Volume 12 (1993)

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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.
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.
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?.
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.
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 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.
Graphic Objects: A Mathematical Abstract Model for Computer Graphics
(Blackwell Science Ltd and the Eurographics Association, 1993) Torres, J.C.; Clares, B.
This paper defines an abstract mathematical model for graphic systems which incorporates modelling operations. The model is based on the"graphic object" concept. A graphic object is an abstraction of a graphic entity. Graphic objects are a generalization of the Fiume graphic object concept, supporting modelling operations, which give the set of graphic objects an algebraic structure of vector space and booelan algebra. Fiume visualization formalism can be applied to graphic objects. Further, product operations of graphic objects are defined, which are a generalization of solid sweep operations. Graphic object products may be used to build common 2D and 3D objects such as triangles, squares, cubes, circles and spheres from lines and arcs.
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.
The Determination of Form-Factors by Lookup Table
(Blackwell Science Ltd and the Eurographics Association, 1993) Sun, Jizhou; Zou, L.Q.; Grimsdale, R.L.
Current methods for computer image synthesis using the radiosity algorithm rely heavily on the calculation of geometrical properties, known as form-factors, which quantify the energy exchange between pairs of surfaces in the environment. In this paper, a new method for form-factor calculation is presented, in which form-factors from a differential area to a finite area with various geometric orientations and dimensions can be determined by the summation of three weighted directional form-factors. The three directional form-factors are mutually independent and can be pre-calculated and stored in a lookup table accessed by two indices. Thus, the determination of the generally used complex form-factor integral is greatly simplified and mainly replaced by accessing a pre-established lookup table. Quantitative comparisons of Wallace s ray casting method and the method presented indicate that the new method can provide more accurate form-factors, which implies that the number of sample points necessary on each source patch is comparatively reduced and the process of form-factor calculation can be accelerated.
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.
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.
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.
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.
A Multiprocessor Implementation of Radiosity
(Blackwell Science Ltd and the Eurographics Association, 1993) Ng, Adelene; Slater, Mel
This paper describes a multi-processor implementation of form factor computation in the radiosity method. Form factors are computed using the ray casting method and the algorithm is enhanced with Binary Space Partition (BSP) Trees and bounding boxes. Experimental results are presented together with a discussion of load balance efficiency.
The ARGOSI Classification Scheme for Graphics and Networking Applications
(Blackwell Science Ltd and the Eurographics Association, 1993) Sutcliffe, D.C.; Gallop, J.R.; Maybury, R.; Day, R.A.; Duce?, D.A.; Reynolds?, G.J.
ARGOSI is a project concerned with the relationship between standards for graphics and networking, as rejected in its full title: Applications Related Graphics and OSI Standards Integration. It is a collaborative project between eleven European organizations and is funded under the Esprit-Il programme of the Commission of the European Community.In order to achieve integration of graphics and OSI standards and to meet the requirements of applications, it is necessary to understand the needs of applications to transfer graphical information and the networking services required to support this. A major part of the ARGOSI project has been to derive a classification framework for applications based on a set of metrics describing their use of graphics and networking. Once classified, a study is to be made to determine the set of graphics and OSI standards that will satisfy the requirements of each group of applications or to identify deficiencies or omissions in the set of current standards that prevent the requirements being met. The classification scheme is believed to be a major stepforward in the field.
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.
ANIMA: An Interactive Tool for Scientific Data Animation
(Blackwell Science Ltd and the Eurographics Association, 1993) Moltedo, Laura; Morigi, Serena
This paper describes an animation interactive system that produces image sequences used to study the numerical results of scientific simulations. The fundamental goal of the system is to provide an easy method for observing and exploring scientific computation during its space-time evolution. To do that it is necessary to combine simulation processes, algorithmic and key frame animation with geometric transformations, light effects and camera movements. ANIMA allows the researcher to use animation without special programming, with the aid of a graphic user interface. Modelling, rendering, motion control and synchronization of graphic objects are interactively specified by the animator in order to define an animation script. The system development methodology follows an object-oriented technique using modular programming, abstract data type definition, and graphic metaphor with user interface menus.
Pictorial Editing by Shape Matching Techniques
(Blackwell Science Ltd and the Eurographics Association, 1993) Ventura, A. Della; Ongaro, P.; Schettini, R.
A number ofpainting and retouching packages operate much like the artist s traditional canvas andpalette, with electronic toolsfunctioning like their studio counterparts. These programs, while offering an ample set of tools for creating an image, suffer from an intrinsic limitation as regards its modification, which lies in the fact that changes to the shape of objects and those requiring some kind ofpattern recognition are generally difficult and cannot be accomplished automatically. This paper deals with an original methodfor providing a pictorial editor with the"search-and-replace" facility, that works rather like text substitution in a word processor. The user defines the search (model) and the replacement (target) patterns by example, i.e. by showing the system the patterns taken from the image or an existing catalogue. The editor then searchesfor objects that match the model s pattern and replaces them with the target one in an automatic or user-controlled mode. The method is based on a model-driven matching technique, capable of measuring the similarity of objects that are partially occluded or transformed by translation, rotation, or change of scale. Salient features of the method are its robustness and the limited number of parameters needed to adapt the search procedure to different application contexts. A search-and-replace function used for pattern-editing in the field of textile design, is presented as a working example.

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