Abstract: Most computer graphics pictures have been computed all at once, so that the rendering program takes care of all computations relating to the overlap of objects. There are several applications, however, where elements must be rendered separately, relying on compositing techniques for the anti-aliased accumulation of the full image. This paper presents the case for four-channel pictures, demonstrating that a matte component can be computed similarly to the color channels. The paper discusses guidelines for the generation of elements and the arithmetic for their arbitrary compositing.

Abstract: This paper presents a new reflectance model for rendering computer synthesized images. The model accounts for the relative brightness of different materials and light sources in the same scene. It describes the directional distribution of the reflected light and a color shift that occurs as the reflectance changes with incidence angle. The paper presents a method for obtaining the spectral energy distribution of the light reflected from an object made of a specific real material and discusses a procedure for accurately reproducing the color associated with the spectral energy distribution. The model is applied to the simulation of a metal and a plastic.

Abstract: 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.

Abstract: 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.

Abstract: This paper presents rendering techniques that use volumes as the basic geometric primitives. It defines data structures composed of numerous subvolumes, in excess of 100,000. Over each subvolume, a scalar field describes the variation of some physical quantity. The two rendering methods described herein assume a trilinear variation of this scalar field within each volume element, unlike voxel-based techniques that assume a constant value for each subvolume. The result is a higher order approximation of the structures within the volume. In addition, solid texture mapping, atmospheric attenuation, and transfer functions relating the dynamic range of the scalar field to color and opacity are used to isolate important data features. The result is a new method for the visualization of three-dimensional data resulting from numerical simulations and observations of natural phenomena. This method continuously covers the gap between surface-based and voxel-based techniques.

Abstract: An efficient ray tracing method is presented for calculating interreflections between surfaces with both diffuse and specular components. A Monte Carlo technique computes the indirect contributions to illuminance at locations chosen by the rendering process. The indirect illuminance values are averaged over surfaces and used in place of a constant "ambient" term. Illuminance calculations are made only for those areas participating in the selected view, and the results are stored so that subsequent views can reuse common values. The density of the calculation is adjusted to maintain a constant accuracy, permitting less populated portions of the scene to be computed quickly. Successive reflections use proportionally fewer samples, which speeds the process and provides a natural limit to recursion. The technique can also model diffuse transmission and illumination from large area sources, such as the sky.

Abstract: Detail enhances the visual richness and realism of computer-generated images. Our stochastic modelling approach, called particle systems, builds complex pictures from sets of simple, volume-filling primitives. For example, structured particle systems have been used to generate trees and a grass-covered forest floor. Particle systems can produce so much irregular, three-dimensional detail that exact shading and visible surface calculations become infeasible. We describe approximate and probabilistic algorithms for shading and the visible surface problem. Because particle systems algorithms generate richly-detailed images, it is hard to detect any deviation from an exact rendering. Recent work in stochastic modelling also enables us to model complex motions with random variation, such as a field of grass blowing in the breeze. We analyze the performance of our current algorithms to understand the costs of our stochastic modelling approach.

Abstract: An architecture is presented for fast high-quality rendering of complex images. All objects are reduced to common world-space geometric entities called micropolygons, and all of the shading and visibility calculations operate on these micropolygons. Each type of calculation is performed in a coordinate system that is natural for that type of calculation. Micropolygons are created and textured in the local coordinate sysem of the object, with the result that texture filtering is simplified and improved. Visibility is calculated in screen space using stochastic point sampling with a z buffer. There are no clipping or inverse perspective calculations. Geometric and texture locality are exploited to minimize paging and to support models that contain arbitrarily many primitives.

Abstract: Ray tracing is becoming popular as the best method of rendering high quality images from three dimensional models. Unfortunately, the computational cost is high. Recently, a number of authors have reported on ways to speed up this process by means of space subdivision which is used to minimize the number of intersection calculations. We describe such an algorithm together with an analysis of the factors which affect its performance. The critical operation of skipping an empty space subdivision can be done very quickly, using only integer addition and comparison. A theoretical analysis of the algorithm is developed. It shows how the space and time requirements vary with the number of objects in the scene.

Abstract: Techniques for the efficient ray tracing of animated scenes are presented. They are based on two central concepts: spacetime ray tracing, and a hybrid adaptive space subdivision/boundary volume technique for generating efficient, nonoverlapping hierarchies of bounding volumes. In spacetime ray tracing, static objects are rendered in 4-D space-time using 4-D analogs to 3-D techniques. The bounding volume hierarchy combines elements of adaptive space subdivision and bounding volume techniques. The quality of hierarchy and its nonoverlapping character make it an improvement over previous algorithms, because both attributes reduce the number of ray/object intersections that must be computed. These savings are amplified in animation because of the much higher cost of computing ray/object intersections for motion-blurred animation. It is shown that it is possible to ray trace large animations more quickly with space-time ray tracing using this hierarchy than with straightforward frame-by-frame rendering. >

Abstract: This paper describes a high performance display system that has been incorporated into the overall architecture of the Stellar Graphics Supercomputer Model GS1000. The display system is tightly coupled to the CPU, memory system and vector processing unit of this supercomputer, and is capable of rendering 150,000 shaded triangles/sec, and 600,000 short vectors/sec. The goal of the architecture is to share hardware resources between the CPU and display system and achieve a high bandwidth connection between them. This coupling of the display system and the processor, the architecture of the rendering processor, and the two ASICs that are used to implement the rendering processor are described.In addition, the display system architecture is contrasted to other approaches to high performance graphics, and design trade-offs and possible extensions are described. The implementation of popular display algorithms on the architecture is discussed, and their performance specified. The reader is advised that Stellar Computer Inc. is seeking patent protection for work described in this paper.

Abstract: The complexity of anti-aliased 3-D rendering systems can be controlled by using a tool-building approach like that of the UNIX~text processing tools. Such an approach requires a simple picture representation amenable to anti-aliasing that all rendering programs can produce, a compositing algorithm for that representation and a command language to piece together scenes. This paper advocates a representation that combines Porter and Duff's compositing algebra with a Z-buffer to provide simple anti-aliased 3-D compositing. CR Categories and Subject Descriptors: 1.3.3 IPicture and Image Generationl Display algorithms, Viewing algorithms, 1.3.5 IComputational Geometry and Object Modellingl Curve, surface, solid and object representations, 1.3.7 IThree-Dimensional Graphics and Realisml Visible line/surface algorithms

Abstract: SIMD computer architecture is used in conjunction with a host processor and coordinate processor to render quality, three-dimensional, anti-aliased shaded color images into the frame buffer of a video display system. The method includes a parallel algorithm for rendering an important graphic primitive for accomplishing the production of a smoothly shaded color three-dimensional triangle with anti-aliased edges. By taking advantage of the SIMD architecture and said parallel algorithm, the very time consuming pixel by pixel computations are broken down for parallel execution. A single coordinate processor computes and transmits an overall triangle record which is essentially the same for all blocks of pixels within a given bounding box which box in turn surrounds each triangle. The individual pixel data is produced by a group of M×N pixel processors and stored in the frame buffer in a series of repetitive steps wherein each step corresponds to the processing of an M×N block of pixels within the bounding box of the triangle. Thus, each pixel processor performs the same operation, modifying its computations in accordance with triangle data received from the coordinate processor and positional data unique to its own sequential connectivity to the frame buffer, thus allowing parallel access to the frame buffer.

Abstract: This is a set of proposed extensions to the proposed PHIGS graphics standard (dpANS X3.144-198x. DIS 9592) to cover the areas of lighting, shading and advanced primitives which have thus far not been addressed by that standard. This document is organized to promote its eventual integration with the existing PHIGS documentation and is therefore not tutorial in nature. It assumes that the reader is familiar with PHIGS. with rendering and with curves and surfaces. This specification has been made available to standards bodies for their consideration.

Abstract: An article with at least a portion carrying symbols representing information to be protected against photocopying is formed by a carrier, a continuous layer covering the portion of the carrier and forming a background thereon, and a mainly discontinuous layer applied on the continuous layer and forming the symbols against the background. One of the layers is an iridescent layer of a color that copies dark and the other of the layers has a dark color. Thus photocopying gives an image without distinction between the symbols and the background.

Abstract: The first part of the paper shows that previous theoretical work on the semantics of probabilistic programs (Kozen) and on the correctness of performance annotated programs (Ramshaw) can be used to automate the average-case analysis of simple programs containing assignments, conditionals, and loops. A performance compiler has been developed using this theoretical foundation. The compiler is described, and it is shown that special cases of symbolic simplifications of formulas play a major role in rendering the system usable. The performance compiler generates a system of recurrence equations derived from a given program whose efficiency one wishes to analyze. This generation is always possible, but the problem of solving the resulting equations may be complex. The second part of the paper presents an original method that generalizes the previous approach and is applicable to functional programs that make use of recursion and complex data structures. Several examples are presented, including an analysis of binary tree sort. A key feature of the analysis of such programs is that distributions on complex data structures are represented using attributed probabilistic grammars.

Abstract: The desire for higher performance and higher resolution continuously increases the pixel update rates needed in high performance graphics systems. The increasing density of memory chips on the other hand reduces the pixel update rate that can be provided by the frame buffer. We present the design of a VLSI chip and a graphics system that can sustain sub-nanosecond pixel rendering rates for three-dimensional polygons and can be used to render about a million Z-Buffered and Gourard shaded polygons per second. The chip has been designed at the IBM Research Division's Thomas J. Watson Research Center.

Abstract: Graphics can be implemented as a virtual system resource. This abstraction appears to each application on a multiprocessing workstation as a dedicated rendering and display pipeline. A variety of simple mechanisms support the simultaneous display of different types of images and eliminate the need for low-level device driver software. They permit applications to embed graphics instructions directly in their code. The abstraction allows for cleaner software design, higher performance, and effective concurrent use of the display by several applications.

Abstract: Raster graphics displays are almost always refreshed out of a frame buffer in which a digital representation of the currently visible image is kept. The availability of the frame buffer as a two-dimensional memory array representing the displayable area in a screen coordinate system has motivated the development of algorithms that take advantage of this memory for more than just picture storage. The classic example of such an algorithm is the depth buffer algorithm for determining visible surfaces of a three-dimensional scene. This paper constitutes a first attempt at a disciplined analysis of the power of a frame buffer seen as a computational engine for use in graphics algorithms. We show the inherent power of frame buffers to perform a number of graphics algorithms in terms of the number of data fields (registers) required per pixel, the types of operations allowed on these registers, and the input data. In addition to upper bounds given by these algorithms, we prove lower bounds for most of them and show most of these algorithms to be optimal.One result of this study is the introduction of new frame buffer algorithms for computing realistic shadows and for determining the convex intersection of half spaces, an operation important in computational geometry and in rendering objects defined using planes rather than polygons. Another result is that it shows clearly the relationships between different and important areas of research in computer graphics, such as visible surface determination, compositing, and hardware for smart frame buffers.

Abstract: A magnification change-over device for a camera having a common incident optical path for having rays of light from an object impinge thereinto, a first optical path for guiding the rays of light from the object, impinging into the common incident optical path, to a first aperture, a second optical path for guiding the rays of light from the object, impinging into the common incident optical path, to a second aperture, a change-over device for selecting either the first aperture or the second aperture, and a wide converter for rendering magnification of an image formed at the second aperture different from a magnification of an image formed at the first aperture.

Abstract: Conventional three-dimensional imaging uses thresholding, or surface rendering technique, which limits accuracy and detail, and hinders soft tissue definition. Volumetric image rendering preserves all CT data, not just surface boundaries, and therefore overcomes these limitations. Three-dimensional images thus generated can be used for muscular and vascular anatomy as well as skeletal structures, with preservation of subtle detail. Representative cases are used to illustrate this technique and its implications for therapy and plastic and reconstructive surgery.

Abstract: An algorithm for rendering shaded pictures of parametric surfaces is presented. The algorithm recursively subdivides each surface element on the basis of its screen-space curvature until it is sufficiently close to bilinear to be scan-converted by conventional polygon rendering techniques. The mathematical basis used to carry out the subdivsion yields the curvature criterion as a coefficient so that the tests for termination of the subdivision process are extremely simple. In addition, a surface is subdivided only in the parametric direction in which its curvature deviates from the tolerance. The algorithm incorporates a very simple solution to the problem of separations between subpatches.

Abstract: A method of synthesising and animating a realistic image of a person's face by means of computer graphics is described. The key feature contributing to realism in image synthesis lies in the use of texture mapping in the rendering of surface detail on the face. Full facial animation is made possible by manipulating a 3-D model of the face in conjunction with a relatively small data set of pre-stored sub-images.

Abstract: A survey of human body animation is presented dealing with its geometrical representation, motion control techniques and rendering. A classification of human body animation systems is presented according to different criteria. The human body movement notations are described and the different existing geometric models of the body and the face are analised and compared. The body and face control motion techniques are presented and discussed, as well as human body motion in its environment. Finally, the different problems of human body rendering are presented.

Abstract: A look-ahead image is employed during ray tracing of the image rendering process to eliminate the processing of pixels which are of no interest within a given boundary of the ray. During rendering, ray tracing is carried out by jumping over the pixels of no interest to thereby enhance the rendering speed.

Abstract: A transducer in the form of an integrated circuit comprising a Hall cell, first and second differential amplifiers, an output driver stage, a threshold voltage-generating circuit between said amplifiers, and a control circuit for selectively enabling and disabling the threshold voltage-generating circuit. The second amplifier provides an output signal representative of the enabled-disabled condition of the threshold voltage-generating circuit. A permanent magnet having a temperature coefficient is movable with respect to the transducer between given field-applying and field-removing positions. The transducer operates to change switching states between "operate" and "release" in response to the two different levels of applied magnetic fields, respectively, resulting from the two given operating positions of the magnet. The transducer also has a temperature coefficient at its "operate" point which substantially tracks that of the magnet, thereby rendering the transducer operation essentially independent of ambient temperature changes.

Abstract: Distribution of doping cations between A and B sites of perovskite ABO3 structure obeys certain conditions derived in terms of energy. These can be applied to predict semiconducting BaTiO3-based compositions, to account for yet unexplained anomalies in concentrational dependencies of electrical resistivity and Curie temperature, and to understand the relatively unimportant effect of doping in the case of solid solutions such as Ba1−x Sr x TiO3 and Ba1−x Ca x TiO3.