Browsing by Author "HSIEH, TH"

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A COLOR CONSTANCY MODEL FOR ADVANCED TELEVISION CAMERAS
(1992-06-01)
CHANG, PR
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HSIEH, TH
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YEH, BF
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交大名義發表
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電信工程研究所
In high-fidelity color sensing, one may attempt to use recorded video image data from an electronic camcorder to generate a rendering that appears the same as the original image did at the time of acquisition. To achieve the goal, a color constancy mechanism is proposed to perceive the image color from the strengths of three RGB responses of a color camera or the like, independent of the color of the light illuminating the object. Being able to extract the color descriptors that are independent of the illumination is desirable because of the varity of the situation in which color is important but illumination conditions cannot be controlled. The first step of our method is to use a finite dimensional linear model to estimate the color signals. We have shown that any color signal can be characterized as a linear combination of four principal component basis functions. Once the color signals have been estimated, the unknown illuminant can be determined by the Tominaga and Wandell's estimation method which is based on a dichromatic model. In color constancy, the knowledge of surface reflectance helps in determining the canonical color descriptors despite the variation in the spectral power distribution of the ambient light. It is shown that the estimate of surface reflectance is derived from both the estimated color signal and illuminant straightforwardly. The model of a combination of the estimations of the surface spectral reflectance and the color signals can be employed in designing a color constancy electronic video camera which indeed improves the shortcomings of the traditional video camcorders.
AN ULTRA-LOW COST AND MINIATURE 950-2050 MHZ GAAS MMIC DOWNCONVERTER .1. DESIGN APPROACH AND SIMULATION
(1995-05-01)
HSIEH, TH
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WANG, H
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WANG, TH
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CHEN, TH
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CHIANG, YC
A miniature ultra low cost 950-2050 MHz GaAs MMIC downconverter has been designed for satellite TV application using a 1-mu m gate-length, ion-implanted GaAs MESFET foundry process. To accurately predict circuit performances, both linear and nonlinear equivalent circuit models have been developed to characterize the RF and de behaviors of device. Modeled simulation results show correspondence with the experimental data. This monolithic downconverter is comprised of an RF LNA, a dual-gate MESFET mixer, an IF variable gain amplifies and a varactor tuned oscillator. The primary design specifications are (1) 50-dB conversion gain, (2) 4-dB noise figure, (3) more than 40-dB gain controllable range, and (4) 50-dBc third-order intermodulation distortion. The chip size is 1.4 x 1.5 x 0.18 mm(3). It is encapsulated in a standard low cost mm plastic package. Moreover, this downconverter IC is promising for miniaturization and cost-reduction of a DBS receiver The detailed measured characteristics will be presented in part-II of this paper.
CONSTRAINED NONLINEAR OPTIMIZATION APPROACHES TO COLOR-SIGNAL SEPARATION
(1995-01-01)
CHANG, PR
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HSIEH, TH
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交大名義發表
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電信工程研究所
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National Chiao Tung University
The process of separating a color signal into illumination and surface reflectance components is a fundamental issue in color reproduction and constancy. This color-signal separation can be carried out by minimizing the error in the least squares fit of the product of the illumination and the surface spectral reflectance to the actual color signal. Moreover, when taking in account the physical realizability constraints on both the surface reflectance and illumination, the feasible solutions to the nonlinear least-squares problem should satisfy a number of linear inequalities. Four distinct novel optimization algorithms are presented to employ these constraints to minimize the nonlinear least squares fitting error. The first approach, which is based on Ritter's superlinear convergent method, provides a computationally superior algorithm to find the minimum solution to the nonlinear least-squares error problem subject to linear inequality constraints. Unfortunately, this gradient-like algorithm may sometimes be trapped at a local minimum or become unstable when the parameters involved in the algorithm are not tuned properly. The remaining three methods are based on the stable and promising global minimizer called simulated annealing. The annealing algorithm can always find the global minimum solution with probability one, but its convergence is extremely slow. To tackle this difficulty, a cost-effective variable-separable formulation based on the concept of Golub and Pereyra is adopted to reduce the nonlinear least-squares problem to be a small-scale nonlinear least-squares problem whose solution state space is less than that of the original space. It will be shown that the computational burden is reduced by an order of magnitude. The computational efficiency can be further improved when the original Boltzman generating distribution of the classical annealing is replaced by the Cauchy distribution. Finally, a number of test samples are conducted to verify the effectiveness of the proposed methods.
QUANTUM CONFINEMENT EFFECTS ON LOW-DIMENSIONAL ELECTRON-MOBILITY
(1993-07-01)
WANG, TH
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HSIEH, TH
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CHEN, TW
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交大名義發表
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電子工程學系及電子研究所
A study of quantum confinement effects on the low-dimensional electron mobility in various AlGaAs/GaAs quantum well/wire structures has been performed. The influence of the electron envelop wave function and the subband structure on the low-dimensional electron scattering rates is evaluated. The electron transport behavior is studied through a Monte Carlo simulation. The result shows that the low-dimensional electron mobility varies significantly with the quantum well/wire geometry. The one-dimensional electron mobility of 9200 cm2/V s is obtained in a rectangular quantum wire with a geometry of 110 angstrom X 110 angstrom. This value is much improved in comparison with the bulk electron mobility of 8000 cm2/V s in intrinsic GaAs and the maximum two-dimensional electron mobility of 8600 cm2/V s in a 120 angstrom GaAs quantum well. It is also noticed that the highest low-dimensional electron mobility is achieved in a quantum well/wire structure where the energy separation between the first subband and the second subband is about two polar optical phonon energy.
QUANTUM-WELL GEOMETRICAL EFFECTS ON 2-DIMENSIONAL ELECTRON-MOBILITY
(1992-11-01)
WANG, TH
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HSIEH, TH
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CHEN, YT
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交大名義發表
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電控工程研究所
A Monte Carlo analysis to study the quantization effects on the low-field electron mobility in various AlGaAs/GaAs/AlGaAs quantum well structures has been performed. The influence of the electron envelop wave-function and the subband structure on the two-dimensional electron scattering rates was evaluated. Our results showed that a maximum two-dimensional electron mobility can be achieved in a quantum well structure where the energy difference between the first subband and the second subband is about two times the polar optical phonon energy.