Issue 3

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https://diglib.eg.org/handle/10.2312/86

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Accelerated Walkthroughs of Virtual Environments Based on Visibility Preprocessing and Simplification
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Wang, Yigang; Bao, Hujun; Peng, Qunsheng
This paper proposes a new preprocessing method for interactive rendering of complex polygonal virtual environments. The approach divides the space that observer can reach into many rectangular viewpoint regions. For each region, an outer rectangular volume (ORV) is established to surround it. By adaptively partitioning the boundary of the ORV together with the viewpoint region, all the rays that originate from the viewpoint region are divided into the beams whose potentially visible polygon number is less than a preset threshold. If a resultant beam is the smallest and intersects many potentially visible polygons, the beam is simplified as a fixed number of rays and the averaged color of the hit polygons is recorded. For other beams, their potentially visible sets (PVS) of polygons are stored respectively. During an interactive walkthrough, the visual information related to the current viewpoint is retrieved from the storage. The view volume clipping, visibility culling and detail simplification are efficiently supported by these stored data. The rendering time is independent of the scene complexity.
Animation of Biological Organ Growth Based on L-systems
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Durikovic, Roman; Kaneda, Kazufumi; Yamashita, Hideo
In contrast with the growth of plants and trees, human organs can undergo significant changes in shape through a variety of global transformations during the growth period, such as bending or twisting. In our approach, the topology of a human organ is represented by a skeleton in the form of a tree or cycled graph. The length of skeleton growth can be simulated by an algebraic L-system that also produces discrete events. The paper shows how to include global transformations into the formalism of L-systems to obtain a continuous process. The shape of the organ is approximated by a number of ellipsoidal clusters centred at points on the skeleton. The proposed growth model of the organ continually responds to the positional changes of surrounding organs, thereby changing the organ shape locally. In our study, the stomach of a human embryo is used for the demonstration of organ development, and the methodology employed is also applicable to the animation of animal organs and their development.
Anisotropic Solid Texture Synthesis Using Orthogonal 2D Views
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Dischler, J.M.; Ghazanfarpour, D.; Freydier, R.
Analytical approaches, based on digitised 2D texture models, for an automatic solid (3D) texture synthesis have been recently introduced to Computer Graphics. However, these approaches cannot provide satisfactory solutions in the usual case of natural anisotropic textures (wood grain for example). Indeed, solid texture synthesis requires particular care, and sometimes external knowledge to "guess" the internal structure of solid textures because only 2D texture models are used for analysis. By making some basic assumptions about the internal structure of solid textures, we propose a very efficient method based on a hybrid analysis (spectral and histogram) for an automatic synthesis of solid textures. This new method allows us to obtain high precision solid textures (closely resembling initial models) in a large number of cases, including the difficult case of anisotropic textures.
Anno 2010 - Remembering Our Future: Challenges and Frontiers of Human-Media Technology as the Kernel for Human-Centered Computing
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Encarnacao, Jose
Based on a forecast by Battelle, Human-Media Technology is one of "technologyâ s top 10 challenges and opportunities" for the year 2010. The subject hereby is: "Humans live, science finds out how technology conforms". The goal is to develop environments that allow users to cooperate in the most efficient and natural way. Human-centered systems will have to incorporate people as an explicit design component. This lecture will address the main goals in developing such systems based on their general characteristics and the corresponding enabling technologies: Visualization (seeing the unseen), Virtual and Augmented Reality (environment must be immersive), and also Multimedia (to introduce the combination of visual, auditory and voice data). Examples from applications and case studies will support the clarification of ideas and goals. Several videos will be used to show the impact.So far, the human-centered interfaces to accommodate human perception and human response capabilities and limitations will have been presented and discussed. These interfaces allow to integrate the desired amount of immersion and cooperation (CSCW). Based on this, some "hands-on" life demos will be shown to discuss the state of the art of these technologies, like Virtual Tables (responsive workbenches), special I/O technologies, etc. Some of these demos will be stand-alone demos; others will show the potential of telecommunication for collaboration by connecting the floor with other locations to demonstrate CSCW-based visual tele-applications.
Author Index
(Blackwell Publishers Ltd and the Eurographics Association, 1998)
A Bernstein-Bezier Based Approach to Soft Tissue Simulation
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Roth, S.H.; Gross, Markus H.; Turello, Silvio; Carls, Friedrich R.
This paper discusses a Finite Element approach for volumetric soft tissue modeling in the context of facial surgery simulation. We elaborate on the underlying physics and address some computational aspects of the finite element discretization.In contrast to existing approaches speed is not our first concern, but we strive for the highest possible accuracy of simulation. We therefore propose an extension of linear elasticity towards incompressibility and nonlinear material behavior, in order to describe the complex properties of human soft tissue more accurately. Furthermore, we incorporate higher order interpolation functions using a Bernstein-Bezier formulation, which has various advantageous properties, such as its integral polynomial form of arbitrary degree, efficient subdivision schemes, and suitability for geometric modeling and rendering. In addition, the use of tetrahedral Finite Elements does not put any restriction on the geometry of the simulated volumes.Experimental results obtained from a synthetic block of soft tissue and from the Visible Human Data Set illustrate the performance of the envisioned model.
A Collaborative Scene Editor for VRML Worlds
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Lu, Tain-chi; Chiang, Chuanwen; Lin, Ming-tang; Lee, Chungnan
In this paper, we analyze the requirements for a Web-based collaborative infrastructure within a virtual world. Additionally, we combine several tools and methodologies to propose a flexible and fluid collaborative environment using Java language to create a VRML scene graph. The proposed prototype aims at four aspects: a shared workspace of scene editor, an active entity composition algorithm in Java, collaborative control in the multi-user environment, and access control mechanism toward the shared data.
Colour Illustrations
(Blackwell Publishers Ltd and the Eurographics Association, 1998)
Conservative Visibility and Strong Occlusion for Viewspace Partitioning of Densely Occluded Scenes
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Cohen-Or, Daniel; Fibich, Gadi; Halperin, Dan; Zadicario, Eyal
Computing the visibility of out-door scenes is often much harder than of in-door scenes. A typical urban scene, for example, is densely occluded, and it is effective to precompute its visibility space, since from a given point only a small fraction of the scene is visible. The difficulty is that although the majority of objects are hidden, some parts might be visible at a distance in an arbitrary location, and it is not clear how to detect them quickly. In this paper we present a method to partition the viewspace into cells containing a conservative superset of the visible objects. For a given cell the method tests the visibility of all the objects in the scene. For each object it searches for a strong occluder which guarantees that the object is not visible from any point within the cell. We show analytically that in a densely occluded scene, the vast majority of objects are strongly occluded, and the overhead of using conservative visibility (rather than visibility) is small. These results are further supported by our experimental results. We also analyze the cost of the method and discuss its effectiveness.
The Convergence of Graphics and Imaging
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Foley, James D.
Over twenty years ago a SIGGRAPH panel session addressed the convergence of computer graphics and image processing. At that time the emphasis was on low-level operations such as filtering to avoid anti-aliasing, and related psycho-physics issues. More recently, Graphics and Imaging are converging at a higher level as we move toward blending the synthetic world of computer-generated images with the real world of computer-captured images. In this talk we describe several research directions that relate to this convergence, and illustrate with specific examples of work at MERL - A Mitsubishi Electric Research Laboratory. These research directions are: Analyzing images of the human face to determine identity and orientation and ultimately to reconstruct the shape of the face. Reconstruction of static and dynamic 3D geometries from 2D images separated in time or space: here the objective is to take multiple images of a real-world scene and recreate the 3D geometry of the scene. If objects in the scene are moving, then the objective is extracting the dynamic geometry. Once the geometry has been reconstructed, editing and relighting of the scene becomes possible. Display of 3D scalar fields (also known as volume graphics) concerns 3D as opposed to 2D images, such as CT and MRI scans. These scans can be thought of as 3D images in that they are point samples of a 3D scalar field, just as a computer-captured image is a point sample of a 2D sample field. The objective of volume graphics is to create and display the 3D geometries that underly 3D images. An inexpensive yet real-time (30 fps for a 256 x 256 x 256 image) implementation of Pfister and Kaufmanâ s Cube-4 rendering architecture will be described.
Dithered Color Quantization
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Buhmann, J. M.; Fellner, Dieter W.; Held, M.; Ketterer, J.; Puzicha, J.
Image quantization and digital halftoning are fundamental problems in computer graphics, which arise when displaying high-color images on non-truecolor devices. Both steps are generally performed sequentially and, in most cases, independent of each other. Color quantization with a pixel-wise defined distortion measure and the dithering process with its local neighborhood optimize different quality criteria or, frequently, follow a heuristic without reference to any quality measure.In this paper we propose a new method to simultaneously quantize and dither color images. The method is based on a rigorous cost-function approach which optimizes a quality criterion derived from a generic model of human perception. A highly efficient algorithm for optimization based on a multiscale method is developed for the dithered color quantization cost function. The quality criterion and the optimization algorithms are evaluated on a representative set of artificial and real-world images as well as on a collection of icons. A significant image quality improvement is observed compared to standard color reduction approaches.
Egocentric Object Manipulation in Virtual Environments: Empirical Evaluation of Interaction Techniques
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Poupyrev, I.; Ichikawa, T.; Weghorst, S.; Billinghurst, M.
The acceptance of virtual environment (VE) technology requires scrupulous optimization of the most basic interactions in order to maximize user performance and provide efficient and enjoyable virtual interfaces. Motivated by insufficient understanding of the human factors design implications of interaction techniques and tools for virtual interfaces, this paper presents results of a formal study that compared two basic interaction metaphors for egocentric direct manipulation in VEs, virtual hand and virtual pointer, in object selection and positioning experiments. The goals of the study were to explore immersive direct manipulation interfaces, compare performance characteristics of interaction techniques based on the metaphors of interest, understand their relative strengths and weaknesses, and derive design guidelines for practical development of VE applications.
Emotion Editing using Finite Elements
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Koch, Rolf M.; Gross, Markus H.; Bosshard, Albert A.
This paper describes the prototype of a facial expression editor. In contrast to existing systems the presented editor takes advantage of both medical data for the simulation and the consideration of facial anatomy during the definition of muscle groups. The Cl-continuous geometry and the high degree of abstraction for the expression editing sets this system apart from others. Using finite elements we achieve a better precision in comparison to particle systems. Furthermore, a precomputing of facial action units enables us to compose facial expressions by a superposition of facial action geometries in real-time. The presented model is based on a generic facial model using a thin plate and membrane approach for the surface and elastic springs for facial tissue modeling. It has been used successfully for performing facial surgery simulation. We illustrate features of our system with examples from the Visible Human Dataset.T
An Enhanced Spring Model for Information Visualization
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Theisel, Holger; Kreuseler, Matthias
In this paper we present a new technique for visualizing multidimensional information. We describe objects of a higher dimensional information space as small closed free-form-surfaces in the visualization. The location, size and shape of these surfaces describe the original objects in information space uniquely. The underlying enhanced spring model is introduced. The technique is applied to two test data sets.
Fast Feature-Based Metamorphosis and Operator Design
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Lee, Tong-Yee; Lin, Young-Ching; Sun, Y.N.; Lin, Leeween
Metamorphosis is a powerful visual technique, for producing interesting transition between two images or volume data. Image or volume metamorphosis using simple features provides flexible and easy control of visual effect. The feature-based image warping proposed by Beier and Neely is a brute-force approach. In this paper, first, we propose optimization methods to reduce their warping time without noticeable loss of image quality. Second, we extend our methods to 3D volume data and propose several interesting warping operators allowing global and local metamorphosis of volume data.
A Framework for Synchronized Editing of Multiple Curve Representations
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Grimm, Cindy; Ayers, Matthew
Editing curves and surfaces is difficult in part because their mathematical representations rarely correspond to most peopleâ s idea of a curve or surface. The implementation (and hence, behavior) of most manipulation tools is intertwined with a particular curve or surface representation; this can make reimplementing the tool with a different representation problematic. A system using a single representation must therefore either limit the types of tools available or convert existing tools to work on the systemâ s representation.In this paper we present a framework for editing curves or surfaces which supports multiple representations and ensures that they stay synchronized. As a proof of concept, we have created a curve editor which contains several tools each of which manipulate one of three different curve representations: polylines, NURBs, and multi-resolution B-splines.
Frontiers in User-Computer Interaction
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Van Dam, Andries
In this age of (near-)adequate computing power, the power and usability of the user interface is as key to an applicationâ s success as its functionality. Most of the code in modern desktop productivity applications resides in the user interface. But despite its centrality, the user interface field is currently in a rut: the WIMP (Windows, Icons, Menus, Point-and-Click GUI based on keyboard and mouse) has evolved little since it was pioneered by Xerox PARC in the early â 70s. Computer and display form factors will change dramatically in the near future and new kinds of interaction devices will soon become available. Desktop environments will be enriched not only with PDAs such as the Newton and Palm Pilot, but also with wearable computers and large-screen displays produced by new projection technology, including office-based immersive virtual reality environments. On the input side, we will finally have speech-recognition and force-feedback devices. Thus we can look forward to user interfaces that are dramatically more powerful and better matched to human sensory capabilities than those dependent solely on keyboard and mouse. 3D interaction widgets controlled by mice or other interaction devices with three or more degrees of freedom are a natural evolution from their two-dimensional WIMP counterparts and can decrease the cognitive distance between widget and task for many tasks that are intrinsically 3D, such as scientific visualization and MCAD. More radical post-WIMP UIs are needed for immersive virtual reality where keyboard and mouse are absent. Immersive VR provides good driving applications for developing post-WIMP UIs based on multimodal interaction that involve more of our senses by combining the use of gesture, speech, and haptics.
Getting Rid of Links in Hierarchical Radiosity
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Stamminger, M.; Schirmacher, H.; Slusallek, Ph.; Seidel, H.-P.
Hierarchical radiosity with clustering has positioned itself as one of the most efficient algorithms for computing global illumination in non-trivial environments. However, using hierarchical radiosity for complex scenes is still problematic due to the necessity of storing a large number of transport coefficients between surfaces in the form of links. In this paper, we eliminate the need for storage of links through the use of a modified shooting method for solving the radiosity equation. By distributing only unshot radiosity in each step of the iteration, the number of links decreases exponentially. Recomputing these links instead of storing them increases computation time, but reduces memory consumption dramatically. Caching may be used to reduce the time overhead. We analyze the error behavior of the new algorithm in comparison with the normal gathering approach for hierarchical radiosity. In particular, we consider the relation between the global error of a hierarchical radiosity solution and the local error threshold for each link.
Importance Driven Halftoning
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Streit, L.; Buchanan, J.
Most halftoning techniques have been primarily concerned with achieving an accurate reproduction of local gray-scale intensities while avoiding the introduction of artifacts. A secondary concern in halftoning has been the preservation of edges in the halftoned image. In this paper, we will introduce a new halftoning technique that utilizes a bandpass pyramid to achieve an accurate reproduction of important attributes in the image. Ink is distributed through the bandpass pyramid primarily according to a user defined importance function. This technique has three main characteristics. First, our technique can produce results similar to many other halftoning techniques by allowing a generic importance function to be specified. If the chosen importance function is average intensity we obtain results similar to traditional halftoning. We also show how the importance function can be changed to highlight areas with high variance. Second, in addition to changing the importance function, the drawing primitives can also be changed. By using line segments instead of single pixels as drawing primitives we illustrate how edge enhancement can be achieved. Third, this technique allows the user to easily limit the number drawing primitives used. This is useful in limited resource rendering.In addition to providing a tailorable halftoning technique our method can easily be adapted to produce two tone non-photorealistic (NPR) images. We illustrate this by showing how sketched effects can be achieved by aligning the drawing primitives according to different image attributes.
Importance Driven Texture Coordinate Optimization
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Sloan, Peter-Pike J.; Weinstein, David M.; Brederson, J.
Traditionally, texture coordinates have been generated based solely on the modelâ s geometry, often even before a modelâ s textures have been created. With the arrival of new technologies, such as 3D paint programs, weaknesses of a static optimization pre-process are becoming apparent. These weaknesses arise from constructing a parameterization based solely on the modelâ s geometry, ignoring the fact that detail is not uniformly spaced throughout the texture space. In fact, certain regions of the texture are more important than other regions. In this paper we introduce the notion of the "importance map" and describe how importance values are derived from both intrinsic properties of the texture and user-guided highlights. Furthermore, we describe how importance maps are used to drive the texture coordinate optimization. Finally, we show how this optimization process can be integrated into a 3D painting environment, enabling periodic optimization at any stage of texture design.

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