Katsumi Tadamura

Optical Flow Computation on Compute Unified Device Architecture

In this study, the implementation of an image processing technique on compute unified device architecture (CUDA) is discussed. CUDA is a new hardware and software architecture developed by NVIDIA Corporation for the general- purpose computation on graphics processing units. CUDA features an on-chip shared memory with very fast general read and write access, which enables threads in a block to share their data effectively. CUDA also provides a user- friendly development environment through an extension to the C programming language. This study focused on CUDA implementation of a representative optical flow computation proposed by Horn and Schunck in 1981. Their method produces the dense displacement field and has a straightforward processing procedure. A CUDA implementation of Horn and Schuncks method is proposed and investigated based on simulation results.

Modeling of Skylight and Rendering of Outdoor Scenes

Photorealistic animated images are extremely effective for pre‐evaluating visual impact of city renewal and construction of tall buildings. In order to generate a photorealistic image not only the direct sunlight but also skylight must be considered.

Rendering of landscapes for environmental assessment

Abstract These days, computer graphics are playing an important role in giving lifelike information for the estimation of landscapes after finishing large-scale construction projects. However, how to create vivid photo-realistic images based on exact geometry and optical phenomena is still an essential issue. The authors introduce rendering techniques for visual environmental landscape assessment using computer graphics and/or video sequence images. The techniques are classified into three categories: computer generated images and montages for visualizing landscapes with photo-realistic rendering techniques, panoramic images and panoramic montages employing image-based rendering techniques made from video sequence images, and panned/zoomed video sequence images composited with computer generated images. The basic techniques and their validity are discussed by using practical examples.

Fast Photo-Realistic Rendering of Trees in Daylight

We propose a fast approach for photo‐realistic rendering of trees under various kinds of daylight, which is particularlyuseful for the environmental assessment of landscapes. In our approach the 3D tree models are transformedto a quasi‐3D tree database registering geometrical and shading information of tree surfaces, i.e. their normalvectors, relative depth, and shadowing of direct sunlight and skylight, by using a combination of 2D buffers.Thus the rendering speed of quasi‐3D trees depends on their display sizes only, regardless of the complexity oftheir original 3D tree models. By utilizing a two‐step shadowing algorithm, our proposed method can create highquality forest scenes illuminated by both sunlight and skylight at a low cost. It can generate both umbrae andpenumbrae on a tree cast by other trees and any other objects such as buildings or clouds. Transparency, specularreflection and inter‐reflection of leaves, which influence the delicate shading effects of trees, can also be simulatedwith verisimilitude.

Synchronizing computer graphics animation and audio

Our prototype authoring tool synchronizes computer graphics animation, narration and background music. It lets users visualize the contents of a background music track and narration along a single time line and displays an animations scenario sharing the same time line. A graphical user interface supports interactive editing of both background music and narration without any loss in quality.

Rendering optimal solar shadows with plural sunlight depth buffers

We propose a novel method, based on the two-pass Z-buffer algorithm, to calculate shadows with sufficient precision and efficiency for rendering a daytime landscape with solar penumbrae. The special feature of the proposed method is that the shadows can be preserved with a precision superior to that of any visible surface. We use the optimal number of plural shadow buffers to do this; it gives a fairly satisfying trade–off between computation time and quality of shadows.

CUDA Implementation of Deformable Pattern Recognition and its Application to MNIST Handwritten Digit Database

In this study we propose a deformable pattern recognition method with CUDA implementation. In order to achieve the proper correspondence between foreground pixels of input and prototype images, a pair of distance maps are generated from input and prototype images, whose pixel values are given based on the distance to the nearest foreground pixel. Then a regularization technique computes the horizontal and vertical displacements based on these distance maps. The dissimilarity is measured based on the eight-directional derivative of input and prototype images in order to leverage characteristic information on the curvature of line segments that might be lost after the deformation. The prototype-parallel displacement computation on CUDA and the gradual prototype elimination technique are employed for reducing the computational time without sacrificing the accuracy. A simulation shows that the proposed method with the k-nearest neighbor classifier gives the error rate of 0.57% for the MNIST handwritten digit database.

A Model of Skylight and Calculation of Its Illuminance

It has still been extremely expensive to make outdoor scenes illuminated by direct sunlight and skylight because of the limited models of these light sources and expensive algorithms of rendering. In this paper, a multi-layered parallelepiped is proposed for representing skylight and direct sunlight sources; the total energy of their light is regulated due to time and the position of a scene to be rendered. With this model, the illuminance on a calculation point is calculated. Then two methods for reducing the calculation cost, grouping and classifying obstacles, are discussed. This model makes a good trade-off between the cost and accuracy of rendering, and gives solar penumbra effects with a low cost.

Photorealism in computer graphics—Past and present

Abstract The aim of this paper is to trace the development of photorealism in computer graphics, especially as used for lighting simulation and landscape assessment. First, we briefly review the progress of rendering techniques since the beginning of computer graphics in the 1960s up until the present—how many different kind of attributes the objects in computer graphics have acquired in order to create photorealistic images. Then, we introduce two models in our research; trees using two pictures and light in/above the water. Lastly, the problems for creating photorealistic images to be solved in the future are outlined.

Automatically compositing still images and landscape video sequences

We present an approach to deliver high-quality composites of panned, tilted, and zoomed landscape video sequences with computer-generated still images, targeted at large-scale construction projects. We propose a fully automatic camera-tracking algorithm to accurately composite computer-generated still images into panned, tilted, and zoomed video-sequence frames taken by hand or from a tripod. It provides an excellent means for a visual environmental assessment. First, we recover the camera parameters in fully automatic mode. Meanwhile, we initiate the matrix to match the coordinates between computer-generated objects and the video sequences first frame image by employing our algorithm and using the surrounding terrain map. We render computer-generated objects on a noninterlaced plane and erase the regions of their foreground by using image retouching software. Then, the algorithm automatically modifies the images and interlaces them to match each video-sequence frame by using the camera parameters. The images are also automatically composited with the video-sequence frames.