Volume 12 (1993)

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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.
Electronic Kaleidoscopes for the Mind
(Blackwell Science Ltd and the Eurographics Association, 1993) Pickover, Clifford A.; Rudolph, Larry
The goal ofthis article is to present an informal introduction and tutorial on aestheticallypleasing kaleidoscopic images. The article is intended for the non-mathematical reader interested in computer art. Simple generating formulas and recipes are included.
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.
A Note on 3D-Clip Optimisation
(Blackwell Science Ltd and the Eurographics Association, 1993) Hubl, Josef
In order to optimize the transformation-clipping-pipeline of PHIGS or GKS-3D it is sometimes necessary to determine whether a plane intersects a perpendicular volume or not. The solution to this problem is not very complicated. This paper offers a more effective procedure that handles this task.
The Method of Dynamic Palette Construction in Realistic Visualization Systems
(Blackwell Science Ltd and the Eurographics Association, 1993) Voloboj, Aleksej G.
The paper describes the colour approximation problem and the method of dynamic palette construction is suggested for its solution. The method uses the graphic display palette based on the computed true colour of the individual picture. Some aspects of human colour perception are considered. Two metrics in colour space are introduced to estimate closeness of the suggested colour approximation. The method was applied to visualize 3D scenes generated by ray tracing.
A Survey of 3D Solid Reconstruction from 2D Projection Line Drawings
(Blackwell Science Ltd and the Eurographics Association, 1993) Wang, Weidong; Grinstein, Georges G.
The reconstruction of a 3D object from its 2D projection(s) and its corresponding problem of 3D object recognition are two of the important research areas in the field of computer vision and artificial intelligence. Reconstruction involves determining the geometric and topological relationship of an object s atomic parts whereas recognition involves identifying an object by some form of template matching. Nagendra and Gujar1 gave a survey of several papers on reconstruction of 3D object from its 2D views. In this paper we present a taxonomy of 3D object reconstruction from 2D projection line drawings. We base the classification on the number of 2D views of the 3D solid object, the degree of user interaction necessary for correct reconstruction, and the internal representation used in the reconstruction process. We discuss the basic issues associated with this problem, review the relevant literature and present topics for future research.
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.
The Potential Equation and Importance in Illumination Computations
(Blackwell Science Ltd and the Eurographics Association, 1993) Pattanaik, S. N.; Mudur, S. P.
An equation adjoint to the luminance equation for describing the global illumination can be formulated using the notion of a surface potential to illuminate the region of interest. This adjoint equation which we shall call as the potential equation, is fundamental to the adjoint radiosity equation used to devise the importance driven radiosity algorithm. In this paper we first briefly derive the adjoint system of integral equations and then show that the adjoint linear equations used in the above algorithm are basically discrete formulations of the same. We also show that the importance entity of the linear equations is basically the potential function integrated over a patch. Further we prove that the linear operators in the two equations are indeed transposes of each other.
Spanning a C1-Surface over a Given Wireframe
(Blackwell Science Ltd and the Eurographics Association, 1993) Tokumasu, Shinji; Harashima, Ichirou; Nakajima, Norihiro
A problem of spanning a surface of C1 continuity (C1-surface) over a given wireframe is introduced. By exploiting the concept of a super surface patch introduced in an earlier paper, we proved the existence of an approximate, yet practical solution of the problem. That is, we presented a method or a procedure, by which to span a C1-surface over the wireframe. This technique is intended to be utilized as a flexible surface generation method for the 3D shape design in the industrial world.
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.
A Fractal Method for Digital Elevation Model Construction and its Application to a Mountain Region
(Blackwell Science Ltd and the Eurographics Association, 1993) Brivio, Pietro Alessandro; Marini, Daniele
This paper presents and discusses the results of a methodology for the construction of Digital Elevation Models (DEM), based on mathematical principles of fractal geometry. Classical approaches to DEM are founded on numerical methods of interpolation or approximation of data extracted from contour lines of standard topographic maps. Fractal geometry opens a new and innovative approach in which the irregularity, erraticity and self similarity of fractal structures mimics at best the typical behaviour of high mountain profiles. The adoption of fractal methods requires the identification of the fractal dimension D for a given data set. The determination of the fractal dimension D can be achieved applying some special mathematical method on finite set of samples. Different methods. for D estimation are presented. Once the fractal dimension is given, it is possible to reconstruct a surface relief using different fractal methods which interpolate the original set of elevation data. Our research has also investigated two different interpolation methods, fBm and IFS, both confirming that the fractal approach is very well suited for high relief terrain modeling. Photo realistic rendering of the computed DEM allows to appreciate the quality of the reconstruction through visual inspection.
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.
Symmetrical Patterns from Dynamics
(Blackwell Science Ltd and the Eurographics Association, 1993) Chung, K. W.; Chan, H. S. Y.
Automatic generation of symmetrical patterns belonging to all seventeen wallpaper groups is considered from a dynamical system s point of view. A pseudo-code of the algorithm is provided to generate the computer graphics. The method is shown to be able to create unlimited varieties of patterns and demonstrates the possibility of relaxing the crystallographic restriction to produce aperiodic patterns.
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.

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