EG2009

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https://diglib7.eg.org/handle/10.2312/269

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3D Anatomical Modelling and Simulation Concepts
(The Eurographics Association, 2009) Magnenat-Thalmann, N.; Schmid, J.; Delingette, H.; Agus, M.; Guitian, J. A. Iglesias; K. Museth and D. Weiskopf
Nowadays, a large panel of medical acquisitions devices are made available producing a large amount of information such as high-resolution volumes, temporal sequences or functional images. Although this information helps scientists and physicians better understand the human anatomy and physiology, it becomes more-and-more difficult to analyse and visualise it. In this context, anatomical and functional models that combine multi-modal information are highly demanded. These models are successfully used in medical simulations such as virtual surgical interventions (e.g., bone, liver surgeries) or physiological process analysis (e.g., tumour growth, cartilage degeneration). They improve the diagnosis and assist the physicians. In this tutorial, we will present the current research issues towards the creation of patient-specific anatomical models and their functional simulation. Various topics in medical modelling/simulation will be addressed, focusing on computer-graphics based approaches, such as deformable models in image segmentation, data fusion, interactive physically-based simulation and costefficient visualisation. Examples will be given in the musculoskeletal, cardiac and vascular domains. All speakers are partners of the EU project "3D Anatomical Human" led by MIRALab - University of Geneva.
Adaptive Caustic Maps Using Deferred Shading
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Wyman, Chris; Nichols, Greg
Advanced GPU Volume Rendering for Virtual Endoscopy
(The Eurographics Association, 2009) Krüger, Arno; Kubisch, Christoph; Strauß, Gero; Preim, Bernhard; K. Bühler and D. Bartz
For difficult cases in endoscopic sinus surgery, a careful planning of the intervention is necessary. Virtual endoscopy enables the visualization of the operating field and additional information, such as risk structures and target structures to be removed. The Sinus Endoscopy system provides the functional range of a virtual endoscopic system with special focus on a realistic representation. Furthermore, by using direct volume rendering, we avoid time-consuming segmentation steps for the use of individual patient datasets. However, the image quality of the endoscopic view can be adjusted in a way that a standard computer with a modern standard graphics card achieves interactive frame rates with low CPU utilization. Thereby, characteristics of the endoscopic view are systematically used for the optimization of the volume rendering speed. As a small standalone application it can be instantly used for surgical planning and patient education. The system was used for preoperative planning in 102 cases, provides useful information for intervention planning (e.g., anatomic variations of the Rec. Frontalis), and closely resembles the intraoperative situation.
Analysis and Retrieval Techniques for Motion and Music Data
(The Eurographics Association, 2009) Müller, Meinard; K. Museth and D. Weiskopf
In this tutorial, we study fundamental algorithms and concepts for the analysis, classification, indexing, and retrieval of time-dependent data streams considering motion capture data as well as waveform-based music data as examples. Important aspects concern the design of suitable features, the notion of similarity used to compare data streams, as well as data organization. One general goal of this tutorial is to highlight the interplay between modeling, experimentation, and mathematical theory as well as to give some insights into active research fields.
An Analytical Solution to Single Scattering in Homogeneous Participating Media
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Pegoraro, Vincent; Parker, Steven G.
Despite their numerous applications, efficiently rendering participating media remains a challenging task due to the intricacy of the radiative transport equation. As they provide a generic means of solving a wide variety of problems, numerical methods are most often used to solve the air-light integral even under simplifying assumptions. In this paper, we present a novel analytical approach to single scattering from isotropic point light sources in homogeneous media. We derive the first closed-form solution to the air-light integral in isotropic media and extend this formulation to anisotropic phase functions. The technique relies neither on pre-computation nor on storage, and we provide a practical implementation allowing for an explicit control on the accuracy of the solutions. Finally, we demonstrate its quantitative and qualitative benefits over both previous numerical and analytical approaches.
Animating Pictures of Fluid using Video Examples
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Okabe, Makoto; Anjyo, Ken; Igarashi, Takeo; Seidel, Hans-Peter
We propose a system that allows the user to design a continuous flow animation starting from a still fluid image. The basic idea is to apply the fluid motion extracted from a video example to the target image. The system first decomposes the video example into three components, an average image, a flow field and residuals. The user then specifies equivalent information over the target image. The user manually paints the rough flow field, and the system automatically refines it using the estimated gradients of the target image. The user semi-automatically transfers the residuals onto the target image. The system then approximates the average image and synthesizes an animation on the target image by adding the transferred residuals and warping them according to the user-specified flow field. Finally, the system adjusts the appearance of the resulting animation by applying histogram matching. We designed animations of various pictures, such as rivers, waterfalls, fires, and smoke.
Anisotropic Radiance-Cache Splatting for Efficiently Computing High-Quality Global Illumination with Lightcuts
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Herzog, Robert; Myszkowski, Karol; Seidel, Hans-Peter
Computing global illumination in complex scenes is even with todays computational power a demanding task. In this work we propose a novel irradiance caching scheme that combines the advantages of two state-of-the-art algorithms for high-quality global illumination rendering: lightcuts, an adaptive and hierarchical instant-radiosity based algorithm and the widely used (ir)radiance caching algorithm for sparse sampling and interpolation of (ir)radiance in object space. Our adaptive radiance caching algorithm is based on anisotropic cache splatting, which adapts the cache footprints not only to the magnitude of the illumination gradient computed with light-cuts but also to its orientation allowing larger interpolation errors along the direction of coherent illumination while reducing the error along the illumination gradient. Since lightcuts computes the direct and indirect lighting seamlessly, we use a two-layer radiance cache, to store and control the interpolation of direct and indirect lighting individually with different error criteria. In multiple iterations our method detects cache interpolation errors above the visibility threshold of a pixel and reduces the anisotropic cache footprints accordingly. We achieve significantly better image quality while also speeding up the computation costs by one to two orders of magnitude with respect to the well-known photon mapping with (ir)radiance caching procedure.
Applet Competition as an Educational Tool in Creating Novel e-Textbook
(The Eurographics Association, 2009) Czanner, Silvester; Ferko, Andrej; Stugel, Juraj; Nunukova, Pavla; G. Domik and R. Scateni
We introduce a long-term competition-oriented project, using learning by doing (applets). The output of this project is updated every year at http://www.netgraphics.sk/. Many undergraduate students at the University of Warwick and the Comenius University compete in developing the e-Textbook, called Computer Graphics Virtual Textbook. The current version offers supplementary material for particular CG courses but it is also an independent source of information for all people interested in CG. There is currently 126 students enrolled for this competition. Every year, the number of valuable applets or applet innovations is lower than the total number of students. The three winners of 2008 round of applet competition will be announced before Christmas (and their creations will be presented at the SCCG09 conference). The best units of this project will be submitted to CGEMS.
Applications of Multitouch and Gaming Technology for the Classroom
(The Eurographics Association, 2009) Muto, William; Dobies, Justin; Diefenbach, Paul; G. Domik and R. Scateni
Multi-point touch screens have enjoyed recent popularity due to their natural tendency to create highly intuitive and user-friendly systems for even the novice user. We believe that multitouch is well-suited for educational purposes, since it engages users through an invisible interface and natural, gestural interaction, as well as promoting collaborative learning through equal access, as opposed to individual or "driver and co-pilot" learning at a traditional computer workstation. In this paper, we adopt this powerful interface and combine it with 3D simulation and gaming technology to create a novel teaching tool, incorporating digital learning content co-developed with educators and providing access for administration and student assessment.
Arches: a Framework for Modeling Complex Terrains
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Peytavie, A.; Galin, E.; Grosjean, J.; Merillou, S.
In this paper, we present a framework for representing complex terrains with such features as overhangs, arches and caves and including different materials such as sand and rocks. Our hybrid model combines a volumetric discrete data structure that stores the different materials and an implicit representation for sculpting and reconstructing the surface of the terrain. Complex scenes can be edited and sculpted interactively with high level tools. We also propose an original rock generation technique that enables us to automatically generate complex rocky sceneries with piles of rocks without any computationally demanding physically-based simulation.
Bidirectional Importance Sampling for Unstructured Direct Illumination
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Wang, Rui; Akerlund, Oskar
Recent research in bidirectional importance sampling has focused primarily on structured illumination sources such as distant environment maps, while unstructured illumination has received little attention. In this paper, we present a method for bidirectional importance sampling of unstructured illumination, allowing us to use the same method for sampling both distant as well as local/indirect sources. Building upon recent work in [WFA*05], we model complex illumination as a large set of point lights. The subsequent sampling process draws samples only from this point set. We start by constructing a piecewise constant approximation for the lighting using an illumination cut [CPWAP08]. We show that this cut can be used directly for illumination importance sampling. We then use BRDF importance sampling followed by sample counting to update the cut, resulting in a bidirectional distribution that closely approximates the product of the illumination and BRDF. Drawing visibility samples from this new distribution significantly reduces the sampling variance. As a main advance over previous work, our method allows for unstructured sources, including arbitrary local direct lighting and one-bounce of indirect lighting.
Bilateral Filter Based Compositing for Variable Exposure Photography
(The Eurographics Association, 2009) Raman, Shanmuganathan; Chaudhuri, Subhasis; P. Alliez and M. Magnor
Compositing a scene from multiple images is of considerable interest to graphics professionals. Typical compositing techniques involve estimation or explicit preparation of matte by an artist. In this article, we address the problem of automatic compositing of a scene from images obtained through variable exposure photography. We consider the High Dynamic Range Imaging (HDRI) problem and review some of the existing approaches for directly generating a Low Dynamic Range (LDR) image from multi-exposure images. We propose a computationally efficient method of scene compositing using edge-preserving filters such as bilateral filters. The key challenge is to composite the multi-exposure images in such a way so as to preserve details in both brightly and poorly illuminated regions of the scene within the limited dynamic range.
Character Motion Synthesis by Topology Coordinates
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Ho, Edmond S.L.; Komura, Taku
In this paper, we propose a new method to efficiently synthesize character motions that involve close contacts such as wearing a T-shirt, passing the arms through the strings of a knapsack, or piggy-back carrying an injured person. We introduce the concept of topology coordinates, in which the topological relationships of the segments are embedded into the attributes. As a result, the computation for collision avoidance can be greatly reduced for complex motions that require tangling the segments of the body. Our method can be combinedly used with other prevalent frame-based optimization techniques such as inverse kinematics.
Color correction for tone mapping
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Mantiuk, R.; Mantiuk, R.; Tomaszewska, A.; Heidrich, W.
Tone mapping algorithms offer sophisticated methods for mapping a real-world luminance range to the luminance range of the output medium but they often cause changes in color appearance. In this work we conduct a series of subjective appearance matching experiments to measure the change in image colorfulness after contrast compression and enhancement. The results indicate that the relation between contrast compression and the color saturation correction that matches color appearance is non-linear and smaller color correction is required for small change of contrast. We demonstrate that the relation cannot be fully explained by color appearance models. We propose color correction formulas that can be used with existing tone mapping algorithms. We extend existing global and local tone mapping operators and show that the proposed color correction formulas can preserve original image colors after tone scale manipulation.
Completion and Reconstruction with Primitive Shapes
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Schnabel, Ruwen; Degener, Patrick; Klein, Reinhard
We consider the problem of reconstruction from incomplete point-clouds. To find a closed mesh the reconstruction is guided by a set of primitive shapes which has been detected on the input point-cloud (e.g. planes, cylinders etc.). With this guidance we not only continue the surrounding structure into the holes but also synthesize plausible edges and corners from the primitives intersections. To this end we give a surface energy functional that incorporates the primitive shapes in a guiding vector field. The discretized functional can be minimized with an efficient graph-cut algorithm. A novel greedy optimization strategy is proposed to minimize the functional under the constraint that surface parts corresponding to a given primitive must be connected. From the primitive shapes our method can also reconstruct an idealized model that is suitable for use in a CAD system.
Complex Barycentric Coordinates with Applications to Planar Shape Deformation
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Weber, Ofir; Ben-Chen, Mirela; Gotsman, Craig
Compressive Dual Photography
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Sen, Pradeep; Darabi, Soheil
The accurate measurement of the light transport characteristics of a complex scene is an important goal in computer graphics and has applications in relighting and dual photography. However, since the light transport data sets are typically very large, much of the previous research has focused on adaptive algorithms that capture them efficiently. In this work, we propose a novel, non-adaptive algorithm that takes advantage of the compressibility of the light transport signal in a transform domain to capture it with less acquisitions than with standard approaches. To do this, we leverage recent work in the area of compressed sensing, where a signal is reconstructed from a few samples assuming that it is sparse in a transform domain. We demonstrate our approach by performing dual photography and relighting by using a much smaller number of acquisitions than would normally be needed. Because our algorithm is not adaptive, it is also simpler to implement than many of the current approaches.
Computer Animation Curriculum: An Interdisciplinary Approach
(The Eurographics Association, 2009) Larboulette, Caroline; G. Domik and R. Scateni
This paper presents a Computer Animation curriculum worth 2.5 ECTS intended for graduate students enrolled in a Master s degree of Computer Graphics, Video Games and Virtual Reality. The content of the lecture fits the recommendations made for the topic of Animation I at the Computer Graphics Education Workshop [BCFH06] that was held in Vienna in 2006. The main novelty is, in addition to presenting a detailed curriculum, its interdis- ciplinary aspect. Indeed, while it is intended for a Computer Science degree, it also aims at teaching some artistic and software use aspects.
Continuous Search and Replace in Vector Graphics
(The Eurographics Association, 2009) Loviscach, Joern; P. Alliez and M. Magnor
Many types of vector graphics comprise large numbers of almost identical partial shapes such as serifs in typeface design, ornaments in illustrations, and stylistic elements in icon design. As of today, later design changes of such shapes require the user to edit every instance on its own. Standard features of vector graphics software help with the automated replacement of stand-alone graphical objects, but do not cover partial shapes. Hence, a geometric search & replace function is needed, which is exacerbated by the circumstance that the repeated shapes construction from curve segments tends to vary from instance to instance, which requires a continuous approach that does not rely on a fixed division of a path into segments. This paper presents a geometric search and replace function that addresses these issues, possesses adjustable tolerance against orientation and size changes between the search pattern shape and the retrieved shapes, and is integrated with a standard vector graphics program.
Continuum-based Strain Limiting
(The Eurographics Association and Blackwell Publishing Ltd, 2009) Thomaszewski, Bernhard; Pabst, Simon; Strasser, Wolfgang
We present Continuum-based Strain Limiting (CSL) - a new method for limiting deformations in physically-based cloth simulations. Despite recent developments for nearly inextensible materials, the efficient simulation of general biphasic textiles and their anisotropic behavior remains challenging. Many approaches use soft materials and enforce limits on edge elongations, leading to discretization-dependent behavior. Moreover, they offer no explicit control over shearing and stretching unless specifically aligned meshes are used. Based on a continuum deformation measure, our method allows accurate control over all strain components using individual thresholds. We impose deformation limits element-wise and cast the problem as a 6x6 system of linear equations. CSL can be combined with any cloth simulator and, as a velocity filter, integrates seamlessly into standard collision handling.

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