Fakultät 07 / Institut für Medien- und Phototechnik
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In this work, we propose a novel data-driven approach to recover missing or corrupted motion capture data, either in the form of 3D skeleton joints or 3D marker trajectories. We construct a knowledge-base that contains prior existing knowledge, which helps us to make it possible to infer missing or corrupted information of the motion capture data. We then build a kd-tree in parallel fashion on the GPU for fast search and retrieval of this already available knowledge in the form of nearest neighbors from the knowledge-base efficiently. We exploit the concept of histograms to organize the data and use an off-the-shelf radix sort algorithm to sort the keys within a single processor of GPU. We query the motion missing joints or markers, and as a result, we fetch a fixed number of nearest neighbors for the given input query motion. We employ an objective function with multiple error terms that substantially recover 3D joints or marker trajectories in parallel on the GPU. We perform comprehensive experiments to evaluate our approach quantitatively and qualitatively on publicly available motion capture datasets, namely CMU and HDM05. From the results, it is observed that the recovery of boxing, jumptwist, run, martial arts, salsa, and acrobatic motion sequences works best, while the recovery of motion sequences of kicking and jumping results in slightly larger errors. However, on average, our approach executes outstanding results. Generally, our approach outperforms all the competing state-of-the-art methods in the most test cases with different action sequences and executes reliable results with minimal errors and without any user interaction.
High-quality rendering of spatial sound fields in real-time is becoming increasingly important with the steadily growing interest in virtual and augmented reality technologies. Typically, a spherical microphone array (SMA) is used to capture a spatial sound field. The captured sound field can be reproduced over headphones in real-time using binaural rendering, virtually placing a single listener in the sound field. Common methods for binaural rendering first spatially encode the sound field by transforming it to the spherical harmonics domain and then decode the sound field binaurally by combining it with head-related transfer functions (HRTFs). However, these rendering methods are computationally demanding, especially for high-order SMAs, and require implementing quite sophisticated real-time signal processing. This paper presents a computationally more efficient method for real-time binaural rendering of SMA signals by linear filtering. The proposed method allows representing any common rendering chain as a set of precomputed finite impulse response filters, which are then applied to the SMA signals in real-time using fast convolution to produce the binaural signals. Results of the technical evaluation show that the presented approach is equivalent to conventional rendering methods while being computationally less demanding and easier to implement using any real-time convolution system. However, the lower computational complexity goes along with lower flexibility. On the one hand, encoding and decoding are no longer decoupled, and on the other hand, sound field transformations in the SH domain can no longer be performed. Consequently, in the proposed method, a filter set must be precomputed and stored for each possible head orientation of the listener, leading to higher memory requirements than the conventional methods. As such, the approach is particularly well suited for efficient real-time binaural rendering of SMA signals in a fixed setup where usually a limited range of head orientations is sufficient, such as live concert streaming or VR teleconferencing.
Microphone arrays consisting of sensors mounted on the surface of a rigid, spherical scatterer are popular tools for the capture and binaural reproduction of spatial sound scenes. However, microphone arrays with a perfectly spherical body and uniformly distributed microphones are often impractical for the consumer sector, in which microphone arrays are generally mounted on mobile and wearable devices of arbitrary geometries. Therefore, the binaural reproduction of sound fields captured with arbitrarily shaped microphone arrays has become an important field of research. In this work, we present a comparison of methods for the binaural reproduction of sound fields captured with non-spherical microphone arrays. First, we evaluated equatorial microphone arrays (EMAs), where the microphones are distributed on an equatorial contour of a rigid, spherical 1.
Second, we evaluated a microphone array with six microphones mounted on a pair of glasses. Using these two arrays, we conducted two listening experiments comparing four rendering methods based on acoustic scenes captured in different rooms2. The evaluation includes a microphone-based stereo approach (sAB stereo), a beamforming-based stereo approach (sXY stereo), beamforming-based binaural reproduction (BFBR), and BFBR with binaural signal matching (BSM). Additionally, the perceptual evaluation included binaural Ambisonics renderings, which were based on measurements with spherical microphone arrays. In the EMA experiment we included a fourth-order Ambisonics rendering, while in the glasses array experiment we included a second-order Ambisonics rendering. In both listening experiments in which participants compared all approaches with a dummy head recording we applied non-head-tracked binaural synthesis, with sound sources only in the horizontal plane. The perceived differences were rated separately for the attributes timbre and spaciousness. Results suggest that most approaches perform similarly to the Ambisonics rendering. Overall, BSM, and microphone-based stereo were rated the best for EMAs, and BFBR and microphone-based stereo for the glasses array.
Due to the COVID-19 pandemic, university students worldwide have experienced drastic changes in their academic and social lives, with the rapid shift to online courses and contact restrictions being reported among the major stressors. In the present study, we aimed at examining students’ perceived stress over the course of the pandemic as well as individual psychological and social coping resources within the theoretical framework of the Transactional Model of Stress and Coping in the specific group of STEM students. In four cross-sectional studies with a total of 496 computer science students in Germany, we found that students reported significantly higher levels of perceived stress at both measurement time points in the second pandemic semester (October/November 2020; January/February 2021) as compared to the beginning of the first (April/May 2020), indicating that students rather became sensitized to the constant pandemic-related stress exposure than habituating to the “new normal”. Regarding students’ coping resources in the higher education context, we found that both high (a) academic self-efficacy and (b) academic online self-efficacy as well as low (c) perceived social and academic exclusion among fellow students significantly predicted lower levels of students’ (d) belonging uncertainty to their study program, which, in turn, predicted lower perceived stress at the beginning of the first pandemic semester. At the beginning of the second pandemic semester, we found that belonging uncertainty still significantly mediated the relationship between students’ academic self-efficacy and perceived stress. Students’ academic online self-efficacy, however, no longer predicted their uncertainty about belonging, but instead had a direct buffering effect on their perceived stress. Students’ perceived social and academic exclusion among fellow students only marginally predicted their belonging uncertainty and no longer predicted their perceived stress 6 months into the pandemic. We discuss the need and importance of assessing and monitoring students’ stress levels as well as faculty interventions to strengthen students’ individual psychological and social coping resources in light of the still ongoing pandemic.
Risikobasierte Authentifizierung (RBA) ist eine adaptive Sicherheitsmaßnahme zur Stärkung passwortbasierter Authentifizierung. Sie zeichnet Merkmale während des Logins auf und fordert zusätzliche Authentifizierung an, wenn sich Ausprägungen dieser Merkmale signifikant von den bisher bekannten unterscheiden. RBA bietet das Potenzial für gebrauchstauglichere Sicherheit. Bisher jedoch wurde RBA noch nicht ausreichend im Bezug auf Usability, Sicherheit und Privatsphäre untersucht. Dieser Extended Abstract legt das geplante Dissertationsvorhaben zur Erforschung von RBA dar. Innerhalb des Vorhabens konnte bereits eine Grundlagenstudie und eine darauf aufbauende Laborstudie durchgeführt werden. Wir präsentieren erste Ergebnisse dieser Studien und geben einen Ausblick auf weitere Schritte.
Web browsers use HTTP caches to reduce the amount of data to be transferred over the network and allow Web pages to load faster. Content such as scripts, images, and style sheets, which are static most of the time or shared across multiple websites, are stored and loaded locally when recurring requests ask for cached resources. This behaviour can be exploited if the cache is based on a naive implementation. This paper summarises possible attacks on the browser cache and shows through extensive experiments that even modern web browsers still do not provide enough safeguards to protect their users. Moreover, the available built-in as well as addable cache controls offer rather limited functionality in terms of protection and ease of use. Due to the volatile and inhomogeneous APIs for controlling the cache in modern browsers, the development of enhanced user-centric cache controls remains -until further notice- in the hands of browser manufacturers.
Online services such as social networks, online shops, and search engines deliver different content to users depending on their location, browsing history, or client device. Since these services have a major influence on opinion forming, understanding their behavior from a social science perspective is of greatest importance. In addition, technical aspects of services such as security or privacy are becoming more and more relevant for users, providers, and researchers. Due to the lack of essential data sets, automatic black box testing of online services is currently the only way for researchers to investigate these services in a methodical and reproducible manner. However, automatic black box testing of online services is difficult since many of them try to detect and block automated requests to prevent bots from accessing them.
In this paper, we introduce a testing tool that allows researchers to create and automatically run experiments for exploratory studies of online services. The testing tool performs programmed user interactions in such a manner that it can hardly be distinguished from a human user. To evaluate our tool, we conducted - among other things - a large-scale research study on Risk-based Authentication (RBA), which required human-like behavior from the client. We were able to circumvent the bot detection of the investigated online services with the experiments. As this demonstrates the potential of the presented testing tool, it remains to the responsibility of its users to balance the conflicting interests between researchers and service providers as well as to check whether their research programs remain undetected.
Risk-based authentication (RBA) is an adaptive security measure to strengthen password-based authentication. RBA monitors additional implicit features during password entry such as device or geolocation information, and requests additional authentication factors if a certain risk level is detected. RBA is recommended by the NIST digital identity guidelines, is used by several large online services, and offers protection against security risks such as password database leaks, credential stuffing, insecure passwords and large-scale guessing attacks. Despite its relevance, the procedures used by RBA-instrumented online services are currently not disclosed. Consequently, there is little scientific research about RBA, slowing down progress and deeper understanding, making it harder for end users to understand the security provided by the services they use and trust, and hindering the widespread adoption of RBA.
In this paper, with a series of studies on eight popular online services, we (i) analyze which features and combinations/classifiers are used and are useful in practical instances, (ii) develop a framework and a methodology to measure RBA in the wild, and (iii) survey and discuss the differences in the user interface for RBA. Following this, our work provides a first deeper understanding of practical RBA deployments and helps fostering further research in this direction.
Die Blockchain ist nicht nur im Bereich der Finanzwelt angekommen, auch andere Branchen versuchen sich an ihrer Anwendung. In diesem Artikel werden Konzepte und Modelle von Blockchain-Anwendungen außerhalb des Finanzbereichs vorgestellt, indem die zugehörigen Veröffentlichungen referiert und diskutiert werden. Die Anwendungsbereiche variieren aktuell über den Schutz persönlicher Daten bis zur Sicherung und Überwachung von Nahrungsmittelproduktionsketten.
Musik Frequenzen Formeln
(2018)
Diese Arbeit zeigt ein Verfahren zur automatisierten Auswertung von holographischen Interferogrammen für die Formvermessung auf. Es erlaubt die topographische Form eines Objektes qualitativ anhand dessen holographischen Bildes automatisiert zu erfassen. Eine automatisierte Auswertung ermöglicht den wirtschaftlichen Einsatz der holographischen Interferometrie in der Formvermessung.
Die neusten Fortschritte im Bereich Real Time Rendering ermög-lichen virtuelle Produktionsabläufe in weiten Teilen der Industrie. Diese Vorgehensweise setzt latenzfreies Arbeiten und eine akkurate Erscheinung voraus. Daher empfiehlt sich die Verwendung von HDR-Rendering für fotorealistische Ergebnisse und Tone Mapping für die passende Darstellung.
Gleichwohl gibt es bisher nur wenige Publikationen, die sich mit echtzeitfähigem Tone Mapping beschäftigen. Zudem tendieren Tone Mapping Operatoren dazu, Farberscheinungseffekte zu erzeugen, die zu einer Diskrepanz zwischen dargestelltem und realem Produkt führen.
Deshalb werden in dieser Thesis sieben Tone Mapping Operatoren bewertet, die unterschiedliche Ansätze zur Farbkorrektur beinhalten. Sie werden als Fragment Shader implementiert, um Echtzeitverarbeitung zu realisieren. Zusätzlich wird ihre Performance und die subjektive Akkuratesse der Ergebnisse gemessen.
Im Ergebnis schneidet der FilmicTMO als global arbeitender Sigmoid-Operator am besten ab und wird für die weitere Verwendung empfohlen.
State of the art browser games are increasingly complex pieces of software with extensive code basis. With increasing complexity, a software becomes harder to maintain. Automated regression testing can simplify these maintenance processes and thereby enable developers as well as testers to spend their workforce more efficiently.
This thesis addresses the utilization of automated tests in web applications. As a use case test automation is applied to an online-based strategy game for the browser. The introduction presents the general conditions for a software project that makes use of automated tests and different approaches of test automation. The main section introduces a specific solution of test automation applied on the game “Forge of Empires”, produced by Innogames GmbH. The created framework of the company is presented. It implements different software frameworks. The conclusion consists of a comparison and analysis about the presented methods and technologies.
Diese Arbeit untersucht die zeitliche Interpolation von Videosignalen. Durch die
Einführung des Ultra High Definition Television Standard wird eine höhere Bildwiederholrate benötigz um
Judder-Artefakte zu vermeiden. In diesem Zusammenhang kommt der zeitlichen Interpolation von nicht nativem UHD Material eine besondere Bedeutung zu. Neben der räumlichen Interpolation ist diese essenziell. In dieser Arbeit wird eine Übersicht über die Anforderungen an UHD Video gegeben. Bewegungskompensierende
Verfahren für das Deinterlacing und Upscaling in Verbindung mit einer Phasenkorrelation werden behandelt. Ein MATLAB-Programm wird entwickelt mit dem ein Upscaling und Deinterlacing von HD Material durchgeführt werden kann.
In dieser Arbeit wird auf die theoretischen Grundlagen von digitalen Filmkameras, des Dynamikumfangs und der HDR Technologie eingegangen. Im Einzelnen werden die Spezifikationen der digitalen Filmkamera RED Epic sowie des Tonemapping-Operators iCAM06 aufgeführt. In der Durchführung war es das Ziel, den erhöhten Dynamikumfang einer mit dieser Kamera aufgezeichneten Szene mit iCAM06 zu komprimieren und diesen auf einem handelsüblichen Monitor darzustellen. In der Auswertung werden Bildergebnisse für unterschiedliche Übergabeparameter demonstriert und dokumentiert.
Diese Bachelorarbeit zeigt auf, welche Probleme bei der Verwendung der Videofunktion von digitalen Consumer-Kameras wie Digitalkameras mit Videofunktion, Mobiltelefonen oder Camcordern entstehen können. Auf der Basis dieser Arbeit wird die Firma Image Engineering ein Testverfahren zur Videoanalyse entwickeln.
Entwicklung und Gestaltung neuer Multimedia-Formate am Beispiel des Projekts "Bluthochdruckvorsorge"
(2012)
Die vorliegende Bachelorarbeit beschäftigt sich mit der Gestaltung und Entwicklung der multimedialen Anwendungen für das Projekt „Bluthochdruckvorsorge“, das am Institut für Photo- und Medientechnik durchgeführt wurde. Nach der Analyse der didaktischen und technischen Voraussetzungen für die Entwicklung bestimmter multimedialer Formate für die Gesundheitsprävention wurden vergleichbare Anwendungen analysiert und bewertet. Anschließend wurde die webbasierte Anwendung „Bluthochdruckvorsorge„ vorgestellt und deren Konzeption und Realisierung erläutert.
Im Rahmen dieser Bachelorarbeit wurde der von Debevec und Malik verwendete Algorithmus zur Erstellung von HDR-Bildern als Plugin für die Bildverarbeitungssoftware ImageJ implementiert. Darüber hinaus wurde die Implementierung durch Tests auf ihre Funktionalität überprüft und Schwachstellen des Algorithmus erläutert. Durch Modifizierungen des erstellten Plugins wurden einige Schwächen des Algorithmus verbessert.
Diese Arbeit beschreibt einen optischen Aufbau zur Herstellung von Holografisch-Optischen Elementen. Der Aufbau nutzt dabei einen räumlichen Lichtmodulator, um die Phasenverteilung eines ebenen Wellenfelds gezielt zu manipulieren. Das Wellenfeld wird mithilfe eines 4f-Aufbaus einer optischen Filterung unterzogen und anschließend mit einer Referenzwelle überlagert. Die Inten- sitätsverteilung des Interferenzmusters, das bei dieser Überla- gerung entsteht, wird in ein Fotopolymer belichtet. Die Belich- tung regt dabei Polymerisationsprozesse im Fotopolymer an, die zu einer räumlichen Modulation des Brechungsindex führen. So- mit kann eine definierte räumliche Phasenverteilung in das Foto- polymer geschrieben werden, welches als Holografisch-Optisches Element bezeichnet wird. Aufgrund der geringen Dauer des ge- samten Prozesses wird dieser als Rapid Prototyping bezeichnet.