removed seams must be established to avoid flicker in the resulting video. By making certain assumptions, the available depth information can be harnessed to improve the quality achieved by seam carving. Assuming that closer pixels are more important, the algorithm can focus on removing distant pixels first. Furthermore, we assume that coherent pixels belonging to the same object have similar depth. By avoiding to cut through edges in the depth map, we can thus avoid cutting through object boundaries.
  • Benjamin Guthier, Johannes Kiess, Stephan Kopf and Wolfgang Effelsberg. IEEE, 2013 Seam Carving for STereoscopic Video . Piscataway, NJ
  • Benjamin Guthier, Stephan Kopf and Wolfgang Effelsberg. 2013 Algorithms for a Real-Time HDR Video System Pattern Recognition Letters, 34, 8, 25 -33
  • Jakob Huber, Stephan Kopf and Philipp Schaber. , Technical reports. 2013 Analyse von Bildmerkmalen zur Identifikation wichtiger Bildregionen Mannheim, . 13-004
    Eine zuverlässige Erkennung wichtiger Bildregionen ist die Grundlage für viele Verfahren im Bereich der Bildverarbeitung wie beispielsweise bei der Bildkompression, bei Verfahren zur Anpassung der Bildauflösung oder beim Einfügen digitaler Wasserzeichen in Bilder. Es wurde ein System entwickelt, das Merkmalspunkte in Bildern identifiziert und diese nutzt, um wichtige Bildbereiche zu identifizieren. Zur Berechnung der Merkmalspunkte wird das SURF-Verfahren (Speeded Up Robust Features) verwendet. Die gefundenen Merkmale werden in einem zweiten Schritt einzelnen Bildregionen zugeordnet. Die Qualität der ermittelten Regionen sowie das Laufzeitverhalten der verschiedenen Verfahren werden anhand einer umfangreichen Bilddatenbank analysiert.
  • Stephan Kopf, Benjamin Guthier, Philipp Schaber, Torben Dittrich and Wolfgang Effelsberg. , Technical reports. 2013 Analysis of Disparity Maps for Detecting Saliency in Stereoscopic Video Mannheim, . 13-003
    We present a system for automatically detecting salient image regions in stereoscopic videos. This report extends our previous system and provides additional details about its implementation. Our proposed algorithm considers information based on three dimensions: salient colors in individual frames, salient information derived from camera and object motion, and depth saliency. These three components are dynamically combined into one final saliency map based on the reliability of the individual saliency detectors. Such a combination allows using more efficient algorithms even if the quality of one detector degrades. For example, we use a computationally efficient stereo correspondence algorithm that might cause noisy disparity maps for certain scenarios. In this case, however, a more reliable saliency detection algorithm such as the image saliency is preferred. To evaluate the quality of the saliency detection, we created modified versions of stereoscopic videos with the non-salient regions blurred. Having users rate the quality of these videos, the results show that most users do not detect the blurred regions and that the automatic saliency detection is very reliable.
  • Michael Magin and Stephan Kopf. , Technical reports. 2013 A Collaborative Multi-Touch UML Design Tool Mannheim, . 13-001
    The design and development of software projects is usually done in teams today. Collaborative systems based on multi-touch walls or large table-top screens could support these highly interactive tasks. We present a novel collaborative design tool which allows several developers to jointly create complex UML (Unified Modeling Language) diagrams. We have developed new algorithms to recognize the gestures drawn by the users, to create the respective elements of the diagram, to adjust the edges between classes, and to improve the layout of the classes automatically. Auxiliary lines provide the user with means to align classes precisely so a more consistent layout is achieved. Export functionality for XML and Java code skeletons completes the application; the UML diagram can thus be used in further steps of the software design process. User evaluations confirm considerable benefits of our proposed system.
  • Philip Mildner, Frederik Claus, Stephan Kopf and Wolfgang Effelsberg. ACM, 2013 Navigating Videos by Location . New York, NY
  • Dominik Schneider, Denny Stohr, Joachim Tingvold, Andre B. Amundsen, Lydia Weiland, Ansgar Scherp, Stephan Kopf and Wolfgang Effelsberg. , . 2013 fulgeo-Design of an Intuitive User Interface for a Multimedia Search Engine Mannheim [u.a.], .
    Multimedia documents like PowerPoint presentations or Flash documents are widely adopted in the Internet and exist in context of lots of different topics. However, so far there is no user friendly way to explore and search for this content. The aim of this work is to address this issue by developing a new, easy-to-use user interface approach and prototype search engine. Our system is called fulgeo and specifically focuses on a suitable multimedia interface for visualizing the query results of Flash documents. The prototype is available online as live demo at: http://fulgeo.komsys.org/
  • Daniel Schön, Melanie Klinger, Stephan Kopf and Wolfgang Effelsberg. AACE, 2013 HomeQuiz: Blending Paper Sheets with Mobile Self-Assessment Tests . Chesapeake, Va.
  • Stefan Wilk, Stephan Kopf, S Schulz and Wolfgang Effelsberg. AACE, 2013 Social Video: A Collaborative Video Annotation Environment to Support E-Learning . Chesapeake, Va.Our social video system allows users to enrich video by additional information like external websites, hypertext, images, other videos, or communication channels. Users are able to annotate whole videos, scenes, and objects in the video. We do not focus on a single user accessing the system but on multiple users watching the video and accessing the annotations others have created. Our web-based prototype differs from classical hypervideo systems because it allows annotation (authoring) and navigation in videos by focusing on collaboration and communication between the users. The prototype is integrated into the online social network Facebook and was evaluated with more than 300 users. The evaluation analyzes the usage of the system with a learning scenario in mind and indicates a learning success of users.

2012

2011

  • Benjamin Guthier, Stephan Kopf, Marc Eble and Wolfgang Effelsberg. SPIE, 2011 Flicker Reduction in Tone Mapped High Dynamic Range Video Proceedings of SPIE. Bellingham, Wash.
  • Benjamin Guthier, Stephan Kopf and Wolfgang Effelsberg. , 2011 Optimal Shutter Speed Sequences for Real-Time HDR Video , .
    A technique to create High Dynamic Range (HDR) video frames is to capture Low Dynamic Range (LDR) images at varying shutter speeds. They are then merged into a single image covering the entire brightness range of the scene. While shutter speeds are often chosen to vary by a constant factor, we propose an adaptive approach. The scene's histogram together with functions judging the contribution of an LDR exposure to the HDR result are used to compute a sequence of shutter speeds. This sequence allows for the estimation of the scene's radiance map with a high degree of accuracy. We show that, in comparison to the traditional approach, our algorithm achieves a higher quality of the HDR image for the same number of captured LDR exposures. Our algorithm is suited for creating HDR videos of scenes with varying brightness conditions in real-time, which applications like video surveillance benefit from.
  • Stephan Kopf, Benjamin Guthier, Dirk Farin and Jungong Han. IEEE, 2011 Analysis and Retargeting of Ball Sports Video . Piscataway, NJ [u.a.]
  • Stephan Kopf, Thomas Haenselmann, Johannes Kiess, Benjamin Guthier and Wolfgang Effelsberg. 2011 Algorithms for Video Retargeting Multimedia Tools and Applications, 51, 18, 819-861
  • Philip Mildner, Tonio Triebel, Stephan Kopf and Wolfgang Effelsberg. ICST, 2011 A scalable Peer-to-Peer-overlay for real-time massively multiplayer online games . Brussels

2010

2009

2008

2007

2006

  • Thomas Haenselmann, Marcel Busse, Stephan Kopf, Thomas King and Wolfgang Effelsberg. Technische Univ., 2006 Multi-Camera Video Stitching . Eindhoven
  • Thomas King, Thomas Butter, Matthias Brantner, Stephan Kopf, Thomas Haenselmann, Alexander Biskop, Andreas Färber and Wolfgang Effelsberg. , Technical reports. 2006 Distribution of Fingerprints for 802.11-based Positioning Systems Mannheim, . 06-019
    While indoor positioning systems based on 802.11 and fingerprinting work pretty well, it is unknown how to distribute a large amount of fingerprint data to mobile devices. Even worse, many mobile devices are restricted in terms of memory. In this demo proposal, we present two distribution approaches for fingerprints that fill this gap: the Strongest Access Point (SAP) and the Intersection of Access Points (IAP) algorithms. These approaches utilize the 802.11 infrastructure to download only a subset of the complete fingerprint data to a mobile device. The subset covers the area close to the actual position of the mobile device in such a way that position estimates can be computed. For the MDM~2007 demo session, we offer to demonstrate how these distribution approaches for fingerprint data work. The demo will include live indoor positioning of visitors using mobile devices while concurrently displaying the distribution of fingerprint data.
  • Thomas King, Thomas Haenselmann, Stephan Kopf and Wolfgang Effelsberg. , Technical Reports. 2006 Overhearing the Wireless Interface for 802.11-based Positioning Systems Mannheim, . 06-018
    Not only the proliferation of 802.11, but also the capability to determine the position of mobile devices make 802.11 highly appealing for many application areas. Typically, a mobile device that wants to know its position regularly performs active or passive scans to obtain the signal strength measurements of neighboring access points. Active and passive scanning are survey techniques originally intended to be performed once in a while to learn about the presence and signal reception quality of access points within communication range. Based on this survey the best suitable access point is selected as the gateway to the wired network. However, so far, no investigations are known to have been launched into how regular scanning affects concurrent data transmissions from an end-user point of view. In this paper, we explore how common data communication is affected while actively or passively scanning at the same time. We found that with an active scanning interval of less than 2 seconds the network conditions such as throughput and round trip delay are insufficient for interactive applications. The same is true for passive scanning if a scanning interval of less than 7 seconds is chosen. Furthermore, we present a novel scan scheme called Monitor Sniffing to reduce client service disruptions. Monitor Sniffing exploits the fact that 802.11 operates on overlapping channels by overhearing the wireless interface. We have implemented our Monitor Sniffing algorithm using commodity 802.11g hardware, and we demonstrate that it is faster than active and passive scanning and does not disturb concurrent data communication. Finally, our approach only requires software modifications on the client side, making the adoption process quite easy.
  • Thomas King, Thomas Haenselmann, Stephan Kopf and Wolfgang Effelsberg. 2006 Positionierung mit Wireless-LAN und Bluetooth Praxis der Informationsverarbeitung und Kommunikation : PIK, 29, 4, 9-17
  • Thomas King, Stephan Kopf and Wolfgang Effelsberg. Verl. Dr. Hut, 2006 Positionserkennung von Studierenden in Hörsälen mit dem Chi-Quadrat-Anpassungstest . München
  • Thomas King, Stephan Kopf, Thomas Haenselmann, Christian Lubberger and Wolfgang Effelsberg. , Technical Reports. 2006 COMPASS: A Probabilistic Indoor Positioning System Based on 802.11 and Digital Compasses Mannheim, . 06-012
    Positioning systems are one of the key elements required by context-aware application and location-based services. This paper presents the design, implementation and anaylsis of a positioning system called COMPASS which is based on 802.11 compliant network infrastructure and digital compasses. On the mobile device, COMPASS samples the signal strength values of different access points in communication range and utilizes the orientation of the user to preselect a subset of the training data. The remaining training data is used by a probabilistic position determination algorithm to determine the position of the user. While prior systems show only limited accuracy due to blocking effects caused by human bodies, we apply digital compasses to detect the orientations of the users so that we can handle these blocking effects. After a short period of training our approach achieves an average error distance of less than 1.65~meters in our experimental environment of 312 square meters.
  • Thomas King, Stephan Kopf, Thomas Haenselmann, Christian Lubberger and Wolfgang Effelsberg. ACM, 2006 COMPASS: A Probabilistic Indoor Positioning System Based on 802.11 and Digital Compasses . New York, NY
  • Stephan Kopf. 2006 Computergestützte Inhaltsanalyse von digitalen Videoarchiven
    Der Übergang von analogen zu digitalen Videos hat in den letzten Jahren zu großen Veränderungen innerhalb der Filmarchive geführt. Insbesondere durch die Digitalisierung der Filme ergeben sich neue Möglichkeiten für die Archive. Eine Abnutzung oder Alterung der Filmrollen ist ausgeschlossen, so dass die Qualität unverändert erhalten bleibt. Zudem wird ein netzbasierter und somit deutlich einfacherer Zugriff auf die Videos in den Archiven möglich. Zusätzliche Dienste stehen den Archivaren und Anwendern zur Verfügung, die erweiterte Suchmöglichkeiten bereitstellen und die Navigation bei der Wiedergabe erleichtern. Die Suche innerhalb der Videoarchive erfolgt mit Hilfe von Metadaten, die weitere Informationen über die Videos zur Verfügung stellen. Ein großer Teil der Metadaten wird manuell von Archivaren eingegeben, was mit einem großen Zeitaufwand und hohen Kosten verbunden ist. Durch die computergestützte Analyse eines digitalen Videos ist es möglich, den Aufwand bei der Erzeugung von Metadaten für Videoarchive zu reduzieren. Im ersten Teil dieser Dissertation werden neue Verfahren vorgestellt, um wichtige semantische Inhalte der Videos zu erkennen. Insbesondere werden neu entwickelte Algorithmen zur Erkennung von Schnitten, der Analyse der Kamerabewegung, der Segmentierung und Klassifikation von Objekten, der Texterkennung und der Gesichtserkennung vorgestellt. Die automatisch ermittelten semantischen Informationen sind sehr wertvoll, da sie die Arbeit mit digitalen Videoarchiven erleichtern. Die Informationen unterstützen nicht nur die Suche in den Archiven, sondern führen auch zur Entwicklung neuer Anwendungen, die im zweiten Teil der Dissertation vorgestellt werden. Beispielsweise können computergenerierte Zusammenfassungen von Videos erzeugt oder Videos automatisch an die Eigenschaften eines Abspielgerätes angepasst werden. Ein weiterer Schwerpunkt dieser Dissertation liegt in der Analyse historischer Filme. Vier europäische Filmarchive haben eine große Anzahl historischer Videodokumentationen zur Verfügung gestellt, welche Anfang bis Mitte des letzten Jahrhunderts gedreht und in den letzten Jahren digitalisiert wurden. Durch die Lagerung und Abnutzung der Filmrollen über mehrere Jahrzehnte sind viele Videos stark verrauscht und enthalten deutlich sichtbare Bildfehler. Die Bildqualität der historischen Schwarz-Weiß-Filme unterscheidet sich signifikant von der Qualität aktueller Videos, so dass eine verlässliche Analyse mit bestehenden Verfahren häufig nicht möglich ist. Im Rahmen dieser Dissertation werden neue Algorithmen vorgestellt, um eine zuverlässige Erkennung von semantischen Inhalten auch in historischen Videos zu ermöglichen.
  • Stephan Kopf, Thomas King, Fleming Lampi and Wolfgang Effelsberg. ACM, 2006 Video Color Adaptation for Mobile Devices . New York, NY
  • Stephan Kopf, Thomas King, Fleming Lampi and Wolfgang Effelsberg. Ges. für Informatik, 2006 Automatische Kamerasteuerung in Interaktiven Vorlesungen GI-Edition / Proceedings. Bonn
  • Stephan Kopf and Manuel Knaus. , Technical reports. 2006 Verbesserung der Qualität von historischen Filmen Mannheim, . 06-001
    Historische Filme stellen einen wichtigen Baustein für die Erhaltung des kulturellen Erbes dar. Durch eine Digitalisierung können diese für die Zukunft erhalten werden, ohne dass Filme durch Materialermüdung der Filmrollen bzw. Bänder Schaden nehmen. Viele der historischen Aufnahmen sind durch Abspielen oder Lagerung bereits deutlich beschädigt. In diesem Bericht werden Algorithmen zur Erkennung und Behebung solcher Fehler in historischen Schwarzweißfilmen vorgestellt. Dabei handelt es sich um die Erkennung und Beseitigung von horizontalen Störlinien, um die Helligkeits- und Kontrastkorrektur sowohl bei starken Helligkeitsschwankungen als auch bei überdunkelten oder überhellten Sequenzen, sowie um die Entfernung von Verwackelungen bei Kameraeinstellungen.
  • Stephan Kopf, Fleming Lampi, Thomas King and Wolfgang Effelsberg. ACM, 2006 Automatic Scaling and Cropping of Videos for Devices with Limited Screen Resolution . New York, NY
  • Fleming Lampi, Stephan Kopf and Wolfgang Effelsberg. Ges. für Informatik, 2006 Mediale Aufbereitung von Lehrveranstaltungen und ihre automatische Veröffentlichung - Ein Erfahrungsbericht GI-Edition / Proceedings. Bonn

2005

  • Till Aldinger, Stephan Kopf, Nicolai Scheele and Wolfgang Effelsberg. AACE, 2005 Participatory Simulation of a Stock Exchange . Norfolk, Va.
  • Thomas King, Thomas Haenselmann, Stephan Kopf and Wolfgang Effelsberg. , . 2005 Positionierung mit Wireless-LAN und Bluetooth , .
    In diesem Artikel wird ein Überblick über bestehende Wireless-LAN- und Bluetooth-basierte Positionierungssysteme gegeben. Eine detaillierte identifikation der Merkmale und Eigenschaften der unterschiedlichen Systeme soll helfen, Positionierungsverfahren anhand ihrer Eigenschaften einzuordnen.
  • Thomas King, Stephan Kopf and Wolfgang Effelsberg. Fernuniv., Fachbereich Informatik , 2005 A Location System based on Sensor Fusion: Research Areas and Software Architecture Informatik-Berichte. Hagen
  • Stephan Kopf. , . 2005 Verfahren zur Inhaltsadaption von Darstellungselementen , .
    Dieser Bericht gibt einen Überblick über bekannte Verfahren und Technologien zur automatischen Adaption von Darstellungselementen für mobile Endgeräte, wobei der Schwerpunkt bei Verfahren zur Adaption von Bildern, Videos, Webseiten und Audiodateien liegt. Ziel ist es, basierend auf den Eigenschaften des Endgerätes und den Interaktionsmöglichkeiten, geeignete Darstellungsformate automatisch abzuleiten. Als mögliche Endgeräte werden Mobiltelefone, PDAs, Tablet PCs und Notebook PCs betrachtet. Ein guter Adaptionsalgorithmus sollte eine computergestützte Umformatierung von nur einmal bereit gestellten Inhalten für die verschiedenen Formfaktoren, Auflösungen, Bildschirmgrößen, Interaktionstechniken (Maus, Stift, Touch-Screen usw.) und Netzbandbreiten unterstützen.
  • Stephan Kopf, Thomas Haenselmann and Wolfgang Effelsberg. , . 2005 Robust Character Recognition in Low-Resolution Images and Videos , .
    Although OCR techniques work very reliably for high-resolution documents, the recognition of superimposed text in low-resolution images or videos with a complex background is still a challenge. Three major parts characterize our system for recognition of superimposed text in images and videos: localization of text regions, segmentation (binarization) of characters, and recognition. We use standard approaches to locate text regions and focus in this paper on the last two steps. Many approaches (e.g., projection profiles, k-mean clustering) do not work very well for separating characters with very small font sizes. We apply in a vertical direction a shortest-path algorithm to separate the characters in a text line. The recognition of characters is based on the curvature scale space (CSS) approach which smoothes the contour of a character with a Gaussian kernel and tracks its inflection points. A major drawback of the CSS method is its poor representation of convex segments: Convex objects cannot be represented at all due to missing inflection points. We have extended the CSS approach to generate feature points for concave and convex segments of a contour. This generic approach is not only applicable to text characters but to arbitrary objects as well. In the experimental results, we compare our approach against a pattern matching algorithm, two classification algorithms based on contour analysis, and a commercial OCR system. The overall recognition results are good enough even for the indexing of low resolution images and videos.
  • Stephan Kopf, Thomas Haenselmann and Wolfgang Effelsberg. IEEE Operations Center, 2005 Enhancing curvature scale space features for robust shape classification . Piscataway, NJThe curvature scale space (CSS) technique, which is also part of the MPEG-7 standard, is a robust method to describe complex shapes. The central idea is to analyze the curvature of a shape and derive features from inflection points. A major drawback of the CSS method is its poor representation of convex segments: Convex objects cannot be represented at all due to missing inflection points. We have extended the CSS approach to generate feature points for concave and convex segments of a shape. This generic approach is applicable to arbitrary objects. In the experimental results, we evaluate as a comprehensive example the automatic recognition of characters in images and videos.
  • Stephan Kopf, Thomas King and Wolfgang Effelsberg. Fernuniv., Fachbereich Informatik, 2005 Improvement of Accuracy for GPS Informatik-Berichte. Hagen
  • Stephan Kopf and Alexander Oertel. , . 2005 Gesichtserkennung in Bildern und Videos mit Hilfe von Eigenfaces , .
    In dieser Arbeit wird ein System vorgestellt, um Gesichter von Personen in Graustufenbildern zu lokalisieren und die Gesichter dann mit gespeicherten Charakteristika anderer Gesichter zu vergleichen. Der Ansatz, der hierzu verwendet wurde, behandelt die Gesichtserkennung als echtes zweidimensionales Erkennungsproblem, und greift nicht auf dreidimensionale Geometrie zurück. Außerdem wurde ausgenutzt, dass Gesichter in Bildern normalerweise aufrecht auftreten und somit durch eine kleine Anzahl von zweidimensionalen Charakteristika beschrieben werden können. Das System funktioniert, indem Gesichter in einen Eigenschaftenraum projiziert werden, der aus den wichtigsten Bestandteilen bekannter Gesichter aufgespannt wird. Diese aussagekräftigen Bestandteile werden Eigenfaces genannt, weil sie die Eigenvektoren (Hauptbestandteile) der Menge von Gesichtern sind, die als Lernmenge angegeben wurde. Die Eigenvektoren entsprechen jedoch nicht unbedingt den, aus dem menschlichen Blickwinkel, wichtigen Eigenschaften eines Gesichtes, wie Augen, Ohren und Nasen. Eine Projektion des Ursprungsbildes in den Gesichtsraum wird durch die gewichtete Summe der Eigenschaften der Eigenfaces charakterisiert. Eine Erkennung eines bestimmten Gesichtes erfolgt durch einen Vergleich der Gewichtsvektoren mit Gewichtsvektoren bereits bekannter Gesichter.
  • Stephan Kopf, Nicolai Scheele and Wolfgang Effelsberg. , . 2005 The Interactive Lecture: Teaching and Learning Technologies for Large Classrooms , .
    Conventional lectures in large classrooms are connected to fundamental didactic problems due to a lack of interactivity and feedback opportunities. In an interactive lecture each student is equipped with a light-weight, mobile device that can be used to interact with the lecturer during the lesson, thus creating an additional channel of communication. These devices support new teaching and learning paradigms such as participatory simulations. In this paper, we present our experiences with the usage of mobile devices in lectures. After discussing the didactic benefits of interactive lectures, we introduce the software toolkits used in our scenarios, we highlight selected tools like a quiz tool or a support tool for participatory simulation, and present major results from six studies we have conducted.
  • Stephan Kopf, Nicolai Scheele, Lilli Winschel and Wolfgang Effelsberg. WIT Press, 2005 Improving Activity and Motivation of Students with Innovative Teaching and Learning Technologies . Southampton [u.a.]

2004

  • Stephan Kopf, Thomas Haenselmann and 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.
  • Stephan Kopf, Thomas Haenselmann, Dirk Farin and 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 and 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.
  • Lilli Winschel and Stephan Kopf. , . 2004 Entwicklung einer Börsensimulation mit der multiagentenbasierten Entwicklungsumgebung NetLogo , .
    In diesem Bericht werden die Möglichkeiten der Modellierungssumgebung "NetLogo" für die Realisierung von multiagentenbasierten Simulationen für Lehrveranstaltungen evaluiert. In diesem Rahmen wird die Entwicklungsumgebung "NetLogo", ihre Skriptsprache und das für die Vernetzung der Agenten zustädige Zusatzpaket "HubNet" anhand der Implementierung einer simulierten Börse getestet. In der simulierten Börse können Marktteilnehmer unterschiedliche Aktien handeln. Mehrere Benutzer sollen gleichzeitig an der Simulation teilnehmen und dabei die Rolle eines Käufers bzw. Verkäufers einnehmen können. Zusätzlich zu den Benutzern sind virtuelle Marktteilnehmer implementiert worden, die am Handel beteiligt sind. Ein Administrator hat die Möglichkeit, den Benutzern während des Handels zusätzliche Informationen zukommen zu lassen. Das implementierte Modell ist mit mehreren Teilnehmern getestet worden.

2003