EG 1993 Conference Proceedings

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https://diglib.eg.org/handle/10.2312/13892

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An Integral Geometry Based Method for Fast Form-Factor Computation
(Blackwell Science Ltd and the Eurographics Association, 1993) Sbert, Mateu
Monte Carlo techniques have been widely used in rendering algorithms for local integration. For example, to compute the contribution of a patch to the luminance of another. In the present paper we propose an algorithm based on Integral geometry where Monte Carlo is applied globally. We give some results of the implementation to validate the proposition and we study the error of the technique, as well as its complexity.
Verve
(Blackwell Science Ltd and the Eurographics Association, 1993) Knittel, Gunter
The design principles of a hardware acceleratorfor volume rendering are described. The architecture represents a voxel subsystem which interfaces easily to any existing workstation. Host requirements are low since it contains a multiport memory holding the complete data set and all arithmetic units needed to perform an effective visualization.Our approach aims at virtual reality by providing some"real-world" examination techniques. The user (e.g., a physician) is enabled to analyze the data set from an arbitrary viewpoint and, even more, to"walk through" the volume model. For a realistic impression, the machine produces perspective projections, supports the illumination by non-parallel light comingfrom a freely movable point light source and provides depth cueing. The objects are Phong shaded at a rate of 107 operations/s and can be displayed semitransparently. One unit achieves interactive speed: for real-time operation only a small number of units (typically 4-16) must be placed in parallel.
Abstract Interaction Objects
(Blackwell Science Ltd and the Eurographics Association, 1993) Duke, D.J.; Harrison, M.D.
The concept of an interactor has been introduced by Faconti and Paterno [6] as an abstraction of an entity in interactive graphics capable of both input and output. However the notion of interaction object need not be confined to graphics systems- it represents a useful structure for thinking and reasoning about the behaviour of interactive systems in general. As part of Esprit Basic Research Action 7040 (Amodeus-2) we are using the concept of interactor, and existing work on state-based processes and agents, to develop a model and theory of interactive systems. In this paper we describe two formal models for interaction objects and sketch how they can be used to build a small vocabulary of operators to support the rigorous specification of a graphics system. Our model differs from the approach of Faconti and Paterno in that it abstracts away from any specific graphics framework and is thus suited to the level of abstraction demanded by formal approaches to system development.
On the Application of Quantization and Dithering Techniques to History of Arts
(Blackwell Science Ltd and the Eurographics Association, 1993) Coltelli, P.; Faconti, G.; Marfori, F.
The diffusion of computing techniques within humane studies is considerably increasing, due to technological advances and reduction in computing costs, with History of Arts being one of the most interesting fields of application. In fact, several domains related to works of arts might be investigated other than archival and retrieval of information: this includes the planning for the preservation and restoration, the developing of critical examinations of artworks as well as the supporting of less specialized activities such as teaching, presentation of museum exhibitions and spreading of information.Within this framework, it is of particular interest to review already known image compression techniques from other fields and to evaluate their applicability taking into account the peculiarities and the requirements of this specific domain. A distinguishing aspect of History of Arts is the requirement to keep the maximum approximation of the original information on each point of an image. This peculiarity strongly requires that the set of pixels of the same color in the original image is bound to a unique color in the final image and that each color in the final image uniquely determines the set of colors it represents. This requirement constrains the applicability in this domain to those quantization algorithms satisfying this property while still minimizing the quantization error.The paper gives a formal definition of the above requirement and justifies the use of the quantization and dithering algorithms based on the octree reduction technique. Following, the results given by the application of these techniques to several paintings are shown. Finally, the measured quantization errors are compared with those obtained by applying the median-cut algorithm.
Interactive Neural Network Texture Analysis and Visualization for Surface Reconstruction in Medical Imaging
(Blackwell Science Ltd and the Eurographics Association, 1993) Busch, C.; Gro?, M.H.
The following paper describes a new approach for the automatic segmentation and tissue classification of anatomical objects such as brain tumors from magnetic resonance imaging (MRI) data sets using artificial neural networks. These segmentations serve as an input for 3D-reconstruction algorithms. Since MR images require a careful interpretation of the underlying physics and parameters, we first give the reader a tutorial style introduction to the physical basics of MR technology. Secondly, we describe our approach that is based on a two-pass method including non-supervised cluster analysis, dimensionality reduction and visualization of the texture features by means of nonlinear topographic mappings. An additional classification of the MR data set can be obtained using a post-processing technique to approximate the Bayes decision boundaries. Interactions between the user and the network allow an optimization of the results. For fast 3D-reconstructions, we use a modified marching cubes algorithm but our scheme can easily serve as a preprocessor for any kind of volume renderer.The applications we present in our paper aim at the automatic extraction and fast reconstruction of brain tumors for surgery and therapy planning. We use the neural networks on pathological data sets and show how the method generalizes to physically comparable data sets.
Nonsplitting Macro Patches for Implicit Cubic Spline Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1993) Guo, B.
Macro patches are important for generating quadric or cubic implicit spline surfaces from the input of a polyhedron. All existing macro patches split the triangular facets of the polyhedron- this paper presents cubic nonsplitting macro patches (NMP) that do not split these facets. The NMP s are based on a necessary and sufficient condition for nonsplitting constructions of implicit cubic spline surfaces. This condition can be satisfied for most practical applications, so the NMP s lead to an efficient and powerful spline surface scheme using implicit cubics. The free parameters in an NMP are set using a new technique for excluding topological anomalies such as extraneous sheets, splits, unwanted holes, self-intersections, and unwanted handles. Each cubic patch obtained by this technique best approximates, in a least-squares sense, a quadric patch from a single algebraic component of a monotone polynomial derived from the input data.
Updating Polygonizations*
(Blackwell Science Ltd and the Eurographics Association, 1993) Abellanas, M.; Garcia, J.; Hernbandez, G.; Hurtado, F.; Serra, O.; Urrutia, J.
In this paper we consider polygonizations that are robust when faced with changes in the vertices that are present or in their position. We analyze the dynamic maintenance of different types of polygonizations (monotone, star-shaped.) and we introduce monotone half-convex polygonizations that are specially interesting because they provide minimum cost per insertion or deletion. If we had to delete not only one point but several external layers of the set, then the onion polygonizations would be suited, because they can be updated in constant time. We also consider the case of points that can be moved to contiguous positions and we show how to polygonize the set for updating in linear time. We deal too with security problems for a polygon: What is the maximum distance the vertices of a polygon could be moved away of their position in such a way that the topology on the boundary of the polygon (or its convexity) remains the same?.
An Object Model for Multimedia Programming
(Blackwell Science Ltd and the Eurographics Association, 1993) Arbab, F.; Herman, I.; Reynolds, G.J.
The development of multimedia applications is a complex task. Much of this complexity stems from requirements associated with programming multiple media objects and the control of dependences and inter-relationships between these media objects and the user(s). It is clearly necessary to have a basic framework on which to build multimedia applications in the face of such complexities. Such a conceptual model is what we have called an object model and it is the main subject of this paper. The MADE object model represents a novel approach to multimedia application programming that is founded on the two principal concepts of active objects and delegation. Although these concepts are not novel in themselves, we believe that their combined use in a multimedia development environment represents a substantial enhancement to more traditional approaches to programming in this area.
An Integrated System for Modeling, Animating and Rendering Hair
(Blackwell Science Ltd and the Eurographics Association, 1993) Daldegan, Agnes; Thalmann, Nadia Magnenat; Kurihara, Tsuneya; Thalmann, Daniel
There are basically four problems to solve in order to produce realistic animated synthetic actors with hair: hair modeling and creation, hair motion, collision detection and hair rendering. This paper describes a complete methodology to solve these basic four problems. We present how hair styles may be designed with our Hair Styler module. Then we survey the animation model and emphasize a method of collision processing. Finally, we explain how hair may be rendered using an extension of a standard ray-tracing program. We also show applications of our synthetic actors with various hair styles and different styles of mustaches and beards.
Accurate and Consistent Reconstruction of Illumination Functions Using Structured Sampling
(Blackwell Science Ltd and the Eurographics Association, 1993) Drettakis, George; Fiume, Eugene
The study of common classes of diffuse emitters, such as planar convex polygons, reveals several interesting properties of the functions of illumination these emitters cast on receiver surfaces. Some properties, such as the position of the maximum and the curvature are of particular interest for sampling and reconstruction of illumination across receivers. A computationally efficient approach is presented that identifies these properties, and uses them to select samples of illurnination. In addition these properties are used to determine upper bounds on the error due to linear and quadratic interpolants. These bounds are then used to adaptively subdivide the non-uniform sampling grid, resulting in accurate reconstruction. Results show that the method reduces the error compared to uniform approaches, and produces more consistent animated sequences.
Cooperative Visualization of Computational Fluid Dynamics
(Blackwell Science Ltd and the Eurographics Association, 1993) Gerald-Yamasaki, Michael J.
Tempus Fugit/Interview is a computational fluid dynamics visualization application for which processing is distributed between high performance graphics workstations and supercomputers. Facilities are provided in the application for more than one user to view shared images creating a cooperative visualization environment. The way in which the computation is partitioned between the super computer and the workstations is critical to the capability of the application to present simultaneous, identical, animated images of fluid dynamics to more than one user.
Quality Control of an Interpolation Method for Discontinuous Parametric Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1993) Seron, F.J.; Torrens, J.J; Magallon, J.A.
In this paper we study a finite element interpolation method for fitting discontinuous parametric surfaces when the data points are the nodes of a curvilinear grid. Quality control of the interpolating surfaces is also considered, focussing on the display of isophotes and reflection lines using ray tracing techniques. Finally, graphical and numerical examples are given.
A New Paradigm for Geometric Processing
(Blackwell Science Ltd and the Eurographics Association, 1993) Yamaguchi, Fujio; Niizeki, Masatoshi
A new paradigm for geometric processing is proposed. The paradigm can be featured by the four key phrases: (1) Totally Four Dimensional Homogeneous Processing, (2) 4 ? 4 Matrix Method and 4 ? 4 Determinant Method, (3) Integer Arithmetic with Adaptive Data-Length Control Technique, (4) Systematic Paradigm Structures Based on the Duality.
GKS-9x: Some Implementation Considerations
(Blackwell Science Ltd and the Eurographics Association, 1993) Damnjanovic, L.B.; Duce, D.A.; Robinson, S.K.
The Graphical Kernel System (GKS) was published as an ISO standard for computer graphics programming in August 1985. GKS is now undergoing revision in ISO/IEC and at the time of writing the text of the Draft International Standard of GKS-9x was being finalized. This paper presents a way in which a key part of the new functionality in GKS-9x, namely namesets and selection criteria, can be implemented effectively.
Landscapes Synthesis Achieved through Erosion and Deposition Process Simulation
(Blackwell Science Ltd and the Eurographics Association, 1993) Roudier, P.; Peroche, B.; Perrin, M.
This paper describes an original approach to terrain evolution in landscapes synthesis. In order to create some realistic landforms, we simulate geologically contrasted terrains and apply to them deterministic erosion processes. This allows us to relate the erosion on any point of the landsurface to local geological parameters. Any height field may be chosen as an initial topographic surface. Small perturbations may be introduced to avoid unpleasant regularities. A 3D model defines the geological parameters of each point according to its elevation. Our method is iterative: at each step, rock removal and possible alluvial deposition are computed at each point of the landsurface. The available erosion laws simulate mechanical erosion, chemical dissolution and alluvial deposition. At the end of each iteration, a new landsurface and the corresponding river network are created. Landsurfaces can be visualized at the final stage by two rendering algorithms including natural textures mapping. The stream network and the ridges may also be visualized.
Fast Spheres
(Blackwell Science Ltd and the Eurographics Association, 1993) Patterson, John W.
A new method for generating sphere-like images, using parabolic surfaces delimited by Bresenham s circle- generation algorithm, is presented. In many cases the resultant images are indistinguishable from spheres illuminated from a given single direction. The main form of the algorithm uses first and second integer differences to minimise computation and uses typically not more than one floating-point calculation per sphere. Two variants of the algorithm are given, one optimized for the special case of the light-source being behind the view-point, and one in which values are calculated for a z-buffer hidden-surface algorithm at the same time as the pixel values. The difference formulae can be exploited by differencing hardware or digital signal processors although very little arithmetic, typically five low-weight integer operations, including address calculation operations, is required per pixel on a conventional architecture.
3D Computational Morphology
(Blackwell Science Ltd and the Eurographics Association, 1993) Veltkamp, Remco C.
Computational Morphology is the analysis of form by computational means. This discipline typically uses techniques from Computational Geometry and Computer Aided Geometric Design. The present paper is more specifically about the construction and manipulation of closed object boundaries through a set of scattered points in 3D. Original results are developed in three stages of computational morphology: * impose a geometrical structure on the set of points- * construct a polyhedral boundary surface from this geometrical structure- * build a hierarchy of polyhedral approximations together with localization information-The economic advantage of this approach is that there is no dependency on any specific data source. It can be used for various types of data sources or when the source is unknown.
Storage Support for Multidimensional Discrete Data in Multimedia Databases
(Blackwell Science Ltd and the Eurographics Association, 1993) Furtado, Paula; Teixeira, Jose Carlos
Multidimensional discrete data (MDD) is enormously important for multimedia applications since diverse types of such data are used simultaneously by any multimedia application. However, multidimensional discrete data is not adequately supported by most existing database systems.In this paper we discuss the major management requirements imposed by such data on multimedia database management systems both at the conceptual level and at the internal level. At the internal level, the spatial structure of the data must also be preserved and special emphasis must be given to the efficient spatial access to subrectangles of very large data of arbitrary dimensionality.Our major contribution is the presentation of a Storage Manager for this kind of data which preserves the spatial nature of the data at the internal level of the database management system and provides efficient spatial access. This Storage Manager is based on an innovative combination of the subdivision of data in multidimensional tiles and of a spatial index to access those tiles. Furthermore, it supports advanced registration data.The lower level modules of the Storage Manager are responsible for the access to the data stored in secondary storage. The implementation of these modules can rely on any secondary storage access system to access data on disk. The Storage Manager was implemented using the functionality of a relational database system. The implementation of this relational Storage Manager is presented.
Extracting contour lines from a hierarchical surface model
(Blackwell Science Ltd and the Eurographics Association, 1993) De Floriani, Leila; Mirra, Daniela; Puppo, Enrico
The Hierarchical Triangulated Irregular Network (HTIN) is a structure for representing 2?-dimensional surfaces at different levels of detail through piecewise-linear approximations based on triangulations of the surface domain. In this paper, we present two algorithms that allow extracting a representation of the surface and contour lines at a given level of detail, directly from the HTIN.
Modeling of Skylight and Rendering of Outdoor Scenes
(Blackwell Science Ltd and the Eurographics Association, 1993) Tadamura, Katsumi; Nakamae, Eihachiro; Kaneda, Kazufumi; Baba, Masashi; Yamashita, Hideo and Nishita, Tomoyuki
Photorealistic animated images are extremely effective for pre-evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered.This paper proposes a method of high-fidelity image generation for photorealistic outdoor scenes based on the following ideas: * 1The intensity distribution of skylight taking account of scattering and absorption due to particles in the atmosphere which coincides with CIE standard skylight luminance functions is sought, and realistic images considering about spectrum distribution of skylight for any altitude of the sun can be easily and accurately displayed. * 2A rectangular parallelepiped with a specialized distribution of intensity simulating the skylight is introduced for efficient calculation of illumination due to skylight, and by employing a graphics hardware calculation of the skylight illuminance taking into account shadow effects is obtained with high efficiency- these techniques can be used to generate sequences of images, making animations possible at far lower calculation cost than previous methods.

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