Takafumi Saito

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.

Interactive aesthetic curve segments

To meet highly aesthetic requirements in industrial design and styling, we propose a new category of aesthetic curve segments. To achieve these aesthetic requirements, we use curves whose logarithmic curvature histograms (LCH) are represented by straight lines. We call such curves aesthetic curves. We identify the overall shapes of aesthetic curves depending on the slope of LCH α, by imposing specific constraints to the general formula of aesthetic curves. For interactive control, we propose a novel method for drawing an aesthetic curve segment by specifying two endpoints and their tangent vectors. We clarify several characteristics of aesthetic curve segments.

Two-tone pseudo coloring: compact visualization for one-dimensional data

A new pseudo coloring technique for large scale one-dimensional datasets is proposed. For visualization of a large scale dataset, user interaction is indispensable for selecting focus areas in the dataset. However, excessive switching of the visualized image makes it difficult for the user to recognize overview/ detail and detail/ detail relationships. The goal of this research is to develop techniques for visualizing details as precisely as possible in overview display. In this paper, visualization of a one-dimensional but very large dataset is considered. The proposed method is based on pseudo coloring, however, each scalar value corresponds to two discrete colors. By painting with two colors at each value, users can read out the value precisely. This method has many advantages: it requires little image space for visualization; both the overview and details of the dataset are visible in one image without distortion; and implementation is very simple. Several application examples, such as meteorological observation data and train convenience evaluation data, show the effectiveness of the method.

Quasi-Aesthetic Curves in Rational Cubic Bézier Forms

AbstractDesigning aesthetically appealing models is vital for the marketing success of industrial products. In this paper, we propose quasi-Aesthetic Curves that can be used in CAD systems for aesthetic shape design. Quasi-Aesthetic Curves represented in rational cubic Bezier Forms are curves whose logarithmic curvature histograms (LCHs) become nearly straight lines. The monotonicity of curvature of quasi-Aesthetic Curves is checked by the proposed method. We generate quasi-Aesthetic Curves by approximating the Aesthetic Curves whose LCHs are strictly represented by straight lines. We show that one Aesthetic Curve segment whose change of tangential angle is less than 90 deg. can be replaced by one quasi-Aesthetic Curve segment guaranteeing the monotonicity of the curvature in most of practical situations.

Log-aesthetic space curve segments

For designing aesthetic surfaces, such as the car bodies, it is very important to use aesthetic curves as characteristic lines. In such curves, the curvature should be monotonically varying, since it dominates the distortion of reflected images on curved surfaces. In this paper, we present an interactive control method of log-aesthetic space curves. We define log-aesthetic space curves to be curves whose logarithmic curvature and torsion graphs are both linear. The linearity of these graphs constrains that the curvature and torsion are monotonically varying. We clarify the characteristics of log-aesthetic space curves and identify their family. Moreover, we present a novel method for drawing a log-aesthetic space curve segment by specifying two endpoints, their tangents, the slopes, α and β, of straight lines of the logarithmic curvature and torsion graphs, and the torsion parameter Ω. Our implementation shows that log-aesthetic curve segments can be controlled fully interactively.

Logarithmic curvature and torsion graphs

This paper introduces logarithmic curvature and torsion graphs for analyzing planar and space curves. We present a method for drawing these graphs from any differentiable parametric curves and clarify the characteristics of these graphs. We show several examples of theses graphs drawn from planar and 3D Bezier curves. From the graphs, we can see some interesting properties of curves that cannot be derived from the curvature or torsion plots.

Planar two-point G1 Hermite interpolating log-aesthetic spirals

Log-aesthetic spirals are currently being studied as fair curves that can be used in computer aided design. A family of planar log-aesthetic spirals that include a point of zero curvature is used in this paper. The two-point G^1 Hermite data that is considered has some restrictions on the angles. This paper proves that for any member of the family, a unique segment of that spiral can be found that matches given two-point G^1 Hermite data.

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.

A Visualization of Research Papers Based on the Topics and Citation Network

Survey of research papers is not an easy task for novice researchers, because they are not always good at finding all appropriate keywords for the survey. Moreover, it is not easy for them to understand positions of papers in their research fields instantly, even when they use famous search engines like Google Scholar, it may often take a long time for them to find scholarly literature. On the other hand, many researchers have presented citation visualization techniques for surveying research papers. However, it is still often difficult to observe the complicated relations across multiple research fields or traverse the entire relations in their interest. In this paper, we proposed a visualization technique for citation networks applying topic-based paper clustering. Our technique categorizes papers applying LDA (Latent Dirichlet Allocation), and constructs clustered networks consisting of the papers.

Ray tracing using dynamic subtree-algorithm and speed evaluation

For fast ray tracing computation, it is essential to determine efficiently which object is projected on each pixel of the image plane. The data structure plays a major role in this process, and a hierarchical tree data structure of the objects often is used. This paper proposes a very fast algorithm based on use of a subtree of given hierarchical tree. Experimental results show that the number of intersection computations can be reduced greatly by the use of subtrees and that the computation cost for dynamic construction of a subtree is low. Analysis of the algorithm supports the experimental results. Experimental comparison with Arvos algorithm [6], one of the fastest existing algorithms, shows that our algorithm is faster for primary rays.