EG2015

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https://diglib.eg.org/handle/10.2312/12086

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Real-Time Subspace Integration for Example-Based Elastic Material
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zhang, Wenjing; Zheng, Jianmin; Thalmann, Nadia Magnenat; Olga Sorkine-Hornung and Michael Wimmer
Example-based material allows simulating complex material behaviors in an art-directed way. This paper presents a method for fast subspace integration for example-based elastic material, which is suitable for real-time simulation in computer graphics. At the core of the method is the formulation of a new potential using example-based Green strain tensors. By using this potential, the deformation can be attracted towards the example-based deformation feature space, the example weights can be explicitly obtained and the internal force can be decomposed into the conventional one and an additional one induced by the examples. The real-time subspace integration is then developed with subspace integration costs independent of geometric complexity, and both the reduced conventional internal force and additional one being cubic polynomials in reduced coordinates. Experiments demonstrate that our method can achieve real-time simulation while providing comparable quality with the prior art.
EUROGRAPHICS 2015: Posters Frontmatter
(Eurographics Association, 2015) Barbara Solenthaler; Enrico Puppo;
Robust Statistical Pixel Estimation
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Jung, Jin Woo; Meyer, Gary; DeLong, Ralph; Olga Sorkine-Hornung and Michael Wimmer
Robust statistical methods are employed to reduce the noise in Monte Carlo ray tracing. Through the use of resampling, the sample mean distribution is determined for each pixel. Because this distribution is uni-modal and normal for a large sample size, robust estimates converge to the true mean of the pixel values. Compared to existing methods, less additional storage is required at each pixel because the sample mean distribution can be distilled down to a compact size, and fewer computations are necessary because the robust estimation process is sampling independent and needs a small input size to compute pixel values. The robust statistical pixel estimators are not only resistant to impulse noise, but they also remove general noise from fat-tailed distributions. A substantial speedup in rendering can therefore be achieved by reducing the number of samples required for a desired image quality. The effectiveness of the proposed approach is demonstrated for path tracing simulations.
Big City 3D Visual Analysis
(The Eurographics Association, 2015) Lv, Zhihan; Li, Xiaoming; Zhang, Baoyun; Wang, Weixi; Feng, Shengzhong; Hu, Jinxing; B. Solenthaler and E. Puppo
A big city visual analysis platform based on Web Virtual Reality Geographical Information System (WEBVRGIS) is presented. Extensive model editing functions and spatial analysis functions are available, including terrain analysis, spatial analysis, sunlight analysis, traffic analysis, population analysis and community analysis.
Composition-Aware Scene Optimization for Product Images
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Liu, Tianqiang; McCann, Jim; Li, Wilmot; Funkhouser, Thomas; Olga Sorkine-Hornung and Michael Wimmer
Increasingly, companies are creating product advertisements and catalog images using computer renderings of 3D scenes. A common goal for these companies is to create aesthetically appealing compositions that highlight objects of interest within the context of a scene. Unfortunately, this goal is challenging, not only due to the need to balance the trade-off among aesthetic principles and design constraints, but also because of the huge search space induced by possible camera parameters, object placement, material choices, etc. Previous methods have investigated only optimization of camera parameters. In this paper, we develop a tool that starts from an initial scene description and a set of high-level constraints provided by a stylist and then automatically generates an optimized scene whose 2D composition is improved. It does so by locally adjusting the 3D object transformations, surface materials, and camera parameters. The value of this tool is demonstrated in a variety of applications motivated by product catalogs, including rough layout refinement, detail image creation, home planning, cultural customization, and text inlay placement. Results of a perceptual study indicate that our system produces images preferable for product advertisement compared to a more traditional camera-only optimization.
Interactive Pixel-Accurate Rendering of LR-Splines and T-Splines
(The Eurographics Association, 2015) Hjelmervik, Jon M.; Fuchs, Franz G.; B. Bickel and T. Ritschel
Flexible surface types on irregular grids, such as T-splines and LR-splines, are gaining popularity in science and industry due to the possibility for local grid refinement. We present a novel rendering algorithm for those surface types that guarantees pixel-accurate geometry and water-tight tessellation (no drop-outs). Before rendering, we extract the Bézier coefficients. The resulting irregular grids of Bézier patches are then rendered using a multistage algorithm, that decouples the tesselator and the patch geometry. The implementation using OpenGL utilizes compute shaders and hardware tessellation functionality. We showcase interactive rendering achieved by our approach on three representative use cases.
T-SAH: Animation Optimized Bounding Volume Hierarchies
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Bittner, Jirí; Meister, Daniel; Olga Sorkine-Hornung and Michael Wimmer
We propose a method for creating a bounding volume hierarchy (BVH) that is optimized for all frames of a given animated scene. The method is based on a novel extension of surface area heuristic to temporal domain (T-SAH). We perform iterative BVH optimization using T-SAH and create a single BVH accounting for scene geometry distribution at different frames of the animation. Having a single optimized BVH for the whole animation makes our method extremely easy to integrate to any application using BVHs, limiting the per-frame overhead only to refitting the bounding volumes.We evaluated the T-SAH optimized BVHs in the scope of real-time GPU ray tracing. We demonstrate, that our method can handle even highly complex inputs with large deformations and significant topology changes. The results show, that in a vast majority of tested scenes our method provides significantly better run-time performance than traditional SAH and also better performance than GPU based per-frame BVH rebuild.
High Reliefs from 3D Scenes
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Arpa, Sami; Süsstrunk, Sabine; Hersch, Roger D.; Olga Sorkine-Hornung and Michael Wimmer
We present a method for synthesizing high reliefs, a sculpting technique that attaches 3D objects onto a 2D surface within a limited depth range. The main challenges are the preservation of distinct scene parts by preserving depth discontinuities, the fine details of the shape, and the overall continuity of the scene. Bas relief depth compression methods such as gradient compression and depth range compression are not applicable for high relief production. Instead, our method is based on differential coordinates to bring scene elements to the relief plane while preserving depth discontinuities and surface details of the scene. We select a user-defined number of attenuation points within the scene, attenuate these points towards the relief plane and recompute the positions of all scene elements by preserving the differential coordinates. Finally, if the desired depth range is not achieved we apply a range compression. High relief synthesis is semi-automatic and can be controlled by user-defined parameters to adjust the depth range, as well as the placement of the scene elements with respect to the relief plane.
Tools and Techniques for Direct Volume Interaction
(The Eurographics Association, 2015) Wiebel, Alexander; Isenberg, Tobias; Bruckner, Stefan; Ropinski, Timo; M. Zwicker and C. Soler
Volumetric data, continuous as well as scattered, are close to ubiquitous in natural sciences, medicine and engineering. While the visualization of such data itself is not straightforward, interaction with and manipulation of volumetric data - essential aspects of effective data analysis - pose even further challenges. Due to the three-dimensional nature of the data, it is not straightforward how to select features, pick positions, segment regions or otherwise interact with the rendering or the data themselves in an intuitive manner. In this tutorial we will present state of the art approaches and methods for addressing these challenges. The tutorial will start by reviewing common classes of interaction tasks in volume visualization, motivating the need for direct interaction and manipulation, and describing the usually encountered difficulties. Interaction with visualization traditionally happens in PC-based environments with mouse and 2D displays. The second part of the tutorial discusses specific interaction methods that deal with the challenges in this context. Furthermore, an overview of the range of applications of these techniques is given to demonstrate their utility. The use of alternative paradigms for interaction with volumes is discussed in the third part. Such paradigms, e.g. in the context of touch interfaces or immersive environments, provide novel opportunities for volume exploration and manipulation, but also pose specific challenges themselves. The last part completes the tutorial's scope by a treatment of higher-level interaction techniques guiding users in navigation and exploration of the data using automatic or semiautomatic methods for identifying relevant parameter ranges. Such techniques employ additional, sometimes workflow-specific, information to assist in choosing effective volume visualization techniques and related attributes.
EUROGRAPHICS 2015: Education Papers Frontmatter
(Eurographics Association, 2015) Matthias Teschner; Michael Bronstein;
Redesign of an Introductory Computer Graphics Course
(The Eurographics Association, 2015) Ackermann, Philipp; Bach, Thomas; M. Bronstein and M. Teschner
The redesign of our historically grown Computer Graphics course was primarily triggered by the need to incorporate modern, shader-based OpenGL. This technical modification led to discussions on the relevance of course topics, the order of presentation, the role of sample programs, and problem sets addressed in lab exercises. The redesign resulted in changing from a bottom-up to a top-down approach and in a shift from low-level procedural OpenGL to the use of a high-level object-oriented 3D library on top ofWebGL. This paper presents our motivation, applied principles, first results in teaching the redesigned course, and student feedback.
Sketch-Based Controllers for Blendshape Facial Animation
(The Eurographics Association, 2015) Cetinaslan, Ozan; Orvalho, Verónica; Lewis, John; B. Bickel and T. Ritschel
The blendshape approach is a widely used technique to generate realistic facial animation. However, creating blendshape facial animations using traditional weight editing tools requires either memorizing the function of a large number of parameters, or a trial-and-error search in a high-dimensional space. Direct manipulation interfaces address this problem, allowing the artist to directly move and pin manipulators placed on the surface of the face. Placing manipulators is an open-ended and slightly unnatural task for artists however. In this paper we present a sketch-based approach to this problem, inspired by artists' brush painting on canvas. In this approach the artist simply sketches directly onto the 3D model the positions of the manipulators that they feel are needed to produce particular facial expression. The manipulators activate the blendshapes in the model and allow the user to interactively create the desired facial poses by a dragging operation in screen coordinates. Our hybrid method can be used with any blendshape facial model and allows producing expeditious manipulation in an intuitive way.
Egocentric Normalization of Kinematic Path
(The Eurographics Association, 2015) Molla, Eray; Boulic, Ronan; B. Solenthaler and E. Puppo
We focus on retargetting the class of movements involving self-interactions onto characters with different size and proportion. Such postures may produce self-collisions and/or alter the intended semantics. We introduce a technique to normalize the spatial relationship vectors between the body parts of the source character. This allows for morphological adaptation of these vectors onto the target characters, hence preserving the semantics in postures with and without body-contact.
Morse Complexes for Shape Segmentation and Homological Analysis: Discrete Models and Algorithms
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Floriani, Leila De; Fugacci, Ulderico; Iuricich, Federico; Magillo, Paola; K. Hormann and O. Staadt
Morse theory offers a natural and mathematically-sound tool for shape analysis and understanding. It allows studying the behavior of a scalar field defined on a manifold. Starting from a Morse function, we can decompose the domain of the function into meaningful regions associated with the critical points of the field. Such decompositions, called Morse complexes, provide a segmentation of a shape and are extensively used in terrain modeling and in scientific visualization. Discrete Morse theory, a combinatorial counterpart of smooth Morse theory defined over cell complexes, provides an excellent basis for computing Morse complexes in a robust and efficient way. Moreover, since a discrete Morse complex computed over a given complex has the same homology as the original one, but fewer cells, discrete Morse theory is a fundamental tool for detecting holes efficiently in shapes through homology and persistent homology. In this survey, we review, classify and analyze algorithms for computing and simplifying Morse complexes in the context of such applications with an emphasis on discrete Morse theory and on algorithms based on it.
Skeleton-Intrinsic Symmetrization of Shapes
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zheng, Qian; Hao, Zhuming; Huang, Hui; Xu, Kai; Zhang, Hao; Cohen-Or, Daniel; Chen, Baoquan; Olga Sorkine-Hornung and Michael Wimmer
Enhancing the self-symmetry of a shape is of fundamental aesthetic virtue. In this paper, we are interested in recovering the aesthetics of intrinsic reflection symmetries, where an asymmetric shape is symmetrized while keeping its general pose and perceived dynamics. The key challenge to intrinsic symmetrization is that the input shape has only approximate reflection symmetries, possibly far from perfect. The main premise of our work is that curve skeletons provide a concise and effective shape abstraction for analyzing approximate intrinsic symmetries as well as symmetrization. By measuring intrinsic distances over a curve skeleton for symmetry analysis, symmetrizing the skeleton, and then propagating the symmetrization from skeleton to shape, our approach to shape symmetrization is skeleton-intrinsic. Specifically, given an input shape and an extracted curve skeleton, we introduce the notion of a backbone as the path in the skeleton graph about which a self-matching of the input shape is optimal. We define an objective function for the reflective self-matching and develop an algorithm based on genetic programming to solve the global search problem for the backbone. The extracted backbone then guides the symmetrization of the skeleton, which in turn, guides the symmetrization of the whole shape. We show numerous intrinsic symmetrization results of hand drawn sketches and artist-modeled or reconstructed 3D shapes, as well as several applications of skeleton-intrinsic symmetrization of shapes.
Teaching Graphics To Students Struggling in Math: An Experience
(The Eurographics Association, 2015) Shesh, Amit; M. Bronstein and M. Teschner
Undergraduate students with a negative attitude towards Math present a unique challenge when teaching computer graphics. Most meaningful concepts in computer graphics involve directly working with Math in the classroom, and implementing tasks in programs requires a reasonable grounding in Math concepts and how to apply them. This paper presents a semester-long experience in using three strategies to address difficulties faced by computer science students who are interested in learning computer graphics, but feel less confident or uninterested in Math. Similar to how Math is taught in schools, we focus on giving students more and more practice in implementing progressively complex visual tasks. Students accomplish some tasks individually to develop a basic understanding before completing other tasks in groups. Students achieve more in a semester than before, and our preliminary observations show a higher rate of completion by students, moderate gains in performance in individual assignments and significant gains in overall class performance.
Implicit Formulation for SPH-based Viscous Fluids
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Takahashi, Tetsuya; Dobashi, Yoshinori; Fujishiro, Issei; Nishita, Tomoyuki; Lin, Ming C.; Olga Sorkine-Hornung and Michael Wimmer
We propose a stable and efficient particle-based method for simulating highly viscous fluids that can generate coiling and buckling phenomena and handle variable viscosity. In contrast to previous methods that use explicit integration, our method uses an implicit formulation to improve the robustness of viscosity integration, therefore enabling use of larger time steps and higher viscosities. We use Smoothed Particle Hydrodynamics to solve the full form of viscosity, constructing a sparse linear system with a symmetric positive definite matrix, while exploiting the variational principle that automatically enforces the boundary condition on free surfaces. We also propose a new method for extracting coefficients of the matrix contributed by second-ring neighbor particles to efficiently solve the linear system using a conjugate gradient solver. Several examples demonstrate the robustness and efficiency of our implicit formulation over previous methods and illustrate the versatility of our method.
Eye-tracktive: Measuring Attention to Body Parts when Judging Human Motions
(The Eurographics Association, 2015) Ennis, Cathy; Hoyet, Ludovic; O'Sullivan, Carol; B. Bickel and T. Ritschel
Virtual humans are often endowed with human-like characteristics to make them more appealing and engaging. Motion capture is a reliable way to represent natural motion on such characters, thereby allowing a wide range of animations to be automatically created and replicated. However, interpersonal differences in actors' performances can be subtle and complex, yet have a strong effect on the human observer. Such effects can be very difficult to express quantitatively or indeed even qualitatively. We investigate two subjective human motion characteristics: attractiveness and distinctiveness. We conduct a perceptual experiment, where participants' eye movements are tracked while they rate the motions of a range of actors. We found that participants fixate mostly on the torso, regardless of gait and actor sex, and very little on the limbs. However, they self-reported that they used hands, elbows and feet in their judgments, indicating a holistic approach to the problem.
Shape-from-Operator: Recovering Shapes from Intrinsic Operators
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Boscaini, Davide; Eynard, Davide; Kourounis, Drosos; Bronstein, Michael M.; Olga Sorkine-Hornung and Michael Wimmer
We formulate the problem of shape-from-operator (SfO), recovering an embedding of a mesh from intrinsic operators defined through the discrete metric (edge lengths). Particularly interesting instances of our SfO problem include: shape-from-Laplacian, allowing to transfer style between shapes; shape-from-difference operator, used to synthesize shape analogies; and shape-from-eigenvectors, allowing to generate 'intrinsic averages' of shape collections. Numerically, we approach the SfO problem by splitting it into two optimization sub-problems: metric-from-operator (reconstruction of the discrete metric from the intrinsic operator) and embedding-from-metric (finding a shape embedding that would realize a given metric, a setting of the multidimensional scaling problem). We study numerical properties of our problem, exemplify it on several applications, and discuss its imitations.
Recent Advances in Adaptive Sampling and Reconstruction for Monte Carlo Rendering
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Zwicker, Matthias; Jarosz, Wojciech; Lehtinen, Jaakko; Moon, Bochang; Ramamoorthi, Ravi; Rousselle, Fabrice; Sen, Pradeep; Soler, Cyril; Yoon, Sungeui E.; K. Hormann and O. Staadt
Monte Carlo integration is firmly established as the basis for most practical realistic image synthesis algorithms because of its flexibility and generality. However, the visual quality of rendered images often suffers from estimator variance, which appears as visually distracting noise. Adaptive sampling and reconstruction algorithms reduce variance by controlling the sampling density and aggregating samples in a reconstruction step, possibly over large image regions. In this paper we survey recent advances in this area. We distinguish between “a priori” methods that analyze the light transport equations and derive sampling rates and reconstruction filters from this analysis, and “a posteriori” methods that apply statistical techniques to sets of samples to drive the adaptive sampling and reconstruction process. They typically estimate the errors of several reconstruction filters, and select the best filter locally to minimize error. We discuss advantages and disadvantages of recent state-of-the-art techniques, and provide visual and quantitative comparisons. Some of these techniques are proving useful in real-world applications, and we aim to provide an overview for practitioners and researchers to assess these approaches. In addition, we discuss directions for potential further improvements.

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