Takanori Nagae

Contour tracking and synthesis in image sequences

A method for generating a sequence of synthetic images from two different image sequences is described. The method is composed of two major processes, i.e., an object tracking and an image synthesizing. The process of the object tracking consists of two phases. The first phase is to determine an initial contour which roughly approximates the shape of the object, and the second phase is to extract an accurate contour from the initial one by using an active contour model. An initial contour of an object in the first frame is specified manually, and those in the following frames are determined by referring the extracted contour in the previous frame. The contour extracted in the current frame is deformed by detecting nonrigid object movements and the resultant shape is used as the initial contour of the active contour model in the next frame. The motion parameters representing camera motions are also estimated by calculating optical flows between two successive frames.

Object surface construction from volume data with appropriate topology

The reflection, diffusion, transparency and refraction of a ray on the surface of an object are essential elements to the object. Such optical interference by knowing each intersection of a ray and the surface of the object together with the normal vector at the intersection. In most conventional methods, the surface of an object is detected from a set of volume data, and a shading process is applied to it. This process has a difficulty in forming a continuous surface of an object since the volume data consist of discrete elements. The topology of an object surface also is important in a reconstruction of a 3-dimensional model (e.g., by laser stereo lithography) in which the surface should be closed with no intersection. This paper proposes two types of algorithms for reconstruction of the surface of an object: the modified marching cubes algorithm (a modification of the marching cubes algorithm); and the deformed cubes algorithm. Each of the proposed algorithms reconstructs a sufficiently smooth and topologically appropriate surface of an object.

Surface construction and contour generation from volume data

New surface construction algorithms are presented. The idea is based on Marching Cubes algorithm and the aim of the modification proposed in the present article is to provide topologically appropriate solutions that guarantee to produce triangulated closed surfaces as the equiscalar surface within a volume. There are roughly three variations of modifications; 1- connective, (root)2-connective and Adaptive Marching Cubes. Surface construction algorithms are also applicable to slice-by-slice solid modeling, such as laser stereolithography. An algorithm for obtaining contours on an intermediate slice interpolated between two slices is shown.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Digital halftoning using a generalized Peano scan

There are many kinds of image processing that are essentially sequential. Raster scan is commonly used for such sequential operations, to scan images from left to right, and line by line. Another scanning, called the Peano scan, traverses an image from a pixel to its neighboring one and the direction frequently changes. This scan prevents from producing periodic patterns, which are sometimes observed in images transformed in raster scan line order. However, the Peano scan is applied to only square images, and the horizontal and vertical sizes must be a power of two. We present a new scanning, called a ternary scan, which has the same property as the Peano scan and can fit to any rectangular images. Application of the ternary scan to Floyd-Steinbergs halftoning is shown.

Comparisons of triangulated isosurfaces constructed from volume data

The ray reflection, refraction, diffusion, and transparency are important functions for visualizing 3D objects. Every ray intersection with object boundaries and its normal direction on the intersecting point are used to simulate the optical interference of rays with objects. It is theoretically impossible, however, to construct smoothly interpolated continuous boundaries from a discrete array of sampled values, such as a set of volume elements. Although many volume visualization techniques have been proposed, it is still difficult to ensure appropriate surface topology by a simple algorithm. In the present paper, two new isosurface constructors named MMC (Modified Marching Cubes) and DC (Deformed Cubes) are investigated. MMC is a modification of Marching Cubes algorithm, which is well known as a high resolution isosurface constructor. MMC algorithm produces topologically correct triangulated isosurfaces that are guaranteed to be orientable and closed. DC algorithm is much simpler than MMC, and the produced triangulated isosurfaces are also topologically adequate, and as accurate as MMC. Experimental results and comparisons of the interpolated triangulated isosurfaces in terms of the shape precision between MMC and DC are also presented.

Obtaining 3D shape of potted plants and modeling

An approach obtaining three dimensional object shapes from a series of silhouette images is presented. A two dimensional image sequence of an object put on a turning table is taken by a video camera at regular time intervals to obtain silhouette images from multiple viewpoints. A pillar is obtained by sweeping the silhouette along a line parallel to the viewing direction. An intersection of the pillars from all the viewpoints surrounding the object is sampled to give a set of volume data. The segmentation and the modeling of potted plants are also studied as an application of computer graphics. The set of volume data is segmented into three parts of a potted plant, i.e., a pot, stems and leaves. Then, the pot and the stems are modeled by frustums and each of the leaves is approximated by two Bezier surface patches.