Volume 17 (1998)

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    Announcements
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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    Editorial
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Coquillart, Sabine; Seidel, Hans-Peter
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    Join Now!
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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    Network Service
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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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.
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    Book Reviews
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
    Books reviewed:Donnelly, Daniel. Web Design: The Next GenerationHege, H.-C. and Polthier, K. (editors). Visualization and MathematicsGibson, J. D., Berger, T., Lookabaugh, T., Lindbergh, D. andBaker, R. L. Digital Compression for MultimediaMorgan, Don. Numerical Methods For DSP Systems in CWainer, Howard. Visual Revelations: Graphical Tales of Fate and Deception from Napoleon Bonaparte to Ross PerotMaestri, George. Digital Character AnimationKlimek, Grazyna and Klimek, Maciej. Discovering Curves and Surfaces with MapleTrappl, Robert and Petta, Paolo (editors). Creating Personalities for Synthetic ActorsLohmann, Gabriele. Volumetric Image AnalysisMeinhardt, Hans. The Algorithmic Beauty of Sea Shells (2nd Edition)Palanque, Philippe and Paterno, Fabio (editors) Formal Methods in Human-Computer InteractionDai, Fan (editor). Virtual Reality for Industrial Applications
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    9th Eurographics Workshop on Rendering
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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    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.
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    Color Fidelity in Computer Graphics: a Survey
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Rougeron, Gilles; Peroche, Bernard
    The purpose of this paper is to make a state of the art for color fidelity in computer graphics. Color fidelity includes three steps. The first one is the spectral rendering phase which attributes a spectrum to each pixel of a picture. During the second step, a spectral data is transformed into a set of tristimulus values in the XYZ color space. The purpose of the third step, called Color Reproduction Function, is to determine the RGB values displayable on the screen, in such a way that subjective fidelity is reached. We especially detail the two last steps of the color fidelity process; we also point out the work still remaining to be done in this field and we propose some research ways.
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    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.
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    Adaptive Supersampling in Object Space Using Pyramidal Rays
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Genetti, Jon; Gordon, Dan; Williams, Glen
    We introduce a new approach to three important problems in ray tracing: antialiasing, distributed light sources, and fuzzy reflections of lights and other surfaces. For antialiasing, our approach combines the quality of supersampling with the advantages of adaptive supersampling. In adaptive supersampling, the decision to partition a ray is taken in image-space, which means that small or thin objects may be missed entirely. This is particularly problematic in animation, where the intensity of such objects may appear to vary. Our approach is based on considering pyramidal rays (pyrays) formed by the viewpoint and the pixel. We test the proximity of a pyray to the boundary of an object, and if it is close (or marginal), the pyray splits into 4 sub-pyrays; this continues recursively with each marginal sub-pyray until the estimated change in pixel intensity is sufficiently small.The same idea also solves the problem of soft shadows from distributed light sources, which can be calculated to any required precision. Our approach also enables a method of defocusing reflected pyrays, thereby producing realistic fuzzy reflections of light sources and other objects. An interesting byproduct of our method is a substantial speedup over regular supersampling even when all pixels are supersampled. Our algorithm was implemented on polygonal and circular objects, and produced images comparable in quality to stochastic sampling, but with greatly reduced run times.
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    A Fast Algorithm for Inverse Colormap Computation
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Brun, L.; Secroun, C.
    The inverse colormap operation is the process which allows an image to be displayed with a limited set of colors. In order to obtain a minimal visual distortion between the input image annd the one displayed, inverse colormap algorithms associate each color with its nearest representative. The method presented in this paper is carried out in two steps. First, the 3D Voronoi diagram implicitly used by inverse colormap algorithms is approximated using a Karhunen-Loeve transformation. Then, a correcting step is carried out in order to reduce the in uence of the first approximation. The complexity of our algorithm is independent of the size of the colormap. Moreover, its results are equal or quite close to the optimal solution.
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    Calendar of Events
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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    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.
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    Incident Light Metering in Computer Graphics
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Neumann, Laszlo; Matkovic, Kresimir; Neumann, Attila; Purgathofer, Werner
    Every rendering process consists of two steps. The first is the computing of luminance values by methods like ray tracing or radiosity, and the second step is the mapping of the computed values to values appropriate for displaying. In the last years, as alternative to simple linear scaling which maps the average value to the medium luminance, some new ways of mapping were introduced. These new methods are based on photography analogies and on human vision models. All existing methods follow, implicitly or explicitly, the reflected light metering principle. The method introduced in this paper is the first that follows the incident light metering used in professional photography and in the movie industry. Actually the irradiances are measured using a set of diffusors, which are placed automatically in the scene, and a linear scale factor based on these measurements is used to map the computed radiances to the display device. The diffusors act as half space integrators, they collect the light energy from all half space directions. The light comes from the primary light sources, or it is the result of various interreflections. The newly introduced method reproduces original colors faithfully even for scenes with very low or very high average reflectivity.
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    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.
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    Event Reports
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
    Eurographics â 98 Conference, page 301Eurographics â 98 Awards, page 303EG UK â 98 Conference, page 304Cover Competition Winners, page 306
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    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.
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    1998 Annual Index
    (Blackwell Publishers Ltd and the Eurographics Association, 1998)
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    Siggraph/Eurographics Workshop on Graphics Hardware
    (Blackwell Publishers Ltd and the Eurographics Association, 1998) Schneider, Bengt-Olaf