Volume 11 (1992)

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Simulation of Facial Muscle Actions Based on Rational Free Form Deformations
(Blackwell Science Ltd and the Eurographics Association, 1992) Kalra, Prem; Mangili, Angelo; Thalmann, Nadia Magnenat; Thalmann, Daniel
This paper describes interactive facilities for simulating abstract muscle actions using Rational Free Form Deformations (RFFD). The particular muscle action is simulated as the displacement of the control points of the control-unit for an RFFD defined on a region of interest. One or several simulated muscle actions constitute a Minimum Perceptible Action (MPA), which is defined as the atomic action unit, similar to Action Unit (AU) of the Facial Action Coding System (FACS), to build an expression.
Template-Based Volume Viewing
(Blackwell Science Ltd and the Eurographics Association, 1992) Yagel, Roni; Kaufman, Arie
We present an efficient three-phase algorithm for volume viewing that is based on exploiting coherency between rays in parallel projection. The algorithm starts by building a ray-template and determining a special plane for projection - the base-plane. Parallel rays are cast into the volume from within the projected region of the volume on the base-plane, by repeating the sequence of steps specified in the ray-template. We carefully choose the type of line to be employed and the way the template is being placed on the base-plane in order to assure uniform sampling of the volume by the discrete rays. We conclude by describing an optimized software implementation of our algorithm and reporting its performance.
Modelling and Programming Evolutions of Surfaces
(Blackwell Science Ltd and the Eurographics Association, 1992) Chen, X.; Lienhardt, P.
In recent years, a lot of work has been done on modelling natural phenomena and simulating the evolution of natural objects. For instance, procedural methods have been developed for simulating corpuscular phenomena and tree growth. In this paper we present a new procedural method for simulating evolutions of subdivisions of surfaces (i.e. partitions of surfaces into vertices, edges and faces). The representations of topology, embedding and photometry are clearly distinguished in the geometric model used for the representation of such subdivisions and thus, each of these features may be evolved independently (as in natural metamorphoses). Evolutions are achieved by applying topological and embedding operations on the geometric model. Control of these evolutions is based upon the behaviour concept. Behaviours (i.e. sets of operations) are associated with cells of the modelled subdivision. At each step, and for each cell, the corresponding behaviour is applied to the cell. The definition and computation of parameters have been studied, in order to control such evolutions. The method has been implemented and tested with many examples of surface evolutions (mainly evolutions of vegetal surfaces: leaves, flowers). Based on the method, a language has been defined for programming surface evolutions.
Stochastic Motion-Motion Under the Influence of Wind
(Blackwell Science Ltd and the Eurographics Association, 1992) Shinya, Mikio; Fournier, Alain
Stochastic approaches are very effective for modelling natural phenomena. This paper presents a motion model based on a stochastic process as well as physics, and proposes motion synthesis techniques for stochastic motion-motion under the influence of wind.The motion synthesis process is modelled by a cascade system of three components: wind model, dynamic model, and deformation model. Wind models produce spatio-temporal wind velocity fields using the power spectrum and auto-correlation of wind, just like fractal geometry. Dynamic models describe the dynamic response of the systems, using equation systems or response functions. Deformation models produce deformed shapes of objects according to the geometric models of the objects and the results of the dynamic systems.The biggest advantage of the model is its generality and consistency. The model is applicable to most of the existing trees and grass models, including structural models, particle systems, impressionist models, and 3D texture. It is demonstrated that the coupling of stochastic approaches and physically-based approaches can synthesize realistic motion of trees, grass and snow with modest computational cost.
Two-manifold cell-decomposition of r-sets.
(Blackwell Science Ltd and the Eurographics Association, 1992) Falcidieno, Bianca; Ratto, Ornella
This paper discusses the relationships studied between manifold solids and r-sets by defining an r-set as a decomposition in two-manifold cells. This decomposition is represented as a graph (Two-manifold Cell Decomposition graph TCD) in which each node corresponds to a 2 manifold component of the regular set, while each arc or hyperarc defines a non-manifold adjacency between components. The TCD model and data structure encoding it were designed in order to be compatible with a traditional boundary architecture.
The Fractal Nature of an Ecological Model
(Blackwell Science Ltd and the Eurographics Association, 1992) Bennan, Wang; Yin, Shi
With the help of computer graphics, the chaotic behaviour of an ecological model in the complex plane has been investigated. Convergence maps that show multi-fractal characteristics (science) and beautiful patterns (art) are presented.
An Object-Oriented View of the User Interface
(Blackwell Science Ltd and the Eurographics Association, 1992) Zhou, Tom Z.-Y.; Kubitz, William J.
The object-oriented view of the user interface presented here is a model of object responsibilities-sharing and cooperation for a typical user interface. The model regards the user interface as a three-layer architecture, with the application contributing to one of the layers called the application exposure, The model seeks to promote user interface software reuse by coupling the user interface and the application with well-defined message protocols, by properly allocating user interfacefunctions to the layers so as to reduce and discipline their dependencies, and byfactoring complex abstractions into reusable secondary components.
An Open Model for Hypermedia and Its Application to Geographical Information Systems
(Blackwell Science Ltd and the Eurographics Association, 1992) Hall, W.; Simmons, D.
This paper describes the design and implementation of a multimedia information management environment that is based on an open model for hypermedia. The model, known as Microcosm, is currently implemented in Microsoft Windows and supports many different media types. The open nature of the model and the separation of the links from the data, allows links to be applied across any application running under Windows or the OS/2 version 2 desktop, thus creating a truly integrated environment. One example, which is, discussed in the paper, is the integration of a hypermedia database with a geographical information system. The paper also discusses the application of novel interfaces to dynamic media within a hypermedia system, including the use of moving icons (micons).
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.
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.
PHIFI: A PHIGS Interactive System for the Visualization of Scalar and Vector Fields
(Blackwell Science Ltd and the Eurographics Association, 1992) Ascani, Fabrizio; Moltedo, Laura
This paper describes the characteristics of PHIFI, an interactive system for the visualization of scalar and vector fields. PHIFI has been developed at the IAC where applications of the system have also been investigated.
A Statistical Comparison of Two Hidden Surface Techniques: the Scan-line and Z-buffer Algorithms
(Blackwell Science Ltd and the Eurographics Association, 1992) Slater, Mel; Drake, Kieron; Davison, Allan; Kordakis, Emmanouell and Billyard, Adam and Miranda, Eliot
This paper compares two image space hidden surface removal algorithms for polygonal scenes. These are the z-buffer and scan-line algorithms. There is first an overview of each algorithm, followed by a simulation experiment, designed to compare the number of polygons per second which can be rendered by each algorithm. The simulation varies the number of polygons in the scene, and the size and distribution of polygons over the display. The results suggest that the z-buffer is preferred for a large enough number of polygons, however, smaller polygons and uniform distribution of polygons favour the scan-line approach. The analysis does not take into account the complexity of the shading rule, which is likely also to favour the scan-line method.
A Computer Model For Pinscreen Simulation: A New Animation Paradigm
(Blackwell Science Ltd and the Eurographics Association, 1992) Lopes, Pedro Faria; Gomes, Mario Rui
Actual computer image and motion synthesis paradigms are presented in order to introduce a new computer animation paradigm that simulates the traditional pinscreen animation technique. Pinscreen is a very particular and difficult device that enables a"chiaroscuro" approach to image synthesis. The paper describes the traditional pinscreen technique, the way it is operated, results and related difficulties. An extended computer model, including colour and time extensions, to simulate the pinscreen is presented. Results achieved with vector and raster approaches are discussed. Advantages and possibilities of the method when compared with the traditional method and the problems that arise from this technique will also be explained. Finally current and future work is referenced.
Ray Coherence Between a Sphere and a Convex Polyhedron
(Blackwell Science Ltd and the Eurographics Association, 1992) Horvath, Tamas; Marton, Gabor; Risztics, Peter; Szirmay-Kalos, Laszlo
Using the two ray coherence theorems of Ohta and Maekawa the computation time of ray tracing algorithms for scenes of spheres and convex polyhedra can be reduced considerably. This paper presents further theorems which, together with the first two, may enable further reduction in computation time.
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.
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.
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.
Combined Direct and Inverse Kinematic Control for Articulated Figure Motion Editing
(Blackwell Science Ltd and the Eurographics Association, 1992) Boulic, Ronan; Thalmann, Daniel
A new approach for the animation of articulated figures is presented. We propose a system of articulated motion design which offers a full combination of both direct and inverse kinematic control of the joint parameters. Such an approach allows an animator to specify interactively goal-directed changes to existing sampled joint motions, resulting in a more general and expressive class of possible joint motions. The fundamental idea is to consider any desired-joint space motion as a reference model inserted into the secondary task of an inverse kinematic control scheme. This approach profits from the use of half-space Cartesian main tasks in conjunction with a parallel control of the articulated figure called the coach-trainee metaphor. In addition, a transition function is introduced so as to guarantee the continuity of the control. The resulting combined kinematic control scheme leads to a new methodology of joint-motion editing which is demonstrated through the improvement of a functional model of human walking.
Rendering NURB Regions For 2D Animation
(Blackwell Science Ltd and the Eurographics Association, 1992) Willis, Philip; Oddy, Robert
We describe an accurate method of rendering by scan-conversion of closed regions bounded by NURBs, with particular comments on its application to computer-based 2D animation. It is shown that the method is fast, analytically accurate, and can be readily extended to include anti-aliasing and clipping.
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.

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