Issue 3

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

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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.
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.
Perception Based Color Image Difference
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Neumann, Laszlo; Matkovic, Kresimir; Purgathofer, Werner
A good image metric is often needed in digital image synthesis. It can be used to check the convergence behavior in progressive methods, to compare images rendered using various rendering methods etc. Since images are rendered to be observed by humans, an image metric should correspond to human perception as well. We propose here a new algorithm which operates in the original image space. There is no need for Fourier or wavelet transforms. Furthermore, the new metric is view distance dependent. The new method uses the contrast sensitivity function. The main idea is to place a number of various rectangles in images, and to compute the CIE LUV average color difference between corresponding rectangles. Errors are then weighted according to the rectangle size and the contrast sensitivity function.
A New Approach for Direct Manipulation of Free-Form Curve
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Zheng, J.M.; Chan, K.W.; Gibson, I.
There is an increasing demand for more intuitive methods for creating and modifying free-form curves and surfaces in CAD modeling systems. The methods should be based not only on the change of the mathematical parameters, such as control points, knots, and weights, but also on the userâ s specified constraints and shapes. This paper presents a new approach for directly manipulating the shape of a free-form curve, leading to a better control of the curve deformation and a more intuitive CAD modeling interface. The userâ s intended deformation of a curve is automatically converted into the modification of the corresponding NURBS control points and knot sequence of the curve. The algorithm for this approach includes curve elevation, knot refinement, control point repositioning, and knot removal. Several examples shown in this paper demonstrate that the proposed method can be used to deform a NURBS curve into the desired shape. Currently, the algorithm concentrates on the purely geometric consideration. Further work will include the effect of material properties.
Mass-Spring Simulation using Adaptive Non-Active Points
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Howlett, P.; Hewitt, W.T.
This paper introduces an adaptive component to a mass-spring system as used in the modelling of cloth for computer animation. The new method introduces non-active points to the model which can adapt the shape of the cloth at inaccuracies. This improves on conventional uniform mass-spring systems by producing more visually pleasing results when simulating the drape of cloth over irregular objects. The computational cost of simulation is decreased by reducing the complexity of collision handling and enabling the use of coarser mass-spring networks.
Progressive Iso-Surface Extraction from Hierarchical 3D Meshes
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Grosso, Roberto; Ertl, Thomas
A multiresolution data decomposition offers a fundamental framework supporting compression, progressive transmission, and level-of-detail (LOD) control for large two or three dimensional data sets discretized on complex meshes. In this paper we extend a previously presented algorithm for 3D mesh reduction for volume data based on multilevel finite element approximations in two ways. First, we present efficient data structures which allow to incrementally construct approximations of the volume data at lower or higher resolutions at interactive rates. An abstract description of the mesh hierarchy in terms of a coarse base mesh and a set of integer records offers a high compression potential which is essential for an efficient storage and a progressive network transmission. Based on this mesh hierarchy we then develop a new progressive iso-surface extraction algorithm. For a given iso-value, the corresponding iso-surface can be computed at different levels of resolution. Changing to a higher or coarser resolution will update the surface only in those regions where the volume data is being refined or coarsened. Our approach allows to interactively visualize very large scalar fields like medical data sets, whereas the conventional algorithms would have required at least an order of magnitude more resources.
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.
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.
Maximum Intensity Projection Using Splatting in Sheared Object Space
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Cai, Wenli; Sakas, Georgios
In this paper we present a new Maximum Intensity Projection (MIP) algorithm which was implemented employing splatting in a shear-warp context. This algorithm renders a MIP image by first splatting each voxel on two intermediate spaces called "worksheet" and "shear image". Then, the maximum value is evaluated between worksheet and shear image. Finally, shear image is warped on the screen to generate the result image. Different footprints implementing different quality modes are discussed. In addition, we introduced a line encoded indexing speed-up method to obtain interactive speed. This algorithm allows for a quantitative, predictable trade-off between interactivity and image quality.
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 Vector Approach for Global Illumination in Ray Tracing
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Zaninetti, Jacques; Serpaggi, Xavier; Peroche, Bernard
This paper presents a method taking global illumination into account in a ray tracing environment. A vector approach is introduced, which allows to deal with all the types of light paths and the directional properties of materials. Three types of vectors are defined: Direct Light Vectors associated to light sources, Indirect Light Vectors which correspond to light having been diffusely reflected at least once and Caustic Light Vectors which are associated to light rays emitted by sources and reflected and/or transmitted by specular surfaces. These vectors are estimated at a small number of points in the scene. A weighted interpolation between known values allows to reconstruct these vectors for the other points, with the help of a gradient computation for the indirect component. This approach also allows to take uniform area light sources (spherical, rectangular and circular) into account for all the types of vectors. Computed images are thus more accurate and no discretizing of the geometry of the scene is needed.
Author Index
(Blackwell Publishers Ltd and the Eurographics Association, 1998)
Molecular Dynamics Simulation in Virtual Environments
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Ai, Z.; Frohlich, T.
A virtual environment for interactive molecular dynamics simulation has been designed and implemented at the Fraunhofer Institute for Computer Graphics. Different kinds of virtual reality devices are used in the environment for immersive display and interaction with the molecular system. A parallel computer is used to simulate the physical and chemical properties of the molecular system dynamically. A high-speed network exchanges data between the simulation program and the modeling program. Molecular dynamics simulation virtual environment provides scientists with a powerful tool to study immersively the world of molecules. The dynamic interaction between an AIDS antiviral drug and reverse transcriptase enzyme is illustrated in the paper.
Rapid and Accurate Contact Determination between Spline Models using ShellTrees
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Krishnan, S.; Gopi, M.; Lin, M.; Manocha, D.; Pattekar, A.
In this paper, we present an efficient algorithm for contact determination between spline models. We make use of a new hierarchy, called ShellTree, that comprises of spherical shells and oriented bounding boxes. Each spherical shell corresponds to a portion of the volume between two concentric spheres. Given large spline models, our algorithm decomposes each surface into Bezier patches as part of pre-processing. At runtime it dynamically computes a tight fitting axis-aligned bounding box across each Bezier patch and efficiently checks all such boxes for overlap. Using off-line and on-line techniques for tree construction, our algorithm computes ShellTrees for Bezier patches and performs fast overlap tests between them to detect collisions. The overall approach can trade off runtime performance for reduced memory requirements. We have implemented the algorithm and tested it on large models, each composed of hundred of patches. Its performance varies with the configurations of the objects. For many complex models composed of hundreds of patches, it can accurately compute the contacts in a few milliseconds.
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.
A Light Hierarchy for Fast Rendering of Scenes with Many Lights
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Paquette, Eric; Poulin, Pierre; Drettakis, George
We introduce a new data structure in the form of a light hierarchy for efficiently ray-tracing scenes with many light sources. An octree is constructed with the point light sources in a scene. Each node represents all the light sources it contains by means of a virtual light source. We determine bounds on the error committed with this approximation to shade a point, both for the cases of diffuse and specular reflections. These bounds are then used to guide a hierarchical shading algorithm. If the current level of the light hierarchy provides shading of sufficient quality, the approximation is used, thus avoiding the cost of shading for all the light sources contained below this level. Otherwise the descent into the light hierarchy continues.Our approach has been implemented for scenes without occlusion. The results show important acceleration compared to standard ray-tracing (up to 90 times faster) and an important improvement compared to Wardâ s adaptive shadow testing.
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.
Subdivision Schemes for Thin Plate Splines
(Blackwell Publishers Ltd and the Eurographics Association, 1998) Weimer, Henrik; Warren, Joe
Thin plate splines are a well known entity of geometric design. They are defined as the minimizer of a variational problem whose differential operators approximate a simple notion of bending energy. Therefore, thin plate splines approximate surfaces with minimal bending energy and they are widely considered as the standard "fair" surface model. Such surfaces are desired for many modeling and design applications.Traditionally, the way to construct such surfaces is to solve the associated variational problem using finite elements or by using analytic solutions based on radial basis functions. This paper presents a novel approach for defining and computing thin plate splines using subdivision methods. We present two methods for the construction of thin plate splines based on subdivision: A globally supported subdivision scheme which exactly minimizes the energy functional as well as a family of strictly local subdivision schemes which only utilize a small, finite number of distinct subdivision rules and approximately solve the variational problem. A tradeoff between the accuracy of the approximation and the locality of the subdivision scheme is used to pick a particular member of this family of subdivision schemes.Later, we show applications of these approximating subdivision schemes to scattered data interpolation and the design of fair surfaces. In particular we suggest an efficient methodology for finding control points for the local subdivision scheme that will lead to an interpolating limit surface and demonstrate how the schemes can be used for the effective and efficient design of fair surfaces.
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.
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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