EG1990 Proceedings (Technical Papers)

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Some Possible Applications of CORDIC Processors in Computer Graphics
(Eurographics Association, 1990) Kocsis, F.; Böhme, J.F.
Some application possibilities of an ASIC-type processing element, the CORDIC processor, in computer graphics are discussed. CORDIC-based solutions are derived for some basic computer geometry computations: conversion between coordinate systems, rotations, point-line and pointplane distance calculations, ray-patch intersection computations, intensity and scalar product calculations. The main results are the following. Some basic computational tasks of computer graphics can be advantageously implemented using CORDIC arithmetic. The CORDIC processing element can serve as a building block even in high performance parallel graphics systems. A short example compares the possibilities of the CORDIC-based solution to the performance of the well-known polygon rendering with Pixel-planes.
DaScript Plus A PostScript Extension supporting 3D Graphics with 2D Functionality
(Eurographics Association, 1990) Samara, Veronika; Schaub, Jutta; Noll, Stefan
In the world of electronic publishing page description languages describe a very powerful interface between document creation software and raster output devices. 3D graphics systems offer the possibility to give a more or less realistic description of the 3D world. The current page description languages support 2D graphics only. However, documents also need graphics descriptions that contain 3D information. DaScript Plus provides a sufficient mapping of the PHIGS PLUS functionality. It allows the device independent incorporation of realistic 3D pictures within documents, and their high quality output on laser printers and type setters.
Joint Editing with DAPHNE A System integrating CGMs into SGML Documents
(Eurographics Association, 1990) Scheller, Angela; Fuhrhop, Christian
This paper presents DAPHNE, a document processing system for joint editing within the German Research Network DFN. DAPHNE is based on two international standards in the area of document and graphics processing, the Standard Generalized Markup Language SGML and the Computer Graphics Metafile CGM. The functionality of DAPHNE is described with special emphasis on integrating graphics in documents, as well as the experience with the system in a pilot phase and future plans for extensions.
RECONSTRUCTION OF A BOUNDARY REPRESENTATION MODEL FROM THREE ORTHOGRAPHIC PROJECTIONS: A GEOMETRICAL APPROACH
(Eurographics Association, 1990) Müller, A.; Richter, D.
A method is presented for creating a boundary representation model from engineering projections. Although the topic of this reconstruction method has been studied for a few years the fundamentals of reconstruction are rather scanty. In this paper we provide a combined geometrical and topological approach to reconstruction. All considerations are restricted to polyhedral objects that consist of only one shell and edges belonging to exactly two faces. The reconstruction problem is mathematically described by introducing dome definitions, and criteria are derived that allow to solve the reconstruction problem for the restricted class of objects provided that the three given projections define a three-dimensional object unambiguously.
HYPERIMAGES - AN ALTERNATIVE TO THE CONVENTIONAL DIGITAL IMAGES
(Eurographics Association, 1990) Bieri, Hanspeter
Hyperimages represent a variation of the conventional digital images which implies pixels of different dimensions within the same image. The extent of a hyperimage is the disjoint union of all pixel extents it contains, which are relatively open unit cubes with respect to the euclidean topology of the underlying space. This approach is independent of any specific dimension of image and space, respectively, and allows strict partitioning of images into subimages, not just subdividing. The applicability of hyperimages is illustrated by a number of algorithms useful in image analysis.
A RASTER GRAPHICS APPROACH TO FLOW VISUALIZATION
(Eurographics Association, 1990) van Wijk, Jarke J.
Most techniques for the visualization of fluid dynamics are based on vector graphics. Streamlines or arrows are calculated as vectors, which are converted to pixels for display on raster devices. The techniques described here show that it can be advantageous to use a raster graphics approach to the visualization of fluid dynamics. The properties of raster devices can be exploited better, while also anti-aliasing can be realized in a simple way. Three techniques for visualization of two-dimensional flow are described: for the calculation and display of streamlines; an alternative technique based on particle systems for capturing flow in a still image; and for the creation of animations using particles.
Shading and Shadowing with Linear Light Sources
(Eurographics Association, 1990) Poulin, Pierre; Amanatides, John
In virtually all rendering systems, linear light sources are modeled with a series of point light sources that require considerable computing resources to produce realistic looking results. A general solution for shading surfaces illuminated by a linear light source is proposed. A formulation allowing for faster computation of the diffuse component of light reflection is derived. By assuming Phong's specular component, simple, inexpensive and convincing results are produced with the use of a Chebyshev approximation. A shadowing algorithm is also presented. As shadowing from linear light sources is expensive, two acceleration schemes, extended from ray tracing, are evaluated.
Tightly-Coupled Multiprocessing for a Global Illumination Algorithm
(Eurographics Association, 1990) Drettakis, George; Fiume, Eugene; Fournier, Alain
A prevailing trend in computer graphics is the demand for increasingly realistic global illumination models and algorithms. Despite the fact that the computational power of uniprocessors is increasing, it is clear that much greater computational power is required to achieve satisfactory throughput. The obvious next step is to employ parallel processing. The advent of affordable, tightly-coupled multiprocessors makes such an approach widely available for the first time. We propose a tightly-coupled parallel decomposition of FIAT, a global illumination algorithm, based on space subdivision and power balancing, that we have recently developed. This algorithm is somewhat ambitious, and severely strains existing uniprocessor environments. We discuss techniques for reducing memory contention and maximising parallelism. We also present empirical data on the actual performance of our parallel solution. Since the model of parallel computation that we have employed is likely to persist for quite some time, our techniques are applicable to other algorithms based on space subdivision.
COLOR SHADING IN 2D SYNTHESIS
(Eurographics Association, 1990) Bourdin, J.J.; Braquelaire, J.P.
In interactive 2D synthesis applications, features for filling regions are generally elementary (uniform colouring, filling with a regular pattern.. .). Interactive design of 2D colour shadings raises two major problems: the difficulty of specifying a shading precisely, and the rapidity of related filling algorithms. In this paper, we propose a model to specify 2D colour shading of a region by decomposing it into two components: a support describing the “shape” of the shading, and a colouring function defined on this shape. We then present an incremental algorithm for support generation.
AUTOMATIC MODELLING OF NATURAL SCENES FOR GENERATING SYNTHETIC MOVIES
(Eurographics Association, 1990) Koch, Reinhard
A model based analysis by synthesis algorithm is presented. It combines image analysis and synthesis techniques to obtain a three dimensional scene description and to generate synthetic movies out of that scene description. A 3D model world is generated automatically out of TV image sequences containing 3D objects with naturally textured surfaces. The objects are projected into the 2D image domain and compared with subsequent images of the sequence to be analyzed. Differences between input and synthesized images serve to extract shape, motion and surface texture parameters and to adapt the 3D model scene. The model data base can be manipulated to generate synthetic movies with highly realistic, natural looking images.
AN INTERPOLATION METHOD FOR STOCHASTIC MODELS
(Eurographics Association, 1990) Ramstein, G.
This paper presents a method using stochastic models for the simulation and interpolation of natural phenomena. These models are based on the general concept of random functions with stationary increments, to which the fbm belongs. The consideration of this family of stochastic processes, instead of just considering the fractal one, leads to greater diversity and realism. Another way to enhance realism is to combine analysis and interpolation. We suggest calculating the stochastic parameters from the analysis of existing natural surfaces and to use them as input data for the interpolation algorithm. We propose an interpolation algorithm which respects the stochastic behavior of this class of processes. This method provides a better understanding of the interpolation mechanisms. One can thus study the influence of the stochastic parameters and the data points localization on the interpolated valued. A final advantage of this algorithm is to interpolate surfaces defined by irregular data points. This type of representation is actually often encountered in cartography (contour lines, spot elevations, ...). This possibility is also very interesting for image synthesis applications, since it allows specifying with ease the rough shape of a given image.
CHARACTERIZATION OF TOPOGRAPHIC SURFACES
(Eurographics Association, 1990) Falcidieno, Bianca; Spagnuolo, Michela
This paper presents a method for extracting and representang features of a topographic surface approximated by triangular tales An algorithm as given which computes characteristic regions (a. e. regions having concave, convex or planar shape), characteristic lanes (ridges, ravines, generic creases) and characteristic points (maxima, minima, saddle points) The result as a new surface description an terms of an attributed hypergraph representation called Characteristic Region Configuration Graph, an which characteristic regions are considered the basic describers of the surface shape and correspond to the nodes of the graph, whale the arcs and hyperarcs represent the relationships between regions derived from characteristic lanes and points
COLOR IMAGE RECONSTRUCTION FROM NONUNIFORM SPARSE SAMPLES USING A THIN PLATE MODEL
(Eurographics Association, 1990) Metaxas, Dimitris; Milios, Evangelos
In this paper we solve the problem of reconstructing a color image from sparse, noisy, and nonuniformly distributed color measurements. We apply a method for reconstructing a surface from sparse depth measurements to each of the R, G and B components of the color data, by treating each as a surface, with depth measurements being the R, G and B values. We apply this method to the reconstruction of nonuniformly distributed sparse color data from even 12.5% of the pixels, if no discontinuities are given and from 6.25% of the pixels, if the discontinuities are given. Also we present results of reconstructing a corrupted version of the original image with Gaussian noise of zero-mean and standard deviation 30 from 25% of the data, for color levels between 0 and 255. The applicability of the method is independent of the choice of the color space used.
Relaxed Multi-rate Systolic Array Graphics Engine for High Resolution Real-time Computer Graphics
(Eurographics Association, 1990) Jayasinghe, J.A.K.S.; Herrmann, O.E.
Generation of realistic images while supporting faster interaction is a topic in computer graphics research which has drawn considerable attention. Conventional frame buffer has been identified as a major bottle-neck for faster interaction [11]. Systolic Array Graphics (SAG) engines have been proposed to meet the above requirements by replacing the conventional frame buffer by a processor array. The speed limitations of the hardware restrict the use of SAG engines to displays resolutions of order 512x512 pixels when they are refreshed at 50Hz frame rate. In this paper we present an architectural solution to reduce the speed limitations of hardware. In the new architecture, a faster video stream is achieved by decoupling the speeds of the video and instruction streams by a multi-rate clocking scheme. We relax some timing constrains of the faster video stream by space domain multiplexing, i.e. using more wires.
A PROPOSAL FOR A POSTSCRIPT 3D EXTENSION
(Eurographics Association, 1990) Cesar, Christian L.
A 3D graphics extension to the PostScript language is proposed. The extension maintains the same graphic programming style that characterizes the language's 2D environment. The extensions proposed cover 3D graphics state, 3D coordinate system and transformations, and 3D path, surface and solid volume construction operators. The proposed extensions cover mostly 3D object modelling issues. Rendering extensions are not covered. Consideration is given to how the semantics of 2D graphic operators may be extended into 3D.
AN OBJECT ORIENTED APPROACH TO ENSURE PORTABILITY OF CAD STANDARD PARTS LIBRARIES
(Eurographics Association, 1990) Pierra, Guy
The integration, in CAD systems, of libraries of standard parts is often considered to be one of the key factors for increasing productivity of Computer Aided Design [1] [2] [3]. These libraries must be able to integrate homogeneously both the standard components external to the firm (standardized items and suppliers' standards) and internal firm-specific standards.
Mathematical Models for Semi-globalized Spectral Synthesis
(Eurographics Association, 1990) Anjyo, Ken-ichi
Semi-globalized spectral synthesis is proposed as a new tool for three-dimensional scene description consisting of many natural objects, such as terrain, sea waves, and clouds. The method is based on the mathematical theory of spectral representation of stochastic processes. In this paper, mathematical models in the method are presented under rigorous formulation and then their stochastic properties are shown. Some simple techniques for practical improvements of the original models in depicting scenes are also explained along with the examples obtained.
AN APPROACH TO IMPROVE THE RELIABILITY OF BOOLEAN OPERATION ON A PAIR OF POLYHEDRA
(Eurographics Association, 1990) Li, Xinyou; Sun, Jiaguang; Tang, Zesheng
It is essential and pressing to improve reliability of Boolean operations in geometric modelling systems. The Boolean operations in commercial systems now available are not reliable enough because of numerical calculation errors. Numerical calculation errors hinder us from determining set membership classifications exactly. Some classifications are ambiguous because they are dependent on adopted computing tolerance. Thereby interrelated classifications may conflict with each other and it is very difficult to get correct results of Boolean operations In many cases. We introduce a reliable Boolean operation algorithm which solves the conflicts among interrelated classifications before implementation of Boolean operation by use of reasoning technique. The algorithm has replaced the modelling module of the geometric modelling system GENS 2.0 to form a new system GENS 2.1 on Apollo and Sun workstations. According to tests and compared with Geomod 3.9 and I/ENS, GENS 2.1 is much more reliable.
Fast Rendering of Arbitrary Distributed Volume Densities
(Eurographics Association, 1990) Sakas, Georgios
In recent years a number of techniques have been developed for rendering volume effects (haze, fog, smoke, clouds, etc.). These techniques are either time consuming (ray-tracing, radiosity) or do not account for arbitrary density distributions. In this paper we briefly analyze the physics of illuminations of volumes and we propose several simplifications suitable. for computer graphics practice. In particular, we present a method for rendering arbitrary distributions by means of projective polygonal rendering and solid texturing techniques in approximately the time needed for a usual polygonal object. The proposed method provides good results in a fraction of the computing time required for approaches like ray-tracing or radiosity. Solid texturing is used to define the density distribution and a point-sampling Monte-Carlo method with user-adjustable accuracy to evaluate the illumination model along the path through the volume. Thus, a trade-off between computing time and picture quality exists. With this technique one can move through or around the volume and to place objects and/or light sources in the volume. By means of rendering methods like shadowing polyhedra, objects can cast shadows on the volume and/or the volume can shadow the ground.
3D MODELLING AND MOTION OF DEFORMABLE SOLIDS FROM 2D IMAGES
(Eurographics Association, 1990) Neveu, Marc; Faudot, Dominique
Our work purpose is to elaborate a geometric and motional model for deformable solids, known only by a very small number of general crosssections images. We start from a generic 3D model of the studied solid we distort according to detected boundaries in the above mentioned images. To give the solid motion model, our work uses moving point constraints and inbetweening methods on an image sequence : we select keyframes on which we interpolate characteristic points. Then we use Coons patches to compute the inbetween frames and realize an animation? On an echocardiographic application, we obtained good results in the model precision and detected edges by image processing similar to cardiologists' hand drawn edges. Besides, the model distortion, characteristic points tracking and 2D motion simulation are encouraging, although improvements are necessary.

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