Volume 22 (2003)

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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
EG Network Service Computer Graphics forum
(Blackwell Publishers, Inc and the Eurographics Association, 2003)
Eurographics and Computer Graphics forum offer a variety of services on the international networks. You can find details of our latest events, how to prepare a paper for the conference or for the journal and much more besides. This information can be accessed mainly through the EG website but we also offer some support for ftp and mail server access.
Precise Ink Drawing of 3D Models
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Sousa, Mario Costa; Foster, Kevin; Wyvill, Brian; Samavati, Faramarz
Drawings made with precise pen strokes accurately reveal the geometric forms that give subjects their characteristicshape. We present a system for non-photorealistic rendering of precise drawing strokes over dense 3Dtriangle meshes with arbitrary topology. During an automatic pre-process, we construct an extended version ofthe edge-buffer data structure to allow the calculation of shape measures at each mesh edge, by adapting numericalmethods used in geomorphology. At runtime, feature edges related to shape measures are extracted andrendered as strokes with varying thickness and pen marking styles. Stroke thickness is automatically adjusted byconsidering surface curvature. Pen marking styles and visual effects of ink distribution are both controlled by theuser. We demonstrate precise drawing strokes over complex meshes revealing a variety of shape characteristics.
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
Multi-scale Feature Extraction on Point-Sampled Surfaces
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Pauly, Mark; Keiser, Richard; Gross, Markus
We present a new technique for extracting line-type features on point-sampled geometry. Given an unstructuredpoint cloud as input, our method first applies principal component analysis on local neighborhoods toclassify points according to the likelihood that they belong to a feature. Using hysteresis thresholding, we thencompute a minimum spanning graph as an initial approximation of the feature lines. To smooth out the featureswhile maintaining a close connection to the underlying surface, we use an adaptation of active contour models.Central to our method is a multi-scale classification operator that allows feature analysis at multiplescales, using the size of the local neighborhoods as a discrete scale parameter. This significantly improves thereliability of the detection phase and makes our method more robust in the presence of noise. To illustrate theusefulness of our method, we have implemented a non-photorealistic point renderer to visualize point-sampledsurfaces as line drawings of their extracted feature curves.
Interactive Design of Bonsai Tree Models
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Boudon, Frederic; Prusinkiewicz, Przemyslaw; Federl, Pavol; Godin, Christophe; Karwowski, Radoslaw
Because of their complexity, plant models used in computer graphics are commonly created with proceduralmethods. A difficult problem is the user control of these models: a small number of parameters is insufficient tospecify plant characteristics in detail, while large numbers of parameters are tedious to manipulate and difficultto comprehend. To address this problem, we propose a method for managing parameters involved in plant modelmanipulation. Specifically, we introduce decomposition graphs as multiscale representations of plant structuresand present interactive tools for designing trees that operate on decomposition graphs. The supported operationsinclude browsing of the parameter space, editing of generalized parameters (scalars, functions, and branchingsystem silhouettes), and the definition of dependencies between parameters. We illustrate our method by creatingmodels of bonsai trees.Categories and Subject Descriptors (according to ACM CCS): I.3.6 [Computer Graphics]: Methodology and Techniques
Image Based Interactive Rendering with View Dependent Geometry
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Evers-Senne, J.-F.; Koch, R.
In this paper we present a novel approach for interactive rendering of virtual views from real image sequences.Combining the concepts of light fields, depth-compensated image warping and view dependent texture mapping,this plenoptic modeling approach can handle large and complex scenes. A portable, handheld multi-camera systemhas been developed that allows to record multiple image streams by simply walking around the scene. Theseimage streams are automatically calibrated and depth maps for all views are generated as input to the renderingstage. For rendering a view dependent warping surface is constructed on the fly and depth-compensated imageinterpolation is applied with view-dependent texture mapping. Rendering quality is scalable to allow fast previewand to achieve high-end quality with the same approach. The system can handle large and geometrically complexscenes with hundreds of real images at interactive rates.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Viewing algorithms, I.4.1[Image Processing and Computer Vision]: Digitization and Image Capture, I.4.8 [Image Processing and ComputerVision]: Scene Analysis
A Few Good Lines: Suggestive Drawing of 3D Models
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Sousa, Mario Costa; Prusinkiewicz, Przemyslaw
We present a method for rendering 3D models in the traditionalline-drawing style used in artistic and scientificillustrations. The goal is to suggest the 3D shape of the objectsusing a small number of lines drawn with carefullychosen line qualities. The system combines several known techniquesinto a simple yet effective non-photorealisticline renderer. Feature edges related to the outline and interiorof a given 3D mesh are extracted, segmented, andsmoothed, yielding chains of lines with varying path, length, thickness,gaps, and enclosures. The paper includessample renderings obtained for a variety of models.
The Scale Method for Blending Operations in Functionally-Based Constructive Geometry
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hsu, P.-C.; Lee, C.
This paper presents a scale method for developing high dimensional scale functions to blend implicitly defined objects. Scale functions are differentiable on the entire domain except the origin, provide blending range control, and behave like Min/Max operators everywhere, so even a successive composition of blending operations containing overlapped blending regions can be generated smoothly. Because the scale method is a generalized method, implicit or parametric curves, such as cubic Bezier curves, rational conic curves, and implicit conics and hyper-ellipsoids, can be used to develop scale functions. As a result, it can enhance the flexibility of generating the implicitly blending surfaces in Ricci's constructive geometry, soft objects modeling, and implicit sweep objects.ACM CSS: I.3.5 Computer Graphics-Computational Geometry and Object Modeling - Curve, surface, solid and object representations
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.
Open Issues in Photo-realistic Rendering
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Purgathofer, Werner
For more than two decades Computer graphics researchers have tried to achieve photo-realism in their images as reliable as possible, mainly by simulating the physical laws of light and adding one effect after the other. The recent years have brought a change of efforts towards real-time methods, easy-to-use systems, integration with vision, modelling tools and the like. The quality of images is mostly accepted as sufficient for real world applications, but where are we really? There are still numerous problems to be solved, and there is notable progress in these areas. No question, the plug-in philosophy of some commercial products has enabled several of these new techniques to be distributed quite fast. But unfortunately, many other of these developments happen in isolated systems for the pure purpose of publication, and never make it into commercial software. This presentation wants to make people more aware of such activities, and evaluate the steps we still have to go towards perfect photo-realism.The talk will start with an attempt to give a brief overview of the rendering history, highlighting the main research directions at different times. It will explain the driving forces of the developments, which are complexity, speed, and accuracy, and maybe also expression in recent years. Solved and unsolved areas are examined, and compared to practically solved but theoretically incomplete topics such as translucency, tone mapping, light source and BTF descriptions, and error metrics for image quality evaluation. The difference lies mainly in the difference between believable, correct, and predictive images. Also, for really realistic images modelling complexity is still an issue. Finally, some recent work on polarization and fluorescence is presented.
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
Soft Object Modelling with Generalised ChainMail - Extending the Boundaries of Web-based Graphics
(Blackwell Publishing, Inc and Eurographics Association, 2003) Li, Ying; Brodlie, Ken
Soft object modelling is crucial in providing realistic simulation of many surgical procedures. High accuracy is achievable using the Finite Element Method (FEM), but significant computational power is required. We are interested in providing Web-based surgical training simulation where such computational power is not available, but in return lower accuracy is often sufficient. A useful alternative to FEM is the 3D ChainMail algorithm that models elements linked in a regular, rectangular mesh, mimicking the behaviour of chainmail armour. An important aspect is the ability to make topology changes for example by cutting - an aspect that FEM finds difficult. Our contribution is to extend the 3D ChainMail technique to arbitrary grids in 2D and 3D. This extends the range of applications that can be addressed by the ChainMail approach, to include surfaces and volumes defined on triangular and tetrahedral meshes. We have successfully deployed the algorithm in a Web-based environment, using VRML and Java linked through the External Authoring Interface.ACM CSS: I.3.5 Computer graphics: Computional Geometry and Object Modelling, I.3.2 Computer Graphics: Graphics Systems, J.3 Life and Medical Sciences
The Perspective Silhouette of a Canal Surface
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Kim, Ku-Jin; Lee, In-Kwon
We present an efficient and robust algorithm for parameterizing the perspective silhouette of a canal surface and detecting each connected component of the silhouette. A canal surface is the envelope of a moving sphere with varying radius, defined by the trajectoryC(t)of its center and a radius functionr(t). This moving sphere,S(t), touches the canal surface at a characteristic circleK(t). We decompose the canal surface into a set of characteristic circles, compute the silhouette points on each characteristic circle, and then parameterize the silhouette curve. The perspective silhouette of the sphereS(t)from a given viewpoint consists of a circleQ(t); by identifying the values oftat whichK(t)andQ(t)touch, we can find all the connected components of the silhouette curve of the canal surface.ACM CSS: I.3.7 Computer Graphics-Three Dimensional Graphics and Realism
Editorial
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Duke, David; Scopigno, Roberto
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.
On Visual Similarity Based 3D Model Retrieval
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Chen, Ding-Yun; Tian, Xiao-Pei; Shen, Yu-Te; Ouhyoung, Ming
Granada, 4 September 2003
(Blackwell Publishing, Inc and Eurographics Association, 2003)
Interactive Rendering of Translucent Objects?
(Blackwell Publishers, Inc and the Eurographics Association, 2003) Lensch, Hendrik P.A.; Goesele, Michael; Bekaert, Philippe; Kautz, Jan; Magnor, Marcus A. and Lang, Jochen and Seidel, Hans-Peter
This paper presents a rendering method for translucent objects, in which viewpoint and illumination can be modified at interactive rates. In a preprocessing step, the impulse response to incoming light impinging at each surface point is computed and stored in two different ways: The local effect on close-by surface points is modeled as a per-texel filter kernel that is applied to a texture map representing the incident illumination. The global response (i.e. light shining through the object) is stored as vertex-to-vertex throughput factors for the triangle mesh of the object. During rendering, the illumination map for the object is computed according to the current lighting situation and then filtered by the precomputed kernels. The illumination map is also used to derive the incident illumination on the vertices which is distributed via the vertex-to-vertex throughput factors to the other vertices. The final image is obtained by combining the local and global response. We demonstrate the performance of our method for several models.ACM CSS:I.3.7 Computer Graphics-Three-Dimensional Graphics and Realism Color Radiosity
EG2003 Medical Prize Competition
(Blackwell Publishing, Inc and Eurographics Association, 2003) John, Nigel W.

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