Mikio Shinya

Use of image-based information in judgments of surface-reflectance properties

We examined how well we can recover surface-reflectance properties from shading patterns under changes in surface shape. The stimulus we used was a square surface modulated in depth by a low-pass-filtered random field and rendered by the Phong illumination model [Commun. ACM 18, 311 (1975)]. Two different surface images (target and match) were presented side by side, with either the viewing direction or the surface-normal direction rotating around the horizontal axis. The target shape was manipulated by changing the spatial spectrum, and the target reflectance was manipulated by changing the diffuse-reflection coefficient and the specular-reflection exponent (shininess) of the Phong model. The shape parameters of the match stimulus were fixed, but its reflectance parameters were under the control of subjects, who had to make the apparent reflectance of the two surfaces as similar as possible. The results showed that the constant error (difference between simulated and matched values) was large except when the two surfaces had the same shape parameters or when they differed only in scale. The pattern of the constant errors and response variabilities suggests that the judgments of the subjects were based on the similarity of the luminance histogram of the surface image. Our results demonstrate a limitation of surface-reflectance constancy for changes in shape and the importance of image-based information in reflectance judgments. The results are discussed in relation to previous studies that showed effects of spatial layout on surface-reflectance perception.

Stochastic Motion—Motion Under the Influence of Wind

Stochastic approaches are very effective for modelling natural phenomena. This paper presents a motion model based on a stochastic process as well as physics, and proposes motion synthesis techniques for stochastic motion—motion under the influence of wind.

Interference detection through rasterization

Interference detection is a useful technique, but it is also generally time-consuming. In this paper, a new type of interference detection algorithm is proposed for real-time interference detection. The algorithm first rasterizes the projection of the target objects and calculates the z-values, just as done by the z-buffer visible surface algorithm. For interference detection, all z-values and pointers to the corresponding faces of objects are saved in a z-list for each pixel. Sorting the z-list against the z-values allows the detection of overlapping objects in the z-direction at each pixel position and, thus, finds interfering faces by referring to the face pointers in the z-list. The algorithm is simple and easy to implement. Its computational complexity is directly proportional to the number of polygons, and, in addition, standard graphics hardware can be used to greatly accelerate execution. Another advantage is that the algorithm can be applied to all ‘ray-traceable’ objects, including algebraic surfaces, and procedurally defined objects; traditionally these were not suitable subjects for interference detection. The algorithm is implemented on a graphics workstation using a standard graphics library. Interference detection at a practical interaction speed is achieved for complicated objects such as polyhedra with thousands of polygons. The algorithm can be used in two ways: for inexpensive interference detection, and as an efficient culling method for more precise collision/interference detection algorithms.

Spatial anti-aliasing for animation sequences with spatio-temporal filtering

Anti-aliasing is generally an expensive process because it requires super-sampling or sophisticated rendering. This paper presents a new type of anti-aliasing filter for animation sequences, the pixeltracing filter, that does not require any additional sample nor additional calculation in the rendering phase. The filter uses animation information to calculate correlation among the images, and sub-pixel information is extracted from the sequence based on the correlation. Theoretical studies prove that the filter becomes an ideal antialiasing filter when the filter size is infinite. The algorithm is simple image processing implemented as postfiltering. The computational cost is independent of the complexity of the scene. Experiments demonstrate the efficiency of the filter. Almost complete anti-aliasing was achieved at the rate of about 30 seconds per frame for very complex scenes at a resolution of 256x256 pixels. The pixel tracing filter provides effective antialiasing for animation sequences at a very modest computational cost. CR

Laying out objects with geometric and physical constraints

Modeling scenes involves two tasks:object modeling andobject layout. This paper focuses on object layout and proposes a constraint-based approach which yields a powerful object layout environment. The approach uses collision detection and physical simulation to ensure geometric and physical consistency of the resulting scenes, such as no interpenetration, and physical stability of the objects. A prototype system is developed, providing six basic operations; PUT, PUSH/PULL, TURN/TILT, PICK-UP, TRANSLATE, and ROTATE. The system: ensures geometric and physical consistency; provides easy-to-use operations analogous to object placement in real life; allows twodimensional control easily specified by mouse. Interactive speed is achieved on graphics workstations by using rasterized collision detection and simple quasi-static motion simulation. The system is interfaced to modeling/rendering/animation systems, and realizes an integrated environment for object modeling, object layout, rendering, and animation. We describe several scenes that have been modeled using the system and argue that these experiments confirm that the scene modeling task is greatly simplified by our constraint-based approach.

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.

Unifying measured point sequences of deforming objects

Recent progress in digitizing technologies is making it possible to capture the 3D shapes of moving objects. To efficiently utilize time series records of spatial data, the information must be unified to yield coherent deforming models. We present a general method that unifies unregistered 3D point sequences to generate deforming mesh models. The method does not assume any specific kinematic structure, and is applicable to any digitizer. The method first polygonizes the initial points and then deforms meshes to best fit the subsequent data points while minimizing the deformation energy. Experiments are conducted on real measured data and CG data, and successful results are obtained. As an application of the method, we examine data compression and achieve a 380 fold reduction rate for a measured data sequence.

A Simplified Plane-Parallel Scattering Model and Its Application to Hair Rendering

Fast computation of multiple light reflections and scattering among complex objects is very important in photo-realistic rendering. This paper applies the plane-parallel scattering theory to the rendering of densely distributed objects such as hairs. We propose a simplified plane-parallel model that has very simple analytic solutions. This allows us to deal with multiple scattering phenomena in hair under ambient and area light illumination. The model was successfully applied to hair rendering, and experiments demonstrated the efficiency of the proposed method.

Theories for Mass-Spring Simulation in Computer Graphics: Stability, Costs and Improvements

Spring-mass systems are widely used in computer animation to model soft objects. Although the systems can be numerically solved either by explicit methods or implicit methods, it has been difficult to obtain stable results from explicit methods. This paper describes detailed discussion on stabilizing explicit methods in spring-mass simulation. The simulation procedures are modeled as a linear digital system, and system stability is mathematically defined. This allows us to develop theories of simulation stability. The application of these theories to explicit methods allows them to become as stable as implicit methods. Furthermore, a faster explicit method is proposed. Experiments confirm the theories and demonstrate the efficiency of the proposed methods.

Surface deformation with differential geometric structures

This paper considers the deformation of a given surface to a surface that smoothly connects to previously designed surfaces while reflecting the overall shape of the initial surface. We introduce deformation energy using a Laplacian-based functional, which is defined by the global differential geometric structures of the initial surface. It is shown that the proposed deformation energy does not depend on representations of the initial surface, and relates to the mean curvature vector, a geometric quantity correlated to overall surface shape, and also has a good computational property. An example is presented to demonstrate the effectiveness of our method.