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The back-buffer algorithm: An extension of the radiosity method to dynamic environments

The Visual computer 1986年第5期2卷 298-306页

作者： Baum, Daniel R. Wallace, John R. Cohen, Michael F. Greenberg, Donald P. Cornell University Program of Computer Graphics Cornell University Ithaca 14853 NY 120 Rand Hall United States

An efficient algorithm is introduced for the production of realistic image sequences of dynamic environments. The practicality of the radiosity method, which computes the interreflection of light within complex diffuse environments independent of viewpoint, is extended to dynamic environments where the paths of moving objects have been predefined. The algorithm takes advantage of the object coherence between static portions of an environment. A preprocessing stage executes once for a given image sequence and precalculates constant geometrical relationships in the environment. When the environment geometry changes, an update stage determines the global illumination using information provided by the preprocessor and the current positions of all moving objects. Test environments show speedups of at least twenty-five times over previous radiosity methods. © 1986 Springer-Verlag.

关键词： computer animation Light reflectance models Radiosity

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Rendering Discrete Random Media Using Precomputed Scattering Solutions

Rendering Discrete Random Media Using Precomputed Scattering...

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18th Eurographics Symposium on Rendering Techniques, EGSR 2007

作者： Moon, Jonathan T. Walter, Bruce Marschner, Stephen R. Department of Computer Science Program of Computer Graphics Cornell University Germany

ISBN: (纸本)9783905673524

This paper addresses light transport through a discrete random medium, which we define as a volume filled with macroscopic scattering geometry generated by a random process. This formulation is more general than standard radiative transport, because it can be applied to media that are made up of closely packed scatterers. A new approach to rendering these media is introduced, based on precomputed solutions to a local multiple scattering problem, including a new algorithm for generating paths through random media that moves through the interior of the medium in large strides without considering individual scattering events. A method for rendering homogeneous isotropic random media is described that generates paths using precomputed scattering solutions compressed and randomly sampled using Nonnegative Matrix Factorization. It can efficiently render discrete media, such as a large pile of glass objects, in which the individual scatterers are visible. The method is demonstrated on scenes containing tens of thousands of transparent, specular objects that are nearly impossible to render with standard global illumination techniques. © The Eurographics Association 2007.

关键词： Piles

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An experimental study of the correlation between surface roughness and light scattering for rough metallic surfaces

An experimental study of the correlation between surface rou...

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Advanced Characterization Techniques for Optics, Semiconductors, and Nanotechnologies II

作者： Li, Hongsong Torrance, Kenneth E. Program of Computer Graphics Rhodes Hall Cornell University Ithaca NY 14853

We present an experimental study of the angular distribution of light scattered from several rough metallic surfaces, which cover a range of roughness conditions. The substrate materials are steel or glass;roughened by bead-blasting, grinding, or etching;and aluminum-coated. The measured surface-roughness statistics are filtered by using a composite roughness model. The raw mechanical roughnesses range from 0.21/μm to 2.66/ μum;the high-frequency small-scale roughnesses range from 0.13/μm to 0.86μm. The optical wavelength is 550nm, so that the roughness-to-wavelength ratio is of order one. A BRDF model based on the Kirchhoff approximation is used to establish a relationship between surface-height statistics and the angular distribution of the scattered light. Angular distributions calculated with the BRDF model are fit to the measurements. The best-fit roughness statistics from the BRDF model agree closely with those measured for the high-frequency small-scale roughness component. The latter roughness component, which has the highest surface slopes, is thus the primary contributor to the angular distribution of the reflected light. We show that the Kirchhoff approximation can be applied to rough metallic surfaces that have multiple scales of roughness and near-, but not perfect, Gaussian surface-height distributions.

关键词： Metallic compounds

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Parallel processing techniques for hidden surface removal 79

Parallel processing techniques for hidden surface removal

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6th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1979

作者： Kaplan, Michael Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897910044

Previous work in the hidden-surface problem has revealed two key concepts. First, the removal of nonvisible surfaces is essentially a sorting problem. Second, some form of coherence is essential for the efficient solution of this problem. In order to provide real-time simulations, it is not only the amount of sorting which must be reduced, but the total time required for computation. One potentially economic strategy to attain this goal is the use of parallel processor systems. This approach implies that the computational time will no longer be dependent on the total amount of sorting, but more on the appropriate division of responsibility. This paper investigates two existing algorithmic approaches to the hidden-surface problem with a view towards their applicability to implementation on a parallel machine organization. In particular, the statistical results of a parallel processor implementation indicate the difficulties stemming from a loss of coherence and imply potentially important design criteria for a parallel configuration. © 1979 ACM.

关键词： Parallel processing systems

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Functional Difference Predictors (FDPs): Measuring meaningful image differences

Functional Difference Predictors (FDPs): Measuring meaningfu...

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Conference Record of the Thirty-Seventh Asilomar Conference on Signals, Systems and computers

作者： Ferwerda, James A. Pellacini, Fabio Program of Computer Graphics Cornell University Pixar Animation Studios Emeryville CA

In this paper we introduce Functional Difference Predictors (FDPs), a new class of perceptually-based image difference metrics that predict how image errors affect the ability to perform visual tasks using the images. To define the properties of FDPs, we conduct a psychophysical experiment that focuses on two visual tasks: spatial layout and material estimation. In the experiment we introduce errors in the positions and contrasts of objects reflected in glossy surfaces and ask subjects to make layout and material judgments. The results indicate that layout estimation depends only on positional errors in the reflections and material estimation depends only on contrast errors. These results suggest that in many task contexts, large visible image errors may be tolerated without loss in task performance, and that FDPs may be better predictors of the relationship between errors and performance than current Visible Difference Predictors (VDPs).

关键词： computer graphics

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Coping with friction for non-penetrating rigid body simulation 91

Coping with friction for non-penetrating rigid body simulati...

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18th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1991

作者： Baraff, David Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)0897914368

Algorithms and computational complexity measures for simulating the motion of contacting bodies with friction are presented. The bodies are restricted to be perfectly rigid bodies that contact at finitely many points. Contact forces between bodies must satisfy the Coulomb model of friction. A traditional principle of mechanics is that contact forces are impulsive if and only if non-impulsive contact forces are insufficient to maintain the non-penetration constraints between bodies. When friction is allowed, it is known that impulsive contact forces can be necessary even in the absence of collisions between bodies. This paper shows that computing contact forces according to this traditional principle is likely to require exponential time. An analysis of this result reveals that the principle for when impulses can occur is too restrictive, and a natural reformulation of the principle is proposed. Using the reformulated principle, an algorithm with expected polynomial time behavior for computing contact forces is presented. © 1991 ACM.

关键词： Friction

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A visible polygon reconstruction algorithm 81

A visible polygon reconstruction algorithm

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8th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1981

作者： Sechrest, Stuart Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY11853 United States

ISBN: (纸本)0897910451

An algorithm for determining visible lines or visible surfaces in polygonal form, at object resolution, is presented. The original scene must consist of non-intersecting planar polygons. The procedure relies on image coherence, since the sampling is dependent on the complexity of the image. The reconstruction method is based on an elaborate data structure, which allows the polygonal output to be easily obtained. The polygonal output is useful for smooth shaded or textured images, as well as the for creation of shadows. © 1981 ACM.

关键词： Interactive computer graphics

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Automated three-axis gonioreflectometer for computer graphics applications

Automated three-axis gonioreflectometer for computer graphic...

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Advanced Characterization Techniques for Optics, Semiconductors, and Nanotechnologies II

作者： Li, Hongsong Foo, Sing Choong Torrance, Kenneth E. Westin, Stephen H. Program of Computer Graphics Rhodes Hall Cornell University Ithaca NY 14853

We describe an automated three-axis BRDF measurement instrument that can help increase the physical realism of computer graphics images by providing light scattering data for the surfaces within a synthetic scene that is to be rendered. To our knowledge, the instrument is unique in combining wide angular coverage (beyond 85° from the surface normal), dense sampling of the visible wavelength spectrum (1024 samples), and rapid operation (less than ten hours for complete measurement of an isotropic sample). The gonioreflectometer employs a broadband light source and a detector with a diffraction grating and linear diode array. Validation was achieved by comparisons against reference surfaces and other instruments. The accuracy and spectral and angular ranges of the BRDFs are appropriate for computer graphics imagery, while reciprocity and energy conservation are preserved. Measured BRDFs on rough aluminum, metallic silver automotive paint, and a glossy yellow paint are reported, and an example rendered automotive image is included.

关键词： Reflectometers

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Hidden surface removal using polygon area sorting 77

Hidden surface removal using polygon area sorting

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4th Annual Conference on computer graphics and Interactive Techniques, SIGGRAPH 1977

作者： Weiler, Kevin Atherton, Peter Program of Computer Graphics Cornell University IthacaNY14853 United States

ISBN: (纸本)9781450373555

A polygon hidden surface and hidden line removal algorithm is presented. The algorithm recursively subdivides the image into polygon shaped windows until the depth order within the window is found. Accuracy of the input data is preserved. The approach is based on a two-dimensional polygon clipper which is sufficiently general to clip a concave polygon with holes to the borders of a concave polygon with holes. A major advantage of the algorithm is that the polygon form of the output is the same as the polygon form of the input. This allows entering previously calculated images to the system for further processing. Shadow casting may then be performed by first producing a hidden surface removed view from the vantage point of the light source and then resubmitting these tagged polygons for hidden surface removal from the position of the observer. Planar surface detail also becomes easy to represent without increasing the complexity of the hidden surface problem. Translucency is also possible. Calculation times are primarily related to the visible complexity of the final image, but can range from a linear to an exponential relationship with the number of input polygons depending on the particular environment portrayed. To avoid excessive computation time, the implementation uses a screen area subdivision preprocessor to create several windows, each containing a specified number of polygons. The hidden surface algorithm is applied to each of these windows separately. This technique avoids the difficulties of subdividing by screen area down to the screen resolution level while maintaining the advantages of the polygon area sort method.

关键词： Sorting

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An exploration of three dimensional computer graphics in cockpit avionics

An exploration of three dimensional computer graphics in coc...

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Electroluminescent Materials, Devices, and Large-Screen Displays 1993

作者： Pruyn, Peter W. Greenberg, Donald P. Program of Computer Graphics Cornell University IthacaNY14853 United States

There has been a trend during the 1980s in commercial airliner cockpits of replacing many of the round-faced, analog instruments with CRT displays. However, the computer graphics technology that is utilized in these CRT displays is more than ten years old and frequently simply mimics the appearance of the older, analog displays. We will explore some of the possible uses of state of the art, three dimensional computer graphics as an integrator and as a visualizer of flight information. Using computer models of primary navigational features and the ray-Tracing rendering technique, three-dimensional, symbolic representations of flight information are explored. Right tasks investigated include enroute navigation, collision avoidance, weather, and the instrument approach. © 1993 SPIE. All rights reserved.

关键词： Three dimensional computer graphics

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