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Item Report of The Statutory Auditors to the General Meeting of The Members Of Eurographics Association Geneva(The Eurographics Association and Blackwell Publishing Ltd., 2011) Eduard Groeller and Holly RushmeierItem Diffusion‐Based Snow Cover Generation(The Eurographics Association and Blackwell Publishing Ltd., 2011) Festenberg, Niels v.; Gumhold, Stefan; Eduard Groeller and Holly RushmeierWe present a method to generate snow covers on complex scene geometries. Both volumetric snow shapes and photorealistic texturing are computed. We formulate snow accumulation as a diffusive distribution process on a ground scene. Our theoretical framework is motivated by models for granular material deposition. With the framework we can capture the most relevant features of natural snow cover geometries in a concise local computation scheme. Snow bridges and overhangs are also included. Snow surface texture coordinates are computed to create realistic ground–snow interfaces. Several example scenes and a supplementary snow cover growth animation demonstrate the method's efficiency.Item Exploring Non‐Linear Relationship of Blendshape Facial Animation(The Eurographics Association and Blackwell Publishing Ltd., 2011) Liu, Xuecheng; Xia, Shihong; Fan, Yiwen; Wang, Zhaoqi; Eduard Groeller and Holly RushmeierHuman face is a complex biomechanical system and non‐linearity is a remarkable feature of facial expressions. However, in blendshape animation, facial expression space is linearized by regarding linear relationship between blending weights and deformed face geometry. This results in the loss of reality in facial animation. To synthesize more realistic facial animation, aforementioned relationship should be non‐linear to allow the greatest generality and fidelity of facial expressions. Unfortunately, few existing works pay attention to the topic about how to measure the non‐linear relationship. In this paper, we propose an optimization scheme that automatically explores the non‐linear relationship of blendshape facial animation from captured facial expressions. Experiments show that the explored non‐linear relationship is consistent with the non‐linearity of facial expressions soundly and is able to synthesize more realistic facial animation than the linear one.Item Improved Model‐ and View‐Dependent Pruning of Large Botanical Scenes(The Eurographics Association and Blackwell Publishing Ltd., 2011) Neubert, B.; Pirk, S.; Deussen, O.; Dachsbacher, C.; Eduard Groeller and Holly RushmeierWe present an optimized pruning algorithm that allows for considerable geometry reduction in large botanical scenes while maintaining high and coherent rendering quality. We improve upon previous techniques by applying model‐specific geometry reduction functions and optimized scaling functions. For this we introduce the use of Precision and Recall (PR) as a measure of quality to rendering and show how PR‐scores can be used to predict better scaling values. We conducted a user‐study letting subjects adjust the scaling value, which shows that the predicted scaling matches the preferred ones. Finally, we extend the originally purely stochastic geometry prioritization for pruning to account for view‐optimized geometry selection, which allows to take global scene information, such as occlusion, into consideration. We demonstrate our method for the rendering of scenes with thousands of complex tree models in real‐time.Item Fast Mean‐Curvature Flow via Finite‐Elements Tracking(The Eurographics Association and Blackwell Publishing Ltd., 2011) Chuang, Ming; Kazhdan, Michael; Eduard Groeller and Holly RushmeierIn this paper, we present a novel approach for efficiently evolving meshes using mean‐curvature flow. We use a finite‐elements hierarchy that supports an efficient multigrid solver for performing the semi‐implicit time‐stepping. Although expensive to compute, we show that it is possible to track this hierarchy through the process of surface evolution. As a result, we provide a way to efficiently flow the surface through the evolution, without requiring a costly initialization at the beginning of each time‐step. Using our approach, we demonstrate a factor of nearly seven‐fold improvement over the non‐tracking implementation, supporting the evolution of surfaces consisting of 1M triangles at a rate of just a few seconds per update.Item A Survey of Image Statistics Relevant to Computer Graphics(The Eurographics Association and Blackwell Publishing Ltd., 2011) Pouli, Tania; Cunningham, Douglas W.; Reinhard, Erik; Eduard Groeller and Holly RushmeierThe statistics of natural images have attracted the attention of researchers in a variety of fields and have been used as a means to better understand the human visual system and its processes. A number of algorithms in computer graphics, vision and image processing take advantage of such statistical findings to create visually more plausible results. With this report we aim to review the state of the art in image statistics and discuss existing and potential applications within computer graphics and related areas.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 Flexible and Accurate Transparent - Object Matting and Compositing Using Refractive Vector Field(The Eurographics Association and Blackwell Publishing Ltd., 2011) Duan, Qi; Zheng, Jianmin; Cai, Jianfei; Eduard Groeller and Holly RushmeierIn digital image editing, environment matting and compositing are fundamental and interesting operations that can capture and simulate the refraction and reflection effects of light from an environment. The state‐of‐the‐art real‐time environment matting and compositing method is short of flexibility, in the sense that it has to repeat the entire complex matte acquisition process if the distance between the object and the background is different from that in the acquisition stage, and also lacks accuracy, in the sense that it can only remove noises but not errors. In this paper, we introduce the concept of refractive vector and propose to use a refractive vector field as a new representation for environment matte. Such refractive vector field provides great flexibility for transparent‐object environment matting and compositing. Particularly, with only one process of the matte acquisition and the refractive vector field extraction, we are able to composite the transparent object into an arbitrary background at any distance. Furthermore, we introduce a piecewise vector field fitting algorithm to simultaneously remove both noises and errors contained in the extracted matte data. Experimental results show that our method is less sensitive to artefacts and can generate perceptually good composition results for more general scenarios.Item The State of the Art in Topology‐Based Visualization of Unsteady Flow(The Eurographics Association and Blackwell Publishing Ltd., 2011) Pobitzer, Armin; Peikert, Ronald; Fuchs, Raphael; Schindler, Benjamin; Kuhn, Alexander; Theisel, Holger; Matković, Krešimir; Hauser, Helwig; Eduard Groeller and Holly RushmeierVector fields are a common concept for the representation of many different kinds of flow phenomena in science and engineering. Methods based on vector field topology are known for their convenience for visualizing and analysing steady flows, but a counterpart for unsteady flows is still missing. However, a lot of good and relevant work aiming at such a solution is available. We give an overview of previous research leading towards topology‐based and topology‐inspired visualization of unsteady flow, pointing out the different approaches and methodologies involved as well as their relation to each other, taking classical (i.e. steady) vector field topology as our starting point. Particularly, we focus on Lagrangian methods, space–time domain approaches, local methods and stochastic and multifield approaches. Furthermore, we illustrate our review with practical examples for the different approaches.Item New EUROGRAPHICS Fellows(The Eurographics Association and Blackwell Publishing Ltd., 2011) Eduard Groeller and Holly Rushmeier