Browsing by Author "Ko, Cheng-Hung"

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A new image segmentation method for removing background of object movies by learning shape priors
(2006)
Ko, Cheng-Hung
;
Tsai, Yu-Pao
;
Shih, Zen-Chung
;
Hung, Yi-Ping
;
資訊工程學系
This paper proposes a new object movie (OM) segmentation method that incorporates shape priors into the segmentation algorithm. ne shape prior introduced into every image of the OM is learned from the 3D model reconstructed by the volumetric graph cuts. Here, the constraint derived from the discrete medial axis is used to improve the reconstruction algorithm. Our segmentation method requires only a small amount of user intervention, which is to select a subset of acceptable segmentations of the OM after the initial segmentation process. Compared to other techniques, our method provides not only the better segmentation result but also the better 3D reconstruction result.
Background removal of multiview images by learning shape priors
(2007-10-01)
Tsai, Yu-Pao
;
Ko, Cheng-Hung
;
Hung, Yi-Ping
;
Shih, Zen-Chung
;
資訊工程學系
Image-based rendering has been successfully used to display 3-D objects for many applications. A well-known example is the object movie, which is an image-based 3-D object composed of a collection of 2-D images taken from many different viewpoints of a 3-D object. In order to integrate image-based 3-D objects into a chosen scene (e.g., a panorama), one has to meet a hard challenge-to efficiently and effectively remove the background from the foreground object. This problem is referred to as multiview images (MVIs) segmentation. Another task requires MVI segmentation is image-based 3-D reconstruction using multiview images. In this paper, we propose a new method for segmenting MVI, which integrates some useful algorithms, including the well-known graph-cut image segmentation and volumetric graph-cut. The main idea is to incorporate the shape prior into the image segmentation process. The shape prior introduced into every image of the MVI is extracted from the 3-D model reconstructed by using the volumetric graph cuts algorithm. Here, the constraint obtained from the discrete medial axis is adopted to improve the reconstruction algorithm. The proposed MVI segmentation process requires only a small amount of user intervention, which is to select a subset of acceptable segmentations of the MVI after the initial segmentation process. According to our experiments, the proposed method can provide not only good MVI segmentation, but also provide acceptable 3-D reconstructed models for certain less-demanding applications.
Domain relaxation dynamics in epitaxial BiFeO3 films: Role of surface charges
(2012-09-01)
Chen, Yi-Chun
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Ko, Cheng-Hung
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Huang, Yen-Chin
;
Yang, Jan-Chi
;
Chu, Ying-Hao
The thermodynamic parameters of domain relaxation process in the absence of external electric fields are related to the intrinsic electrostatic and stress/strain conditions inside the materials, such as the states at surface, states at interface with the electrode, and the atomic defects in the bulk. In order to perform systematical studies of these intrinsic effects, we investigated domain relaxation in a monodomain environment, which was obtained in strained epitaxial BiFeO3 (BFO)(111) films. Without as-grown domain walls and grain boundaries, the epitaxial BFO (111) film provided an ideal system for the dynamic observation of 180-degree domain wall motion. Nano-domains were initially created by writing voltage pulses under the tip of a scanning force microscope and then relaxed through time. The downward polarized domains exhibited much better retention behaviors than the upward domains. A two-step backswitching process was observed, and the behaviors varied with the initial domain sizes. Surface potential measurement showed the dissipation of surface screen charges with time, which was strongly coupled with the 1st step relaxation. The asymmetry behaviors for upward and downward backswitchings, and the two-stage relaxation processes can be explained by the mobile vacancies and the redistribution of surface charges. This study provides the basic understanding of the role of surface charges during the ferroelectric domain relaxation. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4746077]