STARs 2008

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Preface and Table of Contents
(The Eurographics Association, 2008) -; Theoharis Theoharis and Philip Dutre
Preface and Table of Contents
Transparent and Specular Object Reconstruction
(The Eurographics Association, 2008) Ihrke, Ivo; Kutulakos, Kiriakos N.; Lensch, Hendrik P. A.; Magnor, Marcus; Heidrich, Wolfgang; Theoharis Theoharis and Philip Dutre
This state of the art report covers reconstruction methods for transparent and specular objects or phenomena. While the 3D acquisition of opaque surfaces with lambertian reflectance is a well-studied problem, transparent, refractive, specular and potentially dynamic scenes pose challenging problems for acquisition systems. This report reviews and categorizes the literature in this field. Despite tremendous interest in object digitization, the acquisition of digital models of transparent or specular objects is far from being a solved problem. On the other hand, real-world data is in high demand for applications such as object modeling, preservation of historic artifacts and as input to data driven modeling techniques. With this report we aim at providing a reference for and an introduction to the field of transparent and specular object reconstruction. We describe acquisition approaches for different classes of objects. Transparent objects/phenomena that do not change the straight ray geometry can be found foremost in natural phenomena. Refraction effects are usually small and can be considered negligible for these objects. Phenomena as diverse as fire, smoke, and interstellar nebulae can be modeled using a straight ray model of image formation. Refractive and specular surfaces on the other hand change the straight rays into usually piecewise linear ray paths, adding additional complexity to the reconstruction problem. Translucent objects exhibit significant sub-surface scattering effects rendering traditional acquisition approaches unstable. Different classes of techniques have been developed to deal with these problems and good reconstruction results can be achieved with current state-of-the-art techniques. However, the approaches are still specialized and targeted at very specific object classes. We classify the existing literature and hope to provide an entry point to this exiting field.
Multiperspective Modeling, Rendering, and Imaging
(The Eurographics Association, 2008) Yu, Jingyi; McMillan, Leonard; Sturm, Peter; Theoharis Theoharis and Philip Dutre
A perspective image represents the spatial relationships of objects in a scene as they appear from a single viewpoint. In contrast, a multiperspective image combines what is seen from several viewpoints into a single image. Despite their incongruity of view, effective multiperspective images are able to preserve spatial coherence and can depict, within a single context, details of a scene that are simultaneously inaccessible from a single view, yet easily interpretable by a viewer. In computer vision, multiperspective images have been used for analyzing structure revealed via motion and generating panoramic images with a wide field-of-view using mirrors. In this STAR, we provide a practical guide on topics in multiperspective modeling and rendering methods and multiperspective imaging systems. We start with a brief review of multiperspective image techniques frequently employed by artists such as the visual paradoxes of Escher, the Cubism of Picasso and Braque, and multiperspective panoramas in cel animations. We then characterize existing multiperspective camera models, with an emphasis on their underlying geometry and image properties. We demonstrate how to use these camera models for creating specific multiperspective rendering effects. Furthermore, we show that many of these cameras satisfy the multiperspective stereo constraints and we demonstrate several multiperspective imaging systems for extracting 3D geometry for computer vision. The participants learn about topics in multiperspective modeling and rendering for generating compelling pictures for computer graphics and in multiperspective imaging for extracting 3D geometry for computer vision. We hope to provide enough fundamentals to satisfy the technical specialist without intimidating curious digital artists interested in multiperspective images. The intended audience includes digital artists, photographers, and computer graphics and computer vision researchers using or building multiperspective cameras. They will learn about multiperspective modeling and rendering, along with many real world multiperspective imaging systems.
Advanced Algorithms in Medical Computer Graphics
(The Eurographics Association, 2008) Klein, Jan; Bartz, Dirk; Friman, Ola; Hadwiger, Markus; Preim, Bernhard; Ritter, Felix; Vilanova, Anna; Zachmann, Gabriel; Theoharis Theoharis and Philip Dutre
Advanced algorithms and efficient visualization techniques are of major importance in intra-operative imaging and image-guided surgery. The surgical environment is characterized by a high information flow and fast decisions, requiring efficient and intuitive presentation of complex medical data and precision in the visualization results. Regions or organs that are classified as risk structures are in this context of particular interest. This paper summarizes advanced algorithms for medical visualization with special focus on risk structures such as tumors, vascular systems and white matter fiber tracts. Algorithms and techniques employed in intra-operative situations or virtual and mixed reality simulations are discussed. Finally, the prototyping and software development process of medical visualization algorithms is addressed.
The Role of Perception for Computer Graphics
(The Eurographics Association, 2008) Bartz, Dirk; Cunningham, Douglas; Fischer, Jan; Wallraven, Christian; Theoharis Theoharis and Philip Dutre
Traditionally, computer graphics strived to achieve the technically best representation of the scenario or scene. For rendering, this lead to the preeminence of representations based on the physics of light interacting with different media and materials. Research in virtual reality has focussed on interactivity and therefore on real-time rendering techniques that improve the immersion of users in the virtual environments. In contrast, visualization has focused on representations that that maximizes the information content. In most cases, such representations are not physically-based, requiring instead more abstract approaches. Recently, the increasing integration of the extensive knowledge and methods from perception research into computer graphics has fundamentally altered both fields, offering not only new research questions, but also new ways of solving existing issues. Against this backdrop of an increasing importance of perceptual research in all areas related to computergenerated imagery, we discuss the state of the art of perception in computer graphics.
Quadruped Animation
(The Eurographics Association, 2008) Skrba, Ljiljana; Reveret, Lionel; Hetroy, Franck; Cani, Marie-Paule; O'Sullivan, Carol; Theoharis Theoharis and Philip Dutre
Films like Shrek, Madagascar, The Chronicles of Narnia and Charlotte s web all have something in common: realistic quadruped animations. While the animation of animals has been popular for a long time, the technical challenges associated with creating highly realistic, computer generated creatures have been receiving increasing attention recently. The entertainment, education and medical industries have increased the demand for simulation of realistic animals in the computer graphics area. In order to achieve this, several challenges need to be overcome: gathering and processing data that embodies the natural motion of an animal which is made more difficult by the fact that most animals cannot be easily motion-captured; build accurate kinematic models for animals, in particular with adapted animation skeletons; and develop either kinematic or physically-based animation methods, either embedding some a priori knowledge about the way that quadrupeds locomote and/or building on some example of real motion. In this state of the art report, we present an overview of the common techniques used to date for realistic quadruped animation. This includes an outline of the various ways that realistic quadruped motion can be achieved, through video-based acquisition, physics based models, inverse kinematics, or some combination of the above. The research presented represents a cross fertilisation of vision, graphics and interaction methods.
A Taxonomy of Modeling Techniques using Sketch-Based Interfaces
(The Eurographics Association, 2008) Olsen, L.; Samavati, F. F.; Sousa, M. Costa; Jorge, J.; Theoharis Theoharis and Philip Dutre
Traditional user interfaces in modeling have followed the WIMP (Window, Icon, Menu, Pointer) paradigm. While functional and powerful, they can also be cumbersome and daunting to a novice user; creating a complex model requires much expertise and effort. A recent trend is toward more accessible and natural interfaces, which has lead to sketch-based interfaces for modeling (SBIM). The goal is to allow hand-drawn sketches to be used in the modeling process, from rough model creation through to fine detail construction. Mapping 2D sketches to a 3D modeling operation is a difficult and ambiguous task, so our categorization is based on how an SBIM application chooses to interpret a sketch, of which there are three primary methods: to create a 3D model, to add details to an existing model, or to deform and manipulate a model. In this STAR, we present a taxonomy of sketchbased interfaces focused on geometric modeling applications. The canonical and recent works are presented and classified, including techniques for sketch acquisition, filtering, and interpretation. The report also includes a discussion of important challenges and open problems for researchers to tackle in the coming years.

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