• Proceedings of the IEEK Conference
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• 2000.06d
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• pp.66-69
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• 2000

In this paper, we proposed a postprocessing algorithm for quantization effects reduction in block coded images using the block classification and adaptive filtering. The proposed method consists of classification, adaptive inter-block filtering, and intra-block filtering. First, each block is classified into one of seven classes based on the characteristics of 8${\times}$8 DCT coefficients. Then each block boundary is filtered by adaptive inter-block filters according to the block classification. Finally for blocks which are classified into edge block, intra-block filtering is peformed. Experimental results show that the proposed method gives better results than the conventional methods from both a subjective and an objective viewpoint.

• Korean Journal of Optics and Photonics
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• v.8 no.4
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• pp.353-355
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• 1997

A single molecule detection system, which consists of confocal fluorescence microscope and single photon counter, has been used to observe the dye concentration dependence of photon counting rate. With increasing concentration, a saturation effect of counting is observed and demonstrated on the basis of the dead time of photon detector. The equations presented here show the relations between the counting rate and some parameters such as probe volume, quantum efficiency of detector, and fluorescence photon number entered onto detector. The signal-to-noise ratio is also discussed briefly.

• Electronics and Telecommunications Trends
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• v.21 no.5 s.101
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• pp.109-118
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• 2006

조셉슨 터널접합을 사용한 초전도 혼합기 또는 믹서(SIS mixer)와 매우 얇은 초전도박막을 이용한 초전도 혼합기(HEB mixer)는 초전도 현상에 있어서의 거시적 양자효과를 유발하는 강한 비선형성을 가지기 때문에, 종래의 전자파 검출기로는 구현이 어렵고 또한 극도로 낮은 잡음특성을 실현한다. 테라헤르츠(THz) 주파수 영역용 고감도검출기로서도 기대되는 질화니오븀(NbN) 박막을 사용한 SIS 혼합기와 HEB 혼합기의 개발현황과 연구결과에 대하여 소개하고자 한다. 그리고 최근에 많이 연구되고 있는 펨토초레이저와 고온초전도 상호작용을 이용한 테라헤르츠 연구결과도 소개한다.

• Proceedings of the KIEE Conference
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• 1999.11c
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• pp.564-566
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• 1999

계측 시스템이나 시스템 식별을 수행할 때 정확히 모델링 되는 플랜트를 가정할 경우, 입출력 신호간 혹은 상태 변수들 사이의 비선형 함수 관계를 유도해 낼 수 있다. 그런데 특히 비선형 함수가 매우 복잡하여 해를 닫힌 형태로 구할 수 없을 경우 고려하는 변수들 양자간의 수학적 모델링을 기반으로 루프내 변수가 방정식의 해로 수렴하는 대수 루프를 구성할 수 있다. 이는 모델을 정확히 아는 시스템에 대하여 출력으로부터 입력을 추정하는 역시스템(inverse system)을 구성하는 것과 유사하다. 이러한 개념을 응용한 간단한 예로 용량형 센서의 입출력 비선형성을 제거해주는 역시스템을 대수 루프를 통하여 구현하였다. 또한 구현한 루프가 항상 유일한 해로 수렴할 수 있도록 하는 조건을 구하였다. 해석된 결과를 바탕으로 구현된 루프가 컴퓨터 시뮬레이션 및 아날로그 회로 실험에서도 잘 동작함을 검증하였다. 시뮬레이션 결과로 보인 잡음에 대한 강인성과 실제 회로 실험 결과는 대수 루프의 구현이 실제 용량형 센서 등에 용이하게 적용될 수 있음을 보여준다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.16 no.1
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• pp.1-8
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• 1979

This paper describes a simple asynchronous time dime division multiplexing system developed by means of a synchronous delta modulation. In realizing asynchronous multlplexlng system time author deals with a technique of multiplexing communication channels by reversing the polarity of output pulse and superimposing the channels at a certain time Interval. The results of experiments on the number of error pulses, signal-to-noise ratio and frequency characteristics have shown fair agreements with the theoretically predicted ones related to the system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.14 no.1
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• pp.22-29
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• 1989

An efficient fixed rate adaptive transform coding is described. Adaptivity is provided by assigning more bits to high ac energy blocks and less bits to low ac energy blocks. Practical and relatively simple adaptation scheme is developed. Overall complexity of our scheme is comparable to the Chen and Smith's scheme. The rate will be adjusted in the same manner as in fixed transform coding. Good performance of the proposed scheme is presented in terms of signal to noise ratio compared with the well known Chen&Smith's scheme. Subjective tests are also presented.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.15 no.6
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• pp.567-572
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• 2004

This paper shudies an automatic gain control(AGC) algorithm used in wireless communication cellular systems. The AGC design includes the selection of the appropriate analog-to-digital converter(ADC) and keeping the input power to the ADC constant to minimize the quantization noise generated from the analog-to-digital conversion process. In this paper the process to determine the required precision or the An is illustrated and the method to set the design parameters of the AGC is proposed. And the validity of the proposed algorithm is verified by computer simulation.

• The Journal of the Acoustical Society of Korea
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• v.4 no.3
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• pp.33-41
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• 1985

이 논문에서는 frequency-weighted MSE를 최소화하는 적응 pre-filter와 post-filter를 음성파형 부호화기에 적용했을 때의 성능을 분석한다. 먼저 여러 다양한 pre-filter와 post-filter에 의한 noise shaping 효과를 이론적으로 보여준다. 그리고 frequency-weighted SNR 척도를 사용하여 적응 pre-filter 와 post filter에 의한 성능면에서의 이득을 이론적으로 유도한다. 적응 pre-filter와 post-filter를 ADM과 ADPCM 부호화기에 적용해본 결과에 의하면 음성파형 부호화기의 성능을 FWSNR\sub SEG\ 척도로 약 3dB 정도 개선할 수 있음을 알 수있다. 또한 pre-filter와 post-filter를 사용하면 청각적으로 중요한 영향을 미치는 1kHz에서 3kHz 사이의 양자화 잡음을 효과적으로 줄일 수 있다.

• Progress in Medical Physics
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• v.23 no.1
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• pp.26-32
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• 2012

The magnification technique has recently become popular in bone radiography, mammography and other diagnostic examination. However, because of the finite size of X-ray focal spot, the magnification influences various imaging properties with resolution, noise and contrast. The purpose of study is to investigate the influence of magnification and focal spot size on digital imaging system using eDQE (effective detective quantum efficiency). Effective DQE is a metric reflecting overall system response including focal spot blur, magnification, scatter and grid response. The adult chest phantom employed in the Food and Drug Administration (FDA) was used to derive eDQE from eMTF (effective modulation transfer function), eNPS (effective noise power spectrum), scatter fraction and transmission fraction. According to results, spatial frequencies that eMTF is 10% with the magnification factor of 1.2, 1.4, 1.6, 1.8 and 2.0 are 2.76, 2.21, 1.78, 1.49 and 1.26 lp/mm respectively using small focal spot. The spatial frequencies that eMTF is 10% with the magnification factor of 1.2, 1.4, 1.6, 1.8 and 2.0 are 2.21, 1.66, 1.25, 0.93 and 0.73 lp/mm respectively using large focal spot. The eMTFs and eDQEs decreases with increasing magnification factor. Although there are no significant differences with focal spot size on eDQE (0), the eDQEs drops more sharply with large focal spot than small focal spot. The magnification imaging can enlarge the small size lesion and improve the contrast due to decrease of effective noise and scatter with air-gap effect. The enlargement of the image size can be helpful for visual detection of small image. However, focal spot blurring caused by finite size of focal spot shows more significant impact on spatial resolution than the improvement of other metrics resulted by magnification effect. Based on these results, appropriate magnification factor and focal spot size should be established to perform magnification imaging with digital radiography system.

• Journal of radiological science and technology
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• v.40 no.3
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• pp.363-370
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• 2017

We aimed to evaluate the physical imaging properties in various digital radiography systems with charged coupled device (CCD), computed radiography (CR), and indirect flat panel detector (FPD). The imaging properties measured in this study were modulation transfer function (MTF) wiener spectrum (WS), and detective quantum efficiency (DQE) to compare the performance of each digital radiography system. The system response of CCD were in a linear relationship with exposure and that of CR and FPD were proportional to the logarithm of exposure. The MTF of both CR and FPD indicated a similar tendency but in case of CCD, it showed lower MTF than that of CR and FPD. FPD showed the lowest WS and also indicated the highest DQE among three systems. According to the results, digital radiography system with different type of image receptor had its own image characteristics. Therefore, it is important to know the physical imaging characteristics of the digital radiography system accurately　to obtain proper image quality.