Eihachiro Nakamae

Continuous tone representation of three-dimensional objects taking account of shadows and interreflection

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.

Display of clouds taking into account multiple anisotropic scattering and sky light

Methods to display realistic clouds are proposed. To display realistic images, a precise shading model is required: two components should be considered. One is multiple scattering due to particles in clouds, and the other factor to be considered is sky light. For the former, the calculation of cloud intensities has been assumed to be complex due to strong forward scattering. However, this paper proposes an efficient calculation method using these scattering characteristics in a positive way. The latter is a very significant factor when sky light is rather stronger than direct sunlight, such as at sunset/sunrise, even though sky light has been ignored in previous methods. This paper describes an efficient calculation method for light scattering due to clouds taking into account both multiple scattering and sky light, and the modeling of clouds. CR Categories and Subject Descriptors:

A shading model for atmospheric scattering considering luminous intensity distribution of light sources

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 montage method: the overlaying of the computer generated images onto a background photograph

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.

A lighting model aiming at drive simulators

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.

Continuous tone representation of three-dimensional objects illuminated by sky light

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.

Shading models for point and linear 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 Crows 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.

Method of displaying optical effects within water using accumulation buffer

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. The method proposed here can effectively calculate optical effects, shaft of light, caustics, and color of the water without such pre-processing by using a scanline Z-buffer and accumulation buffer.

A Method for Displaying Metaballs by using Bezier Clipping

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.

A Modeling and Rendering Method for Snow by Using Metaballs

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.