Issue 3
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Item Fast Photo-Realistic Rendering of Trees in Daylight(Blackwell Publishers, Inc and the Eurographics Association, 2003) Qin, Xueying; Nakamae, Eihachiro; Tadamura, Katsumi; Nagai, YasuoWe propose a fast approach for photo-realistic rendering of trees under various kinds of daylight, which is particularlyuseful for the environmental assessment of landscapes. In our approach the 3D tree models are transformedto a quasi-3D tree database registering geometrical and shading information of tree surfaces, i.e. their normalvectors, relative depth, and shadowing of direct sunlight and skylight, by using a combination of 2D buffers.Thus the rendering speed of quasi-3D trees depends on their display sizes only, regardless of the complexity oftheir original 3D tree models. By utilizing a two-step shadowing algorithm, our proposed method can create highquality forest scenes illuminated by both sunlight and skylight at a low cost. It can generate both umbrae andpenumbrae on a tree cast by other trees and any other objects such as buildings or clouds. Transparency, specularreflection and inter-reflection of leaves, which influence the delicate shading effects of trees, can also be simulatedwith verisimilitude.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three dimensional Graphics and RealismItem Rendering and Affect(Blackwell Publishers, Inc and the Eurographics Association, 2003) Duke, D.J.; Barnard, P.J.; Halper, N.; Mellin, M.Previous studies at the intersection between rendering and psychology have concentrated on issues such as realismand acuity. Although such results have been useful in informing development of realistic rendering techniques,studies have shown that the interpretation of images is influenced by factors that have little to do with realism. Inthis paper, we summarize a series of experiments, the most recent of which are reported in a separate paper, thatinvestigate affective (emotive) qualities of images. These demonstrate significant effects that can be utilized withininteractive graphics, particularly via non-photorealistic rendering (NPR). We explain how the interpretation ofthese results requires a high-level model of cognitive information processing, and use such a model to account forrecent empirical results on rendering and judgement.Categories and Subject Descriptors (according to ACM CCS): I.3.m [Computer Graphics]: MiscellaneousItem Interactive Rendering with Bidirectional Texture Functions(Blackwell Publishers, Inc and the Eurographics Association, 2003) Suykens, Frank; Berge, Karl; Lagae, Ares; Dutre, PhilipWe propose a new technique for efficiently rendering bidirectional texture functions (BTFs). A 6D BTF describesthe appearance of a material as a texture that depends on the lighting and viewing directions. As such, a BTFaccommodates self-shadowing, interreflection, and masking effects of a complex material without needing anexplicit representation of the small scale geometry. Our method represents the BTF as a set of spatially varyingapparent BRDFs, that each encode the reflectance field of a single pixel in the BTF. Each apparent BRDF isdecomposed into a product of three or more two-dimensional positive factors using a novel factorization technique,which we call chained matrix factorization (CMF). The proposed factorization technique is fully automatic andsuitable for both BRDFs and apparent BRDFs (which typically exhibit off-specular peaks and non-reciprocity).The main benefit of CMF is that it delivers factors well suited for the limited dynamic range of conventionaltexture maps. After factorization, an efficient representation of the BTF is obtained by clustering the factors intoa compact set of 2D textures. With this compact representation, BTFs can be rendered on recent consumer levelhardware with arbitrary viewing and lighting directions at interactive rates.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-DimensionalGraphics and RealismItem Field Functions for Blending Range Controls on Soft Objects(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hsu, P. C.; Lee, C.This paper proposes new field functions that have adjustable inner radius and outer radius of influence. Incorporatingthe proposed field functions with soft object modeling, soft blending, Ricci's super-ellipsoid blends, Perlin'sset operations, and R-functions, etc. can have blending range controls by adjusting the inner and the outer radiiof influence of given field functions. As a result, the sizes of the resulting blending surfaces on soft objects willnot be restricted by the sizes of the blended primitive soft objects and can be enlarged and shrunk freely withoutdeforming the overall shapes of blended primitive soft objects. In addition, a small soft object can have a largeblending region, and a large one can have a small blending regionCategories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometry and Object Modeling - Curve, surface, solid and object representationsItem Narrative Use of Sign Language by a Virtual Character for the Hearing Impaired(Blackwell Publishers, Inc and the Eurographics Association, 2003) Rieger, Thomas; Braun, NorbertThis paper describes the concept and control of a 3d virtual character system with facial expressions and gesturesas a conversational user interface with narrative expressiveness for the hearing impaired. The gestures and facialexpressions are based on morphing techniques. The system allows the generation of sign language and mouthmotion in real time from text at the level of lip reading quality. The concept of Narrative Extended Speech Acts(NESA) is introduced, based on Interactive Storytelling techniques and the concepts of Narrative Conflict andSuspense Progression. We define a choice of annotation tags to be used with NESAs. We use the NESAs to classifyconversation fragments and to enhance computer generated sign language. We note, how the sign language gesturesare generated and show the possibilities for editing sign language gestures. Furthermore, we give details onhow the NESAs are mapped to gestures. We show the possibilities of controlling the virtual character's behaviourand gestures in a human-oriented way and provide an outlook on future work.Categories and Subject Descriptors (according to ACM CCS): 1.3.6 [Computer Graphics]: Methodology and TechniquesItem Interactive Cutaway Illustrations(Blackwell Publishers, Inc and the Eurographics Association, 2003) Diepstraten, J.; Weiskopf, D.; Ertl, T.In this paper we discuss different approaches to generate cutaway illustrations. The purpose of such a drawingis to allow the viewer to have a look into an otherwise solid opaque object. Traditional methods to draw thesekinds of illustrations are evaluated to extract a small and effective set of rules for a computer-based renderingof cutaway illustrations. We show that our approaches are not limited to a specific rendering style but can besuccessfully combined with a great variety of well-known artistic or technical illustration techniques. All methodsof this paper make use of modern graphics hardware functionality to achieve interactive frame rates.Item Particle-Based Simulation of Fluids(Blackwell Publishers, Inc and the Eurographics Association, 2003) Premzoe, Simon; Tasdizen, Tolga; Bigler, James; Lefohn, Aaron; Whitaker, Ross T.Due to our familiarity with how fluids move and interact, as well as their complexity, plausible animation of fluidsremains a challenging problem. We present a particle interaction method for simulating fluids. The underlyingequations of fluid motion are discretized using moving particles and their interactions. The method allows simulationand modeling of mixing fluids with different physical properties, fluid interactions with stationary objects, andfluids that exhibit significant interface breakup and fragmentation. The gridless computational method is suitedfor medium scale problems since computational elements exist only where needed. The method fits well into thecurrent user interaction paradigm and allows easy user control over the desired fluid motion.Item A Scalable Approach to Interactive Global Illumination(Blackwell Publishers, Inc and the Eurographics Association, 2003) Benthin, Carsten; Wald, Ingo; Slusallek, PhilippThe addition of global illumination can dramatically increase the realism achievable when rendering virtual environments.In particular with interactive applications we expect the environment to reflect changes in the scenedue to global lighting effects instead of it being just a static backdrop. However, a sufficiently fast and accuratecomputation of global illumination at interactive rates has been difficult even with recent approaches based onrealtime ray tracing.In this paper we present a highly scalable approach to interactive global illumination. It fully recomputes a high-qualitysolution for each frame and thus offers immediate feedback even for dynamic scenes, achieving more than20 fps for simple scenes. Compared to previous systems we increased the raw performance by a factor of up toeight and removed the bottlenecks that were limiting scalability. The system now scales linearly in quality andavailable computing resources, tested with up to 48 CPUs in a commodity PC-cluster. Due to its logarithmicscaling property with respect to scene complexity it even supports lighting simulation in complex scenes with morethan 50 million triangles. This scalability allows applications to perform flexible performance trade-offs. We alsoargue that the realism achievable through interactive global illumination will make it a standard feature of future3D graphics systems once the required computing resources are readily available.Item Hierarchical Context-based Pixel Ordering(Blackwell Publishers, Inc and the Eurographics Association, 2003) Bar-Joseph, Ziv; Cohen-Or, DanielWe present a context-based scanning algorithm which reorders the input image using a hierarchical representationof the image. Our algorithm optimally orders (permutes) the leaves corresponding to the pixels, by minimizing thesum of distances between neighboring pixels. The reordering results in an improved autocorrelation betweennearby pixels which leads to a smoother image. This allows us, for the first time, to improve image compressionrates using context-based scans. The results presented in this paper greatly improve upon previous work in bothcompression rate and running time.Categories and Subject Descriptors (according to ACM CCS): I.3.5 [Computer Graphics]: Computational Geometryand Object Modeling I.3.6 [Computer Graphics]: Methodology and TechniquesItem A Fast Rendering Method for Refractive and Reflective Caustics Due to Water Surfaces(Blackwell Publishers, Inc and the Eurographics Association, 2003) Iwasaki, Kei; Dobashi, Yoshinori; Nishita, TomoyukiIn order to synthesize realistic images of scenes that include water surfaces, the rendering of optical effectscaused by waves on the water surface, such as caustics and reflection, is necessary. However, rendering causticsis quite complex and time-consuming. In recent years, the performance of graphics hardware has made significantprogress. This fact encourages researchers to study the acceleration of realistic image synthesis. We present herea method for the fast rendering of refractive and reflective caustics due to water surfaces. In the proposed method,an object is expressed by a set of texture mapped slices. We calculate the intensities of the caustics on the objectby using the slices and store the intensities as textures. This makes it possible to render caustics at interactive rateby using graphics hardware. Moreover, we render objects that are reflected and refracted due to the water surfaceby using reflection/refraction mapping of these slices.Categories and Subject Descriptors (according to ACM CCS): I.3.1 [Computer Graphics]: Hardware Architecture I.3.7 [Computer Graphics]: Three-Dimensional Graphics and RealismItem 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]: RaytracingItem Volumetric cell-and-portal generation(Blackwell Publishers, Inc and the Eurographics Association, 2003) Haumont, D.; Debeir, O.; Sillion, F.We present an algorithm to generate a cell-and-portal decomposition of general indoor scenes. The method is an adaptation of the 3D watershed transform, computed on a distance-to-geometry sampled field. The watershed is processed using a flooding analogy in the distance field space. Flooding originates from local minima, each minimum producing a region. Portals are built as needed to avoid the merging of regions during their growth. As a result, the cell-and-portal decomposition is closely linked to the structure of the models. In a building, the algorithm finds all the rooms, doors and windows. To restrict the memory load, a hierarchical implementation of the algorithm is presented. We also explain how to handle possible model degeneracies -such as cracks, holes and interpenetrating geometries- using a pre-voxelisation step. The hierarchical algorithm, preceded when necessary by the pre-voxelisation, was tested on a large range of models. We show that it is able to deal with classical architectural models, as well as cave-like environments and large mixed indoor/outdoor scenes. Thanks to the intermediate distance field representation, the algorithm can be used regardless of the way the model is represented: it deals with parametric curves, implicit surfaces, volumetric data and polygon soups in a unified way.Item Advanced Design for a Realistic Virtual Brush(Blackwell Publishers, Inc and the Eurographics Association, 2003) Xu, Songhua; Lau, Francis C.M.; Tang, Feng; Pan, YunheThis 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;Item Real-Time Caustics(Blackwell Publishers, Inc and the Eurographics Association, 2003) Wand, M.; Strasser, W.We present a new algorithm to render caustics. The algorithm discretizes the specular surfaces into samplepoints. Each of the sample points is treated as a pinhole camera that projects an image of the incoming lightonto the diffuse receiver surfaces. Anti-aliasing is performed by considering the local surface curvature at thesample points to filter the projected images. The algorithm can be implemented using programmable texturemapping hardware. It allows to render caustics in fully dynamic scenes in real-time on current PC hardware.Categories and Subject Descriptors: I.3.3 [Computer Graphics]: Picture/Image Generation - Display Algorithms;I.3.7 [Computer Graphics]: Three-Dimensional Graphics and RealismItem Table of Contents CGF 22-3(Blackwell Publishers, Inc and the Eurographics Association, 2003) Fellner, Dieter W.; Brunet, Pere-Item Animation of Bubbles in Liquid(Blackwell Publishers, Inc and the Eurographics Association, 2003) Hong, Jeong-Mo; Kim, Chang-HunWe 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]: AnimationItem Planned Sampling of Spatially Varying BRDFs(Blackwell Publishers, Inc and the Eurographics Association, 2003) Lensch, Hendrik P.A.; Lang, Jochen; Sa, Asla M.; Seidel, Hans-PeterMeasuring reflection properties of a 3D object involves capturing images for numerous viewing and lightingdirections. We present a method to select advantageous measurement directions based on analyzing the estimationof the bi-directional reflectance distribution function (BRDF). The selected directions minimize the uncertaintyin the estimated parameters of the BRDF. As a result, few measurements suffice to produce models that describethe reflectance behavior well. Moreover, the uncertainty measure can be computed fast on modern graphics cardsby exploiting their capability to render into a floating-point frame buffer. This forms the basis of an acquisitionplanner capable of guiding experts and non-experts alike through the BRDF acquisition process. We demonstratethat spatially varying reflection properties can be captured more efficiently for real-world applications using ouracquisition planner.Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three-DimensionalGraphics and Realism Virtual Reality I.4.1 [Computer Vision]: Digitization and Image Capture, ReflectanceItem 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)Item ShieldTester: Cell-to-Cell Visibility Test for Surface Occluders(Blackwell Publishers, Inc and the Eurographics Association, 2003) Navazo, I.; Rossignac, J.; Jou, J.; Shariff, R.We present a novel Cell-To-Cell Visibility (C2CV) algorithm, which given two polyhedra, AandBand a connectedand oriented manifold triangle mesh, S offers a simple, fast and conservative test for detecting when A and B areoccluded from each other by S. Previously disclosed C2CV algorithms either relied on costly occlusion fusion orwere restricted to convex or "apparently convex" occluders, which makes them inappropriate for scenes wherepotential occluders are arbitrary triangulated surfaces, such as the body of a car or a portion of a terrain. Thesimplicity of our C2CV algorithm, named ShieldTester, stems from a new Occlusion Theorem, introduced herewhich permits to establish occlusion by computing the intersection of S with a single ray from a vertex ofAtoa vertex ofB. ShieldTester may be used to establish that pairs of cells in a subdivision of space are hidden fromeach other by a relatively large surface occluder, so that when the viewer is in one cell, the objects in the othercell need not be displayed.Categories and Subject Descriptors (according to ACM CCS): I.3.3 [Computer Graphics]: Computational Geometryand Object Modeling: Occlussion Culling, Visibility Test, Triangle MeshesItem Freeform Shape Representations for Efficient Geometry Processing(Blackwell Publishers, Inc and the Eurographics Association, 2003) Kobbelt, LeifThe most important concepts for the handling and storage of freeform shapes in geometry processing applications are parametric representations and volumetric representations. Both have their specific advantages and drawbacks. While the algebraic complexity of volumetric representations is independent from the shape complexity, the domain of a parametric representation usually has to have the same structure as the surface itself (which sometimes makes it necessary to update the domain when the surface is modified).On the other hand, the topology of a parametrically defined surface can be controlled explicitly while in a volumetric representation, the surface topology can change accidentally during deformation. A volumetric representation reduces distance queries or inside/outside tests to mere function evaluations but the geodesic neighborhood relation between surface points is difficult to resolve. As a consequence, it seems promising to combine parametric and volumetric representations to effectively exploit both advantages.In this talk, a number of projects are presented and discussed in which such a combination leads to efficient and numerically stable algorithms for the solution of various geometry processing tasks. Applications include global error control for mesh decimation and smoothing, topology control for level-set surfaces, and shape modeling with unstructured point clouds.
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