Browsing by Author "Shih, ZC"

Now showing 1 - 15 of 15

A Bayesian approach to video object segmentation via merging 3-D watershed volumes
(2005-01-01)
Tsai, YP
;
Lai, CC
;
Hung, YP
;
Shih, ZC
;
資訊工程學系
In this letter, we propose a Bayesian approach to video object segmentation. Our method consists of two stages. In the first stage, we partition the video data into a set of three-dimensional (3-D) watershed volumes, where each watershed volume is a series of corresponding two-dimensional (2-D) image regions. These 2-D image regions are obtained by applying to each image frame the marker-controlled watershed segmentation, where the markers are extracted by first generating a set of initial markers via temporal tracking and then refining the markers with two shrinking schemes: the iterative adaptive erosion and the verification against a presimplified watershed segmentation. Next, in the second stage, we use a Markov random field to model the spatio-temporal relationship among the 3-D watershed volumes that are obtained from the first stage. Then, the desired video objects can be extracted by merging watershed volumes having similar motion characteristics within a Bayesian framework. A major advantage of this method is that it can take into account the global motion information contained in each watershed volume. Our experiments have shown that the proposed method has potential for extracting moving objects from a video sequence.
An accuracy enhancement algorithm for hierarchical radiosity
(1998-03-01)
Chang, CC
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
In this research, we propose an algorithm to enhance the accuracy of the hierarchical radiosity. The proposed approach particularly creates links on the hierarchy in a bottom-up fashion according to both a user-specified error tolerance and the minimum patch area. It differs from the original hierarchical method that creates the links in a top-down manner. In our approach, the upper-level patches have more accurate estimates of the kernel. More accurate error bounds can be obtained for the upper-level patches. These error bounds make the creation of links on the hierarchy more accurate. Furthermore, more accurate form factors can also be obtained for the upper-level patches. Thus, we enhance the accuracy of hierarchical radiosity. (C) 1998 Elsevier Science Ltd. All rights reserved.
An efficient and stable ray tracing algorithm for parametric surfaces
(2002-07-01)
Wang, SW
;
Shih, ZC
;
Chang, RC
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose an efficient and stable algorithm for finding the ray-surface intersections. Newton's method and Bezier clipping are adapted to form the core of our algorithm. Ray coherence is used to find starting points for Newton iteration. We introduce an obstruction detection technique to verify whether an intersection point found by using Newton's method is the closest one. When Newton's method fails to achieve convergence, we use Bezier clipping as the substitution to find the intersection points. This combination achieves significant improvement in tracing primary rays. A similar approach also successfully improves the performance in tracing secondary rays.
An improved rendering technique for ray tracing Bezier and B-spline surfaces
(2000-09-01)
Wang, SW
;
Shih, ZC
;
Chang, RH
;
資訊工程學系
;
Department of Computer Science
Both numerical and subdivision methods are widely used approaches for ray tracing parametric surfaces. However, the expense of finding the ray-surface intersection points is a major drawback. Thus, simpler and less memory-intensive strategies are needed to improve these methods without further complicating them. This work presents an efficient algorithm for enhancing the performance of both numerical and subdivision methods. The proposed technique can be extended to most applications based on these two methods. The computational time of both approaches is improved by 16-40%. Copyright (C) 2000 John Wiley & Sons, Ltd.
Comparison between immersion-based and toboggan-based watershed image segmentation
(2006-03-01)
Lin, YC
;
Tsai, YP
;
Hung, YP
;
Shih, ZC
;
資訊工程學系
Watershed segmentation has recently become a popular tool for image segmentation. There are two approaches to implementing watershed segmentation: immersion approach and toboggan simulation. Conceptually, the immersion approach can be viewed as an approach that starts from low altitude to high altitude and the toboggan approach as an approach that starts from high altitude to low altitude. The former seemed to be more popular recently (e.g., Vincent and Soille), but the latter had its own supporters (e.g., Mortensen and Barrett). It was not clear whether the two approaches could lead to exactly the same segmentation result and which approach was more efficient. In this paper, we present two "order-invariant" algorithms for watershed segmentation, one based on the immersion approach and the other on the toboggan approach. By introducing a special RIDGE label to achieve the property of order-invariance, we find that the two conceptually opposite approaches can indeed obtain the same segmentation result. When running on a Pentium-III PC, both of our algorithms require only less than 1130 s for a 256 x 256,image and 115 s for a 512 x 512 image, on average. What is more surprising is that the toboggan algorithm, which is less well known in the computer vision community, turns out to run faster than immersion algorithm for almost all the test images we have used, especially when the image is large, say, 512 x 512 or larger. This paper also gives some explanation as to Why the toboggan algorithm can be more efficient in most cases.
Computer-generated Chinese painting for landscapes and portraits
(2001)
Way, DL
;
Hsu, CW
;
Chiu, HY
;
Shih, ZC
;
資訊工程學系
Practiced for more than three thousand years, Chinese painting stresses the notion of "implicit meaning" in which painters use a minimum amount of strokes to express their deepest feelings. Chinese landscape and figure paintings are the two major themes of Chinese painting. Of relevant interest is more thoroughly understand Chinese art by analyzing basic rules of Chinese painting. This paper proposes two novel methods capable of synthesizing rock textures in Chinese landscape painting and synthesizing portraits in Chinese figure painting, respectively In addition to saving time during trial and error, these two methods attempt to synthesize painting styles. After users only specify the contour and parameters, our methods underwrite the complete painting process. With the requirement of familiarity with painting skills, individuals can paint various styles of Chinese painting.
Hierarchical feature-based volume morphing
(2002-01-01)
Ke, HR
;
Tsai, YP
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Morphing techniques have been applied to many fields to create astounding visual effects. In this paper, we present a hierarchical feature-based volume morphing-algorithm, which leverages the idea of feature-element hierarchy to significantly improve morphing effects. A new type of feature element, the cylinder field, is also given to facilitate the task of feature specification and correspondence. Additionally, with a slight modification, the proposed algorithm can be applied to volume animation.
Physical-based model of ink diffusion in Chinese ink paintings
(2003)
Huang, SW
;
Way, DL
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Chinese ink painting is a traditional art that is over three thousand years old. It is a type of non-photorcalistic rendering. However, research on Chinese ink painting is scarce. Simulating the behavior of Chinese ink is challenging work because ink moves in a complex manner. This paper presents a new method for simulating ink diffusion based on observation and analysis. The proposed method can simulate various expressions of tones on different types of paper. The elucidation of the effect of mixing simulated strokes made by different kinds of brushes is an important contribution of the method. Finally, the simulated results are compared with real ink painting.
Physically-based patination for underground objects
(2000)
Chang, YX
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Although current photorealistic rendering techniques can produce very impressive images, the rendered objects are often too clean and shiny. Thus, the resulting images look unnatural. This paper proposes a physically-based model to simulate the appearance of patinas on ancient Chinese bronzes. Buried in the soil for thousands of years, many patinas are found on the surface of ancient bronzes as a result of the aging process and the physical and chemical conditions of the soil environment. The development of patinas is modulated herein by L-systems according to tendencies based on the environmental factors and object geometry. The tendencies are employed to represent the accumulative effect of all factors on patination. The proposed model can be extended to simulate a variety of metallic patinas including the ancient Chinese bronzes discovered at San-hsing-tui, Sichuan, China.
Real-time software method for preserving eye contact in video conferencing
(2004-09-01)
Tsai, YP
;
Kao, CC
;
Hung, YP
;
Shih, ZC
;
資訊工程學系
By maintaining eye contact in visual communication, such as in video conferencing, the feeling of intimacy can be greatly enhanced. Unfortunately, due to the physical constraints on the arrangement of cameras and monitors, it is not easy to preserve eye contact in video conferencing. Most people have tried to solve this problem using hardware approaches, which usually lead to bulky or expensive solutions. In this paper, we propose a real-time software method for preserving eye contact in video conferencing. For each station involved in video conferencing, we use two pre-calibrated cameras to acquire a stereo view of the local participant. Then, we apply disparity-based view morphing to the acquired stereo view to generate the desired view that preserves eye contact with another participant. Our experiments demonstrate that the eye contact problem can indeed be solved in real-time by using our software approach. This is the first time a software approach has been shown to be practical for preserving eye contact in video conferencing.
The synthesis of rock textures in Chinese landscape painting
(2001)
Way, DL
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
In Chinese landscape painting, rock textures portray the orientation of mountains and contribute to the atmosphere. Many landscape-painting skills are required according to the type of rock. Landscape painting is the major theme of Chinese painting. Over the centuries, masters of Chinese landscape painting developed various texture strokes. Hemp-fiber and axe-cut are two major types of texture strokes. A slightly sinuous and fiber stroke is used for describing the gentle sloped of rock formations whereas seemingly broken line, the hemp the axe-cut stroke best depicts hard, rocky surfaces. This paper presents a novel method of synthesizing rock textures in Chinese landscape painting, useful not only to artists who want to paint interactively, but also in automated rendering of natural scenes, The method proposed underwrites the complete painting process after users have specified only the contour and parameters.
The synthesis of rust in seawater
(2003-03-01)
Chang, YX
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Computer graphics researchers have recently revealed that the presence of imperfections is an essential part of the illusion of photorealism. An improved model to simulate the rust development of ferrous metals in seawater is proposed. The tide and the current, under the gravity of the sun and the moon, affect the stability of the environment at the bottom of the ocean. A simple current model is employed to elucidate the periodic transition of currents in the ocean. L-systems, coupled with the current model, modulate the diffusion of rust according to tendencies based on the object geometry and environmental factors. Changing the underlying distributions of tendency allows images of a variety of metallic rusts to be generated.
The synthesis of trees in Chinese landscape painting using silhouette and texture strokes
(2002)
Way, DL
;
Lin, YR
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Practiced for more than three thousand years, Chinese painting emphasizes "implicit meaning", and involves painters' using a minimal number of brush strokes to express their deepest feelings. Landscapes are one of the most important themes in Chinese painting, Trees are the essential painting objects. This paper presents a set of novel methods to automatically draw trees in Chinese ink painting from 3D polygonal models. Outline rendering and texture generation uses the information of the silhouette, shade and orientation of three-dimensional model's surface to draw a particular tree. Four reference maps are established to analyze the information for the bark texture. These methods can draw various styles of bark texture by defining the texture patterns. Finally, this paper demonstrates some results obtained with our method.
Tighter error bounds and weighted error metrics for hierarchical radiosity
(1998-04-01)
Chang, CC
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
In this paper we first derive a tighter error bound on form factors as a subdivision criterion for the hierarchical radiosity algorithm. Such an error bound can reduce more unnecessary links and improve the performance of the hierarchical radiosity algorithm to meet a user-specified error tolerance. We then propose a weighted error metric in form factor computation such that more effort is automatically applied to shadow boundaries. Evaluating form factors along shadow boundaries with a higher degree of precision should enhance the quality of human perception. Using the proposed tighter error bound on the weighted error metric, we not only improve the performance but also increase the accuracy of the hierarchical radiosity algorithm. (C) 1998 John Whey & Sons, Ltd.
Wrinkle rendering of terrain models in Chinese landscape painting
(2006-03-01)
Way, DL
;
Shih, ZC
;
資訊工程學系
;
Department of Computer Science
Landscapes have been the main theme in Chinese painting for over one thousand years. Chinese ink painting is a form of nonphotorealistic rendering. Terrain is the major subject in Chinese landscape painting, and surface wrinkles are important in conveying the orientation of Mountains and contributing to the atmosphere. Over the centuries, masters of Chinese landscape painting have developed various kinds of wrinkles. This work develops a set of novel methods for rendering wrinkles in Chinese landscape painting. A three-dimensional terrain is drawn as an outline and wrinkles, using information oil the shape, shade and orientation of the terrain's polygonal surface. The major contribution of this work lies ill the modeling and implementation of six major types of wrinkles on the surface of terrain. using traditional Chinese brush techniques. Users can select a style of wrinkle and input parameters to control the desired effect. The proposed method then completes the painting process automatically.