Volume 29 (2010)

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gProximity: Hierarchical GPU-based Operations for Collision and Distance Queries
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Lauterbach, C.; Mo, Q.; Manocha, D.
We present novel parallel algorithms for collision detection and separation distance computation for rigid and deformable models that exploit the computational capabilities of many-core GPUs. Our approach uses thread and data parallelism to perform fast hierarchy construction, updating, and traversal using tight-fitting bounding volumes such as oriented bounding boxes (OBB) and rectangular swept spheres (RSS). We also describe efficient algorithms to compute a linear bounding volume hierarchy (LBVH) and update them using refitting methods. Moreover, we show that tight-fitting bounding volume hierarchies offer improved performance on GPU-like throughput architectures. We use our algorithms to perform discrete and continuous collision detection including self-collisions, as well as separation distance computation between non-overlapping models. In practice, our approach (gProximity) can perform these queries in a few milliseconds on a PC with NVIDIA GTX 285 card on models composed of tens or hundreds of thousands of triangles used in cloth simulation, surgical simulation, virtual prototyping and N-body simulation. Moreover, we observe more than an order of magnitude performance improvement over prior GPU-based algorithms.
Towards Perceptual Simplification of Models with Arbitrary Materials
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Menzel, Nicolas; Guthe, Michael
Real-time rendering of models with high polygon count is still an important issue in interactive computer graphics. A common way to improve rendering performance is to generate different levels of detail of a model. These are mostly computed using polygonal simplification techniques, which aim to reduce the number of polygons without significant loss of visual fidelity. Most existing algorithms use geometric error bounds, which are well-suited for silhouette preservation. They ignore the fact that a much more aggressive simplification is possible in low-contrast areas inside the model. The main contribution of this paper is an efficient simplification algorithm based on the human visual system. The key idea is to move the domain of error computation from image-space to vertex-space to avoid a costly per-pixel comparison. This way the error estimation of a simplification operation can be accelerated significantly. To account for the human vision, we introduce a perceptually based metric depending on the contrast and spatial frequency of the model at a single vertex. Finally, we validate our approach with a user study.
Continuum Traffic Simulation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sewall, J.; Wilkie, D.; Merrell, P.; Lin, M. C.
We present a novel method for the synthesis and animation of realistic traffic flows on large-scale road networks. Our technique is based on a continuum model of traffic flow we extend to correctly handle lane changes and merges, as well as traffic behaviors due to changes in speed limit. We demonstrate how our method can be applied to the animation of many vehicles in a large-scale traffic network at interactive rates and show that our method can simulate believable traffic flows on publicly-available, real-world road data. We furthermore demonstrate the scalability of this technique on many-core systems.
Hybrid Simulation of Miscible Mixing with Viscous Fingering
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Shin, Seung-Ho; Kam, Hyeong Ryeol; Kim, Chang-Hun
By modeling mass transfer phenomena, we simulate solids and liquids dissolving or changing to other substances. We also deal with the very small-scale phenomena that occur when a fluid spreads out at the interface of another fluid. We model the pressure at the interfaces between fluids with Darcy s Law and represent the viscous fingering phenomenon in which a fluid interface spreads out with a fractal-like shape. We use hybrid grid-based simulation and smoothed particle hydrodynamics (SPH) to simulate intermolecular diffusion and attraction using particles at a computable scale. We have produced animations showing fluids mixing and objects dissolving.
Two Methods for Fast Ray-Cast Ambient Occlusion
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Laine, Samuli; Karras, Tero
Ambient occlusion has proven to be a useful tool for producing realistic images, both in offline rendering and interactive applications. In production rendering, ambient occlusion is typically computed by casting a large number of short shadow rays from each visible point, yielding unparalleled quality but long rendering times. Interactive applications typically use screen-space approximations which are fast but suffer from systematic errors due to missing information behind the nearest depth layer.In this paper, we present two efficient methods for calculating ambient occlusion so that the results match those produced by a ray tracer. The first method is targeted for rasterization-based engines, and it leverages the GPU graphics pipeline for finding occlusion relations between scene triangles and the visible points. The second method is a drop-in replacement for ambient occlusion computation in offline renderers, allowing the querying of ambient occlusion for any point in the scene. Both methods are based on the principle of simultaneously computing the result of all shadow rays for a single receiver point.
Manifold-Based 3D Face Caricature Generation with Individualized Facial Feature Extraction
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Wang, S.F.; Lai, S.H.
Caricature is an interesting art to express exaggerated views of different persons and things through drawing. The face caricature is popular and widely used for different applications. To do this, we have to properly extract unique/specialized features of a person s face. A person s facial feature not only depends on his/her natural appearance, but also the associated expression style. Therefore, we would like to extract the neutural facial features and personal expression style for different applicaions. In this paper, we represent the 3D neutral face models in BU-3DFE database by sparse signal decomposition in the training phase. With this decomposition, the sparse training data can be used for robust linear subspace modeling of public faces. For an input 3D face model, we fit the model and decompose the 3D model geometry into a neutral face and the expression deformation separately. The neutral geomertry can be further decomposed into public face and individualized facial feature. We exaggerate the facial features and the expressions by estimating the probability on the corresponding manifold. The public face, the exaggerated facial features and the exaggerated expression are combined to synthesize a 3D caricature for a 3D face model. The proposed algorithm is automatic and can effectively extract the individualized facial features from an input 3D face model to create 3D face caricature.
Time-Dependent 2-D Vector Field Topology: An Approach Inspired by Lagrangian Coherent Structures
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sadlo, F.; Weiskopf, D.
This paper presents an approach to a time-dependent variant of the concept of vector field topology for 2-D vector fields. Vector field topology is defined for steady vector fields and aims at discriminating the domain of a vector field into regions of qualitatively different behaviour. The presented approach represents a generalization for saddle-type critical points and their separatrices to unsteady vector fields based on generalized streak lines, with the classical vector field topology as its special case for steady vector fields. The concept is closely related to that of Lagrangian coherent structures obtained as ridges in the finite-time Lyapunov exponent field. The proposed approach is evaluated on both 2-D time-dependent synthetic and vector fields from computational fluid dynamics.
Transparent and Specular Object Reconstruction
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ihrke, Ivo; Kutulakos, Kiriakos N.; Lensch, Hendrik P. A.; Magnor, Marcus; Heidrich, Wolfgang
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 modelling, preservation of historic artefacts and as input to data-driven modelling 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 modelled 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.
Creating and Animating Subject-Specific Anatomical Models
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Gilles, B.; Reveret, L.; Pai, D. K.
Creating and animating subject-specific anatomical models is traditionally a difficult process involving medical image segmentation, geometric corrections and the manual definition of kinematic parameters. In this paper, we introduce a novel template morphing algorithm that facilitates three-dimensional modelling and parameterization of skeletons. Target data can be either medical images or surfaces of the whole skeleton. We incorporate prior knowledge about bone shape, the feasible skeleton pose and the morphological variability in the population. This allows for noise reduction, bone separation and the transfer, from the template, of anatomical and kinematical information not present in the input data. Our approach treats both local and global deformations in successive regularization steps: smooth elastic deformations are represented by an as-rigid-as-possible displacement field between the reference and current configuration of the template, whereas global and discontinuous displacements are estimated through a projection onto a statistical shape model and a new joint pose optimization scheme with joint limits.
Fast Generation of Pointerless Octree Duals
(2010) Thomas Lewiner; Vinicius Mello; Adelailson Peixoto; Sinesio Pesco; Helio Lopes
Geometry processing applications frequently rely on octree structures, since they provide simple and efficient hierarchies for discrete data. However, octrees do not guarantee direct continuous interpolation of this data inside its nodes. This motivates the use of the octree's dual structure, which is one of the simplest continuous hierarchical structures. With the emergence of pointerless representations, with their ability to reduce memory footprint and adapt to parallel architectures, the generation of duals of pointerless octrees becomes a natural challenge. This work proposes strategies for dual generation of static or dynamic pointerless octrees. Experimentally, those methods enjoy the memory reduction of pointerless representations and speed up the execution by several factors compared to the usual recursive generation.
A Dynamic Noise Primitive for Coherent Stylization
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Benard, P.; Lagae, A.; Vangorp, P.; Lefebvre, S.; Drettakis, G.; Thollot, J.
We present a new solution for temporal coherence in non-photorealistic rendering (NPR) of animations. Given the conflicting goals of preserving the 2D aspect of the style and the 3D scene motion, any such solution is a tradeoff. We observe that primitive-based methods in NPR can be seen as texture-based methods when using large numbers of primitives, leading to our key insight, namely that this process is similar to sparse convolution noise in procedural texturing. Consequently, we present a new primitive for NPR based on Gabor noise, that preserves the 2D aspect of noise, conveys the 3D motion of the scene, and is temporally continuous. We can thus use standard techniques from procedural texturing to create various styles, which we show for interactive NPR applications. We also present a user study to evaluate this and existing solutions, and to provide more insight in the trade-off implied by temporal coherence. The results of the study indicate that maintaining coherent motion is important, but also that our new solution provides a good compromise between the 2D aspect of the style and 3D motion.
Embedded Implicit Stand-Ins for Animated Meshes: A Case of Hybrid Modelling
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Kravtsov, D.; Fryazinov, O.; Adzhiev, V.; Pasko, A.; Comninos, P.
In this paper, we address shape modelling problems, encountered in computer animation and computer games development that are difficult to solve just using polygonal meshes. Our approach is based on a hybrid-modelling concept that combines polygonal meshes with implicit surfaces. A hybrid model consists of an animated polygonal mesh and an approximation of this mesh by a convolution surface stand-in that is embedded within it or is attached to it. The motions of both objects are synchronised using a rigging skeleton. We model the interaction between an animated mesh object and a viscoelastic substance, which is normally represented in an implicit form. Our approach is aimed at achieving verisimilitude rather than physically based simulation. The adhesive behaviour of the viscous object is modelled using geometric blending operations on the corresponding implicit surfaces. Another application of this approach is the creation of metamorphosing implicit surface parts that are attached to an animated mesh. A prototype implementation of the proposed approach and several examples of modelling and animation with near real-time preview times are presented.
Patch-based Texture Interpolation
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Ruiters, Roland; Schnabel, Ruwen; Klein, Reinhard
In this paper, we present a novel exemplar-based technique for the interpolation between two textures that combines patch-based and statistical approaches. Motivated by the notion of texture as a largely local phenomenon, we warp and blend small image neighborhoods prior to patch-based texture synthesis. In addition, interpolating and enforcing characteristic image statistics faithfully handles high frequency detail. We are able to create both intermediate textures as well as continuous transitions. In contrast to previous techniques computing a global morphing transformation on the entire input exemplar images, our localized and patch-based approach allows us to successfully interpolate between textures with considerable differences in feature topology for which no smooth global warping field exists.
A Data-driven Segmentation for the Shoulder Complex
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Hong, Q Youn; Park, Sang Il; Hodgins, Jessica K.
The human shoulder complex is perhaps the most complicated joint in the human body being comprised of a set of three bones, muscles, tendons, and ligaments. Despite this anatomical complexity, computer graphics models for motion capture most often represent this joint as a simple ball and socket. In this paper, we present a method to determine a shoulder skeletal model that, when combined with standard skinning algorithms, generates a more visually pleasing animation that is a closer approximation to the actual skin deformations of the human body. We use a data-driven approach and collect ground truth skin deformation data with an optical motion capture system with a large number of markers (200 markers on the shoulder complex alone). We cluster these markers during movement sequences and discover that adding one extra joint around the shoulder improves the resulting animation qualitatively and quantitatively yielding a marker set of approximately 70 markers for the complete skeleton. We demonstrate the effectiveness of our skeletal model by comparing it with ground truth data as well as with recorded video. We show its practicality by integrating it with the conventional rendering/animation pipeline.
Reviewers
(The Eurographics Association and Blackwell Publishing Ltd, 2010)
A Copula-Based BRDF Model
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Oeztuerk, Aydin; Kurt, Murat; Bilgili, Ahmet
In this paper, we introduce a novel approach for modeling surface reflection. We focus on using a family of probability distributions called Archimedean copulas as BRDF models. The Archimedean representation has an attractive property in that the multivariate distributions are characterized by their marginal distributions through a single univariate function only. It is shown that the proposed model meets the reciprocity property of reflection. Based on measured BRDF data, we demonstrate that the proposed approach provides a good approximation to BRDF. Empirical comparisons are made with some classically used BRDF models.
Real-time Realistic Ocean Lighting using Seamless Transitions from Geometry to BRDF
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Bruneton, Eric; Neyret, Fabrice; Holzschuch, Nicolas
Realistic animation and rendering of the ocean is an important aspect for simulators, movies and video games. By nature, the ocean is a difficult problem for Computer Graphics: it is a dynamic system, it combines wave trains at all scales, ranging from kilometric to millimetric. Worse, the ocean is usually viewed at several distances, from very close to the viewpoint to the horizon, increasing the multi-scale issue, and resulting in aliasing problems. The illumination comes from natural light sources (the Sun and the sky dome), is also dynamic, and often underlines the aliasing issues. In this paper, we present a new algorithm for modelling, animation, illumination and rendering of the ocean, in real-time, at all scales and for all viewing distances. Our algorithm is based on a hierarchical representation, combining geometry, normals and BRDF. For each viewing distance, we compute a simplified version of the geometry, and encode the missing details into the normal and the BRDF, depending on the level of detail required. We then use this hierarchical representation for illumination and rendering. Our algorithm runs in real-time, and produces highly realistic pictures and animations.
Compressive estimation for signal integration in rendering
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Sen, Pradeep; Darabi, Soheil
In rendering applications, we are often faced with the problem of computing the integral of an unknown function. Typical approaches used to estimate these integrals are often based on Monte Carlo methods that slowly converge to the correct answer after many point samples have been taken. In this work, we study this problem under the framework of compressed sensing and reach the conclusion that if the signal is sparse in a transform domain, we can evaluate the integral accurately using a small set of point samples without requiring the lengthy iterations of Monte Carlo approaches. We demonstrate the usefulness of our framework by proposing novel algorithms to address two problems in computer graphics: image antialiasing and motion blur. We show that we can use our framework to generate good results with fewer samples than is possible with traditional approaches.
Instant Propagation of Sparse Edits on Images and Videos
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Li, Yong; Ju, Tao; Hu, Shi-Min
The ability to quickly and intuitively edit digital contents has become increasingly important in our everyday life. We propose a novel method for propagating a sparse set of user edits (e.g., changes in color, brightness, contrast, etc.) expressed as casual strokes to nearby regions in an image or video with similar appearances. Existing methods for edit propagation are typically based on optimization, whose computational cost can be prohibitive for large inputs. We re-formulate propagation as a function interpolation problem in a high-dimensional space, which we solve very efficiently using radial basis functions. While simple to implement, our method significantly improves the speed and space cost of existing methods, and provides instant feedback of propagation results even on large images and videos.
Tone Mapping Operators on Small Screen Devices: An Evaluation Study
(The Eurographics Association and Blackwell Publishing Ltd, 2010) Urbano, C.; Magalhaes, L.; Moura, J.; Bessa, M.; Marcos, A.; Chalmers, A.
In the last decade, an increasing number of techniques have been developed to reproduce high dynamic range imagery on traditional displays. These techniques, known as Tone Mapping Operators (TMOs), have been compared and ranked in different ways according to several image characteristics. However, none of these algorithms has been developed specifically for small screen devices (SSD). In this paper, we present an evaluation of currently used TMOs to show that SSDs with limited size, resolution and colour depth require specific research to find or create an appropriate solution. The research described in this paper is based on psychophysical experiments; using three different types of displays (CRT, LCD and SSD). The obtained results show that rankings obtained are similar for the LCD and CRT but are significantly different for the SSD. Furthermore, these rankings show additionally that some characteristics of TMOs need to be emphasized to obtain better high-fidelity mapped images for SSDs.

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