Kazufumi Kaneda

A simple, efficient method for realistic animation of clouds

This paper proposes a simple and computationally inexpensive method for animation of clouds. The cloud evolution is simulated using cellular automaton that simplifies the dynamics of cloud formation. The dynamics are expressed by several simple transition rules and their complex motion can be simulated with a small amount of computation. Realistic images are then created using one of the standard graphics APIs, OpenGL. This makes it possible to utilize graphics hardware, resulting in fast image generation. The proposed method can realize the realistic motion of clouds, shadows cast on the ground, and shafts of light through clouds.

A Quick Rendering Method Using Basis Functions for Interactive Lighting Design

When designing interior lighting effects, it is desirable to compare a variety of lighting designs involving different lighting devices and directions of light. It is, however, time‐consuming to generate images with many different lighting parameters, taking interreflection into account, because all luminances must be calculated and recalculated. This makes it difficult to design lighting effects interactively. To address this problem, this paper proposes a method of quickly generating images of a given scene illustrating an interreflective environment illuminated by sources with arbitrary luminous intensity distributions. In the proposed method, the luminous intensity ditribution is expressed with basis functions. The proposed method uses a series of spherical harmonic functions as basis functions, and calculates in advance each intensity on surfaces lit by the light sources whose luminous intensity distribution are the same as the spherical harmonic functions. The proposed method makes it possible to generate images so quickly that we can change the luminous intensity distribution interactively. Combining the proposed method with an interactive walk‐through that employs intensity mapping, an interactive system for lighting design is implemented. The usefulness of the proposed method is demonstrated by its application to interactive lighting design, where many images are generated by altering lighting devices and/or direction of light.

Animation of Water Droplets on a Glass Plate

This paper proposes a method for generating an animation of water droplets and their streams on a glass plate, such as a windowpane or windshield, taking into account the dynamics between fluid and solid. Water droplets run down an inclined glass plate if their masses are greater than a static critical weight. The streams from the droplets do not run straight down the glass plate but meander and some amount of water remains behind the flow due to the nature of the wetting phenomenon. Therefore, the mass of the water droplet decreases. When the mass becomes smaller than a dynamic critical weight, the flow stops. In this paper, a discrete model of a glass plate is developed to simulate the streams from the water droplets as described above. The glass plate is divided into small meshes. For rendering scenes through a glass plate upon which there are water droplets, we also develop a highspeed rendering method taking into account reflection and refraction of light. Instead of calculating the intersections between the ray and the objects, one of the most time-consuming processes in ray tracing, the proposed method determines pixel colors by using the intersection between the ray and a cuboid onto which objects in a scene are projected. Animations of rain droplets on a pane or windshield demonstrate the usefulness of the proposed method.

An Accurate Illumination Model for Objects Coated with Multilayer Films

Abstract This paper proposes an accurate illumination model for rendering objects coated with multilayer films. Optical phenomena of multilayer films are caused by reflection, refraction, interference, and absorption of light inside each layer of the multiple films, and such physical phenomena are related to each other in a complicated manner. The proposed method calculates composite reflectance and transmittance of multilayer films, taking into account all the physical phenomena described above, and visualizes accurately the optical phenomena caused by the multilayer films. The illumination model proposed in the paper can handle both smooth surfaces and locally smooth rough surfaces. Several examples of objects coated with various kinds of films demonstrate the usefulness of the proposed method.

Skylight for Interior Lighting Design

It is inevitable for indoor lighting design to render a room lit by natural light, especially for an atelier or an indoor pool where there are many windows. This paper proposes a method for calculating the illuminance due to natural light, i.e. direct sunlight and skylight, passing through transparent planes such as window glass. The proposed method makes it possible to efficiently calculate such illuminance accurately, because it takes into account both non‐uniform luminous intensity distribution of skylight and the distribution of transparency of glass according to incident angles of light. Several examples including the lighting design in an indoor pool, are shown to demonstrate the usefulness of the proposed method.

Reconstruction and semi-transparent display method for observing inner structure of an object consisting of multiple surfaces

A system of techniques is proposed for reconstructing the original object from multi-layered cross-section data including open contour lines and for displaying the inner structure as well as the outside using a stereoscopic semi-transparent image and cut-away views. The procedure is divided into three steps: 1) selection/construction of contour lines for each cross-section, 2) reconstruction of the object based on the contour line information including cutting away part of the reconstructed object with a convex polyhedron, and 3) display of the reconstructed image. Control parameters are provided to allow easy and reliable observation of multi-layererd structures.

Visualization of optical phenomena caused by multilayer films based on wave optics

This paper proposes a method for rendering objects coated with multilayer thin films, taking into consideration multiple reflection and refraction, interference, and absorption of light inside the films. The proposed method is based on wave optics, and it can accurately visualize the optical effects of multilayer films consisting of not only dielectric materials, but also metallic and semiconductive materials. Optical properties of a SiO2 film coating on a silicon base, and several kinds of multilayer films coating windowpanes, glasses, or teapots are visualized to demonstrate the usefulness of the proposed method.

A volume-preserving approach for modeling and animating water flows generated by metaballs

This paper presents axa0volume-preserving approach for animating liquid flows modeled by metaballs. Axa0volume of liquid can be adjusted to axa0previous volume by using the influence radius and the maximum density of metaballs as volume-controlling parameters. Recursive subdivision is used to efficiently calculate the volume of implicit surfaces. The criterion for subdivision is obtained by using the concept of interval analysis and the common property of metaball density functions. Providing axa0sequence of parameters, the volume-compensation region can be controlled according to the substance making up the object, resulting in local preservation of the volume. Set partition is used for determining isolated surfaces in order to apply local-volume preservation.

Visualization of optical phenomena caused by multilayer films with complex refractive indices

This paper proposes a method for rendering objects coated with multilayer thin films. Multilayer thin films are widely utilized in industry for example, optical lenses, optical filters, and windowpanes, among others. Demand for visualization of the optical effects of multilayer films has therefore become great. To visualize optical properties of such films, we have developed a method for calculating composite reflectance and transmittance of the system of multilayer thin films, taking into consideration such factors as multiple reflection, interference and absorption of light inside the films. The proposed method is based on wave optics, and is able to accurately visualize the optical effects of multilayer films consisting of not only dielectric materials, but also metallic and semiconductive materials. Metallic and semiconductive materials are able to absorb light, and their refractive indices are expressed as complex values, Dielectric materials, on the other hand, do not absorb light, and the refractive indices are expressed as real values. Taking into consideration complex refractive indices, the proposed method can visualize optical phenomena caused by various kinds of multilayer thin films. The proposed method is implemented using a raytracer and optical properties of a SiO/sub 2/ film coating on a silicon base, and several kinds of multilayer films coating windowpanes or teapot are visualized to demonstrate the usefulness of the proposed method.

A Fast Display Method of Sky Colour Using Basis Functions

Computer graphics are being used for visual environmental assessment or architectural designs. Displaying the sky as a background is indispensable in generating photorealistic images for such applications. In this paper, we propose a fast display method of the sky colour by expressing the intensity distribution of the sky using basis functions, even if the sun position and/or the camera position are altered. In the proposed method, cosine functions are used as basis functions. The sun altitude is altered at certain intervals and the distributions of the sky colour for each sun altitude are precalculated and stored efficiently using basis functions. The colour of the sky in the view direction of an arbitrary sun position can be obtained from the stored distributions and displayed quickly.