23-Issue 3

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https://diglib.eg.org/handle/10.2312/10150

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Now showing 1 - 20 of 47

Anisotropic Filtering of Non-Linear Surface Features
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Hildebrandt, Klaus; Polthier, Konrad
A new method for noise removal of arbitrary surfaces meshes is presented which focuses on the preservation and sharpening of non-linear geometric features such as curved surface regions and feature lines. Our method uses a prescribed mean curvature flow (PMC) for simplicial surfaces which is based on three new contributions: 1. the definition and efficient calculation of a discrete shape operator and principal curvature properties on simplicial surfaces that is fully consistent with the well-known discrete mean curvature formula, 2. an anisotropic discrete mean curvature vector that combines the advantages of the mean curvature normal with the special anisotropic behaviour along feature lines of a surface, and 3. an anisotropic prescribed mean curvature flow which converges to surfaces with an estimated mean curvature distribution and with preserved non-linear features. Additionally, the PMC flow prevents boundary shrinkage at constrained and free boundary segments.
Applied Geometry:Discrete Differential Calculus for Graphics
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Desbrun, Mathieu
Geometry has been extensively studied for centuries, almost exclusively from a differential point of view. However, with the advent of the digital age, the interest directed to smooth surfaces has now partially shifted due to the growing importance of discrete geometry. From 3D surfaces in graphics to higher dimensional manifolds in mechanics, computational sciences must deal with sampled geometric data on a daily basis-hence our interest in Applied Geometry.In this talk we cover different aspects of Applied Geometry. First, we discuss the problem of Shape Approximation, where an initial surface is accurately discretized (i.e., remeshed) using anisotropic elements through error minimization. Second, once we have a discrete geometry to work with, we briefly show how to develop a full- blown discrete calculus on such discrete manifolds, allowing us to manipulate functions, vector fields, or even tensors while preserving the fundamental structures and invariants of the differential case. We will emphasize the applicability of our discrete variational approach to geometry by showing results on surface parameterization, smoothing, and remeshing, as well as virtual actors and thin-shell simulation.Joint work with: Pierre Alliez (INRIA) , David Cohen-Steiner (Duke U.), Eitan Grinspun (NYU), Anil Hirani (Caltech), Jerrold E. Marsden (Caltech), Mark Meyer (Pixar), Fred Pighin (USC), Peter Schroeder (Caltech), Yiying Tong (USC).
Approximate Soft Shadows win an Image-Space Flood-Fill Algorithm
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Arvo, Jukka; Hirvikorpi, Mika; Tyystjaervi, Joonas
Most former soft shadow algorithms have either suffered from restricted self-shadowing capabilities, been too slow for interactive applications, or could only be used with a limited types of geometry. In this paper, we propose an efficient image-based approach for computing soft shadows. Our method is based on shadow mapping and provides the associated benefits. We use pixel-based visibility computations for rendering penumbra regions directly into the screen-space. This is accomplished by using a modified flood-fill algorithm which enables us to implement the algorithm using programmable graphics hardware. Even though the resulting images are most often high quality, we do not claim that the proposed method is physically correct. The computation time and memory requirements for soft shadows depend on image resolution and the number of lights, not geometric scene complexity.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Three-Dimensional Graphics and Realism]: Color, shading, shadowing, and texture
Approximated Centroidal Voronoi Diagrams for Uniform Polygonal Mesh Coarsening
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Valette, Sebastien; Chassery, Jean-Marc
We present a novel clustering algorithm for polygonal meshes which approximates a Centroidal Voronoi Diagram construction. The clustering provides an efficient way to construct uniform tessellations, and therefore leads to uniform coarsening of polygonal meshes, when the output triangulation has many fewer elements than the input mesh. The mesh topology is also simplified by the clustering algorithm. Based on a mathematical framework, our algorithm is easy to implement, and has low memory requirements. We demonstrate the efficiency of the proposed scheme by processing several reference meshes having up to 1 million triangles and very high genus within a few minutes on a low- end computer.
Balancing Considered Harmful - Faster Photon Mapping using the Voxel Volume Heuristic -
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Wald, Ingo; Guenther, Johannes; Slusallek, Philipp
Photon mapping is one of the most important algorithms for computing global illumination. Especially for efficiently producing convincing caustics, there are no real alternatives to photon mapping. On the other hand, photon mapping is also quite costly: Each radiance lookup requires to find the k nearest neighbors in a kd-tree, which can be more costly than shooting several rays. Therefore, the nearest-neighbor queries often dominate the rendering time of a photon map based renderer.In this paper, we present a method that reorganizes - i.e. un balances - the kd-tree for storing the photons in a way that allows for finding the k-nearest neighbors much more efficiently, thereby accelerating the radiance estimates by a factor of 1.2-3.4. Most importantly, our method still finds exactly the same k-nearest-neighbors as the original method, without introducing any approximations or loss of accuracy. The impact of our method is demonstrated with several practical examples.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Global Illumination I.3.7 [Computer Graphics]: Raytracing
A Biophysically-Based Spectral Model of Light Interaction with Human Skin
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Krishnaswamy, Aravind; Baranoski, Gladimir V.G.
Despite the notable progress in physically-based rendering, there is still a long way to go before we can automatically generate predictable images of biological materials. In this paper, we address an open problem in this area, namely the spectral simulation of light interaction with human skin. We propose a novel biophysically based model that accounts for all components of light propagation in skin tissues, namely surface reflectance, subsurface reflectance and transmittance, and the biological mechanisms of light absorption by pigments in these tissues. The model is controlled by biologically meaningful parameters, and its formulation, based on standard Monte Carlo techniques, enables its straightforward incorporation into realistic image synthesis frameworks. Besides its biophysically-based nature, the key difference between the proposed model and the existing skin models is its comprehensiveness, i.e., it computes both spectral (reflectance and transmittance) and scattering (bidirectional surface-scattering distribution function) quantities for skin specimens. In order to assess the predictability of our simulations, we evaluate their accuracy by comparing results from the model with actual skin measured data. We also present computer generated images to illustrate the flexibility of the proposed model with respect to variations in the biological input data, and its applicability not only in the predictive image synthesis of different skin tones, but also in the spectral simulation of medical conditions.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Coherent Hierarchical Culling: Hardware Occlusion Queries Made Useful
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Bittner, Jiri; Wimmer, Michael; Piringer, Harald; Purgathofer, Werner
We present a simple but powerful algorithm for optimizing the usage of hardware occlusion queries in arbitrary complex scenes. Our method minimizes the number of issued queries and reduces the delays due to the latency of query results. We reuse the results of occlusion queries from the last frame in order to initiate and schedule the queries in the next frame. This is done by processing nodes of a spatial hierarchy in a front-to-back order and interleaving occlusion queries with rendering of certain previously visible nodes. The proposed scheduling of the queries makes use of spatial and temporal coherence of visibility. Despite its simplicity, the algorithm achieves good culling efficiency for scenes of various types. The implementation of the algorithm is straightforward and it can be easily integrated in existing real-time rendering packages based on common hierarchical data structures.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Combined Correlated and Importance Sampling in Direct Light Source Computation and Environment Mapping
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Szecsi, Laszlo; Sbert, Mateu; Szirmay-Kalos, Laszlo
This paper presents a general variance reduction method that is a quasi-optimal combination of correlated and importance sampling. The weights of the combination are selected automatically in order to keep the merits of both importance and correlated sampling. The proposed sampling method is used for efficient direct light source computation of large area sources and for the calculation of the reflected illumination of environment maps. Importance sampling would be good in these cases if the sources are hidden, while correlated sampling is efficient if the sources are fully visible. The proposed method automatically detects the particular case and provides results that inherit the advantages of both techniques.
Computing Maximal Tiles and Application to Impostor-Based Simplification
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Andujar, C.; Brunet, P.; Chica, A.; Navazo, I.; Rossignac, J.; Vinacua, A.
The computation of the largest planar region approximating a 3D object is an important problem with wide applications in modeling and rendering. Given a voxelization of the 3D object, we propose an efficient algorithm to solve a discrete version of this problem. The input of the algorithm is the set of grid edges connecting the interior and the exterior of the object (called sticks). Using a voting-based approach, we compute the plane that slices the largest number of sticks and is orientation-compatible with these sticks. The robustness and efficiency of our approach rests on the use of two different parameterizations of the planes with suitable properties. The first of these is exact and is used to retrieve precomputed local solutions of the problem. The second one is discrete and is used in a hierarchical voting scheme to compute the global maximum. This problem has diverse applications that range from finding object signatures to generating simplified models. Here we demonstrate the merits of the algorithm for efficiently computing an optimized set of textured impostors for a given polygonal model.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
Crowd of Virtual Humans: a New Approach for Real Time Navigation in Complex and Structured Environments
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Lamarche, Fabrice; Donikian, Stephane
The navigation activity is an every day practice for any human being capable of locomotion. Our objective in this work is to reproduce this crucial human activity inside virtual environments. Putting together the high complexity of a realistic environment such as a city, a big amount of virtual humans and the real-time constraint requires to optimize each aspect of the animation process. In this paper, we present a suitable topological structuring of the geometric environment to allow fast path finding as well as an efficient reactive navigation algorithm for virtual humans evolving inside a crowd.
Deferred Splatting
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Guennebaud, Gael; Barthe, Loic; Paulin, Mathias
In recent years it has been shown that, above a certain complexity, points become the most efficient rendering primitives. Although the programmability of the lastest graphics hardware allows efficient implementation of high quality surface splatting algorithms, their performance remains below those obtained with simpler point based rendering algorithms when they are used for scenes of high complexity. In this paper, our goal is to apply high quality point based rendering algorithms on complex scenes. For this purpose, we show how to take advantage of temporal coherency in a very accurate hardware accelerated point selection algorithm allowing the expensive computations to be peformed only on visible points. Our algorithm is based on a multi-pass hardware accelerated EWA splatting. It is also suitable for any rendering application since no pre-process is needed and no assumption is made on the data structure. In addition, we briefly discuss the association of our method with other existing culling techniques and optimization for particular applications.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Viewing algorithms
The Design of an Inexpensive Very High Resolution Scan Camera System
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Wang, Shuzhen; Heidrich, Wolfgang
DiFi: Fast 3D Distance Field Computation Using Graphics Hardware
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Sud, Avneesh; Otaduy, Miguel A.; Manocha, Dinesh
We present an algorithm for fast computation of discretized 3D distance fields using graphics hardware. Given a set of primitives and a distance metric, our algorithm computes the distance field for each slice of a uniform spatial grid baly rasterizing the distance functions of the primitives. We compute bounds on the spatial extent of the Voronoi region of each primitive. These bounds are used to cull and clamp the distance functions rendered for each slice. Our algorithm is applicable to all geometric models and does not make any assumptions about connectivity or a manifold representation. We have used our algorithm to compute distance fields of large models composed of tens of thousands of primitives on high resolution grids. Moreover, we demonstrate its application to medial axis evaluation and proximity computations. As compared to earlier approaches, we are able to achieve an order of magnitude improvement in the running time.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Distance fields, Voronoi regions, graphics hardware, proximity computations
Dupin Cyclide Blends Between Quadric Surfaces for Shape Modeling
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Foufou, Sebti; Garnier, Lionel
We introduce a novel method to define Dupin cyclide blends between quadric primitives. Dupin cyclides are non-spherical algebraic surfaces discovered by French mathematician Pierre-Charles Dupin at the beginning of the 19th century. As a Dupin cyclide can be fully characterized by its principal circles, we have focussed our study on how to determine principal circles tangent to both quadrics being blended. This ensures that the Dupin cyclide we are constructing constitutes aG1blend. We use the Rational Quadratic Bezier Curve (RQBC) representation of circular arcs to model the principal circles, so the construction of each circle is reduced to the determination of the three control points of the RQBC representing the circle.In this work, we regard the blending of two quadric primitives A and B as two complementary blending operations: primitive A-cylinder and cylinder-primitive B; two Dupin cyclides and a cylinder are then defined for each blending operation. In general the cylinder is not useful and may be reduced to a simple circle. A complete shape design example is presented to illustrate the modeling of Eurographics'04 Hugo using a limited number of quadrics combined using Dupin cyclide blends.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling
Dye Advection Without the Blur: A Level-Set Approach for Texture-Based Visualization of Unsteady Flow
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Weiskopf, D.
Dye advection is an intuitive and versatile technique to visualize both steady and unsteady flow. Dye can be easily combined with noise-based dense vector field representations and is an important element in user-centric visual exploration processes. However, fast texture-based implementations of dye advection rely on linear interpolation operations that lead to severe diffusion artifacts. In this paper, a novel approach for dye advection is proposed to avoid this blurring and to achieve long and clearly defined streaklines or extended streak-like patterns. The interface between dye and background is modeled as a level-set within a signed distance field. The level-set evolution is governed by the underlying flow field and is computed by a semi-Lagrangian method. A reinitialization technique is used to counteract the distortions introduced by the level-set evolution and to maintain a level-set function that represents a local distance field. This approach works for 2D and 3D flow fields alike. It is demonstrated how the texture-based level-set representation lends itself to an efficient GPU implementation and therefore facilitates interactive visualization.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Exchanging Faces in Images
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Blanz, Volker; Scherbaum, Kristina; Vetter, Thomas; Seidel, Hans-Peter
Pasting somebody's face into an existing image with traditional photo retouching and digital image processing tools has only been possible if both images show the face from the same viewpoint and with the same illumination. However, this is rarely the case for given pairs of images. We present a system that exchanges faces across large differences in viewpoint and illumination. It is based on an algorithm that estimates 3D shape and texture along with all relevant scene parameters, such as pose and lighting, from single images. Manual interaction is reduced to clicking on a set of about 7 feature points, and marking the hairline in the target image. The system can be used for image processing, virtual try-on of hairstyles, and face recognition. By separating face identity from imaging conditions, our approach provides an abstract representation of images and a novel, high-level tool for image manipulation.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation
Fast Surface Modelling Using a 6th Order PDE
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Zhang, Jian. J.; You, L. H.
Although the control-point based parametric approach is used most widely in free-form surface modelling, complementary techniques co-exist to meet various specialised requirements. The partial differential equation (PDE) based modelling approach is especially suitable for satisfying surface boundary constraints. They are also effective for the generation of families of free-form surfaces, which share a common base and differ in their secondary features. In this paper, we present a fast surface modelling method using a sixth order PDE. This PDE provides enough degrees of freedom not only to accommodate tangent, but also curvature boundary conditions and offers more shape control parameters to serve as user controls for the manipulation of surface shapes. In order to achieve real-time performance, we have constructed a surface function and developed a high-precision approximate solution to the 6th order PDE. Unlike some existing PDE-based techniques, this resolution method can satisfy the boundary conditions exactly, and is able to create free-form surfaces as fast and almost as accurately as the closed-form (analytical) solutions. Due to the fact that it has sufficient degrees of freedom to accommodate the continuity of 3-sided and 4-sided surface patches at their boundaries, this method is able to model complex surfaces consisting of multiple patches. Compared with existing PDE-based modelling methods, this method is both fast and can solve a larger class of surface modelling problems.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Curves, surfaces, solid, and object representations; physically based modelling
GPU-Based Nonlinear Ray Tracing
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Weiskopf, Daniel; Schafhitzel, Tobias; Ertl, Thomas
In this paper, we present a mapping of nonlinear ray tracing to the GPU which avoids any data transfer back to main memory. The rendering process consists of the following parts: ray setup according to the camera parameters, ray integration, ray-object intersection, and local illumination. Bent rays are approximated by polygonal lines that are represented by textures. Ray integration is based on an iterative numerical solution of ordinary differential equations whose initial values are determined during ray setup. To improve the rendering performance, we propose acceleration techniques such as early ray termination and adaptive ray integration. Finally, we discuss a variety of applications that range from the visualization of dynamical systems to the general relativistic visualization in astrophysics and the rendering of the continuous refraction in media with varying density.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism
Hardware-Accelerated Rendering of Photo Hulls
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Li, Ming; Magnor, Marcus; Seidel, Hans-Peter
This paper presents an efficient hardware-accelerated method for novel view synthesis from a set of images or videos. Our method is based on the photo hull representation, which is the maximal photo-consistent shape. We avoid the explicit reconstruction of photo hulls by adopting a view-dependent plane-sweeping strategy. From the target viewpoint slicing planes are rendered with reference views projected onto them. Graphics hardware is exploited to verify the photo-consistency of each rasterized fragment. Visibilities with respect to reference views are properly modeled, and only photo-consistent fragments are kept and colored in the target view. We present experiments with real images and animation sequences. Thanks to the more accurate shape of the photo hull representation, our method generates more realistic rendering results than methods based on visual hulls. Currently, we achieve rendering frame rates of 2-3 fps. Compared to a pure software implementation, the performance of our hardware-accelerated method is approximately 7 times faster.Categories and Subject Descriptors (according to ACM CCS): CR Categories: I.3.3 [Computer Graphics]: Picture/Image Generation; I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.
Hierarchical Retargetting of Fine Facial Motions
(The Eurographics Association and Blackwell Publishing, Inc, 2004) Na, Kyunggun; Jung, Moonryul
We present a novel technique for retargetting captured facial animation to new facial models. We use dense motion data that can express fine motions such as wrinkles. We use a normal mesh, which is a special multi-resolution mesh, to represent source and target models. A normal mesh is defined by the base mesh and sequence of normal offsets from it. Our retargetting consists of two steps: base mesh and detail mesh retargetting. For base mesh retargetting, we use an example-based technique to take advantage of the intuition of the user in specifying the similarity between source and target expressions. In detail mesh retargetting, the variations of normal offsets in the source mesh are hierarchically computed and transferred to the target mesh. Our retargetting scheme is able to produce robust and delicate results for unusual target models from highly detailed motion data.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three Dimensional Graphics and Realism - Animation; I.3.5 [Computer Graphics]: Computational Geometry and Object Modelling - hierarchy and geometric transformation, object hierarchy

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