• IEIE Transactions on Smart Processing and Computing
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• v.6 no.3
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• pp.141-150
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• 2017

Images obtained from underwater are usually degraded due to the environmental conditions. Some of the typical degradation factors include turbidity and color degradation. These degradations can be attributed to the absorptive and scattering properties of underwater degradation in terms of optical parameters, such as modulation transfer function (MTF), optical transfer function (OTF),point spread function (PSF), and color constancy. In this paper, we use the CODE V optical simulation software to mimic underwater conditions and model the imaging platform, thereby studying various parameters, such as PSF and MTF, and we use the PSF to remove the underwater turbidity. Experimental results show increased performance with the algorithm, compared to other existing methods.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.3B no.2
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• pp.103-110
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• 2003

With significant development of power electronics technology, the proliferation of nonlinear loads such as static power converters has deteriorated power quality in power transmission and distribution systems. Notably, voltage harmonics resulting from current harmonics produced by the nonlinear loads have become a serious problem in many countries. Many photovoltaic power generation systems installed in building systems have harmonics that are the worst object for distribution systems as a utility interactive system, and it tends to spread out continuously. Proposed and implemented in this paper is a multi-function inverter control strategy that allows a shunt active filter function to the power inverter of the photovoltaic power generation system established on a building system. The effectiveness of the proposed system is demonstrated through the simulation of a hypothetical power system using PSCAD/EMTDC.

• Korean Journal of Optics and Photonics
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• v.7 no.4
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• pp.434-439
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• 1996

To investigate influence of the incident beams which have the truncated Gaussian amplitude and of the shapes of bump on read-out signal is an optical disc, and the point spread function on bump, the scalar diffraction theory is used in this paper. We consider the truncated Gaussian amplitudes which are $\sigma$=0, 0.5, 1.5, and 2.5, the height of bump which is given by $n{\Delta}_0={\lambda}/4$, and the phase height of bump which is then given by ${\Phi}_0={\pi}$. We also consider the shapes of the bump which are a rectangular shape, a frustoconical shape, and a conical shape. It is shown that as the truncation of incident beam reduces the radius of central spot on bump decreases, the maximum value of read-out signal increases, and that the size of bump decreases. From these results, we get better read-out signal and the reduced cross-talk in optical disc when the truncation of incident beam reduces. Therefore a laser beam having less truncated Gaussian amplitude may useful for an actual optical disc.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.46 no.6
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• pp.26-35
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• 2009

In this paper, we present morphology-based step region extraction and regularized iterative point-spread-function (PSF) estimation methods. The proposed PSF estimation method uses canny edge detector to extract the edge of the input image. We extract feasible vertical and horizontal edges using morphology analysis, such as the hit-or-miss transform. Given extracted edges we estimate the optimal step-response using flattening and normalization processes. The PSF is finally characterized by solving the equation which relates the optimal step response and the 2D isotropic PSF. We shows the restored image by the estimated PSF. The proposed algorithm can be applied a fully digital auto-focusing system without using mechanical focusing parts.

• Journal of the Optical Society of Korea
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• v.19 no.2
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• pp.136-143
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• 2015

Image deblurring by a deconvolution method requires accurate knowledge of the blur kernel. Existing point spread function (PSF) models in the literature corresponding to lens aberrations and defocus are either parameterized and spatially invariant or spatially varying but discretely defined. In this paper, a parameterized model is developed and presented for a PSF which is spatially varying due to lens aberrations and defocus in an imaging system. The model is established from the Seidel third-order aberration coefficient and the Hu moment. A skew normal Gauss model is selected for parameterized PSF geometry structure. The accuracy of the model is demonstrated with simulations and measurements for a defocused infrared camera and a single spherical lens digital camera. Compared with optical software Code V, the visual results of two optical systems validate our analysis and proposed method in size, shape and direction. Quantitative evaluation results reveal the excellent accuracy of the blur kernel model.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.42 no.9 s.339
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• pp.19-28
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• 2005

We establish a statistical model for the ultra-wide bandwidth (UMB) indoor channel based on over 2000 frequency response measurements campaign in a Practical apartment. The approach is based on the investigation of the statistical properties of the multipath profiles measured in different place with different rooms. Based on the experimental results, a characterization of the propagation channel from theoretic view point is described. Also we describe a method for measurement of the channel impulse response and channel transfer function. Using the measured data, the authors compares channel impulse responses obtained from time-domain and channel transfer functions obtained from frequency-domain with statistical path loss model. The bandwidth of the signal used in this experiment is from 10MHz to 8.01 GHz. The time-domain results such as maximum excess delay, men excess delay and ms delay spread are presented. As well as, omni-directional biconical antenna were used for transmitter and receiver In addition, measurements presented here support m channel model including the antenna characteristics.

• The Korean Journal of Applied Statistics
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• v.36 no.4
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• pp.309-322
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• 2023

The Hawkes process is a point process with self-exciting characteristics. It has been mainly used to describe seismic phenomena in which aftershocks occur due to the main earthquake. Recently, it has been used to explain various phenomena with self-exciting properties, such as the spread of infectious diseases and the spread of news on SNS. The Hawkes process can be flexibly modified according to the characteristics of events by using various types of excitation functions. Since it is difficult to implement a maximum likelihood estimator numerically, estimation methods have been improved until recently. In this paper, the conditional intensity function and excitation function are explained to describe the Hawkes process. Then, existing examples of Hawkes processes used in seismic, epidemiological, criminal, and financial fields are described and estimation methods are introduced. I analyze earthquakes that occurred in gyeongsang-do, Korea from November 2017 to December 2022, using R package ETAS.

• Journal of the Korean Society for Nondestructive Testing
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• v.34 no.6
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• pp.441-446
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• 2014

A 3D ultrasound image is desired in many medical examinations. However, the implementation of a 2D array, which is needed for a 3D image, is challenging with respect to fabrication, interconnection and cabling. A 2D sparse array, which needs fewer elements than a dense array, is a realistic way to achieve 3D images. Because the number of ways the elements can be placed in an array is extremely large, a method for optimizing the array configuration is needed. Previous research placed the target point far from the transducer array, making it impossible to optimize the array in the operating range. In our study, we focused on optimizing a 2D sparse array transducer for 3D imaging by using a simulated annealing method. We compared the far-field optimization method with the near-field optimization method by analyzing a point-spread function (PSF). The resolution of the optimized sparse array is comparable to that of the dense array.

• IEIE Transactions on Smart Processing and Computing
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• v.5 no.5
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• pp.319-322
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• 2016

We propose a parametric blind deconvolution method for bi-level images with unknown intensity levels that estimates unknown parameters for point spread functions and images by minimizing a penalized nonlinear least squares objective function based on normalized correlation coefficients and two regularization functions. Unlike conventional methods, the proposed method does not require knowledge about true intensity values. Moreover, the objective function of the proposed method can be effectively minimized, since it has the special structure of nonlinear least squares. We demonstrate the effectiveness of the proposed method through simulations and experiments.

• Journal of Biomedical Engineering Research
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• v.11 no.1
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• pp.113-120
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• 1990

In this paper, the deconvolution method utilizing a modified Wiener filter is applied for the enhancement of lateral resolution of ultrasonic B-scan Images. For this purpose, a phantom composed of wires which are 0.6mm of diameter and apart in the range between 3 to 9mm is constructed. The modified Wiener filter with optimal parameter is applied to the phantom for the analysis of ultrasonic image. The results obtained are as follows'When all parameters of the modified Wiener filter are optimal, the resolution of B-scan images is enhanced by 50 percent : Othenrise, the images are blurred, spilt at peak points, or noises are strengthened severely. When the point-spread function representing the characteristic function of the system is determined, the selection ranges of op- timum parameters may be narrowed. It is expected that the proposed method may be able to apply to clinic situations for more accurate image analysis by means of reducing the loss of important information.