EG1992

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Accurate Image Generation and Interactive Image Editing with the A-buffer
(Blackwell Science Ltd and the Eurographics Association, 1992) Lau, Wing Hung; Wiseman, Neil
The A-buffer suggested by Carpenter [2] is a hidden surface removal method which deals with arbitrary overlapping edges in a pixel. In this paper, we suggest a way of increasing the subpixel resolution by storing the bitmask index rather than the bitmask. This allows much more accurate images to be generated while at the same time, minimising memory usage. It also allows zooming to reveal more information. We also suggest an enhancement to the A-buffer by allowing the creation of dynamic objects. These dynamic objects can then be edited (deleted, moved, etc.) interactively as image modification and assembly is going on. This new buffer forms part of the image composition system we have been working on.
An adaptive Discretization Method For Radiosity
(Blackwell Science Ltd and the Eurographics Association, 1992) Languenou, Eric; Bouatouch, Kadi; Tellier, Pierre
When using radiosiiy, the visual quality of the rendered images strongly depends on the method employed for discretizing the scene into patches. A too fine discretization may give rise to artifacts, while with a coarse discretization areas with high radiosity gradient may appear. To overcome these problems, the discretization must adapt to the scene. That is, the interaction between two patches must account for the distance between them as well as their surface area. In other words, surfaces far away are discretized less finely than nearby surfaces. These aspects are considered by the new adaptive discretiration method described in this paper. It performs both discretization and system resolution at each iteration of the shooting process, allowing then interactivity.
Adaptive Sampling of Area Light Sources in Ray Tracing Including Diffuse Interreflection
(Blackwell Science Ltd and the Eurographics Association, 1992) Kok, Arjan J. F.; Jansen, Frederik W.
Ray tracing algorithms that sample both the light received directly from light sources and the light received indirectly by diffuse reflection from other patches, can accurately render the global illumination in a scene and can display complex scenes with accurate shadowing. A drawback of these algorithms, however, is the high cost for sampling the direct light which is done by shadow ray testing. Although several strategies are available to reduce the number of shadow rays, still a large number of rays will be needed, in particular to sample large area light sources. An adaptive sampling strategy is proposed that reduces the number of shadow rays by using statistical information from the sampling process and by applying information from a radiosity preprocessing. A further reduction in shadow rays is obtained by applying shadow pattern coherence, i.e. reusing the adaptive sampling pattern for neighboring sampling points.
Affine Texture Mapping and Antialiasing Using Integer Arithmetic
(Blackwell Science Ltd and the Eurographics Association, 1992) Nehlig, P.; Ghazanfarpour, D.
Texture mapping techniques are very useful for generating more realistic images. However, texture compression, generally induced by geometric transformations, is at the origin of aliasing artifacts especially the well-known"moire" patterns. Two discrete affine texture mapping methods based exclusively on integer arithmetic are presented here. This original approach of discrete affine mapping is adequate for antialiasing in the case of compressed textures.
Area Sampling Buffer: Tracing Rays with Z-Buffer Hardware
(Blackwell Science Ltd and the Eurographics Association, 1992) Sung, Kelvin
An algorithm that allows the use of z-buffer hardware in assisting area sampling for a ray tracing style renderer is described. The implementation issues involved in discretizing the sampling area and light source area are discussed and solutions are proposed. The effects of the hardware-assisted ray tracing approach on frame-buffer systems and image synthesis processes are considered.
A CAD System for Color Design of a Car
(Blackwell Science Ltd and the Eurographics Association, 1992) Oshima, Tetsuya; Yuasa, Shinji; Sakanoshita, Ken-ichi; Ogata, Yoshinori
We have developed a color CAD system which enables a color designer to evaluate and create body colors of a car on a graphic display and put this system into practical use. The system has three features- generating realistic images comparable to photography to satisfy the car designer s needs, through close analysis of the physical phenomena taking place in the real environment, reproducing the desired colors very accurately on a CRT monitor, through analysis of the CRT colorimetric characteristics of reproducing the specified colors in response to the input signals, and utilizing a parallel computer to generate realistic images at a high speed and to control colors through interactive operation. Application of the CAD system reported here to the field of color design made it possible to fully evaluate and create body colors by means of computer graphics, replacing the conventional method which requires the painting of clay models or prototype cars.
Composing Hierarchically Structured Images
(Blackwell Science Ltd and the Eurographics Association, 1992) Patterson, John W.; Cockton, Gilbert
This paper begins by examining the classical raster-based composition model, establishing its weakness, and developing a new composition algebra based on line drawing. It then examines the role of composition in the Hierarchical Display Model, demonstrates that the forms of composition assumed in this model are inadequate to deal correctly with the interactions of two-dimensional representations of three-dimensional objects, and shows that our composition algebra resolves this difficulty. The composition steps required can be packaged with the use of a single attribute which constrains the apparent order of composition. This attribute is associated with the object which is to be taken out of order , obviating any needsfor layers.
Computing Dynamic Changes to BSP Trees
(Blackwell Science Ltd and the Eurographics Association, 1992) Chrysanthou, Y.; Slater, M.
This paper investigates a new method for dynamically changing Binary Space Partition (BSP) trees. A BSP tree representation of a 3D polygonal scene provides an ideal data structure for rapidly performing the hidden surface computations involved in changing the viewpoint. However, BSP trees have generally been thought to be unsuitable for applications where the geometry of objects in the scene changes dynamically. The purpose of this paper is to introduce a dynamic BSP tree algorithm which does allow for such changes, and which maintains the simplicity and integrity of the BSP tree representation. The algorithm is extended to include dynamic changes to shadows. We calibrate the algorithms by transforming a range of objects in a scene, and reporting on the observed timing results.
A Development Environment for Constructing Graph-Based Editing Tools
(Blackwell Science Ltd and the Eurographics Association, 1992) Chen, M.; Townsend, P.; Wang, C.Y.
Scientists and engineers use numerous kinds of graph notations to model various objects in the real world and their relationships in an abstract pictorial form. However, developing a specific graph editing tool for each of these notations is often very costly in terms of time and resources. This paper outlines a design of a suitable development environment for constructing graph-based editing tools, based on the requirements analysis of such an environment derived from a survey of more than 60 different graph notations.
Equidistant Smoothing of Polyhedra with Arbitrary Topologies
(Blackwell Science Ltd and the Eurographics Association, 1992) Ma, Lizhuang; Liang, Youdong; Peng, Qunsheng
Smoothing of polyhedron with arbitrary topology is an important issue in CAGD and CAD/CAM, but so far it is deemed to be difficult to smooth the complex corners of a polyhedron. In this paper, the concept of distance surfaces of a surface and a solid is introduced, and the incisive properties of such surfaces are addressed which provide a theoretical foundation for modifying a general corner. The method is based on making constricted volume and the maximum distance the volume can be constricted is given too. It is shown that by the proposed method in this paper any polyhedron can be G1 smoothed with quadraic and, sometimes toroidal surfaces. The new approach is suitable for engineering design and NC machining. The associated algorithm based on the classification theorem of corners is simple, fast and robust.
Fast Generation and Surface Structuring Methods for Terrain and Other Natural Phenomena
(Blackwell Science Ltd and the Eurographics Association, 1992) Koh, Eng-Kiat; Hearn, D. D.
Fractal geometry has proven to be a powerful tool for modeling natural phenomena. Using discrete approximations to fractional Brownian motion over a finite grid plane, computer graphics terrain-rendering algorithms are able to generate highly realistic topographical displays. Similar procedures can be applied to model other natural phenomena, such as clouds and water. Two important considerations in these algorithms are computational efficiency and the ability to control macroscopic surface features. Here we introduce a technique for structuring surface features so as to conform to a specified"elevation" envelope. We also present methods for implementing this technique using a recursive random midpoint-displacement procedure.
Fractals and Solid Modeling
(Blackwell Science Ltd and the Eurographics Association, 1992) Groller, Eduard
Trying to combine fractal geometry and solid modeling seems to be a contradiction in itself, In this paper a new type of 3D objects is presented that accomplishes this combination in a specific way. Objects with a fractal macro structure and a 3D solid micro structure can be specified and rendered efficiently by using context free, attribute, geometric grammars. This new object type can be incorporated into the CSG-modeling technique (Constructive Solid Geometry) in two ways: a) using CSG for the specification of the micro structure of the new object type, b) using these fractal like objects as a new type of primitive in the CSG model. Ray tracing is used for generating high quality images of these geometrically complex objects.
A Functional Approach to the Visual Simulation of Gaseous Turbulence
(Blackwell Science Ltd and the Eurographics Association, 1992) Sakas, Georgios; Westermann, Rudiger
This paper presents a functional method for the visual simulation of 2-D or 3-D turbulent gaseous motion by using time-varying fractals. The used function incorporates results from the"spectral theory of turbulence", thereby providing a physics-based approach adapted to the needs of computer graphics. The involved turbulence function is band-limited, continuous, differentiable, anisotrop, and smooth, provides different fractal dimensions along each axis, may be evaluated locally with different parameters, and requires only minimal storage space, thus supporting an implementation on large parallel processing networks with small nodes. Inhomogeneity in the form of local disturbances of the turbulence field may also be easily considered. The parameters used to describe turbulent motion are rather intuitive, so that they may be utilized easily by users. Examples for modeling different types of clouds and fire are given.
The Graphical Translation of English Text into Signed English in the Hand Sign Translator System
(Blackwell Science Ltd and the Eurographics Association, 1992) Holden, E.J.; Roy, G.G.
Signed English is a manual interpretation of English using fingerspelling and signs. A prototype of the Hand Sign Translator (HST) system was developed to graphically translate English into Signed English, using two-handed animation. The HST consists of a practical interface that aims to help users learn Signed English, and the translation process where English text is transformed into a series of images that represent corresponding signs. This paper describes the translation process which involves two stages- the input environment and the animation process. The input environment consists of text analysis in order to extract corresponding kinematic data from the database, named English-Sign Dictionary (ESD). The data is then used as an input to the animation process, Firstly, the skeleton models of keyframe images and their in-between poses are calculated. Secondly, appropriate volume models are applied in order to surround the surface of skin. Then the shapes that are suitable for painting are generated, and finally images are drawn and rendered using a smooth animation technique.
HAGI, a High-level Application/Graphics Interface
(Blackwell Science Ltd and the Eurographics Association, 1992) Hsu, Y. H.; Kuo, Y. S.
HAGI is an object-oriented graphics system developed on top of the X window system. In addition to providing facilities that structured graphics systems such as GKS usually have, HAGI supports a high- level graphics paradigm with the following features: * + In addition to graphical objects, the system provides a class of application objects with a higher level of abstraction than graphical objects. * + Graphics manipulation operations can be issued simplyfrom application objects without explicitly referring to specific graphical objects. Thus graphics manipulation appears to be transparent to application programmers. * + Graphical objects are designed to encompass more semantics, thus are at a level close to the application. For example, they useflexible visual objects to determine their visual appearance.HAGI provides such a high-level application/graphics interface by maintaining a dependency relationship between graphical objects and application objects.
The Input Model of Standard Graphics Systems Revisited by Formal Specification
(Blackwell Science Ltd and the Eurographics Association, 1992) Faconti, Giorgio P.; Zani, Nicola; Paterno , Fabio
This paper describes the specification of an input model for graphics systems. The initial aim of the work reported in this paper was to revise the input model adopted by graphics standards by means of formal specification techniques in order to acquire a deep knowledge of its capabilities, to eventually discover errors and to develop improvements. Taking into account similar works done in this area by others and considering a number of major issues related to input recently discussed within the graphics community, a new model is being proposed that addresses the very key concepts of parallelism, extensibility and reconfigurability. The model is based upon composition operations defined over basic components specified as a set of concurrent processes. Composition operations and process definitions have been formally specified by using the LOTOS notation and investigated by means of the LOTOS Interactive Tools Environment. In the first part of the paper, the input model of graphics standards is shortly examined in the light of the results so far achieved by related works on formal specification of computer graphics systems. Subsequently, an improved model is presented. Finally, its capability of simulating the traditional operating modes of logical input devices and a methodology for defining new operating modes is demonstrated.
Interactive Shape Control of Interpolating B-splines
(Blackwell Science Ltd and the Eurographics Association, 1992) Krokos, M. A.; Slater, M.
This paper presents a new methodfor providing interactive shape control of interpolating B-splines. The CAD designer can directly interact with geometric entities defined on the B-spline at any interpolated data point- shape adjustments can be performed either globally or locally. Our approach is based on B?-splines of order k (?,k ?1), i.e. ?-reparametrized, classical B-splines. The method presented can be easily generalised to surfaces defined either as tensor products or by using the skinning technique- interactive shape control can be provided in both surface parametric directions.
A line clipping algorithm and its analysis
(Blackwell Science Ltd and the Eurographics Association, 1992) Krammer, Gergely
One of the classical problems of Computer Graphics: line clipping against a rectangle is revisited. Coordinate raster refinement and some unusual forms of the parametric equation of the line are used to develop formulae for a line clipping algorithm. The algorithm is first presented in a form, where clarity of presentation is the prime concern. It is then transformed into one big nested branch, which after optimisation is assumed to be the most efficient form with a heavy cost on size. It is assumed that any mathematical consideration of the clipping problem would after a similar optimisation lead to a branching structure of equal complexity and speed. Line clipping thus belongs to the class of problems for which after a proper mathematical and logical analysis automatic program transformations may do the rest.This work has been supported by a grant from the Hungarian Academy of Sciences, Project No. OTKA 2572/1991
Modeling with Time and Events in Computer Animation
(Blackwell Science Ltd and the Eurographics Association, 1992) Kalra, Devendra; Barr, Alan H.
In this paper, we present a general, systematic and consistent treatment of time and events for computer animation. We first formalize the concepts of events and create a time primitive called an event unit. We then present a succession of organization schemes to compose event units for generating complex motion sequences. We present a directed graph representation for the organization of time and events that suggests the form of an event-based time programming language. Details of implementation of a general event simulation system are given. Our approach provides a clean partitioning for the problem of motion design, a hierarchical scheme to compose motion behaviors from time primitives and a programming model for organizing animation. Traditional methods of kinematic controls and key frame interpolation are special cases of our general scheme. In addition, our treatment of events can be combined with kinematics, dynamics or constraint-based systems to generate powerful motion modeling systems.
Modelling the Texture of Paint
(Blackwell Science Ltd and the Eurographics Association, 1992) Cockshott, Tunde; Patterson, John; England, David

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