The visual appearance of many materials is created by micro-scale details of their surface geometry. In this article, we investigate a new approach to capturing the appearance of metal surfaces without reflectance measurements, by deriving microfacet distributions directly from measured surface topography. Modern profilometers are capable of measuring surfaces with subwavelength resolution at increasingly rapid rates. We consider both wave- and geometric-optics methods for predicting BRDFs of measured surfaces and compare the results to optical measurements from a gonioreflectometer for five rough metal samples. Surface measurements are also used to predict spatial variation, or texture, which is especially important for the appearance of our anisotropic brushed metal samples. Profilometer-based BRDF acquisition offers many potential advantages over traditional techniques, including speed and easy handling of anisotropic, highly directional materials. We also introduce a new generalized normal distribution function, the ellipsoidal NDF, to compactly represent nonsymmetric features in our measured data and texture synthesis.

Simulating a complex luminaire such as a chandelier is expensive and slow, even using state-of-the-art algorithms. A more practical alternative is to use precomputation to accelerate rendering. Prior approaches cached information on an aperture surface that separates the luminaire from the scene, but many luminaires have large or ill-defined apertures leading to excessive data storage and inaccurate results. In this article, we separate luminaire rendering into illumination and appearance components. A precomputation stage simulates the complex light flow inside the luminaire to generate two data structures: a set of anisotropic point lights (APLs) and a radiance volume. The APLs are located near apparent sources and represent the light leaving the luminaire, allowing its nearand far-field illumination to be accurately and efficiently computed at render time. The luminaire's appearance consists of high- and low-frequency components, which are both visually important. High-frequency components are computed dynamically at render time, while the more computationally expensive low-frequency components are approximated using the precomputed radiance volume. Results are shown for several complex luminaires, demonstrating orders of magnitude faster rendering compared to the best global illumination algorithms and higher fidelity with greatly reduced storage requirements compared to previous precomputed approaches.

The illumination and appearance of the solar/skydome is critical for many applications in computer graphics, computer vision, and daylighting studies. Unfortunately, physically accurate measurements of this rapidly changing illumination source are difficult to achieve, but necessary for the development of accurate physically-based sky illumination models and comparison studies of existing simulation models. To obtain baseline data of this time-dependent anisotropic light source, we design a novel acquisition setup to simultaneously measure the comprehensive illumination properties. Our hardware design simultaneously acquires its spectral, spatial, and temporal information of the skydome. To achieve this goal, we use a custom built spectral radiance measurement scanner to measure the directional spectral radiance, a pyranometer to measure the irradiance of the entire hemisphere, and a camera to capture high-dynamic range imagery of the sky. The combination of these computer-controlled measurement devices provides a fast way to acquire accurate physical measurements of the solar/skydome. We use the results of our measurements to evaluate many of the strengths and weaknesses of several sun-sky simulation models. We also provide a measurement dataset of sky illumination data for various clear sky conditions and an interactive visualization tool for model comparison analysis available at http://www.graphics.cornell.edu/resources/clearsky/.

Multidimensional lightcuts is a new scalable method for efficiently rendering rich visual effects such as motion blur, participating media, depth of field, and spatial anti-aliasing in complex scenes. It introduces a flexible, general rendering framework that unifies the handling of such effects by discretizing the integrals into large sets of gather and light points and adaptively approximating the sum of all possible gather-light pair interactions.We create an implicit hierarchy, the product graph, over the gather-light pairs to rapidly and accurately approximate the contribution from hundreds of millions of pairs per pixel while only evaluating a tiny fraction (e.g., 200--1,000). We build upon the techniques of the prior Lightcuts method for complex illumination at a point, however, by considering the complete pixel integrals, we achieve much greater efficiency and scalability.Our example results demonstrate efficient handling of volume scattering, camera focus, and motion of lights, cameras, and geometry. For example, enabling high quality motion blur with 256x temporal sampling requires only a 6.7x increase in shading cost in a scene with complex moving geometry, materials, and illumination.

This paper introduces a new multipass algorithm for efficiently computing direct illumination in scenes with many lights and complex occlusion. Images are first divided into 8 x 8 pixel blocks and for each point to be shaded within a block, a probability density function (PDF) is constructed over the lights and sampled to estimate illumination using a small number of shadow rays. Information from these samples is then aggregated at both the pixel and block level and used to optimize the PDFs for the next pass. Over multiple passes the PDFs and pixel estimates are updated until convergence. Using aggregation and feedback progressively improves the sampling and automatically exploits both visibility and spatial coherence. We also use novel extensions for efficient antialiasing. Our adaptive multipass approach computes accurate direct illumination eight times faster than prior approaches in tests on several complex scenes.

Lightcuts is a scalable framework for computing realistic illumination. It handles arbitrary geometry, non-diffuse materials, and illumination from a wide variety of sources including point lights, area lights, HDR environment maps, sun/sky models, and indirect illumination. At its core is a new algorithm for accurately approximating illumination from many point lights with a strongly sublinear cost. We show how a group of lights can be cheaply approximated while bounding the maximum approximation error. A binary light tree and perceptual metric are then used to adaptively partition the lights into groups to control the error vs. cost tradeoff.We also introduce reconstruction cuts that exploit spatial coherence to accelerate the generation of anti-aliased images with complex illumination. Results are demonstrated for five complex scenes and show that lightcuts can accurately approximate hundreds of thousands of point lights using only a few hundred shadow rays. Reconstruction cuts can reduce the number of shadow rays to tens.

In this paper we introduce a new perceptual metric for efficient, high quality, global illumination rendering. The metric is based on a rendering-by-components framework in which the direct, and indirect diffuse, glossy, and specular light transport paths are separately computed and then composited to produce an image. The metric predicts the perceptual importances of the computationally expensive indirect illumination components with respect to image quality. To develop the metric we conducted a series of psychophysical experiments in which we measured and modeled the perceptual importances of the components. An important property of this new metric is that it predicts component importances from inexpensive estimates of the reflectance properties of a scene, and therefore adds negligible overhead to the rendering process. This perceptual metric should enable the development of an important new class of efficient global-illumination rendering systems that can intelligently allocate limited computational resources, to provide high quality images at interactive rates.

Image-based modeling techniques permit the creation of visually interesting geometric models from photographs. But traditional image-based texturing (IBT) techniques often result in extracted textures of poor, uneven quality. This paper introduces a novel technique to improve the quality of image-based textures. We compute a simple and efficient texture quality metric based on the Jacobian of the imaging transform. We identify the correlation between the values of the Jacobian metric and the levels of an image pyramid, allowing us to formulate a novel texture synthesis approach which operates over textures from 3D surfaces in a scene. Our technique allows the creation of uniform, high-resolution textures, relieving the user of the burden of collecting large numbers of images while increasing the visual quality of image-based models. This improved quality is important to create compelling visual experiences in interactive environments.

This paper presents a new interactive rendering and display technique for complex scenes with expensive shading, such as global illumination. Our approach combines sparsely sampled shading (points) and analytically computed discontinuities (edges) to interactively generate high-quality images. The edge-and-point image is a new compact representation that combines edges and points such that fast, table-driven interpolation of pixel shading from nearby point samples is possible, while respecting discontinuities.The edge-and-point renderer is extensible, permitting the use of arbitrary shaders to collect shading samples. Shading discontinuities, such as silhouettes and shadow edges, are found at interactive rates. Our software implementation supports interactive navigation and object manipulation in scenes that include expensive lighting effects (such as global illumination) and geometrically complex objects. For interactive rendering we show that high-quality images of these scenes can be rendered at 8--14 frames per second on a desktop PC: a speedup of 20--60 over a ray tracer computing a single sample per pixel.

Texture mapping has become indispensable in image synthesis as an inexpensive source of rich visual detail. Less obvious, but just as useful, is its ability to mask image errors due to inaccuracies in geometry or lighting. This ability can be used to substantially accelerate rendering by eliminating computations when the resulting errors will be perceptually insignificant. Our new method precomputes the masking ability of textures using aspects of the JPEG image compression standard. This extra information is stored as threshold elevation factors in the texture's mip-map and interpolated at image generation time as part of the normal texture lookup process. Any algorithm which uses error tolerances or visibility thresholds can then take advantage of texture masking. Applications to adaptive shadow testing, irradiance caching, and path tracing are demonstrated. Unlike prior methods, our approach does not require that initial images be computed before masking can be exploited and incurs only negligible runtime computational overhead. Thus, it is much easier to integrate with existing rendering systems for both static and dynamic scenes and yields computational savings even when only small amounts of texture masking are present. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Color, shading, shadowing, and texture

Placing shadows is difficult task since shadows depend on the relative positions of lights and objects in an unintuitive manner. To simplify the task of the modeler, we present a user interface for designing shadows in 3d environments. In our interface, shadows are treated as first-class modeling primitives just like objects and lights. To transform a shadow, the user can simply move, rescale or rotate the shadow as if it was a 2d object on the scene's surfaces.When the user transforms a shadow, the system moves lights or objects in the scene as required and updates the shadows in realtime during mouse movement. To facilitate interaction, the user can also specify constraints that the shadows must obey, such as never casting a shadow on the face of a character. These constraints are then verified in real-time, limiting mouse movement when necessary. We also integrate in our interface fake shadows typically used in computer animation. This allows the user to draw shadowed and non-shadowed regions directly on surfaces in the scene.

In this paper, we present a system for interactive computation of global illumination in dynamic scenes. Our system uses a novel scheme for caching the results of a high quality pixel-based renderer such as a bidirectional path tracer. The Shading Cache is an object-space hierarchical subdivision mesh with lazily computed shading values at its vertices. A high frame rate display is generated from the Shading Cache using hardware-based interpolation and texture mapping. An image space sampling scheme refines the Shading Cache in regions that have the most interpolation error or those that are most likely to be affected by object or camera motion.Our system handles dynamic scenes and moving light sources efficiently, providing useful feedback within a few seconds and high quality images within a few tens of seconds, without the need for any pre-computation. Our approach allows us to significantly outperform other interactive systems based on caching ray-tracing samples, especially in dynamic scenes. Based on our results, we believe that the Shading Cache will be an invaluable tool in lighting design and modelling while rendering.

Shadow maps provide a fast and convenient method of identifying shadows in scenes but can introduce aliasing. This paper introduces the Adaptive Shadow Map (ASM) as a solution to this problem. An ASM removes aliasing by resolving pixel size mismatches between the eye view and the light source view. It achieves this goal by storing the light source view (i.e., the shadow map for the light source) as a hierarchical grid structure as opposed to the conventional flat structure. As pixels are transformed from the eye view to the light source view, the ASM is refined to create higher-resolution pieces of the shadow map when needed. This is done by evaluating the contributions of shadow map pixels to the overall image quality. The improvement process is view-driven, progressive, and confined to a user-specifiable memory footprint. We show that ASMs enable dramatic improvements in shadow quality while maintaining interactive rates.

We present a method to accelerate global illumination computation in prerendered animations by taking advantage of limitations of the human visual system. A spatiotemporal error tolerance map, constructed from psychophysical data based on velocity dependent contrast sensitivity, is used to accelerate rendering. The error map is augmented by a model of visual attention in order to account for the tracking behavior of the eye. Perceptual acceleration combined with good sampling protocols provide a global illumination solution feasible for use in animation. Results indicate an order of magnitude improvement in computational speed.

Human vision takes time to adapt to large changes in scene intensity, and these transient adjustments have a profound effect on visual appearance. This paper offers a new operator to include these appearance changes in animations or interactive real-time simulations, and to match a user's visual responses to those the user would experience in a real-world scene.

In this paper we introduce a new light reflection model for image synthesis based on experimental studies of surface gloss perception. To develop the model, we've conducted two experiments that explore the relationships between the physical parameters used to describe the reflectance properties of glossy surfaces and the perceptual dimensions of glossy appearance. In the first experiment we use multidimensional scaling techniques to reveal the dimensionality of gloss perception for simulated painted surfaces. In the second experiment we use magnitude estimation methods to place metrics on these dimensions that relate changes in apparent gloss to variations in surface reflectance properties. We use the results of these experiments to rewrite the parameters of a physically-based light reflection model in perceptual terms. The result is a new psychophysically-based light reflection model where the dimensions of the model are perceptually meaningful, and variations along the dimensions are perceptually uniform. We demonstrate that the model can facilitate describing surface gloss in graphics rendering applications. This work represents a new methodology for developing light reflection models for image synthesis.

In this paper we present a technique for computing the direct lighting in a three-dimensional scene containing area light sources.Our method correctly handles partial visibility between luminaires and receivers, and is able to efficiently generate accurate soft shadows in scenes modeled with general bidirectional reflectance distribution functions.In most current algorithms, the form factor between a light source and receiver is computed using a stochastic ray casting approach which evaluates partial visibility.Such an approach often leads to noisy artifacts or aliasing problems.Generating significantly more rays is often the only solution to improving image quality.Our approach first stores visibility information in the image plane, using lazy evaluation of the visibility function.In a second phase, illumination values for each pixel are generated, using analytic or stochastic integration.Soft shadows and other shading effects are generated with high accuracy in less time than with existing shading algorithms.Coherence in specific blockerlight source relationships across the image plane is exploited to amortize the cost of analytic form factor calculations.By storing information in the image plane, our method is currently designed for generating a single image, and is thus view-dependent.

We introduce a new concept for accelerating realistic image synthesis algorithms. At the core of this procedure is a novel physical error metric that correctly predicts the perceptual threshold for detecting artifacts in scene features. Built into this metric is a computational model of the human visual system's loss of sensitivity at high background illumination levels, high spatial frequencies, and high contrast levels (visual masking). An important feature of our model is that it handles the luminance-dependent processing and spatiallydependent processing independently. This allows us to precompute the expensive spatially-dependent component, making our model extremely efficient. We illustrate the utility of our procedure with global illumination algorithms used for realistic image synthesis. The expense of global illumination computations is many orders of magnitude higher than the expense of direct illumination computations and can greatly benefit by applying our perceptually based technique. Results show our method preserves visual quality while achieving significant computational gains in areas of images with high frequency texture patterns, geometric details, and lighting variations.

In this paper we develop a computational model of adaptation and spatial vision for realistic tone reproduction. The model is based on a multiscale representation of pattern, luminance, and color processing in the human visual system. We incorporate the model into a tone reproduction operator that maps the vast ranges of radiances found in real and synthetic scenes into the small fixed ranges available on conventional display devices such as CRT's and printers. The model allows the operator to address the two major problems in realistic tone reproduction: wide absolute range and high dynamic range scenes can be displayed; and the displayed images match our perceptions of the scenes at both threshold and suprathreshold levels to the degree possible given a particular display device. Although in this paper we apply our visual model to the tone reproduction problem, the model is general and can be usefully applied to image quality metrics, image compression methods, and perceptually-based...

In this paper we develop a computational model of visual masking based on psychophysical data.The model predicts how the presence of one visual pattern affects the detectability of another.The model allows us to choose texture patterns for computer graphics images that hide the effects of faceting, banding, aliasing, noise and other visual artifacts produced by sources of error in graphics algorithms.We demonstrate the utility of the model by choosing a texture pattern to mask faceting artifacts caused by polygonal tesselation of a flat-shaded curved surface.The model predicts how changes in the contrast, spatial frequency, and orientation of the texture pattern, or changes in the tesselation of the surface will alter the masking effect.The model is general and has uses in geometric modeling, realistic image synthesis, scientific visualization, image compression, and image-based rendering.

Our goal is to develop physically based lighting models and perceptually based rendering procedures for computer graphics that will produce synthetic images that are visually and measurably indistinguishable from real-world images. Fidelity of the physical simulation is of primary concern. Our research framework is subdivided into three sub-sections: the local light reflection model, the energy transport simulation, and the visual display algorithms. The first two subsections are physically based, and the last is perceptually based. We emphasize the comparisons between simulations and actual measurements, the difficulties encountered, and the need to utilize the vast amount of psychophysical research already conducted. Future research directions are enumerated. We hope that results of this research will help establish a more fundamental, scientific approach for future rendering algorithms. This presentation describes a chronology of past research in global illumination and how parts of our new system are currently being developed.

We introduce a new class of primitive functions with non-linear parameters for representing light reflectance functions.The functions are reciprocal, energy-conserving and expressive.They can capture important phenomena such as off-specular reflection, increasing reflectance and retro-reflection.We demonstrate this by fitting sums of primitive functions to a physically-based model and to actual measurements.The resulting representation is simple, compact and uniform.It can be applied efficiently in analytical and Monte Carlo computations.

This paper describes a technique for using a simple shading method, such as the Phong lighting model, to approximate the appearance calculated by a more accurate method.The results are then suitable for rapid display using existing graphics hardware and portable via standard graphics API's.Interactive walkthroughs of view-independent nondiffuse global illumination solutions are explored as the motivating application.

This article presents the density estimation framework for generating view-independent global illumination solutions. It works by probabilistically simulating the light flow in an environment with light particles that trace random walks origination at luminaires and then using statistical density estimation techniques to reconstruct the lighting on each surface. By splitting the computation into separate transport and reconstruction stages, we gain many advantages including reduced memory usage, the ability to simulate nondiffuse transport, and natural parallelism. Solutions to several theoretical and practical difficulties in implementing this framework are also described. Light sources that vary spectrally and directionally are integrated into a spectral particle tracer using nonuniform rejection. A new local linear density estimation technique eliminates boundary bias and extends to arbitrary polygons. A mesh decimation algorithm with perceptual calibration is introduced to simplify the Gouraud-shaded representation of the solution for interactive display.

In this paper we develop a computational model of visual adaptation for realistic image synthesis based on psychophysical experiments. The model captures the changes in threshold visibility, color appearance, visual acuity, and sensitivity over time that are caused by the visual system's adaptation mechanisms. We use the model to display the results of global illumination simulations illuminated at intensities ranging from daylight down to starlight. The resulting images better capture the visual characteristics of scenes viewed over a wide range of illumination levels. Because the model is based on psychophysical data it can be used to predict the visibility and appearance of scene features. This allows the model to be used as the basis of perceptually-based error metrics for limiting the precision of global illumination computations. CR Categories and Subject Descriptors: I.3.0 [Computer Graphics]: General; I.3.6 [Computer Graphics]: Methodology and Techniques. Additional Key Words...

Intravascular ultrasonography and x-ray angiography provide two complimentary techniques for imaging the moving coronary arteries. We present a technique that combines the strengths of both, by recovering the moving threedimensional arterial tree from a stereo pair of angiograms through the use of compound-energy “snakes”, placing the intravascular ultrasound slices at their proper positions in time and space, and dynamically displaying the combined data. Past techniques have assumed that the ultrasound slices are parallel and that the vessel being imaged is straight. For the first time, by applying simple but effective techniques from computer graphics, the moving geometry of the artery from the angiogram and the time-dependent images of the interior of the vessel wall from the intravascular ultrasound can be viewed simultaneously, showing the proper geometric and temporal relations of the slice data and the angiogram projections. By using texture-mapped rectangles the combined ultrasound slice/angiogram display technique is well suited to run in real time on current graphics workstations. CR

The physical mechanisms and physiological causes of glare in human vision are reviewed. These mechanisms are scattering in the cornea, lens, and retina, and di#raction in the coherent cell structures on the outer radial areas of the lens. This scattering and di#raction are responsible for the "bloom" and "flare lines" seen around very bright objects. The di#raction e#ects cause the "lenticular halo". The quantitative models of these glare e#ects are reviewed, and an algorithm for using these models to add glare e#ects to digital images is presented. The resulting digital point-spread function is thus psychophysically based and can substantially increase the "perceived" dynamic range of computer simulations containing light sources. Finally, a perceptual test is presented that indicates these added glare e#ects increase the apparent brightness of light sources in digital images. CR Categories and Subject Descriptors: I.3.0 [Computer Graphics]: General; I.3.6 [Computer Graphics]: Method...

We present a method for determining a posteriori bounds and estimates for local and total errors in radiosity solutions. The ability to obtain bounds and estimates for the total error is crucial for reliably judging the acceptability of a solution. Realistic estimates of the local error improve the efficiency of adaptive radiosity algorithms, such as hierarchical radiosity, by indicating where adaptive refinement is necessary. First, we describe a hierarchical radiosity algorithm that computes conservative lower and upper bounds on the exact radiosity function, as well as on the approximate solution. These bounds account for the propagation of errors due to interreflections, and provide a conservative upper bound on the error. We also describe a non-conservative version of the same algorithm that is capable of computing tighter bounds, from which more realistic error estimates can be obtained. Finally, we derive an expression for the effect of a particular interaction on the total erro...

We present an approach for accelerating hierarchical radiosity by clustering objects. Previous approaches constructed effective hierarchies by subdividing surfaces, but could not exploit a hierarchical grouping on existing surfaces. This limitation resulted in an excessive number of initial links in complex environments. Initial linking is potentially the most expensive portion of hierarchical radiosity algorithms, and constrains the complexity of the environments that can be simulated. The clustering algorithm presented here operates by estimating energy transfer between collections of objects while maintaining reliable error bounds on each transfer. Two methods of bounding the transfers are employed with different tradeoffs between accuracy and time. In contrast with the O(s2) time and space complexity of the initial linking in previous hierarchical radiosity algorithms, the new methods have complexities of O(slogs) and O(s) for both time and space. Using these methods we have obtained speedups of two orders of magnitude for environments of moderate complexity while maintaining comparable accuracy.

We introduce a new approach for the computation of viewindependent solutions to the diffuse global illumination problem in polyhedral environments. The approach combines ideas from hierarchical radiosity and discontinuity meshing to yield solutions that are accurate both numerically and visually. First, we describe a modified hierarchical radiosity algorithm that uses a discontinuitydriven subdivision strategy to achieve better numerical accuracyand faster convergence. Second, we present a new algorithm based on discontinuity meshing that uses the hierarchical solution to reconstruct an object-space approximation to the radiance function that is visually accurate. Our results show significant improvements over both hierarchical radiosity and discontinuity meshing algorithms. CR Categories and Subject Descriptors: I.3.3---[Computer Graphics]: Picture/Image Generation; I.3.7---[Computer Graphics ]: Three-Dimensional Graphics and Realism. Additional Key Words and Phrases: diffuse refle...

Article Painting with light Share on Authors: Chris Schoeneman View Profile , Julie Dorsey View Profile , Brian Smits View Profile , James Arvo View Profile , Donald Greenberg View Profile Authors Info & Claims SIGGRAPH '93: Proceedings of the 20th annual conference on Computer graphics and interactive techniquesSeptember 1993 Pages 143–146https://doi.org/10.1145/166117.166135Online:01 September 1993Publication History 98citation1,320DownloadsMetricsTotal Citations98Total Downloads1,320Last 12 Months47Last 6 weeks2 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteGet Access

No abstract available.

This paper describes the philosophy and implementation of a modeling system that is easy to use yet addresses some of the difficulties of design. It does this by supporting concurrent schematic and geometric representations, alternative solution schemes, ambiguous and incomplete specification, and multiple levels of detail through a wide range of scale. The system treats an object as a hierarchical record of design decisions and treats geometry as an artifact of traversing a decision tree. For displaying geometry, the system incorporates fast rendering techniques for interactive use and global illumination algorithms for design evaluation and final presentation. The system is intended to serve as an extensible testbed for long-term research in modeling and design. Vigorous use by students in the Department of Architecture at Cornell is the vehicle for system evaluation and redirection of research goals.

Image Synthesis research combines new ideas with existing techniques. A collection of software modules that provide such techniques is extremely useful for simplifying the development process. We describe the design and implementation of a new Testbed for Image Synthesis that provides such support. This Testbed differs from previous Testbeds in both its goals and its design decisions. The Testbed design addresses the problems of high model complexity, complicated global illumination algorithms and coarse grain parallel processing environments. The implementation is modular, portable and extensible. It allows for statistical comparison of algorithms and measurement of incremental image improvements, as well as quantitative comparison of Testbed images and light reflectance measured from physical models. The Testbed is designed to interface with any available modeling system. This compatibility was achieved through careful design of the data format that represents environments. The software modules of the Testbed are organized in a hierarchical fashion, simplifying application programming.

A major problem challenging opera designers is the inability to co-ordinate lighting, projection systems, and set designs in the preliminary planning phase. New computer graphics techniques, which provide the set and lighting designer the opportunity to evaluate, test, and control opera designs prior to the construction of full scale systems are presented. These techniques---light source input, simulation of directional lighting, modeling of scenic projection systems, and full three-dimensional simulation---show the potential for the use of computer graphics in theater design.The light source input component consists of a program for assigning light source attributes with a set of theater lighting icons. This module allows a designer to specify light source characteristics in a way familiar to the discipline and to make preliminary evaluations of the lighting conditions.An extended progressive radiosity method is introduced to simulate the directional lighting characteristics which are specified by the input program.A new projection approach is presented to simulate the optical effects of scenic projectors. In addition, a solution to the distortion problem produced by angular projections is described.The above components are integrated to produce full three-dimensional simulations of the global illumination effects in an opera scene.

A new general reflectance model for computer graphics is presented. The model is based on physical optics and describes specular, directional diffuse, and uniform diffuse reflection by a surface. The reflected light pattern depends on wavelength, incidence angle, two surface roughness parameters, and surface refractive index. The formulation is self consistent in terms of polarization, surface roughness, masking/shadowing, and energy. The model applies to a wide range of materials and surface finishes and provides a smooth transition from diffuse-like to specular reflection as the wavelength and incidence angle are increased or the surface roughness is decreased. The model is analytic and suitable for Computer Graphics applications. Predicted reflectance distributions compare favorably with experiment. The model is applied to metallic, nonmetallic, and plastic materials, with smooth and rough surfaces.

A general light transfer simulation algorithm for environments composed of materials with arbitrary reflectance functions is presented. This algorithm removes the previous practical restriction to ideal specular and/or ideal diffuse environments, and supports complex physically based reflectance distributions, This is accomplished by extending previous two-pass ray-casting radiosity approaches to handle non-uniform intensity distributions, and resolving all possible energy transfers between sample points. An implementation is described based on a spherical harmonic decomposition for encoding both bidirectional reflectance distribution functions for materials, and directional intensity distributions for illuminated surfaces. The method compares favorably with experimental measurements.

The progressive refinement radiosity method provides a means for computing the global illumination of an environment in time proportional to the size of the environment. Additionally, the method supplies a sequence of solutions that monotonically converge to a high-quality result, allowing it to be used for interactive applications that deliver "near real-time" updates as the computation proceeds. This paper presents two methods for accelerating the radiosity method. First, the traditional hemi-cube algorithm is modified to accelerate the expensive form-factor calculation. Second, the radiosity method is parallelized across a coarse-grain network, and the efficiency of the parallel system is discussed.

We present a real-time robot motion planner that is fast and complete to a resolution. The technique is guaranteed to find a path if one exists at the resolution, and all paths returned are safe. The planner can handle any polyhedral geometry of robot and obstacles, including disjoint and highly concave unions of polyhedra.The planner uses standard graphics hardware to rasterize configuration space obstacles into a series of bitmap slices, and then uses dynamic programming to create a navigation function (a discrete vector-valued function) and to calculate paths in this rasterized space. The motion paths which the planner produces are minimal with respect to an L1 (Manhattan) distance metric that includes rotation as well as translation.Several examples are shown illustrating the competence of the planner at generating planar rotational and translational plans for complex two and three dimensional robots. Dynamic motion sequences, including complicated and non-obvious backtracking solutions, can be executed in real time.

Computer simulations can be used to generate the spatial and temporal data describing the acoustical behavior of performance halls, but typically the analytical results are difficult to assimilate and compare. By using computer graphics to display the multi-dimensional data, substantially greater amounts of information than that conveyed by standard techniques can be communicated to the designer. This allows designs of different acoustical spaces to be tested, evaluated, and compared.An example comparing the acoustical behavior of three different concert halls demonstrates these techniques and allows for the simultaneous assimilation of much of the information necessary to evaluate the acoustical nature of a space. The use of three-dimensional images, color, animation and abstract representation allows for the comprehension of the complex results of a scientific simulation. Specifically, the simultaneous display of particular icons familiar to the discipline enabled the simultaneous presentation of up to twelve parameters.From a more general point of view, the procedures demonstrate how computer graphics can be utilized for the portrayal of multi-dimensional time dependent data. The visualization techniques are potentially useful for the display of three-dimensional vector fields in many scientific and design applications.

No abstract available.

A reformulated radiosity algorithm is presented that produces initial images in time linear to the number of patches. The enormous memory costs of the radiosity algorithm are also eliminated by computing form-factors on-the-fly. The technique is based on the approach of rendering by progressive refinement. The algorithm provides a useful solution almost immediately which progresses gracefully and continuously to the complete radiosity solution. In this way the competing demands of realism and interactivity are accommodated. The technique brings the use of radiosity for interactive rendering within reach and has implications for the use and development of current and future graphics workstations.

View-independent and view-dependent image synthesis techniques, represented by radiosity and ray tracing, respectively, are discussed. View-dependent techniques are found to have advantages for calculating the specular component of illumination and view-independent techniques for the diffuse component. Based on these observations a methodology is presented for simulating global illumination within complex environments using a two-pass approach. The first pass is view-independent and is based on the hemi-cube radiosity algorithm, with extensions to include the effects of diffuse transmission, and specular to diffuse reflection and transmission. The second pass is view-dependent and is based on an alternative to distributed ray tracing in which a z-buffer algorithm is used to sample the intensities contributing to the specularly reflected or transmitted intensity.

A general radiosity method accounting for all interreflections of light between diffuse and nondiffuse surfaces in complex environments is introduced. As contrasted with previous radiosity methods, surfaces are no longer required to be perfectly diffuse reflectors and emitters. A complete, viewer independent description of the light leaving each surface in each direction is computed, allowing dynamic sequences of images to be rendered with little additional computation per image. Phenomena such as "reflection tracking", reflections following a moving observer across a specular surface are produced. Secondary light sources, such as the light from a spotlight reflecting off a mirror onto a wall are also accounted for.

Accurate simulation of light propagation within an environment and perceptually based imaging techniques are necessary for the creation of realistic images. A physical experiment that verifies the simulation of reflected light intensities for diffuse environments was conducted. Measurements of radiant energy flux densities are compared with predictions using the radiosity method for those physical environments. By using color science procedures the results of the light model simulation are then transformed to produce a color television image. The final image compares favorably with the original physical model. The experiment indicates that, when the physical model and the simulation were viewed through a view camera, subjects could not distinguish between them. The results and comparison of both test procedures are presented within this paper.

This paper presents a comprehensive method to calculate object to object diffuse reflections within complex environments containing hidden surfaces and shadows. In essence, each object in the environment is treated as a secondary light source. The method provides an accurate representation of the "diffuse" and "ambient" terms found in typical image synthesis algorithms. The phenomena of "color bleeding" from one surface to another, shading within shadow envelopes, and penumbras along shadow boundaries are accurately reproduced. Additional advantages result because computations are indepedent of viewer position. This allows the efficient rendering of multiple views of the same scene for dynamic sequences. Light sources can be modulated and object reflectivities can be changed, with minimal extra computation. The procedures extend the radiosity method beyond the bounds previously imposed.

A method is described which models the interaction of light between diffusely reflecting surfaces. Current light reflection models used in computer graphics do not account for the object-to-object reflection between diffuse surfaces, and thus incorrectly compute the global illumination effects. The new procedure, based on methods used in thermal engineering, includes the effects of diffuse light sources of finite area, as well as the “color-bleeding” effects which are caused by the diffuse reflections. A simple environment is used to illustrate these simulated effects and is presented with photographs of a physical model. The procedure is applicable to environments composed of ideal diffuse reflectors and can account for direct illumination from a variety of light sources. The resultant surface intensities are independent of observer position, and thus environments can be preprocessed for dynamic sequences.

This paper describes algorithmic procedures that have been implemented to reduce the computational expense of producing ray-traced images.The selection of bounding volumes is examined to reduce the computational cost of the ray-intersection test.The use of object coherence, which relies on a hierarchical description of the environment, is then presented.Finally, since the building of the rayintersection trees is such a large portion of the computation, a method using image coherence is described.This visible-surface preprocessing method, which is dependent upon the creation of an "item buffer," takes advantage of a priori image information.Examples that indicate the efficiency of these techniques for a variety of representative environments are presented.

Colleges and universities are not meeting industry needs for graduates trained in the use or implementation of computer-aided design and manufacturing systems since few schools have experience in teaching CAD/CAM. Furthermore, many Bachelor's-level graduates are going directly into industry, rather than pursuing graduate degrees, thereby compounding this problem. Members of this panel represent both schools and industry and together attempt to outline approaches to developing more extensive CAD/CAM emphasis in education, including- the role colleges and universities can or should play in addressing industry needs in this area- user- and implementor-oriented CAD/CAM education- CAD/CAM education as an integral part of university engineering curricula- problems encountered in organizing and implementing CAD/CAM curriculum- universities' relationships with industry.It is our hope that panelists' experiences will help guide schools in structuring CAD/CAM programs to best insure that the United States remain at the forefront of technology and compete industrially world-wide.Frank PuhlVictor LangerDonald P. GreenbergMark S. ShepardHerb VoelckerUniversities' Relationships With IndustryFrank PuhlAmerican industry needs engineers who have been brought up with the realization that computers are intimately involved in all aspects of design, analysis, and manufacturing. Industry, of course, needs engineers who are already trained in fundamental CAD/CAM principles and in solving real world problems using computers, as well as those who have been taught to be productivity- and cost-conscious.To help meet these needs, we must now provide answers to several significant questions:What part should industry play in encouraging and sponsoring research and education in CAD/CAM?How can we resolve conflicts between industries' “trade secrets” and universities' “open research”?How can industry and educational institutions work together to increase U.S. productivity so as to regain our competitive edge?Lockheed Corporation and CADAM, Inc. are addressing these issues by supporting selected schools, installing CADAM systems, and providing fellowships for education and research at upperclass and graduate levels. In addition, we are involved in various joint research projects with universities, and we look optimistically toward continuing these projects.CADD CAM User EducationCADD CAM User EducationVictor LangerGeneral Electric Medical Systems Division in Milwaukee experienced a severe shortage of CADD CAM operators and encouraged MATC to develop a training program which started in 1980. A three-year NSF- CAUSE grant and a partial donation of a Computervision CADDS 3 (now CADD 4 Designer V six-station) system resulted in a program for upgrading employed designers and for two-year associate degree full-time students. The program enrolls 200 students per semester, with 70% continuing education students and 30% full-time students. Before students can effectively apply CADD CAM education, they must have drafting and design experience or at least a year of engineering training, plus ability to use spatial relationships and a course in descriptive geometry. With this background, students learn to create geometry for a 2-D drawing database and gain sufficient experience in the first course to be as productive as employees with six months' full-time experience. In the final semester or in the second advanced course, students create 3-D geometry and apply analytical computer capabilities for design, specializing for uses in mechanical, electrical, structural, architectural, and graphics arts applications. The defined geometry is also used in CAM for generating numerical control machining and flame-cutting paths, and for robotic control.Each course has been evaluated, follow-up studies have been completed, and an advisory committee has guided development. Employees have verified success and ease in transferring geometric skills to many different CADD CAM systems in the market. Beginning in the Fall of 1982, Apple microcomputers will be used to teach all 2-D computer graphics skills previously taught on the Computervision system, and CADD CAM education is now becoming available on an economical basis to all users.Some Problems in CAD EducationDonald GreenbergIt is imperative that universities educating the next generation of engineers introduce computer-aided design courses into their curricula. There are many obstacles in accomplishing this within a university structure. This presentation describes the facilities and operation at Cornell University and discusses the potential benefits and difficulties.CAD/CAM Education in an Engineering CurriculumMark S. ShepardToday there is a large industrial demand for engineering graduates that understand CAD/CAM techniques and computer graphics. Therefore, many colleges and universities already have or are planning to introduce computer graphics and CAD/CAM concepts into their curriculum. The major questions to be addressed in integrating these techniques into the curriculum include type and amount of hardware, development and maintenance of software and method of introduction into the curriculum.In 1977, RPI's school of engineering established the Center for Interactive Computer Graphics which is charged with integrating interactive computer graphics into the entire undergraduate engineering curriculum and providing a facility for graduate instruction and research. With heavy industrial support, the Center has also developed a research program in computer graphics and CAD/CAM. This presentation will discuss RPI's overall approach to integrating interactive computer graphics into the engineering curriculum.A Postgraduate Program in “Programmable Automation”Ari RequichaHerb Voelcker“Programmable Automation” designates the emerging body of knowledge surrounding CAD/CAM and industrial robotics. Graduate study in the field is aimed at (1) understanding the informational aspects of design and production in the discrete goods industries, and (2) developing new technologies for producing goods automatically with programmable, general-purpose tools. Some of the knowledge and techniques used in Programmable Automation are drawn from established fields (computer science, material science, control theory, ...), but the distinctive character of Programmable Automation is set mainly by the pervasive roles played by geometry and computation.A postgraduate program in Programmable Automation is being launched at the University of Rochester to train MS/level systems engineers for industry, and Ph.D-level researchers and teachers. The program's evolution reflects a “trickle-down” philosophy of education, wherein major new fields enter engineering education through on-going research; research begets seminars, seminars sometimes evolve into graduate courses, and graduate courses sometimes spawn undergraduate courses. (Put differently, the process starts with mature minds grappling with poorly understood concepts and ends with immature minds assimilating tightly codified concepts.)The Rochester program is sited in Electrical Engineering and draws heavily on the staff and facilities of the Production Automation Project; it also has strong links with Mechanical Engineering and Computer Science. The initial curriculum is based on two core courses in computational geometry, a graphics lab, and a systems seminar; these are supplemented with established courses in computer science, digital systems, finite-element analysis, control theory, and so forth. An NC Systems course and lab will be introduced a year hence. Plans for linking the program with Rochester's VLSI program, and for launching robotics research and teaching, are still in an embryonic stage.

An interactive computer graphics system has been developed for the architecture profession which provides a “design environment” for the evaluation of building energy consumption. The system includes an integrated set of graphic input tools which generate the geometric and attribute data necessary for the determination of thermal load in buildings. In addition, a comprehensive set of graphical output routines has been created to allow the designer to visually interpret the results of alternative design strategies.

This paper presents an interactive method for specifying a path in space and time through a three-dimensional environment. A sequence is generated by showing the series of views along the path. The sequence is previewed on a vector scope, and after it is interactively refined, each frame is rendered on a raster device. The path is represented by a B-spline to provide smooth, continuous motion. The timing along the path is also defined by a B-spline so that changes in velocity are smooth. The use of “path coherence” is introduced. The utilization of the available data from the a priori temporal and spatial path definition holds great promise for frame to frame coherence. The path coherence can be used to reduce the number of polygons which need to be considered in a viewed environment. This reduction makes the previewing of complex environments appear less cluttered. Furthermore, the computational expense of the culling and sorting operations in the visible line/surface determination is reduced. One sample usage of this is a tree-structured partitioned environment where the priority ordering of the environment must be changed only when the path crosses a partition boundary.

article A Visible Polygon Reconstruction Algorithm Share on Authors: S. Sechrest Program of Computer Graphics, Cornell University, Ithaca, NY Program of Computer Graphics, Cornell University, Ithaca, NYView Profile , D. P. Greenberg Program of Computer Graphics, Cornell University, Ithaca, NY Program of Computer Graphics, Cornell University, Ithaca, NYView Profile Authors Info & Claims ACM Transactions on GraphicsVolume 1Issue 1Jan. 1982 pp 25–42https://doi.org/10.1145/357290.357294Online:01 January 1982Publication History 19citation885DownloadsMetricsTotal Citations19Total Downloads885Last 12 Months14Last 6 weeks1 Get Citation AlertsNew Citation Alert added!This alert has been successfully added and will be sent to:You will be notified whenever a record that you have chosen has been cited.To manage your alert preferences, click on the button below.Manage my AlertsNew Citation Alert!Please log in to your account Save to BinderSave to BinderCreate a New BinderNameCancelCreateExport CitationPublisher SiteGet Access

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.

Perceptually uniform color spaces can be a useful tool for solving computer graphics color selection problems. However, before they can be used effectively some basic principles of tristimulus colorimetry must be understood and the color reproduction device on which they are to be used must be properly adjusted. The Munsell Book of Color and the Optical Society of America (OSA) Uniform Color Scale are two uniform color spaces which provide a useful way of organizing the colors of a digitally controlled color television monitor. The perceptual uniformity of these color spaces can be used to select color scales to encode the variations of parameters such as temperature or stress.

Previous work in the hidden-surface problem has revealed two key concepts. First, the removal of non-visible surfaces is essentially a sorting problem. Second, some form of coherence is essential for the efficient solution of this problem.

Simple transparency algorithms which assume a linear transparency over an entire surface are the type most often employed to produce computer synthesized images of transparent objects with curved surfaces. Although most of the images created with these algorithms do give the impression of transparency, they usually do not look realistic. One of the most serious problems is that the intensity of the light that is transmitted through the objects is generally not proportional to the amount of material through which it must pass. Another problem is that the image seen behind the objects is not distorted as would naturally occur when the light is refracted as it passes through a material of different density. Use of a non-linear transparency algorithm can provide a great improvement in the realism of an image at a small additional cost. Making the transparency proportional to the normal to the surface causes it to decrease towards the edges of the surface where the path of the light through the object is longer. The exact simulation of refraction, however, requires that each sight ray be individually traced from the observer, through the picture plane and through each transparent object until an opaque surface is intersected. Since the direction of the ray would change as each material of differing optical density was entered, the hidden surface calculations required would be very time consuming. However, if a few assumptions are made about the geometry of each object and about the conditions under which they are viewed, a much simpler algorithm can be used to approximate the refractive effect. This method proceeds in a back-to-front order, mapping the current background image onto the next surface, until all surfaces have been considered.

A general purpose method for generating shadows using a polygonal coordinate data base is presented. The method is based on an object space polygon clipping hidden surface removal algorithm. Output from the program is in the same three-dimensional polygon format as the input. Thus, a shadowed data environment may be easily created and viewed from any observer position with no additional depth sorting time required for the hidden surface removal process. Shadows can also be cast by more than one light source. Since the shadows are generated in object space, the results can be used for both visual display and numerical analysis.

Input preprocessors have come to be recognized as important components of modern finite element programs. A method is described which utilizes interactive computer graphics digitizing techniques to create a powerful input preprocessor for finite element analysis. A limited number of general mesh generators based on linear blending functions permit the program to handle virturally all two-dimensional topologies. The processes of geometric input and specification of problem-specific “attributes” have been kept separate so that the mesh generation routines may be used with a variety of analysis programs. Graphical editors have been implemented to specify attributes for structural mechanics problems. Although this type of graphical preprocessor shows considerable promise for applications in three dimensions, there are still unresolved problems in the areas of geometrical description, perception, and interactive hardware.

Normal human color perception is a product of three independent sensory systems. By mirroring this mechanism, full-color display devices create colors as mixtures of three primaries. Any displayable color can be described by the corresponding values of these primaries. Frequently it is more convenient to define various other color spaces, or coordinate systems, for color representation or manipulation. Several such color spaces are presented which are suitable for applications involving user specification of color, along with the defining equations and illustrations. The use of special color spaces for particular kinds of color computations is discussed.

Two computer graphics systems for the presentation of biomedical information for diagnosis and treatment planning are described. Both systems presented utilize computer tomographic (CT) data as input. One of the systems produces three-dimensional surface representations of organs and anatomical features found within the body. The other system is a radiation treatment planning aid which uses tomographic data in its computations.

This paper describes the facilities and operation of the Program of Computer Graphics at Cornell University. A variety of graphic procedures are used for both input and output. The laboratory has the capability for producing dynamic vector displays and for generating full color images. Numerous research projects in a variety of disciplines which are actively using this multi-user graphics environment are presented.

No abstract available.