Volume 19 (2000)
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Item An Adaptive Spectral Rendering with a Perceptual Control(Blackwell Publishers Ltd and the Eurographics Association, 2000) Claude Iehl, Jean; Peroche, BernardIn this paper, we present a spectral rendering method based on a ray tracing algorithm and guided by a perceptual control of the error made. An adaptive representation of spectral data for light sources and materials is used and induces, for each pixel, the evaluation of an algebraic expression. For each visible wavelength, the computations of complex spread in refractive and dispersive materials, based on several photon maps, are locally restricted by an adaptive evaluation of the expression. This method allows to simulate high quality physically-based pictures and, in particular, some specific phenomena like dispersion in transparent objects, scattered caustics,. . .Item An Advanced Color Representation for Lossy Compression of CMYK Prepress Images(Blackwell Publishers Ltd and the Eurographics Association, 2000) De Neve, P.; Denecker, K.; Philips, W.; Lemahieu, I.CMYK color images are used extensively in prepress applications. When compressing those color images one has to deal with four different color channels. Usually compression algorithms only take into account the spatial redundancy that is present in the image data. This approach does not yield an optimal data reduction since there also exists a high correlation between the different colors in natural images.This paper shows that a significant gain in data reduction can be achieved by exploiting this color redundancy. Some popular transform coders, including DCT-based JPEG and the SPIHT wavelet coder, were used for reducing the spatial redundancy. The performance of the algorithms was evaluated using a quality criterion based on human perception like the mean CIEL*a*b*?E error.Item Announcements(Blackwell Publishers Ltd and the Eurographics Association, 2000)Item Augmented Reality with Back-Projection Systems using Transflective Surfaces(Blackwell Publishers Ltd and the Eurographics Association, 2000) Bimber, Oliver; Encarnacao, L. Miguel; Schmalstieg, DieterIn this paper, we introduce the concept of Extended VR (extending viewing space and interaction space of back-projection VR systems), by describing the use of a hand-held semi-transparent mirror to support augmented reality tasks with back-projection systems. This setup overcomes the problem of occlusion of virtual objects by real ones linked with such display systems. The presented approach allows an intuitive and effective application of immersive or semi-immersive virtual reality tasks and interaction techniques to an augmented surrounding space. Thereby, we use the tracked mirror as an interactive image-plane that merges the reflected graphics, which are displayed on the projection plane, with the transmitted image of the real environment. In our implementation, we also address traditional augmented reality problems, such as real-object registration and virtual-object occlusion. The presentation is complemented by a hypothesis of conceivable further setups that apply transflective surfaces to support an Extended VR environment.Item Automatic Camera Placement for Image-Based Modeling(Blackwell Publishers Ltd and the Eurographics Association, 2000) Fleishman, Shachar; Cohen-Or, Daniel; Lischinski, DaniWe present an automatic camera placement method for generating image-based models from scenes with known geometry. Our method first approximately determines the set of surfaces visible from a given viewing area and then selects a small set of appropriate camera positions to sample the scene from. We define a quality measure for a surface as seen, or covered, from the given viewing area. Along with each camera position, we store the set of surfaces which are best covered by this camera. Next, one reference view is generated from each camera position by rendering the scene. Pixels in each reference view that do not belong to the selected set of polygons are masked out.The image-based model generated by our method, covers every visible surface only once, associating it with a camera position from which it is covered with quality that exceeds a user-specified quality threshold. The result is a compact non-redundant image-based model with controlled quality.The problem of covering every visible surface with a minimum number of cameras (guards) can be regarded as an extension to the well-known Art Gallery Problem. However, since the 3D polygonal model is textured, the camera-polygon visibility relation is not binary; instead, it has a weight - the quality of the polygon's coverage.Item Automatic Creation of Object Hierarchies for Radiosity Clustering(Blackwell Publishers Ltd and the Eurographics Association, 2000) Muller, Gordon; Schafer, Stephan; Fellner, Dieter W.Using object clusters for hierarchical radiosity greatly improves the efficiency and thus usability of radiosity computations. By eliminating the quadratic starting phase very large scenes containing about 100k polygons can be handled efficiently. Although the main algorithm extends rather easily to using object clusters, the creation of 'good' object hierarchies is a difficult task both in terms of construction time and in the way how surfaces or objects are grouped to clusters. The quality of an object hierarchy for clustering depends on its ability to accurately simulate the hierarchy of the energy flow in a given scene. Additionally it should support visibility computations by providing efficient ray acceleration techniques.In this paper we will present a new approach of building hierarchies of object clusters. Our hybrid structuring algorithm provides accuracy and speed by combining a highly optimized bounding volume hierarchy together with uniform spatial subdivisions for nodes with regular object densities. The algorithm works without user intervention and is well suited for a wide variety of scenes. First results of using these hierarchies in a radiosity clustering environment are very promising and will be presented here.The combination of very deep hierarchies (we use a binary tree) together with an efficient ray acceleration structure shifts the computational effort away from form factor and visibility calculation towards accurately propagating the energy through the hierarchy. We will show how an efficient single pass gathering can be used to minimize traversal costs.Item Automatic Generation of Virtual Woodblocks and Multicolor Woodblock Printing(Blackwell Publishers Ltd and the Eurographics Association, 2000) Mizuno, S.; Kasaura, T.; Okouchi, T.; Yamamoto, S.; Okada, M.; Toriwaki, J.In this paper, we study a method to synthesize a multicolor virtual woodblock print by using several virtual woodblocks. It consists of two sections: carving and printing, to synthesize a virtual print. In the carving section, virtual woodblocks are generated by a user with supporting of an automatically carving method based on feature extraction of a gray value image. And woodblocks are also generated automatically by using a full-color image as a draft. In the printing section, a "paper sheet", a "printing brush" and "ink" are prepared in addition to the "woodblock" in the virtual space and the user synthesizes a woodblock print interactively. As the printing factors, a color of ink, a moisture value and a grain change the finish of the print. Using several virtual woodblocks and printing to a paper sheet in succession, a printing image of each woodblock is combined based on the printing factors and a multicolor virtual prints is synthesized.Item Automatic Surface Reconstruction from Point Sets in Space(Blackwell Publishers Ltd and the Eurographics Association, 2000) Attene, Marco; Spagnuolo, MichelaIn this paper an algorithm is proposed that takes as input a generic set of unorganized points, sampled on a real object, and returns a closed interpolating surface. Specifically, this method generates a closed 2-manifold surface made of triangular faces, without limitations on the shape or genus of the original solid. The reconstruction method is based on generation of the Delaunay tetrahedralization of the point set, followed by a sculpturing process constrained to particular criteria. The main applications of this tool are in medical analysis and in reverse engineering areas. It is possible, for example, to reconstruct anatomical parts starting from surveys based on TACs or magnetic resonance.Item Binding Virtual Environments to Toolkit Capabilities(Blackwell Publishers Ltd and the Eurographics Association, 2000) Smith, Shamus P.; Duke, David J.There are many toolkits and development environments that aid the process of constructing virtual environment applications. Many of these development environments encourage customising a virtual environment's design while rapid prototyping within the confines of a toolkit's capabilities. Thus the choice of the technology and its associated support has been made independent of the end-use requirements of the final system. This can bias a virtual environment's design by implementation based constraints. We propose that an alternative approach is the consideration of virtual environment requirements in the context of an inspectable design model, to identify the requirements that a toolkit will need to support. In the context of an example, we present a selection of design requirements that we consider important for virtual environment design in general. We explore how these requirements might be mapped to different capabilities using Virtual Reality Modelling Language (VRML) as a concrete example of a platform technology.Item Book Reviews(Blackwell Publishers Ltd and the Eurographics Association, 2000)Books reviewed:Salomon, David. Computer Graphics and Geometric ModelingGovil-Pai, Shalini and Pai, Rajesh. Learning Computer GraphicsRoelofs, Greg. PNG: The Definitive GuideMarsh, Duncan. Applied Geometry for Computer Graphics and CADMarchand, Patrick. Graphics and GUIs with MATLAB (2nd edition)Ammerall, Leen. Computer Graphics for Java ProgrammersItem Book Reviews(Blackwell Publishers Ltd and the Eurographics Association, 2000)Books reviwed:F. S. Hill Jr, Computer Graphics using OpenGL (Second edition)Barry Blundell, and Adam Schwarz, Volumetric Three Dimensional Display SystemsEdward Angel, Interactive Computer Graphics: A Top-Down approach with OpenGL (Second Edition)J.-R Sack, and J. Urrutia, (eds) Handbook of Computational GeometryTomas Moller, and Eric Haines, Real-Time RenderingItem Carla Vandoni - A Remarkable Lady(Blackwell Publishers Ltd and the Eurographics Association, 2000) Duce, DavidItem Collaborative Virtual Simulation Environment for Radiotherapy Treatment Planning(Blackwell Publishers Ltd and the Eurographics Association, 2000) Cai, Wenli; Walter, Stefan; Karangelis, Grigorios; Sakas, GeorgiosThe simulation of Radiotherapy Treatment Planning (RTP) is a normal procedure in oncology clinics carried out on a Simulator machine. The Virtual Simulation of RTP replaces the real Simulator machine with a virtual one by using the CT data sets of a patient instead of the real patient. In this paper, we present a collaborative virtual simulation environment of RTP, named EU-VIRTUOSO, which is based on volume rendering and telecommunication techniques. The RTP procedure is visualised on a virtual patient, which is created by using the CT data of the patient. Different volume rendering and volume interaction techniques, such as DRR, MIP, gradient surface, and iso-surface, supply physicians with high quality rendering images to simulate the real working environment of the Simulator machine. In the collaborative environment, physicians distributed at different locations can work together via network to plan the treatment or to validate the treatment plan on-line by a collaborative application sharing approach. Both concepts virtualised planning and collaborative planning improve the efficiency and accuracy of a radiotherapy treatment while reducing the effort for an individual patient.Item Color Distribution - A New Approach to Texture Compression(Blackwell Publishers Ltd and the Eurographics Association, 2000) Ivanov, Denis V.; Kuzmin, Yevgeniy P.Texture compression is recently one of the most important topics of 3D scene rendering techniques, because it allows rendering more complicated high-resolution scenes. However, because of some special requirements for these type of techniques, the commonly used block decomposition approach may introduce visual degradation of image details due to lack of colors. We present here a new approach to texture compression, which allows sharing of one color by several blocks providing a larger number of unique colors in each particular block and the best compression ratio. We also present an iterative algorithm for obtaining distributed colors on a texture, and discuss some advantages of our approach. The paper concludes with comparison of our technique with S3TC and other block decomposition methods.Item Colour Section(Blackwell Publishers Ltd and the Eurographics Association, 2000)Item Computation of Irradiance from Triangles by Adaptive Sampling(Blackwell Publishers Ltd and the Eurographics Association, 2000) Urena, C.We introduce an algorithm for sample positioning in a planar triangle, which can be used to make numerical integration of an arbitrary function defined on it. This algorithm has some interesting properties which make it suitable for applications in the context of realistic rendering. We use an adaptive triangle partitioning procedure, driven by an appropriate measure of the error. The underlying variance is shown to be bounded, and in fact it can be controlled, so that it approaches the minimum possible value. We show results obtained when applying the method to irradiance computation, in the context of final-gather algorithms. We also describe a C++ class which offers all required functionality, and we made available its source code.Item Conflict Neutralization on Binary Space Partitioning(Blackwell Publishers Ltd and the Eurographics Association, 2000) James, A.; Day, A.M.The Binary Space Partitioning (BSP) tree achieves fast hidden surface removal for most practical applications where an observer can move through a scene of static objects. However, the BSP algorithm generally increases the number of polygons in a scene due to its splitting stage resulting in a detrimental effect on the priority ordering and more significantly, the display calculations (shading, lighting, shadows, etc.) of the rendering pipeline.We present the Conflict Neutralization algorithm which attempts to reduce the number of splits more effectively than existing techniques whilst maintaining the 'standard' model of a BSP tree. Our idea is similar to Conflict Minimization proposed by Fuchs; the significant difference is that our algorithm recognizes that a polygon suitable for selection in the Minimization criterion may subsequently stop the remainder of polygons achieving some reductions in cuts-with Conflict Neutralization, such a polygon is demoted.We compare the results of Conflict Neutralization against Conflict Minimization, the Least-crossed with Most-crossed tie-breaking criterion and our own, enhanced implementation of Conflict Minimization. We show how these techniques fall into different 'depths of analysis'.Item Constructive Volume Geometry(Blackwell Publishers Ltd and the Eurographics Association, 2000) Chen, Min; Tucker, John V.We present an algebraic framework, called Constructive Volume Geometryn (CVG), for modelling complex spatial objects using combinational operations. By utilising scalar fields as fundamental building blocks, CVG provides high-level algebraic representations of objects that are defined mathematically or built upon sampled or simulated datasets. It models amorphous phenomena as well as solid objects, and describes the interior as well as the exterior of objects. We also describe a hierarchical representation scheme for CVG, and a direct rendering method with a new approach for consistent sampling. The work has demonstrated the feasibility of combining a variety of graphics data types in a coherent modelling scheme.Item Context-based Space Filling Curves(Blackwell Publishers Ltd and the Eurographics Association, 2000) Dafner, Revital; Cohen-Or, Daniel; Matias, YossiA context-based scanning technique for images is presented. An image is scanned along a context-based space filling curve that is computed so as to exploit inherent coherence in the image. The resulting one-dimensional representation of the image has improved autocorrelation compared with universal scans such as the Peano-Hilbert space filling curve. An efficient algorithm for computing context-based space filling curves is presented. We also discuss the potential of improved autocorrelation of context-based space filling curves for image and video lossless compression.Item Direct Manipulation and Interactive Sculpting of PDE Surfaces(Blackwell Publishers Ltd and the Eurographics Association, 2000) Du, Haixia; Qin, HongThis paper presents an integrated approach and a unified algorithm that combine the benefits of PDE surfaces and powerful physics-based modeling techniques within one single modeling framework, in order to realize the full potential of PDE surfaces. We have developed a novel system that allows direct manipulation and interactive sculpting of PDE surfaces at arbitrary location, hence supporting various interactive techniques beyond the conventional boundary control. Our prototype software affords users to interactively modify point, normal, curvature, and arbitrary region of PDE surfaces in a predictable way. We employ several simple, yet effective numerical techniques including the finite-difference discretization of the PDE surface, the multigrid-like subdivision on the PDE surface, the mass-spring approximation of the elastic PDE surface, etc. to achieve real-time performance. In addition, our dynamic PDE surfaces can also be approximated using standard bivariate B-spline finite elements, which can subsequently be sculpted and deformed directly in real-time subject to intrinsic PDE constraints. Our experiments demonstrate many attractive advantages of our dynamic PDE formulation such as intuitive control, real-time feedback, and usability to the general public.