Volume 22 (2003)

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3D Video Recorder: a System for Recording and Playing Free-Viewpoint Video?
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Wurmlin, Stephan; Lamboray, Edouard; Staadt, Oliver G.; Gross, Markus H.
We present the 3D Video Recorder, a system capable of recording, processing, and playing three-dimensional video from multiple points of view. We first record 2D video streams from several synchronized digital video cameras and store pre-processed images to disk. An off-line processing stage converts these images into a time-varying 3D hierarchical point-based data structure and stores this 3D video to disk. We show how we can trade-off 3D video quality with processing performance and devise efficient compression and coding schemes for our novel 3D video representation. A typical sequence is encoded at less than 7 Mbps at a frame rate of 8.5 frames per second. The 3D video player decodes and renders 3D videos from hard-disk in real-time, providing interaction features known from common video cassette recorders, like variable-speed forward and reverse, and slow motion. 3D video playback can be enhanced with novel 3D video effects such as freeze-and-rotate and arbitrary scaling. The player builds upon point-based rendering techniques and is thus capable of rendering high-quality images in real-time. Finally, we demonstrate the 3D Video Recorder on multiple real-life video sequences.ACM CSS: I.3.2 Computer Graphics-Graphics Systems, I.3.5 Computer Graphics-Computational Geometry and Object Modelling, I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism
Adaptive Logarithmic Mapping For Displaying High Contrast Scenes
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Drago, F.; Myszkowski, K.; Annen, T.; Chiba, N.
We propose a fast, high quality tone mapping technique to display high contrast images on devices with limited dynamicrange of luminance values. The method is based on logarithmic compression of luminance values, imitatingthe human response to light. A bias power function is introduced to adaptively vary logarithmic bases, resultingin good preservation of details and contrast. To improve contrast in dark areas, changes to the gamma correctionprocedure are proposed. Our adaptive logarithmic mapping technique is capable of producing perceptually tunedimages with high dynamic content and works at interactive speed. We demonstrate a successful application of ourtone mapping technique with a high dynamic range video player enabling to adjust optimal viewing conditions forany kind of display while taking into account user preference concerning brightness, contrast compression, anddetail reproduction.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Image Processing and Computer Vision]: Image Representation
Adaptive Ray Tracing of Subdivision Surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Müller, Kerstin; Techmann, Torsten; Fellner, Dieter W.
Subdivision Surfaces as well as (interactive) ray tracing have become an important issue in computer graphics.But ray tracing of subdivision surfaces has received only little attention. We present a new approach for raytracing of subdivision surfaces. The algorithm uses a projection of the ray onto the surface and works mainly intwo dimensions along this projection. While proceeding from patch to patch, we examine the bounding volume oftheir borders: the lower the distance between ray and subdivision surface, the more refinement steps are adaptivelyapplied to the surface but only along the projection of the ray. The adaptive refinement of a patch is controlled bycurvature, size, its membership to the silhouette, and its potential contribution to the light transport. The algorithmis simple and mainly consists of elementary geometric computations. Hence it is fast and easy to implementwithout the need for elaborate preprocessing. The algorithm is robust in the sense that it deals with all features ofsubdivision surfaces like creases and corners.Categories and Subject Descripters (according to ACM CCS): I.3.7 [Computer Graphics]: Raytracing
Advanced Design for a Realistic Virtual Brush
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Xu, Songhua; Lau, Francis C.M.; Tang, Feng; Pan, Yunhe
This paper proposes a novel algorithmic framework for an advanced virtual brush to be used in interactive digitalpainting. The framework comprises the following components: a geometry model of the brush using a hierarchicalrepresentation that leads to substantial savings in every step of the painting process; fast online brush motionsimulation assisted by offline calibration that guarantees an accurate and stable simulation of the brush's dynamicbehavior; a new pigment model based on a diffusion process of random molecules that considers delicateand complex pigment behavior at dipping time as well as during painting; and a user-adaptation component thatenables the system to cater for the personal painting habits of different users. A prototype system has been implementedbased on this framework. Compared with other virtual brushes, this new system is designed to presenta realistic brush in the sense that the system accurately and stably simulates the complex painting functionalityof a running brush, and therefore is capable of creating high-quality digital paintings with minute aesthetic detailsthat can rival the real artwork. The advanced features also give rise to a high degree of expressiveness ofthe virtual brush that the user can comfortably manipulate. http://www.csis.hku.hk/songhuale-brush/ providessupplementary materials for this paper.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Methodology and Techniques]: Interactiontechniques; I.3.5 [Computational Geometry and Object Modeling]: Physically based modeling; I.3.4 [GraphicsUtilities]: Paint systems;
Animating Hair with Loosely Connected Particles
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Bando, Yosuke; Chen, Bing-Yu; Nishita, Tomoyuki
This paper presents a practical approach to the animation of hair at an interactive frame rate. In our approach,we model the hair as a set of particles that serve as sampling points for the volume of the hair, which covers thewhole region where hair is present. The dynamics of the hair, including hair-hair interactions, is simulated usingthe interacting particles. The novelty of this approach is that, as opposed to the traditional way of modeling hair,we release the particles from tight structures that are usually used to represent hair strands or clusters. Therefore,by making the connections between the particles loose while maintaining their overall stiffness, the hair can bedynamically split and merged during lateral motion without losing its lengthwise coherence.Categories and Subject Descriptions (according to ACM CCS): I.3.7 [Computer Graphics]: Three-DimensionalGraphics and Realism, I.3.3 [Computer Graphics]: Picture/Image Generation
Animation of Bubbles in Liquid
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hong, Jeong-Mo; Kim, Chang-Hun
We present a new fluid animation technique in which liquid and gas interact with each other, using the exampleof bubbles rising in water. In contrast to previous studies which only focused on one fluid, our system considersboth the liquid and the gas simultaneously. In addition to the flowing motion, the interactions between liquid andgas cause buoyancy, surface tension, deformation and movement of the bubbles. For the natural manipulationof topological changes and the removal of the numerical diffusion, we combine the volume-of-fluid method andthe front-tracking method developed in the field of computational fluid dynamics. Our minimum-stress surfacetension method enables this complementary combination. The interfaces are constructed using the marching cubesalgorithm. Optical effects are rendered using vertex shader techniques.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Animation
Announcement
(Blackwell Publishers, Inc and the Eurographics Association, 2003)
Approximating Parametric Curves With Strip Trees Using Affine Arithmetic
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Henrique de Figueiredo, Luiz; Stolfi, Jorge; Velho, Luiz
We show how to use affine arithmetic to represent a parametric curve with a strip tree. The required bounding rectangles for pieces of the curve are computed by exploiting the linear correlation information given by affine arithmetic. As an application, we show how to compute approximate distance fields for parametric curves.ACM CSS: I.3.3 Computer Graphics-Curve, surface, solid, and object representations, G.1.2 Numerical Analysis-Approximation of surfaces and contours, G.1.0 Numerical Analysis-Interval arithmetic
Auditor-s Report
(Blackwell Publishing, Inc and Eurographics Association, 2003)
Author Index Volume 22 (2003) and Contents
(2003)
Automatic Hybrid Hierarchy Creation: a Cost-model Based Approach
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Masso, J. P. Molina; Lopez, P. Gonzalez
While using hierarchical search structures has been proved as one of the most efficient acceleration techniques when rendering complex scenes, automatic creation of appropriate hierarchies is not solved yet. Well-known algorithms for automatic creation of bounding volume hierarchies are not enough. Higher performance is achieved by introducing spatial uniform subdivision, although algorithms proposed up to now are not truly automatic, as they need some parameters to be adjusted. In this paper we present a full-automatic hierarchy creation scheme that structures the scene in a hybrid way, combining bounding volumes and voxel grids in the same tree, selecting the search structure that best fits to each scene region. It uses no parameters at all. This efficient proposal relies on a new cost model that estimates the goodness of a hybrid hierarchy if used for rendering the scene.ACM CSS: I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism
Automatic texture atlas generation from trimmed NURBS models
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Guthe, M.; Klein, R.
A Texture Atlas is a two dimensional representation of a 3D model usable for paint systems or as a sewing pattern.The field of texture atlas generation from polygonal models has been well exploited in the recent years. The developedalgorithms work on piecewise linear surface representations, but not on parametric surfaces like NURBS,that are still the main surface representation in CAD systems. If a texture atlas is generated from a triangulatedNURBS model, the result cannot be edited further in a CAD system, since the separation into charts is not basedon the separate NURBS patches of the original model. We present a method for automatic generation of a textureatlas directly from trimmed NURBS models, while preserving the original NURBS representation. The resultingtexture atlas is build of several charts, each consisting of the original NURBS patches sewn together.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture/Image Generation;I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling; I.3.7 [Computer Graphics]: Three-DimensionalGraphics and Realism - Color, Shading and Texture; J.6 [Computer-aided Engineering]: Computer-aideddesign (CAD)
Automatic View Selection Using Viewpoint Entropy and its Application to Image-Based Modelling
(Blackwell Publishing, Inc and Eurographics Association, 2003) Vazquez, Pere-Pau; Feixas, Miquel; Sbert, Mateu; Heidrich, Wolfgang
In the last decade a new family of methods, namely Image-Based Rendering, has appeared. These techniques rely on the use of precomputed images to totally or partially substitute the geometric representation of the scene. This allows to obtain realistic renderings even with modest resources. The main problem is the amount of data needed, mainly due to the high redundancy and the high computational cost of capture. In this paper we present a new method to automatically determine the correct camera placement positions in order to obtain a minimal set of views for Image-Based Rendering. The input is a 3D polyhedral model including textures and the output is a set of views that sample all visible polygons at an appropriate rate. The viewpoints should cover all visible polygons with an adequate quality, so that we sample the polygons at sufficient rate. This permits to avoid the excessive redundancy of the data existing in several other approaches. We also reduce the cost of the capturing process, as the number of actually computed reference views decreases. The localization of interesting viewpoints is performed with the aid of an information theory-based measure, dubbed viewpoint entropy. This measure is used to determine the amount of information seen from a viewpoint. Next we develop a greedy algorithm to minimize the number of images needed to represent a scene. In contrast to other approaches, our system uses a special preprocess for textures to avoid artifacts appearing in partially occluded textured polygons. Therefore no visible detail of these images is lost.ACM CSS: I.3.7 Computer Graphics'-Three-Dimensional Graphics and Realism
BDAM - Batched Dynamic Adaptive Meshes for High Performance Terrain Visualization
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Cignoni, P.; Ganovelli, F.; Gobbetti, E.; Marton, F.; Ponchio, F.; Scopigno, R.
This paper describes an efficient technique for out-of-core rendering and management of large textured terrainsurfaces. The technique, called Batched Dynamic Adaptive Meshes (BDAM), is based on a paired tree structure:a tiled quadtree for texture data and a pair of bintrees of small triangular patches for the geometry. These smallpatches are TINs and are constructed and optimized off-line with high quality simplification and tristrippingalgorithms. Hierarchical view frustum culling and view-dependent texture and geometry refinement is performedat each frame through a stateless traversal algorithm. Thanks to the batched CPU/GPU communication model,the proposed technique is not processor intensive and fully harnesses the power of current graphics hardware.Both preprocessing and rendering exploit out-of-core techniques to be fully scalable and to manage large terraindatasets.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Picture and Image Generation;I.3.7 [Computer Graphics]: Three-Dimensional Graphics and Realism.
Beyond Stippling - Methods for Distributing Objects on the Plane
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hiller, Stefan; Hellwig, Heino; Deussen, Oliver
Conventionally, stippling is an effective technique for representing surfaces in pen-and-ink. We present new efficientmethods for stipple drawings by computer. In contrast to already existing techniques, arbitrary shapes canbe used in place of dots. An extension of Lloyd's Method enables us to position small objects on a plane in a visuallypleasing form. This allows us to generate new illustration styles. Similar methods can be used for positioningobjects in other applications.
Bias Compensation for Photon Maps
(Blackwell Publishing, Inc and Eurographics Association, 2003) Roland Schregle
Density estimation techniques such as the photon map method rely on a particle transport simulation to reconstruct indirect illumination, which is proportional to the particle density. In the photon map framework, particles are usually located using nearest-neighbour methods due to their generality. However, these methods have an inherent tradeoff between local bias and noise in the reconstructed illumination, which depends on the density estimate bandwidth. This paper presents a bias compensating operator for nearest-neighbour density estimation which adapts the bandwidth according to the estimated bias in the reconstructed illumination.ACM CSS: I.3.7 Three-Dimensional Graphics and Realism Raytracing
BRDF Measurement Modelling using Wavelets for Efficient Path Tracing
(Blackwell Publishing, Inc and Eurographics Association, 2003) Claustres, L.; Paulin, M.; Boucher, Y.
Physically based rendering needs numerical models from real measurements, or analytical models from material definitions, of the Bidirectional Reflectance Distribution Function (BRDF). However, measured BRDF data sets are too large and provide no functionalities to be practically used in Monte Carlo path tracing algorithms. In this paper, we present a wavelet-based generic BRDF model suitable for both physical analysis and path tracing. The model is based on the separation of spectral and geometrical aspect of the BRDF and allows a compact and efficient representation of isotropic, anisotropic and/or spectral BRDFs. After a brief survey of BRDF and wavelet theory, we present our software architecture for generic wavelet transform and how to use it to model BRDFs. Then, modelling results are presented on real and virtual BRDF measurements. Finally, we show how to exploit the multiresolution property of the wavelet encoding to reduce the variance by importance sampling in a path tracing algorithm.ACM CSS: I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism
Cloth Motion Capture
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Pritchard, D.; Heidrich, W.
Recent years have seen an increased interest in motion capture systems. Current systems, however, are limitedto only a few degrees of freedom, so that effectively only the motion of linked rigid bodies can be acquired. Wepresent a system for the capture of deformable surfaces, most notably moving cloth, including both geometry andparameterisation. We recover geometry using stereo correspondence, and use the Scale Invariant Feature Transform(SIFT) to identify an arbitrary pattern printed on the cloth, even in the presence of fast motion. We describea novel seed-and-grow approach to adapt the SIFT algorithm to deformable geometry. Finally, we interpolatefeature points to parameterise the complete geometry.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Physically based modelingI.4.8 [Image Processing and Computer Vision]: Scene analysis
Compression of 2D Vector Fields Under Guaranteed Topology Preservation
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Theisel, H.; Rossl, Ch.; Seidel, H.-P.
In this paper we introduce a new compression technique for 2D vector fields which preserves the complete topology, i.e., the critical points and the connectivity of the separatrices. As the theoretical foundation of the algorithm, we show in a theorem that for local modifications of a vector field, it is possible to decide entirely by a local analysis whether or not the global topology is preserved. This result is applied in a compression algorithm which is based on a repeated local modification of the vector field - namely a repeated edge collapse of the underlying piecewise linear domain. We apply the compression technique to a number of data sets with a complex topology and obtain significantly improved compression ratios in comparison to pre-existing topology-preserving techniques.
Computer Graphics forum
(Blackwell Publishing, Inc and Eurographics Association, 2003) Duke, David; Scopigno, Roberto

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