Abstract We propose a fast approach for photo‐realistic rendering of trees under various kinds of daylight, which is particularlyuseful for the environmental assessment of landscapes. In our approach the 3D tree models are transformedto a quasi‐3D tree database registering geometrical and shading information of tree surfaces, i.e. their normalvectors, relative depth, and shadowing of direct sunlight and skylight, by using a combination of 2D buffers.Thus the rendering speed of quasi‐3D trees depends on their display sizes only, regardless of the complexity oftheir original 3D tree models. By utilizing a two‐step shadowing algorithm, our proposed method can create highquality forest scenes illuminated by both sunlight and skylight at a low cost. It can generate both umbrae andpenumbrae on a tree cast by other trees and any other objects such as buildings or clouds. Transparency, specularreflection and inter‐reflection of leaves, which influence the delicate shading effects of trees, can also be simulatedwith verisimilitude. Categories and Subject Descriptors (according to ACM CCS): I.3.7 [Computer Graphics]: Three dimensional Graphics and Realism

We propose a novel method, based on the two-pass z-buffer algorithm, to calculate shadows with sufficient precision and efficiency for rendering a daytime landscape with solar penumbrae. The feature of the proposed method is that the precision of the shadows can be preserved to be superior than that of any visible surface by using the appropriate number of plural shadow buffers; it gives a fairly satisfactory trade-off between computation time and quality of shadows. By using the shadow buffers, before calculating solar illuminance we can divide visible surfaces into three types of fragments, that is, bright regions, umbra regions, and the remaining penumbra regions. Thus, we can efficiently render a daytime landscape with sufficient precision of penumbrae because the algorithm can set the calculation points of solar illuminance variably, with their number depending on the type of region they belong to.

Here we present an approach to offer a precise panoramic image composited from panned video sequence images, which are taken by a video camera on a tripod. The varying exposure levels due to the panned view fields taken by a camera with auto iris are adjusted. Any geometrical distortions in each frame, due to camera lens and/or CCD and perspective projection, are calibrated. The interlaced video sequence images commonly used for video systems are deinterlaced in order to create a high quality panoramic image.

We present very simple but effective algorithms to playback a standard video tape recording at a higher/slower rational time speed in accordance with varying demand. To avoid temporal signal sampling errors for a slow speed playback and spatial ones for a high speed one, the following four-step algorithms have been developed: (1) sequences are separated into even and odd fields, and intermediate noninterlaced frames are made by vertical interpolation; (2) for slowing down the playback speed of video sequences, linear interpolation between two frames surrounding a fractional frame position is used; (3) for speeding up, an average frame in a window surrounding the desired frame (with the window size depending on the speed up factor) is used; (4) sequences are post processed by decimation to get back interlaced images. The proposed algorithms give quite smooth sequence images for slow speed sequences and nondiscontinuous and less jittering ones with appropriate motion blur for high speed ones.

We present a novel approach to offer at a reasonable cost, panned landscape video sequence images well matched with photorealistic computer generated still images of large scale construction projects, such as bridges and electric power transmission towers. Our newly developed compositing algorithms can be used with the equipment which consists of a regular camcorder sold on the market, a video editing system, and our own software for rendering day-time scenes under various weather conditions. Other types of equipment such as an elaborate camera controller or special reference points in the landscapes, are unnecessary. The proposed algorithms provide the following features: (1) the computer generated still images are well harmonized with panned video sequence images at any time of day under various weather conditions, in terms of both optical and geometrical accuracy; (2) a precise panorama composited from video sequence images is created, in which varying exposure levels due to changing camera view fields can be coped with and any geometrical distortion is eliminated.

Interpolating contours and reconstructing a rational surface from a contour map are two essential problems in terrain modeling. They are often met in the field of computer graphics and CAD systems based on geographic information systems. Although many approaches have been developed for these two problems, one difficulty still remains. That is how to ensure that the reconstructed surface is both smooth globally and coincides with the given contours exactly simultaneously. In this paper we solve the two problems in a unified framework. We use gradient controlled partial differential equation (PDE) surfaces to express terrain surfaces, in which the surface shapes can be globally determined by the contours, their locations, height and gradient values. The surface generated by this method is accurate in the sense of exactly coinciding with the original contours and smooth with C/sup 1/ continuity everywhere. The method can reveal smooth saddle shapes caused by surface branching of one to more and can make rational interpolated sub-contours between two or more neighboring contours.

The display of natural scenes such as mountains, trees, the earth as viewed from space, the sea, and waves have been attempted. Here a method to realistically display snow is proposed. In order to achieve this, two important elements have to be considered, namely the shape and shading model of snow, based on the physical phenomenon. In this paper, a method for displaying snow fallen onto objects, including curved surfaces and snow scattered by objects, such as skis, is proposed. Snow should be treated as particles with a density distribution since it consists of water particles, ice particles, and air molecules. In order to express the material property of snow, the phase functions of the particles must be taken into account, and it is well‐known that the color of snow is white because of the multiple scattering of light. This paper describes a calculation method for light scattering due to snow particles taking into account both multiple scattering and sky light, and the modeling of snow.

Article Free Access Share on Display of clouds taking into account multiple anisotropic scattering and sky light Authors: Tomoyuki Nishita Fukuyama University, Sanzo, Higashimura-cho, Fukuyama, 729-02 Japan Fukuyama University, Sanzo, Higashimura-cho, Fukuyama, 729-02 JapanView Profile , Yoshinori Dobashi Hiroshima University, 1-4-1, kagamiyama, Higashi-hiroshima, 739 Japan Hiroshima University, 1-4-1, kagamiyama, Higashi-hiroshima, 739 JapanView Profile , Eihachiro Nakamae Hiroshima Prefectural University, Nanatsuka-cho, Shoubara City, 727 Japan Hiroshima Prefectural University, Nanatsuka-cho, Shoubara City, 727 JapanView Profile Authors Info & Claims SIGGRAPH '96: Proceedings of the 23rd annual conference on Computer graphics and interactive techniquesAugust 1996 Pages 379–386https://doi.org/10.1145/237170.237277Published:01 August 1996Publication History 92citation2,177DownloadsMetricsTotal Citations92Total Downloads2,177Last 12 Months145Last 6 weeks14 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 SiteeReaderPDF

A precise shading model is required to display realistic images. Recently research on global illumination has been widespread. In global illumination, problems of diffuse reflection have been solved fairly well, but some optical problems after specular reflection and refraction still remain. Some natural phenomena stand out in reflected/refracted light from the wave surface of water. Refracted light from water surface converges and diverges, and creates shafts of light due to scattered light from particles. The color of the water is influenced by scattering/absorption effects of water molecules and suspensions. For these effects, the intensity and direction of incident light to particles plays an important role, and it is difficult to calculate them in conventional ray-tracing because light refracts when passing through waves. Therefore, the pre-processing tracing from light sources is necessary.

Abstract For rendering curved surfaces, one of the most popular techniques is metaballs, an implicit model based on isosurfaces of potential fields. This technique is suitable for deformable objects and CSG model. For rendering metaballs, intersection tests between rays and isosurfaces are required. By defining the higher degree of functions for the field functions, richer capability can be expected, i.e., the smoother surfaces. However, one of the problems is that the intersection between the ray and isosurfaces can not be solved analytically for such a high degree function. Even though the field function is expressed by degree six polynomial in this paper (that means the degree six equation should be solved for the intersection test), in our algorithm, expressing the field function on the ray by Bézier functions and employing Bézier Clipping , the root of this function can be solved very effectively and precisely. This paper also discusses a deformed distribution function such as ellipsoids and a method displaying transparent objects such as clouds.

Article Free Access Share on Display of the earth taking into account atmospheric scattering Authors: Tomoyuki Nishita View Profile , Takao Sirai View Profile , Katsumi Tadamura View Profile , Eihachiro Nakamae View Profile Authors Info & Claims SIGGRAPH '93: Proceedings of the 20th annual conference on Computer graphics and interactive techniquesSeptember 1993 Pages 175–182https://doi.org/10.1145/166117.166140Published:01 September 1993Publication History 83citation2,037DownloadsMetricsTotal Citations83Total Downloads2,037Last 12 Months298Last 6 weeks31 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 SiteeReaderPDF

Abstract A high precision illumination model is indispensable for lighting simulation and realistic image synthesis. For the purpose of improving realism, research on global illumination has been done, and several papers on radiosity methods have been presented. In the most recently proposed methods, the shapes of light sources and objects are restricted to polygons or simple curved surfaces. We present a more general method which can handle the kind of free‐form surfaces widely used in industrial products and in architecture. The method proposed here solves the problem of the interreflection of light (i.e., radiosities) between patches, and form‐factors, which play an important role in this process, are precisely calculated without aliasing through the use of an area sampling method (i.e., pyramid tracing). Furthermore the method can handle both non‐uniform intensity curved sources and non‐diffuse surfaces.

Abstract Photorealistic animated images are extremely effective for pre‐evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered. This paper proposes a method of high‐fidelity image generation for photorealistic outdoor scenes based on the following ideas: The intensity distribution of skylight taking account of scattering and absorption due to particles in the atmosphere which coincides with CIE standard skylight luminance functions is sought, and realistic images considering about spectrum distribution of skylight for any altitude of the sun can be easily and accurately displayed. A rectangular parallelepiped with a specialized distribution of intensity simulating the skylight is introduced for efficient calculation of illumination due to skylight, and by employing a graphics hardware calculation of the skylight illuminance taking into account shadow effects is obtained with high efficiency; these techniques can be used to generate sequences of images, making animations possible at far lower calculation cost than previous methods.

Abstract In order to observe the physical values (magnetic flux density and eddy current) in 3D magnetic field analysis, an interactive and highly manipulative visualization system depicting stereo images is intalled in a graphics workstation with high functional graphic processors. The system has the following characteristics: An interactive and highly manipulative menu window with many functions: it enables visualization of complex phenomena in a 3D field through observation of various combinations of physical values from various viewpoints. Simultaneous display of both magnetic flux density and eddy current by using the appropriate use of two colour display methods for stream lines and distribution maps of density: this function facilitates observation of the mutual relations between two physical values in a 3D field. Animations and stereo displays: since they give extremely distinct images, observers can easily understand even highly complex 3D phenomena. In this paper, the calculation method of density vectors, their display methods, and interactive functions are described. Some examples are also illustrated.

Many techniques for rendering natural objects such as the sea, terrains, and trees have been developed; they are indispensable for flight simulators. In this paper, techniques for rendering road surfaces under various conditions are discussed. Rendering road surfaces is quite useful for the evaluation of driving safety, and it will play an important part in the development of drive simulators. Light sources with high intensity often disturb drivers especially under wet road surface conditions.This paper proposes two models, a reflection model for road surfaces taking into account weather conditions, and a model on streaks of light taking into account both refraction and diffraction of light. Some examples demonstrate the possibility of applications for drive simulators in the future.

A technique for compositing computer generated images of buildings and background images created from aerial photographs is described. The aerial photo data are mapped onto a terrain model based on cartographic data. The technique can be used to pre-evaluate visual impact of large scale construction by means of not only still images but also animations.The technique can be briefly described as follows: 1) an accurate, three-dimensional terrain model is created based on cartographic data. 2) a hierarchy of aerial photo data at various resolutions is mapped onto the terrain model as a texture. 3) the height of trees is taken into account in regions near the viewpoint. 4) allowing intersections of terrain models with constructions facilitates geometric adjustments and shadowing.

Studio spotlights produce dazzling shafts of light, while light scattered from fog illuminated by automobile headlights renders driving difficult. This is because the particles in the illuminated volume become visible by scattering light. A shading model for scattering and absorption of light caused by particles in the atmosphere is proposed in this paper. The method takes into account luminous intensity distribution of light sources, shadows due to obstacles, and density of particles. The intensity at a viewpoint is calculated by integration of light scattered by particles between the viewpoint and a given point on an object. The regions to be treated in this manner are localized by considering illumination volumes and shadow volumes caused by obstacles in the illumination volumes.

A system of computer programs has been established to generate high quality montage image of considerable usefulness in architectural simulation which combine computer-generated images and photographed background pictures.Traditionally, there are two methods of creating architectural montages: (1) an artist paints new buildings onto a background scene usually generated photographically, and (2) a three-dimensional scale model is created to simulate the whole landscape, and this model is then photographed. The montage method described here combines aspects of both traditional montage methods with significant improvement in accuracy and reduction of time and cost of preparation. Specifically, a digitized photograph is used as a background scene onto which is superimposed a 3D computer-generated image of a new building. The outstanding points of the new method are:(i) The shading and shadows of each computer generated image are calculated with higher accuracy, (ii) the fog effect is taken into account, and (iii) a new anti-aliasing technique improves the quality of the final montage image.

Natural lighting models to date have been limited to calculation of direct sunlight. However, this paper proposes an improved model for natural lighting calculations that adequately considers both direct sunlight and scattered light caused by clouds and other forms of water vapor in the air. Such indirect natural light is termed skylight and can be an important factor when attempting to render realistic looking images as they might appear under overcast skies.In the proposed natural lighting model, the sky is considered to be a hemisphere with a large radius (called the sky dome) that acts as a source of diffuse light with nonuniform intensity. In order to adequately take into account the nonuniform intensity of such skylight, the sky dome is subdivided into bands. The light intensity within individual bands can be assumed to be transversely uniform and longitudinally nonuniform and therefore the total luminance emanating from each band can be calculated more accurately.The proposed method significantly improves the realism of natural lighting effects. Its advantages are particularly apparent when simulating lighting under an overcast sky or when rendering surfaces that fall within a shadow cast by an obstruction lit by direct sunlight.

The effect of shadows and interreflection created by room obstructions is an important factor in the continuous tone representation of interiors. For indirect illumination, in most cases a uniform ambient light has been considered, even though the interreflection gives very complex effects with the shaded images.The proposed method for indirect lighting with shadows results in the following advanced points:1) The indirect illuminance caused by the surfaces of objects such as ceilings, floors, walls, desks, bookcases etc. gives added realism to images.2) The proposed method is suitable for every type of light source such as point sources, linear sources, and area sources.

The degree of realism of the shaded image of a tree-dimensional scene depends on the successful simulation of shading effects. The shading model has two main ingredients, properties of the surface and properties of the illumination falling on it. Most previous work has concentrated on the former rather than the latter. This paper presents an improved version for generating scenes illuminated by point and linear light sources. The procedure can include intensity distributions for point light sources and output both umbrae and penumbrae for linear light sources, assuming thr environment is composed of convex polyhedra. This paper generalizes Crow's procedure for computing shadow volumes caused by the end points of the linear source results in an easy determination of the reions of penumbrae and umbrae on the face prior to shading calculation. This paper also discusses a method for displaying illuminance distribution on a shaded image aby using colored isolux contours.

Computer graphics techniques for visualizing the following simulation results are developed: (1) lighting designs for different type sources such as point sources, linear sources, area sources, and polyhedron sources, (2) shaded time at arbitrary positions such as windows, walls, and even the inside of a room, (3) montages for view environment evaluation, (4) quasi-semi-transparent models for observing life generation process in anatomy, and (5) two and three dimensional magnetic fields analyzed by the finite element method.