Kyung-Yong Chwa

Image metamorphosis with scattered feature constraints

This paper describes an image metamorphosis technique to handle scattered feature constraints specified with points, polylines, and splines. Solutions to the following three problems are presented: feature specification, warp generation, and transition control. We demonstrate the use of snakes to reduce the burden of feature specification. Next, we propose the use of multilevel free-form deformations (MFFD) to compute C/sup 2/-continuous and one-to-one mapping functions among the specified features. The resulting technique, based on B-spline approximation, is simpler and faster than previous warp generation methods. Furthermore, it produces smooth image transformations without undesirable ripples and foldovers. Finally, we simplify the MFFD algorithm to derive transition functions to control geometry and color blending. Implementation details are furnished and comparisons among various metamorphosis techniques are presented.

Image metamorphosis using snakes and free-form deformations

This paper presents new solutions to the following three problems in image morphing: feature specification, warp generation, and transition control. To reduce the burden of feature specification, we first adopt a computer vision technique called snakes. We next propose the use of multilevel free-form deformations (MFFD) to achieve -continuous and one-to-one warps among feature point pairs. The resulting technique, based on B-spline approximation, is simpler and faster than previous warp generation methods. Finally, we simplify the MFFD method to construct -continuous surfaces for deriving transition functions to control geometry and color blending.

Schemes for fault-tolerant computing: A comparison of modularly redundant and t-diagnosable systems

In this paper we compare the performances, in the presence of faults, of two basic classes of computing systems: the modularly redundant systems and the t-diagnosable systems. We, then, introduce an undirected graph model for t-diagnosable systems to avoid certain difficulties in diagnostic testing which may arise in ordinary (digraph model) t-diagnosable systems. An optimal diagnosis algorithm for this new model is also presented.

Image Morphing Using Deformation Techniques

This paper presents a new image morphing method using a two-dimensional deformation technique which provides an intuitive model for a warp. The deformation technique derives aC1-continuous and one-to-one warp from a set of point pairs overlaid on two images. The resulting in-between image precisely reflects the correspondence of features specified by an animator. We also control the transition behaviour in a metamorphosis sequence by taking another deformable surface model, which is simpler and thus more efficient than the deformation technique for a warp. The proposed method separates transition control from feature interpolation and is easier to use than the previous techniques. The multigrid relaxation method is employed to solve a linear system in deriving a warp or transition rates. This method makes our image morphing technique fast enough for an interactive environment.

Visibility-Based Pursuit-Evasion in a Polygonal Region by a Searcher

We consider the most basic visibility-based pursuit-evasion problem defined as follows: Given a polygonal region, a searcher with 360° vision, and an unpredictable intruder that is arbitrarily faster than the searcher, plan the motion of the searcher so as to see the intruder. In this paper, we present simple necessary and sufficient conditions for a polygon to be searchable, which settles a decade-old open problem raised in [13]. We also show that every searchable polygon is also searchable by a searcher with two flashlights (that is, two ray visions). This implies, combined with the previous work [7], that there is an O(n2)-time algorithm for constructing a search path for an n-sided polygon.

Hamiltonian properties on the class of hypercube-like networks

Hamiltonian properties of hypercube variants are explored. Variations of the hypercube networks have been proposed by several researchers. In this paper, we show that all hypercube variants are hamiltonian-connected or hamiltonian-laceable. And we also show that these graphs are bipancyclic.

Recursive circulants and their embeddings among hypercubes

We propose an interconnection structure for multicomputer networks, called recursive circulant. Recursive circulant G(N,d) is defined to be a circulant graph with N nodes and jumps of powers of d. G(N,d) is node symmetric, and has some strong hamiltonian properties. G(N,d) has a recursive structure when N=cdm, 1⩽c<d. We develop a shortest-path routing algorithm in G(cdm,d), and analyze various network metrics of G(cdm,d) such as connectivity, diameter, mean internode distance, and visit ratio. G(2m,4), whose degree is m, compares favorably to the hypercube Qm. G(2m,4) has the maximum possible connectivity, and its diameter is ⌈(3m−1)/4⌉. Recursive circulants have interesting relationship with hypercubes in terms of embedding. We present expansion one embeddings among recursive circulants and hypercubes, and analyze the costs associated with each embedding. The earlier version of this paper appeared in Park and Chwa (Proc. Internat. Symp. Parallel Architectures, Algorithms and Networks ISPAN’94, Kanazawa, Japan, December 1994, pp. 73–80).

Scheduling broadcasts with deadlines

We investigate the problem of scheduling broadcasts in data delivering systems via broadcast, where a number of requests from several clients can be simultaneously satisfied by one broadcast of a server. Most of prior work has focused on minimizing the total flow time of requests. It assumes that once a request arrives, it will be held until satisfied. In this paper, we are concerned with the situation that clients may leave the system if their requests are still unsatisfied after waiting for some time, that is, each request has a deadline. The problem of maximizing the throughput, for example, the total number of satisfied requests, is developed, and there are given online algorithms achieving constant competitive ratios.

Searching a polygonal room with one door by a 1-searcher

The 1-searcher is a mobile guard whose visibility is limited to a ray emanating from his position, where the direction of the ray can be changed continuously with bounded angular rotation speed. Given a polygonal region with a specified boundary point d, is it possible for a 1-searcher to eventually see a mobile intruder that is arbitrarily faster than the searcher within , before the intruder reaches d? We decide this question in O (n log n)-time for an n-sided polygon. Our main result is a simple characterization of the class of polygons (with a boundary point d) that admits such a search strategy. We also present a simple O(n2)-time algorithm for constructing a search schedule, if one exists. Finally, we compare the search capability of a 1-searcher with that of two guards.

Image morphing using deformable surfaces

This paper presents a new image morphing technique using deformable surfaces. Drawbacks of previous techniques are overcome by a physically-based approach which provides an intuitive model for a warp. A warp is derived by two deformable surfaces which specify horizontal and vertical displacements of points on an image. This paper also considers the control of transition behavior in a metamorphosis sequence. The presented technique separates the transition control from interpolating features making it much easier to use than the previous techniques. The multigrid relaxation method is used to compute a deformable surface for a warp or transition rates. This method makes the presented image morphing technique fast enough for an interactive environment.<<ETX>>