Tokiichiro Takahashi

Comprehensible rendering of 3-D shapes

We propose a new rendering technique that produces 3-D images with enhanced visual comprehensibility. Shape features can be readily understood if certain geometric properties are enhanced. To achieve this, we develop drawing algorithms for discontinuities, edges, contour lines, and curved hatching. All of them are realized with 2-D image processing operations instead of line tracking processes, so that they can be efficiently combined with conventional surface rendering algorithms.Data about the geometric properties of the surfaces are preserved as Geometric Buffers (G-buffers). Each G-buffer contains one geometric property such as the depth or the normal vector of each pixel. By using G-buffers as intermediate results, artificial enhancement processes are separated from geometric processes (projection and hidden surface removal) and physical processes (shading and texture mapping), and performed as postprocesses. This permits a user to rapidly examine various combinations of enhancement techniques without excessive recomputation, and easily obtain the most comprehensible image.Our method can be widely applied for various purposes. Several of these, edge enhancement, line drawing illustrations, topographical maps, medical imaging, and surface analysis, are presented in this paper.

NC machining with G-buffer method

The G-buffer method is applied to NC machining. A total NC system is created that consists of all essential functions, such as tool path generation, path verification, and feed rate control. Moreover, any combination of object surface and tool shape is acceptable. By utilizing G-buffers created from a parallel projection, the required NC functions are realized as image processing operations. This ensures that the NC software is independent from surface description. Conventional rendering software can be used to make the G-buffers. Any surface can be milled if it can be rendered by parallel projection. Tool shape changes can be easily handled by changing the image processing filters. 3D examples of geometric surfaces, mesh data, and volume data are milled with this method, and the results show that the method is very effective.

Sight-dedicated computer graphics machine

The. architecture of, and a performance estimate for, the dedicated graphics processor ‐ SIGHT, a high‐speed ray tracing machine, are presented. Ray tracing is a vector calculation in 3–dimensional (3–D) space and each ray to be traced can be calculated independently. The SIGHT is designed so that it speeds up the execution of the ray tracing algorithm at two levels of parallel operations: the pixel‐level parallel operation by multiprocessors and the instruction‐level parallel operation by the new processing element (PE) architecture. The features of the PE are:

Fast Analytic Shading and Shadowing for Area Light Sources

This paper describes a fast analytic algorithm that generates exact highlights and soft shadows from area light sources. In order to realize fast shadowing, we propose the ray‐oriented buffer which segments 3D space by following light rays from polygonal sources. Each cell of the buffer stores objects that intersect a related subspace. Candidate objects which may cast shadows onto a point are selected by referring to the buffer. The candidates are then tested with their shadow bounding volumes to suppress objects that never occlude light sources.

Highlighting Rounded Edges

This paper proposes an efficient method for rendering highlights on rounded edges, which is important for photorealism and comprehensibility. The rounded edges are shaded as thin cylinders separately from the planar surfaces. To ensure coherence with the planar surfaces, an edge shading equation is proposed, which derives an appropriate edge shading model from any conventional model. The final image is obtained by drawing edges like wire-frames onto the planar surface image. Using this method, aliasing-free edge highlights can be generated from simple edge data with little increase in computation cost.

Generalized symmetry and its application to 3D shape generation

A new method for easily and rapidly generating three-dimensional shapes from two-dimensional line-drawings is presented. This method is based on the generalized symmetry constraint. Generalized symmetry is an extended concept of threedimensional symmetry and its axis is a 3D smooth curve. This paper first develops the definition and constraint of generalized symmetry, and then describes an algorithm which generates the three-dimensional shape of an object from its linedrawing. The generation algorithm is extended to generate generalized cylindrical objects from line-drawings. Several experiments by computer simulation verify that the algorithm can generate three-dimensional shapes from line-drawings.

Non-photorealistic rendering technique for depicting 3D objects motion

A still image extracted from a 3D animation sequence does not contain any information about the motions of 3D objects. In order to represent fast-moving 3D objects in a still image, the motion blur technique has been used. However, it cannot easily depict other kinds of motions. Several non-photorealistic rendering approaches [1] [2] have been proposed to depict the motions of 3D objects using “speed lines”. Speed lines, introduced by Masuch [1], are defined and drawn as difference vectors between the current and previous position vectors of the vertices of 3D object contours on a projected screen plane. Kawagishi et al. [2] generated very thin polygons instead of difference vectors. However, it is a tedious task to describe speed line types suitable for motion speed manually and repeatedly. We are studying a new non-photorealistic rendering technique that can depict various kinds of motions of 3D objects in animation scenes automatically and in real time. First, a motion is divided into a translation of and a rotation around the object’s center of gravity. For translation motion, we obtain the difference vectors of only the object’s center of gravity instead of those of the vertices of the 3D object’s contours. Texture-mapped polygons are generated as speed lines. Experimental results verify that our technique is effective and efficient enough to depict various motions of 3D objects automatically in real time.

Precise rendering method for exact anti-aliasing and highlighting

This paper introduces the Precise Rendering Method, which generates accurately anti-aliased and highlighted images from tessellated polygons. The Precise Rendering Method first solves the aliasing problems of hidden surface removal by using the Cross Scanline Algorithm. This algorithm can exactly calculate polygon areas projected onto each pixel by using horizontal and vertical scanlines. Aliasing artifacts in shading are then prevented by the Reflection Intergration Method, which analytically integrates the intensity of reflection in the solid angle defined by surface normals at vertices of the projected area. Several synthesized images are created to show the efficiency of the Precise Rendering Method.

A dedicated graphics processor SIGHT-2

SIGHT-2 is a multiprocessor system that is intended to efficiently execute the ray tracing algorithm. To achieve high efficiency, three kinds of parallel execution mechanisms; (i) a multiprocessor configuration, (ii) a parallel execution of three dimensional vector operations, and (iii) functionally distributed parallel processing are introduced. Owing to the latter two techniques, each processing element (PE) has the ability to execute the standard ray tracing algorithm 10 times faster than a VAX11/780 with a floating point accelerator. In the present configuration, SIGHT-2 utilizes 16 PEs, which results in a peak power of 66.72 MFLOPS / 133.28 MIPS. During ray tracing, the efficiency of each PE is over 99% under static load balancing. In this paper, SIGHT-2 system architecture, its PE configuration, and VLSIs design are discussed. The system performance is also discussed.

Rust aging simulation considering object's geometries

Realistic representation of nature scenes is one of the most challenging areas in computer graphics community. There are important factors to synthesize realistic scenes in 3D CG which are decayed materials such as dead trees, weathered statues, rusty metals and so on. We are interested in the methodology for simulating its decaying processes. In this paper, we propose a simple method for rust aging simulation based on a probabilistic cellular automaton model taking into account objects geometries.