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Computer Graphics and Applications, IEEE

Issue 3 • Date May 1995

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Displaying Results 1 - 10 of 10
  • Wavelets for computer graphics: a primer.1

    Page(s): 76 - 84
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (767 KB)  

    Wavelets are a mathematical tool for hierarchically decomposing functions. They allow a function to be described in terms of a coarse overall shape, plus details that range from broad to narrow. Regardless of whether the function of interest is an image, a curve, or a surface, wavelets offer an elegant technique for representing the levels of detail present. The article is intended to provide people working in computer graphics with some intuition for what wavelets are, as well as to present the mathematical foundations necessary for studying and using them. We discuss the simple case of Haar wavelets in one and two dimensions, and show how they can be used for image compression.<> View full abstract»

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  • Interactive simulation of solid rigid bodies

    Page(s): 63 - 75
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1048 KB)  

    The article describes the implementation of an interactive system for simulating rigid bodies with contact and friction. The system can simulate moderately complex mechanical systems at interactive rates (20-30 Hz on low end Silicon Graphics workstations). New objects and user specified constraints can be added into the simulation environment on the fly. The system uses analytical methods to compute contact forces, as opposed to the penalty methods common in other interactive systems. Currently, the system's weakest feature is that it can fail to detect high speed collisions. Objects that move at high speeds (relative to the step size of the simulation) are subject to a form of aliasing and may tunnel through other objects without causing a collision. Other simplifications of the system involve approximating collision times and locations by interpolation methods, and periodic error correction adjustments of geometric tolerances. It is difficult to try to quantify the error incurred by a given approximation or tradeoff. Some of the design choices will likely curtail the system's use for highly predictive applications. However, they do not seriously affect simulating the basic dynamics of a mechanism like a feeder. In general, the system performs with sufficient accuracy and realism to be considered a viable interactive simulation environment View full abstract»

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  • Alice: rapid prototyping for virtual reality

    Page(s): 8 - 11
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    Virtual reality has sparked many people's imaginations, but writing VR programs remains difficult. Besides the obvious problems of managing arcane I/O devices (trackers, gloves, and so on), the programs must allow the participant to operate effectively in the immersive environment. Virtual environments present a new medium for both the participant and the programmer/author. In the University of Virginia's User Interface Group, we believe the best way to accelerate development in a new medium such as VR is to provide tools that allow people without highly technical backgrounds to create programs for it. These novice authors must be able to quickly try different nuances of an idea. They must be able to easily ask “what if” questions. To support this goal, we are developing Alice, a rapid prototyping environment that can generate VR environments. The name “Alice” honors Lewis Carroll's heroine, who explored a rapidly changing, dynamic environment View full abstract»

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  • Object-oriented visualization

    Page(s): 54 - 62
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    Feature based techniques incorporated into standard visualization algorithms can greatly enhance the quantification and visualization of observed phenomena, as described in the article. The methods to isolate and recognize coherent 3D structures are analogous to 2D vision techniques. The overall goals are the same in both fields, namely, to interpret an image (data) and construct a model to describe it. Although the article uses data sets from numerical simulations of fluid flow, the concepts are applicable to other domains where scientists study the evolution and morphologies of 4D space time vector and scalar fields. More work is needed to explore complex features based upon domain specific knowledge and to define the parameters for classification and tracking. Sophisticated databases for storage and retrieval of feature based data sets are also an interesting area of study. The ultimate goal of visualization is to aid in the understanding and analysis of data. With faster parallel computers and more sophisticated laboratory equipment, information is being produced in ever greater amounts. This information must be presented to the scientist in a form suitable for cogent assimilation and manipulation. The article presents issues and algorithms for an object oriented approach to this problem and demonstrates its usefulness for visualization View full abstract»

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  • Color correction for an image sequence

    Page(s): 38 - 42
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    The color correction technique presented constructs a mapping from the registered overlapping regions of two adjacent images in an image sequence. The method involves two main steps. In the first step we use multiple regression to find the relationship between the registered overlapping regions of two adjacent images in the sequence. We then use the derived mapping to correct the color in one image so that it matches the adjacent image. After describing the basic method and discussing strategies far dealing with specific problems that arise, we present and analyze relevant test results View full abstract»

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  • At Oak Ridge, a car crash on the World Wide Web

    Page(s): 16 - 18
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    Researchers at Oak Ridge National Laboratory are using a massively parallel computer to model car crashes as part of a project to develop vehicles that protect their inhabitants while getting triple the gas mileage of today's models. Oak Ridge's Center for Computational Sciences modeled a 50 percent offset crash of two Ford Tauruses moving at 35 miles per hour on an Intel Paragon. The simulation, which took days to run on a serial supercomputer, completed in about eight hours on the Paragon, using a finite element model code that was ported to Oak Ridge's parallel machine. In addition to using new hardware and software that speeds the modeling process, the center is also sharing its results in a new way, by posting them on its World Wide Web site. In fact, the Web has become an important channel for internal and external communication at Oak Ridge, as well as throughout the Department of Energy and the other federal government agencies involved with its High Performance Computing and Communications initiative. Posting images and animations along with text on the Web allows other researchers, project partners, and in some cases the general public to share the benefits of visualization. The Web's hyperlink capabilities also allow a user to quickly learn about other projects at Oak Ridge, as well as at other national labs and throughout the community of federal agencies and contractors working within the HPCC community View full abstract»

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  • After the storm: considerations for information visualization

    Page(s): 12 - 15
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    “Study of a Numerically Modeled Severe Storm” is a well known animation within the scientific visualization community. The visualization is among the best of its genre, featuring full storyboarding, well chosen representations, high quality rendering, and professional narration. We recently revisited the thunderstorm to consider what we would do differently if we were to make that video again. We wanted to demonstrate several principles of effective information presentation, drawing from the fields of graphic design and visual perception. Our purpose was not to find fault with bad visualization. Rather, we wanted to study how to make a good thing better. The original video was produced using the modeling, animation, and rendering capabilities of Wavefront's Advanced Visualizer. To facilitate comparison, we did most of the current work with the same software. However, many points discussed here apply to interactive visualization tools as well. The original visualization and our revised version are both based on data generated by a simulation run on a Cray supercomputer at NCSA. The simulation models the genesis and lifetime of a severe storm by solving a set of time dependent equations over a collection of regularly spaced grid points in a three dimensional rectangular space View full abstract»

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  • Generating exact ray-traced animation frames by reprojection

    Page(s): 43 - 52
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    Reprojection techniques can create approximate ray traced animation frames. Extending an existing algorithm yields exact frames and full ray tracing, with up to 92 percent savings in rendering time. We present an algorithm that exploits spatiotemporal coherence between frames to significantly decrease the rendering time of ray traced animations. This method produces inferred ray traced images of any scene that can be ray traced using a point sampled method. The images created by the algorithm are not approximated frames created from weighted averages of other frames, nor are they frames patched together from near frame pixel values. The algorithm guarantees that a color seen in a subpixel would be returned by a ray passing somewhere through that subpixel, but not necessarily though the center. This algorithm efficiently creates frames of any view that can be ray traced. While the savings increase with the complexity of the rendered objects and the preponderance of diffuse objects, significant savings occur with reflective and refractive objects. However, the technique requires the ray tracing method to be point sample oriented View full abstract»

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  • Expressive rendering: a review of nonphotorealistic techniques

    Page(s): 29 - 37
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    The success of graphics systems that render photorealistic output has obscured parallel developments in nonphotorealistic rendering. A review of these “expressive” systems suggests a framework for further development. One of the authors, Simon Schofield, has developed a prototype system that gives users a wide variety of automatic rendering styles-from the almost photorealistic, through the styles resembling artists' sketches or paintings, to abstract renderings of entirely new forms. The significant problems associated with NPR are primarily aesthetic and only secondarily technical. The culturally oriented theoretical problems surrounding the field are many and, at their most difficult, broach central issues of perception and representation. We therefore begin by discussing the limitations of photorealism as a representational style. However, the technical problems of implementing an NPR system are not trivial. As far as we know, the literature defines no general framework for an NPR system, although it does include an array of more focused solutions. We survey more than 15 of these solutions. On the basis of this survey, we then define a framework for NPR systems that distinguishes them from systems focused on photorealism. We also identify the characteristics of NPR systems that go beyond the tendency to simulate traditional media, functioning instead as 3D renderers. In this context, we briefly describe Schofield's system, called Piranesi, which operates this way View full abstract»

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  • Aesthetic considerations unique to interactive multimedia

    Page(s): 24 - 28
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    Using early multimedia art pieces often resembled reading paragraphs ripped out of Shakespeare and handed to you at random. The mistakes in plot and composition made by beginning writers and artists can find new power to convey incoherence when automated by a computer. What are the compositional issues? How about basic hypermedia structures and their aesthetic effects? What should be random, and what must be deterministic, if you wish to be more artist than noise generator? We address some of the issues based on our own experience as multimedia artists View full abstract»

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IEEE Computer Graphics and Applications bridges the theory and practice of computer graphics.

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Meet Our Editors

Editor-in-Chief
L. Miguel Encarnação
University of Iowa