Browsing by Author "Tai, SC"

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Evidence of birefringence and anomalous electromagnetic-pulse propagation in an organic light-emitting diode
(2005-06-05)
Tai, SC
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Chern, JL
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Huang, YC
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Tseng, MR
;
Lin, HK
dHigh-speed electromagnetic characteristics of an organic light-emitting diode (OLED) are explored in this paper. When a high-frequency (similar to 14 GHz) microwave pulse is injected into an OLED, the pulse is split into two peaks: one peak is delayed by 1.725 ns and another one is advanced by 0.183 ns, which also suggests the existence of an extremely low-speed group velocity. The effective thickness of the OLED sample is similar to 355.8 nm and, as a result, the effective index of refraction is similar to 107 when the splitting phenomenon occurs. (c) 2005 Wiley Periodicals, Inc.
Predictive classifier for image vector quantization
(2000-09-01)
Tai, SC
;
Wu, YG
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Kuo, IS
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資訊工程學系
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Department of Computer Science
A new scheme for a still image encoder using vector quantization (VQ) is proposed. The new method classifies the block into a suitable class and predicts both the classification type and the index information. To achieve better performance, the encoder decomposes images into smooth and edge areas by a simple method. Then, it encodes the two kinds of region using different algorithms to promote the compression efficiency. Mean-removed VQ (MRVQ) with block sizes 8 x8 and 16x16 pixels compress the smooth areas at high compression ratios. A predictive classification VQ (CVQ) with 32 classes is applied to the edge areas to reduce the bit rate further. The proposed prediction method achieves an accuracy ratio of about 50% when applied to the prediction of 32 edge classes. Simulation demonstrates its efficiency in terms of bit rate reduction and quality preservation. When the proposed encoding scheme is applied to compress the "Lena" image, it achieves the bit rate of 0.219 bpp with the peak SNR (PSNR) of 30.59 dB. (C) 2000 Society of Photo-Optical Instrumentation Engineers. [S0091-3286(00)00908-9].