EG2015

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

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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.
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.
A Virtual and Augmented Reality Course Based on Inexpensive Interaction Devices and Displays
(The Eurographics Association, 2015) Santos, Beatriz Sousa; Dias, Paulo; Madeira, Joaquim; M. Bronstein and M. Teschner
In the last years a plethora of affordable displays, sensors, and interaction devices has reached the market, fostering the application of Virtual and Augmented Reality to many new situations. Yet, creating such applications requires a good understanding of the field and specific technical skills typically not provided by current Computer Science and Engineering education. This paper presents a graduate level course offered to MSc. Programs in Computer and Electrical Engineering which introduces the main concepts, techniques and tools in Virtual and Augmented Reality. The aim is to provide students with enough background to understand, design, implement and test such applications. The course organization, the main issues addressed and bibliography, the sensors, interaction devices and displays used, and a sample of the practical projects are briefly described. Major issues are discussed and conclusions are drawn.
Separation of Manga Line Drawings and Screentones
(The Eurographics Association, 2015) Ito, Kota; Matsui, Yusuke; Yamasaki, Toshihiko; Aizawa, Kiyoharu; B. Bickel and T. Ritschel
Screentones are unique expressions of Japanese comics (manga), which enrich their visual expression. However, such screentones have a very different visual nature from that of line drawing areas; this prevents us from applying various kinds of image processing techniques to manga. We propose a method for extracting line drawings and removing screentones. We employ Laplacians of Gaussian filters and flow-based differences of Gaussian filters, one for removing screentones and the other for preserving lines, and make a binary mask for separating line drawings from manga by merging the results of the two filters. We show that the proposed method successfully separates line drawings and is better than existing methods in comparative studies.
Guided Analysis of Cardiac 4D PC-MRI Blood Flow Data
(The Eurographics Association, 2015) Köhler, Benjamin; Preim, Uta; Grothoff, Matthias; Gutberlet, Matthias; Fischbach, Katharina; Preim, Bernhard; H.-C. Hege and T. Ropinski
Four-dimensional phase-contrast magnetic resonance imaging (4D PC-MRI) allows the non-invasive acquisition of temporally resolved, three-dimensional blood flow information. Quantitative and qualitative data analysis helps to assess the cardiac function, severity of diseases and find indications of different cardiovascular pathologies. However, various steps are necessary to achieve expressive visualizations and reliable results. This comprises the correction of special MR-related artifacts, the segmentation of vessels, flow integration with feature extraction and the robust quantification of clinically important measures. A fast and easy-to-use processing pipeline is essential since the target user group are physicians. We present a system that offers such a guided workflow for cardiac 4D PC-MRI data. The aorta and pulmonary artery can be analyzed within ten minutes including vortex extraction and robust determination of the stroke volume as well as the percentaged backflow. 64 datasets of healthy volunteers and of patients with variable diseases such as aneurysms, coarctations and insufficiencies were processed so far.
Self Tuning Texture Optimization
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Kaspar, Alexandre; Neubert, Boris; Lischinski, Dani; Pauly, Mark; Kopf, Johannes; Olga Sorkine-Hornung and Michael Wimmer
The goal of example-based texture synthesis methods is to generate arbitrarily large textures from limited exemplars in order to fit the exact dimensions and resolution required for a specific modeling task. The challenge is to faithfully capture all of the visual characteristics of the exemplar texture, without introducing obvious repetitions or unnatural looking visual elements. While existing non-parametric synthesis methods have made remarkable progress towards this goal, most such methods have been demonstrated only on relatively low-resolution exemplars. Real-world high resolution textures often contain texture details at multiple scales, which these methods have difficulty reproducing faithfully. In this work, we present a new general-purpose and fully automatic selftuning non-parametric texture synthesis method that extends Texture Optimization by introducing several key improvements that result in superior synthesis ability. Our method is able to self-tune its various parameters and weights and focuses on addressing three challenging aspects of texture synthesis: (i) irregular large scale structures are faithfully reproduced through the use of automatically generated and weighted guidance channels; (ii) repetition and smoothing of texture patches is avoided by new spatial uniformity constraints; (iii) a smart initialization strategy is used in order to improve the synthesis of regular and near-regular textures, without affecting textures that do not exhibit regularities. We demonstrate the versatility and robustness of our completely automatic approach on a variety of challenging high-resolution texture exemplars.
Real-time Content Adaptive Depth Retargeting for Light Field Displays
(The Eurographics Association, 2015) Adhikarla, Vamsi Kiran; Marton, Fabio; Barsi, Attila; Kovács, Péter Tamás; Balogh, Tibor; Gobbetti, Enrico; B. Solenthaler and E. Puppo
Light field display systems present visual scenes using a set of directional light beams emitted from multiple light sources as if they are emitted from points in a physical scene. These displays offer better angular resolution and therefore provide more depth of field than other automultiscopic displays. However in some cases the size of a scene may still exceed the available depth range of a light field display. Thus, rendering on these displays requires suitable adaptation of 3D content for providing comfortable viewing experience. We propose a content adaptive depth retargeting method to automatically modify the scene depth to suit to the needs of a light field display. By analyzing the scene and using display specific parameters, we formulate and solve an optimization problem to non-linearly adapt the scene depth to display depth. Our method synthesizes the depth retargeted light field content in real-time for supporting interactive visualization and also preserves the 3D appearance of the displayed objects as much as possible.
Augmented Reality as a Tool to Deliver e-Learning based Blended Content in and out of the Class-room
(The Eurographics Association, 2015) Erdt, Marius; Maroothynaden, Jason; Peng, Junming; Müller-Wittig, Wolfgang; Gagnon, Paul; M. Bronstein and M. Teschner
In this paper, we present a mobile Augmented Reality application that can be used for undergraduate anatomical education. It can be used in and out of the classroom. In the classroom, the application can track and augment 3D objects such as a cadaveric solid organ (e.g. heart) specimens as well as 3D plastic anatomical models without the use of observable markers. Out-side the classroom, virtual representations of the hearts were computed and added as an offline version to the application allowing students to self-learn. To allow students to ''sense-make'' concepts and add additional educational value to offline content, the application can also track 2D content like printed posters. Augmentation in 2D and 3D views via various digital content modalities supports students in learning and ''sense-making'' anatomical terms and concepts.
A Cut-Cell Geometric Multigrid Poisson Solver for Fluid Simulation
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Weber, Daniel; Mueller-Roemer, Johannes; Stork, André; Fellner, Dieter W.; Olga Sorkine-Hornung and Michael Wimmer
We present a novel multigrid scheme based on a cut-cell formulation on regular staggered grids which generates compatible systems of linear equations on all levels of the multigrid hierarchy. This geometrically motivated formulation is derived from a finite volume approach and exhibits an improved rate of convergence compared to previous methods. Existing fluid solvers with voxelized domains can directly benefit from this approach by only modifying the representation of the non-fluid domain. The necessary building blocks are fully parallelizable and can therefore benefit from multi- and many-core architectures.
High-Order Recursive Filtering of Non-Uniformly Sampled Signals for Image and Video Processing
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Gastal, Eduardo S. L.; Oliveira, Manuel M.; Olga Sorkine-Hornung and Michael Wimmer
We present a discrete-time mathematical formulation for applying recursive digital filters to non-uniformly sampled signals. Our solution presents several desirable features: it preserves the stability of the original filters; is well-conditioned for low-pass, high-pass, and band-pass filters alike; its cost is linear in the number of samples and is not affected by the size of the filter support. Our method is general and works with any non-uniformly sampled signal and any recursive digital filter defined by a difference equation. Since our formulation directly uses the filter coefficients, it works out-of-the-box with existing methodologies for digital filter design. We demonstrate the effectiveness of our approach by filtering non-uniformly sampled signals in various image and video processing tasks including edge-preserving color filtering, noise reduction, stylization, and detail enhancement. Our formulation enables, for the first time, edge-aware evaluation of any recursive infinite impulse response digital filter (not only low-pass), producing high-quality filtering results in real time.
EUROGRAPHICS 2015: Dirk Bartz Prize Frontmatter
(Eurographics Association, 2015) Hans-Christian Hege; Timo Ropinski;
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 Facial Appearance Capture
(The Eurographics Association and John Wiley & Sons Ltd., 2015) Klehm, Oliver; Rousselle, Fabrice; Papas, Marios; Bradley, Derek; Hery, Christophe; Bickel, Bernd; Jarosz, Wojciech; Beeler, Thabo; K. Hormann and O. Staadt
Facial appearance capture is now firmly established within academic research and used extensively across various application domains, perhaps most prominently in the entertainment industry through the design of virtual characters in video games and films. While significant progress has occurred over the last two decades, no single survey currently exists that discusses the similarities, differences, and practical considerations of the available appearance capture techniques as applied to human faces. A central difficulty of facial appearance capture is the way light interacts with skin-which has a complex multi-layered structure-and the interactions that occur below the skin surface can, by definition, only be observed indirectly. In this report, we distinguish between two broad strategies for dealing with this complexity. “Image-based methods” try to exhaustively capture the exact face appearance under different lighting and viewing conditions, and then render the face through weighted image combinations. “Parametric methods” instead fit the captured reflectance data to some parametric appearance model used during rendering, allowing for a more lightweight and flexible representation but at the cost of potentially increased rendering complexity or inexact reproduction. The goal of this report is to provide an overview that can guide practitioners and researchers in assessing the tradeoffs between current approaches and identifying directions for future advances in facial appearance capture.
Isogeometric Analysis for Modelling and Design
(The Eurographics Association, 2015) Riffnaller-Schiefer, Andreas; Augsdörfer, Ursula H.; Fellner, Dieter W.; B. Bickel and T. Ritschel
We present an isogeometric design and analysis approach based on NURBS-compatible subdivision surfaces. The approach enables the description of watertight free-form surfaces of arbitrary degree, including conic sections and an accurate simulation and analysis based directly on the designed surface. To explore the seamless integration of design and analysis provided by the isogeometric approach, we built a prototype software which combines free-form modelling tools with thin shell simulation tools to offer the designer a wide range of design and analysis instruments.
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.
InfoView3D: A Solution Showing Educational Model on Multi-Touch Surfaces
(The Eurographics Association, 2015) Ming, Qi; Erdt, Marius; Kan, Chen; Lee, Eugene; Voß, Gerrit; Müller-Wittig, Wolfgang; M. Bronstein and M. Teschner
In this paper, we present a solution for educational presentation which can integrate images, documents, videos, and especially 3D models in a tree based structure. The solution is based on HTML5 and JavaScript, using SVG and X3D techniques and interacting with multi-touch events, therefore supporting multi-touch surfaces that can run a fully-functional browser. In practice, our solution is used for demonstrations both on tablet PCs and a multi-touch video wall.

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