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Item An Error Bound for Decoupled Visibility with Application to Relighting(The Eurographics Association, 2011) Schwenk, Karsten; Fellner, Dieter W.; N. Avis and S. LefebvreMonte Carlo estimation of direct lighting is often dominated by visibility queries. If an error is tolerable, the calculations can be sped up by using a simple scalar occlusion factor per light source to attenuate radiance, thus decoupling the expensive estimation of visibility from the comparatively cheap sampling of unshadowed radiance and BRDF. In this paper we analyze the error associated with this approximation and derive an upper bound. We demonstrate in a simple relighting application how our result can be used to reduce noise by introducing a controlled error if a reliable estimate of the visibility is already available.Item Generative Object Definition and Semantic Recognition(The Eurographics Association, 2011) Ullrich, Torsten; Fellner, Dieter W.; H. Laga and T. Schreck and A. Ferreira and A. Godil and I. Pratikakis and R. Veltkamp''What is the difference between a cup and a door?'' These kinds of questions have to be answered in the context of digital libraries. This semantic information, which describes an object on a high, abstract level, is needed in order to provide digital library services such as indexing, markup and retrieval. In this paper we present a new approach to encode and to extract such semantic information. We use generative modeling techniques to describe a class of objects: each class is represented by one algorithm; and each object is one set of high-level parameters, which reproduces the object if passed to the algorithm. Furthermore, the algorithm is annotated with semantic information, i.e. a human-readable description of the object class it represents. We use such an object description to recognize objects in real-world data e.g. laser scans. Using an algorithmic object description, we are able to identify 3D subparts, which can be described and generated by the algorithm. Furthermore, we can determine the needed input parameters. In this way, we can classify objects, recognize them semantically and we can determine their parameters (cup's height, radius, etc.).Item Visual Analysis of Large Graphs: State-of-the-Art and Future Research Challenges(The Eurographics Association and Blackwell Publishing Ltd., 2011) Landesberger, T. von; Kuijper, A.; Schreck, T.; Kohlhammer, J.; Wijk, J.J. van; Fekete, J.‐D.; Fellner, Dieter W.; Eduard Groeller and Holly RushmeierThe analysis of large graphs plays a prominent role in various fields of research and is relevant in many important application areas. Effective visual analysis of graphs requires appropriate visual presentations in combination with respective user interaction facilities and algorithmic graph analysis methods. How to design appropriate graph analysis systems depends on many factors, including the type of graph describing the data, the analytical task at hand and the applicability of graph analysis methods. The most recent surveys of graph visualization and navigation techniques cover techniques that had been introduced until 2000 or concentrate only on graph layouts published until 2002. Recently, new techniques have been developed covering a broader range of graph types, such as time‐varying graphs. Also, in accordance with ever growing amounts of graph‐structured data becoming available, the inclusion of algorithmic graph analysis and interaction techniques becomes increasingly important. In this State‐of‐the‐Art Report, we survey available techniques for the visual analysis of large graphs. Our review first considers graph visualization techniques according to the type of graphs supported. The visualization techniques form the basis for the presentation of interaction approaches suitable for visual graph exploration. As an important component of visual graph analysis, we discuss various graph algorithmic aspects useful for the different stages of the visual graph analysis process. We also present main open research challenges in this field.Item Simple and Efficient Normal Encoding with Error Bounds(The Eurographics Association, 2011) Schinko, Christoph; Ullrich, Torsten; Fellner, Dieter W.; Ian Grimstead and Hamish CarrNormal maps and bump maps are commonly used techniques to make 3D scenes more realistic. Consequently, the efficient storage of normal vectors is an important task in computer graphics. This work presents a fast, lossy compression/decompression algorithm for arbitrary resolutions. The complete source code is listed in the appendix and is ready to use.Item Smooth Transitions for Large Scale Changes in Multi-Resolution Images(The Eurographics Association, 2011) Lancelle, Marcel; Fellner, Dieter W.; Peter Eisert and Joachim Hornegger and Konrad PolthierToday's super zoom cameras offer a large optical zoom range of over 30x. It is easy to take a wide angle photograph of the scene together with a few zoomed in high resolution crops. Only little work has been done to appropriately display the high resolution photo as an inset. Usually, to hide the resolution transition, alpha blending is used. Visible transition boundaries or ghosting artifacts may result. In this paper we introduce a different, novel approach to overcome these problems. Across the transition, we gradually attenuate the maximum image frequency. We achieve this with a Gaussian blur with an exponentially increasing standard deviation.Item Believable Virtual Characters in Human-Computer Dialogs(The Eurographics Association, 2011) Jung, Yvonne; Kuijper, Arjan; Fellner, Dieter W.; Kipp, Michael; Miksatko, Jan; Gratch, Jonathan; Thalmann, Daniel; N. John and B. WyvillFor many application areas, where a task is most naturally represented by talking or where standard input devices are difficult to use or not available at all, virtual characters can be well suited as an intuitive man-machineinterface due to their inherent ability to simulate verbal as well as nonverbal communicative behavior. This type of interface is made possible with the help of multimodal dialog systems, which extend common speech dialog systems with additional modalities just like in human-human interaction. Multimodal dialog systems consist at least of an auditive and graphical component, and communication is based on speech and nonverbal communication alike. However, employing virtual characters as personal and believable dialog partners in multimodal dialogs entails several challenges, because this requires not only a reliable and consistent motion and dialog behavior but also regarding nonverbal communication and affective components. Besides modeling the mind and creating intelligent communication behavior on the encoding side, which is an active field of research in artificial intelligence, the visual representation of a character including its perceivable behavior, from a decoding perspective, such as facial expressions and gestures, belongs to the domain of computer graphics and likewise implicates many open issues concerning natural communication. Therefore, in this report we give a comprehensive overview how to go from communication models to actual animation and rendering.