Issue 3

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https://diglib.eg.org/handle/10.2312/74

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Special Effects with Half-Toning
(Blackwell Science Ltd and the Eurographics Association, 1996) Buchanan, John W.
Half-toning is the process by which gray-scale images are approximated with sets of black and white pixels. The process works because our eyes perceive a local average, thus half-toning seeks to approximate the local average. Ideally this approximation should be accomplished without introducing undesirable artifacts.In many situations the stylized display of images is desired. Often this stylized display is accomplished by the addition of semi-structured artifacts. In current applications the designer processes the image using tools provided by some image processing package. The resulting image is then half-toned and printed. Half-toning these processed images can reduce the visual impact of the special effects that have been introduced in the image.In this paper we show that the processes of controlled artifact introduction and half-toning can successfully be combined. By combining these two processes we ensure that the printed image is what the designer intended. We present a brief overview of the current error-diffusion half-toning techniques. We then propose several ways in which artifacts can be introduced to the image. This discussion is accompanied by a set of illustrative images.In particular, we discuss the introduction of false edges and the alteration of the scan pattern. We illustrate these techniques with a variety of images.We conclude the paper with a discussion on these new half-toning methods for the generation of binary gray-scale textures. In addition to showing how to generate these binary gray-scale textures we also show how these gray-scale textures can be used to half-tone images.
Extraction of Typographic Elements from Outline Representations of Fonts
(Blackwell Science Ltd and the Eurographics Association, 1996) Shainir, Ariel; Rappoport, Ari
Digital typefaces for computer graphics and multimedia applications should be capable of supporting operations such as font variations, transformations. deformations and blending. A powerful implementation of such operations must rely on the inherent typographic attributes of the typeface. However, even today s most advanced typeface representations support only geometric outline representations and basic font variations.In this paper we discuss high-level typeface representations which we term Parametric Typographic Representations (PTRs). We present an algorithm for automatically extracting typographic elements of typefaces from their outline representation, which, is an essential initial step in converting typefaces from outline representations to PTRs. The extracted typographic elements include serifs, bars. sterns, slants, bows, arcs, curve stems and curve bars. Most notable is the treatment of serifs, which are represented by finite-automata. The algorithm only needs to learn a serif type once, and is then capable of automatically recognizing it in different typefaces.We show an application of a PTR for automatic high-quality hinting of fonts, which is one of the most important stages in, digital font production. Our system was used to generate hints for dozens of thousands of Kanji, Roman and Hebrew characters.
A Platform for User-Tailored Interaction Development in 2D, 3D, and VR
(Blackwell Science Ltd and the Eurographics Association, 1996) Encarnacao, L. Miguel; Fechter, Jurgen; Grunert, Thomas; Strasser, Wolfgang
The discussion on the advantages and disadvantages of 2D, 3D, and VR interfaces and their applicability to different types of systems, users, and information led to a series of stand-alone implementations that lack the possibility of realizing an integrated approach. The acceptance of the different interaction techniques will depend on their success in practical applications, i.e. with systems that are used by different users for different purposes. Since this acceptance is especially hard to achieve in computer-critical environments, such as medicine, we developed a software environment that allows for the development, integration, and user-centered evaluation of existing and new interaction techniques for their use in medical applications. This environment is equipped with an innovative message-passing functionality that provides the communication to and among application objects in 2D, 3D, and VR. Furthermore, the environment contains a component for user-adapted interaction and system support at runtime.
A Three Dimensional Image Cache for Virtual Reality
(Blackwell Science Ltd and the Eurographics Association, 1996) Schaufler, Gernot; Sturzlinger, Wolfgang
Despite recent advances in rendering hardware, large and complex virtual environments cannot be displayed with a sufficiently highframe rate, because of limitations in the available rendering performance.This paper presents a new approach of software accelerated rendering which draws from the concepts of impostors, hierarchical scene subdivision and levels of detail. So far software optimization in real-time rendering has merely considered individual objects. This work is actually optimizing the rendering of the whole virtual environment by implementing a three dimensional image cache. It speeds up rendering for large portions of the scene by exploiting the coherence inherent in any smooth frame sequence.The implementation of the three dimensional image cache is discussed and the savings in rendering load achievable on a suitable hardware platform are presented.
Vector Field Based Texture Mapping of Animated Implicit Objects
(Blackwell Science Ltd and the Eurographics Association, 1996) Smets-Solanes, Jean-Paul
This paper shows that an adequate use of vectorfields can solve most inconsistencies related to texture mapping that appear in current animation and rendering systems based on implicit objects. The method used is based on the concept of a virtual skin. A skin with its own texture mapping is spread over an implicit object and is constrained to stick to the deformation of the implicit object. A vectorfield is used to compute the relationship between the motion of the skin and the deformation of the object. Visual and implementation issues are discussed with respect to typical applications of implicit objects in computer graphics.
Simplification of Global-Illumination Meshes
(Blackwell Science Ltd and the Eurographics Association, 1996) Hughes, Merlin; Lastra, Anselmo A.; Saxe, Edward
We present a methodfor simplifying the meshes produced as solutions to global illumination problems, reducing geometric complexity while retaining the perceived imagefidelity. The method has been applied to produce meshes of linearly, quadratically and cubically colour-interpolated triangles. The goal of our work is to permit interactive rendering of more complex global illumination solutions through the application of simplification algorithms as well as the use of more powerful rendering primitives.
Three-Dimensional Modeling and Effects on Still Images
(Blackwell Science Ltd and the Eurographics Association, 1996) Zakait, Yaron; Rappoport, Ari
Designers and creative artists use computer graphics and image processing effects on stall photographs in application areas such as advertising entertainment broadcasting and the arts Most of the effects available in research arid commercial work are two-dimensional in nature, for example image processing filters [blur, edge enhancement) and creative effects (tilings, reflections) There is almost no usage of information taken from the 3-D world in which the objects appearing an the image are located.In this paper we present a novel method for creating 3-D effects on photographs or in general on any image created by rendering a 3-D world The artist interacts with the image using a set of intuitive direct manipulation interface objects These objects let the user define a 3-D model, display at, and manipulate it in a 3-D space which is correlated with that of the input image.The generated model can be an arbitrarily complex 3-D polyhedron Any texture, including texture taken from the input photograph, can be mapped into any of its faces arid used for special effects We discuss and show examples for effects such as copy and paste, motion blur, model editing and deformations lighting effects, and shadows.
Compositing Computer and Video Image Sequences: Robust Algorithms for the Reconstruction of the Camera Parameters
(Blackwell Science Ltd and the Eurographics Association, 1996) Berger, M.-O.; Chevrier, C.; Simon, G.
Augmented reality shows great promises in fields where a simulation in situ would be impossible or too expensive. When mixing synthetic and real objects in the same animated sequence, we must be sure that the geometrical coherence as well as the photometrical coherence is ensured. One major challenge is to compute the camera viewpoint with sufficient accuracy to ensure a satisfactory composition. We especially address this point in this paper using computer vision techniques and robust statistical methods. We prove that such techniques make it possible to compute almost automatically the viewpoint for long video sequences even for bad quality images in outdoor environments. Significant results on the lighting simulation of the bridges of Paris are shown.
Method for Calculation of Sky Light Luminance Aiming at an Interactive Architectural Design
(Blackwell Science Ltd and the Eurographics Association, 1996) Dobashi, Yoshinori; Kaneda, Kazufumi; Yamashita, Hideo; Nishita, Tomoyuki
Recently, computer graphics are frequently used for both architectural design and visual environmental assessment. Using computer graphics, designers can easily compare the effect of the natural light on their architectural designs under various conditions, such as different times of day, seasons, atmospheric conditions (clear or overcast sky) or building wall materials. In traditional methods of calculating the luminance due to sky light, however, all calculation must be performed from scratch if such conditions undergo change. Therefore, to compare the architectural designs under different conditions, a great deal of time has to be spent on generating the images.This paper proposes a new method of quickly generating images of an outdoor scene, taking into account glossy specular reflection, even if such conditions change. In this method, luminance due to sky light is expressed by a series of basis functions, and basis luminances corresponding to each basis function are precalculated and stored in a compressed form in the preprocess. Once the basis luminances are calculated, the luminance due to sky light can be quickly calculated by the weighted sum of the basis luminances. Several examples of an architectural design demonstrate the usefulness of the proposed method.
3D Reconstruction of Complex Polyhedral Shapes from Contours using a Simplified Generalized Voronoi Diagram
(Blackwell Science Ltd and the Eurographics Association, 1996) Oliva, J-M.; Perrin, M.; Coquillart, S.
We are interested in modelling the suface of very irregular objects known through a few planar polygonal cross-sections. This problem is considered difficult when severe topology and morphology variations appear between neighbouring cross-sections (multi-branching, holes, disconnected areas). Only few methods deal with this problem in a systematic way.The paper describes an original method allowing to build, in a fully automatic and systematic way, an external surface with a valid topology in any case. It moreover allows to adjust details of the reconstructed surface in view of the morphologies and topologies of the various initial cross-sectional contours.At first, a global correspondence is operated between each couple of adjacent cross-sections by extracting polygonal areas of difference. Next steps are based on the computation in each area of difference of the bisector network, a well-defined simplified generalised Voronoi diagram. This structure is used both for connecting initial contour points and for interpolating new intermediate portions of contours. It depends on the complexity of initial 2D shapes. Interpolation stage is then recursively operated until a satisfactory surface has been obtained or until a maximum number of new intermediate cross-sectional contours have been built. The valid final suface is directly obtained by concatenating all the tiling areas of difference without need of any post processing step. The processing of several real data related to geological bodies or human organs has proved that the described method allows detailed modelling of irregular objects with very performing CPU times. The reconstruction appears insensitive to severe variations of the object shape, including apparitions of holes or disconnections.
CCD-Camera Based Optical Beacon Tracking for Virtual and Augmented Reality
(Blackwell Science Ltd and the Eurographics Association, 1996) Madritsch, Franz; Gervautz, Michael
We introduce a scheme for optical beacon tracking using two CCD-cameras and LED beacons. Due to the sub-pixel accuracy of the beacon detection algorithm a very high precision can be achieved so that the tracking method is suitable for augmented reality applications. We describe the assembly of the equipment needed for the whole tracking system, the behavior of LED-beacons, and how three beacons can be combined to form a 6-DOF tracker. A report on our accuracy evaluation and its results are given. Furthermore we describe two application prototypes in which the tracker was incorporated and tested.
Interpolatory Subdivision on Open Quadrilateral Nets with Arbitrary Topology
(Blackwell Science Ltd and the Eurographics Association, 1996) Kobbelt, Leif
A simple interpolatory subdivision scheme for quadrilateral nets with arbitrary topology is presented which generates C1 surfaces in the limit. The scheme satisfies important requirements for practical applications in computer graphics and engineering. These requirements include the necessity to generate smooth surfaces with local creases and cusps. The scheme can be applied to open nets in which case it generates boundary curves that allow a C0-join of several subdivision patches. Due to the local support of the scheme, adaptive refinement strategies can be applied. We present a simple device to preserve the consistency of such adaptively refined nets.
Surface Graph Sketching
(Blackwell Science Ltd and the Eurographics Association, 1996) Hutchinson, D.; Lin, F.; Hewitt, W.T.
The production of patterns and designs upon surfaces has received only limited attention, with texturing techniques being accepted as adequate. Texturing, however, can be a very unsatisfactory and clumsy method of producing complex and accurate designs upon a surface, even more so with surfaces such as NURBS where a texture may appear very much distorted when mapped to a surface. This paper introduces a new approach called surface graph sketching which draws upon ideas from planar graph sketching for the construction of complex curve networks across parametrically defined surfaces. Surface curves can be created by a number of methods and stored in the parameter space of the surface thereby allowing intricate and more importantly accurate surface designs to be created. Regions of the surface may be assigned a property such as colour or texture, or cut away to produce holes. Surface graph sketching has a number of applications, in the design of trimming curves, surface patterning and texture map definitions.
Intelligent Control for Haptic Displays
(Blackwell Science Ltd and the Eurographics Association, 1996) Munch, Stefan; Stangenberg, Martin
Usually, a mouse is used for input activities only, whereas output from the computer is sent via the monitor and one or two loudspeakers. But why not use the mouse for output, too? For instance, if it would be possible to predict the next interaction object the user wants to click on, a mouse with a mechanical brake could stop the cursor movement at the desired position. This kind of aid is especially attractive for small targets like resize handles of windows or small buttons.In this paper, we present an approach for the integration of haptic feedback in everyday graphical user interfaces. We use a specialized mouse which, is able to apply simple haptic information, to the user s hand and index finger. A multi-agent system has been designed which observes the user in order to predict the next interaction object and launch haptic feedback, thus supporting positioning actions with the mouse. Although primarily designed in order to provide intelligent haptic feedback, the system can be combined with other output modalities as well, due to its modular and flexible architecture.
3D Interactive Topological Modeling using Visible Human Dataset
(Blackwell Science Ltd and the Eurographics Association, 1996) Beylot, P; Gingins, P; Kalra, P; Thalmann, N Magnenat; Maurel, W; Thalmann, D; Fasel, J
Availability of Visible Human Dataset (VHD)has provided numerous possibilities for its exploitation in both medical applications and 3D animation. In this paper, we present our interactive tools which enable extraction of surfaces for different organs, including bones, muscles, fascia, and skin, from the VHD. The reconstructed surfaces then are used for defining the inter-relationship of organs, a process we refer to as topological modeling. A data base is constructed, which encapsulates structural, topological, mechanical and other relevant information about organs. A 3D interactive tool enables the building and editing of this data base. Such a data base can later be used for different applications in fields such as medicine, sports, education, and entertainment.
Generation of Smooth Surfaces by Controlling Curvature Variation
(Blackwell Science Ltd and the Eurographics Association, 1996) Higashi, Masatake; Tsutamori, Hideo; Hosaka, Mamoru
To satisfy a designer s intention for constructing aesthetic shapes such as automotive bodies, we propose a surface generation method. In the surface design process, designers determine shapes according to their great concern for the reflected images of vehicle surroundings, shade lines and highlight lines. Since reflection and shading are affected by changes of surface normal, the curvature variation of the surface, which represents the change of the surface normal, should be smooth and distributed as designers want. The proposed method controls curvature distribution directly by determining a surface shape from an evolute, which is a locus of the curvature center of the generatrix and moves along directrices to form the surface. It first generates evolutes of boundary curves to be generatrices as rational Bezier curves, then interpolates their shapes with the Bezier polygons, and locates the interpolated shape to the corresponding position of the directrices. By applying this method, we have confirmed that a smooth shape is generated from four boundary curves.
BOXTREE: A Hierarchical Representation for Surfaces in 3D
(Blackwell Science Ltd and the Eurographics Association, 1996) Barequet, Gill; Chazelle, Bernard; Guibas, Leonidas J.; Mitchell, Joseph S.B.; Tal, Ayellet
We introduce the boxtree, a versatile data structure for representing triangulated or meshed surfaces in 3D. A boxtree is a hierarchical structure of nested boxes that supports efficient ray tracing and collision detection. It is simple and robust, and requires minimal space. In situations where storage is at a premium, boxtrees are effective alternatives to octrees and BSP trees. They are also more flexible and efficient than R-trees, and nearly as simple to implement.
Demand-Driven Geometry Transmission for Distributed Virtual Environments
(Blackwell Science Ltd and the Eurographics Association, 1996) Schmalstieg, Dieter; Gervautz, Michael
We present a strategy for rendering in distributed virtual environments. A geometry database is maintained by a server, while users invoke individual clients to interact with the environment. Instead of downloading a complete copy of the geometry data, the data is distributed on demand, thus gaining signifcant savings in network bandwidth. Our strategy combines several techniques, including levels of detail, progressive refinement and graceful degradation to deliver the data"just in time" over the network to the rendering process. The method allows operate on a tight resource budget, which important if attempting to use low cost systems for virtual reality applications.
Fractal modeling using free form techniques
(Blackwell Science Ltd and the Eurographics Association, 1996) Zair, Chems Eddine; Tosan, Eric
IFS models have become a powerful tool for the construction of fractal sets. They offer a straightforward way to generate complex, self-similar figures as attractors. However, they present the fundamental disadvantage of providing little control over the global form of the attractor. In contrast, free form techniques give a high control over smooth man-made objects with the use of a set of control points.In this paper, we present a new approach of fractal modeling which is based on IFS theory. We shall use free form techniques to give a practical and efficient way to build controlled fractal attractors. The resulting effect consists on the ability to deform a fractal shape interactively into the desired shape, in the same way as parametric forms (Bezier, splines).
Computation of Higher Order Illumination with a Non-Deterministic Approach
(Blackwell Science Ltd and the Eurographics Association, 1996) Bouatouch, Kadi; Pattanaik, S. N.; Zeghers, Eric
In spite of the number of efforts made by the computer graphics researchers, till today the computation of view-independent global illumination in an environment containing non-diffusely reflecting objects is a non-resolved problem. In general, non-deterministic techniques seem to be capable of solving this problem. In this article we propose one such non-deterministic method which will permit such calculation by using a combined technique of higher order function approximation and particle tracing. We have used multi-wavelets as basis functions and have calculated the illumination function approximation coefficients by exploiting the adjointness between the radiance equation and the potential equation.

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