• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.603-605
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• 1997

A new algorithm using 1-dimensional wavelet transform for autofocusing of optical instrument has been developed. Previous studies based on the conventional frequency analysis have shown that as the lens-object distance approaches the optimum value, the high frequency energy in the corresponding image shows a consistent increase. However, as conventional frequency analysis techniques hide spatial distribution of each band energy, shape information in the original signal cannot be easily utilized. In this paper, a newly devised wavelet based focus measuring scheme is presented. Unlike other frequency domain analysis techniques that simply produce "frequency-only" spectra, wavelet analysis provides a "time-frequency" localized view of a given signal. As a result, both frequency band filtering and spatial distribution filtering can easily be realized. Depending on the proposed focus quality measuring algorithm, a fast and reliable automatic focus adjustment of optical devices could be implemented.

• Journal of the Optical Society of Korea
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• v.20 no.1
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• pp.150-155
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• 2016

To evaluate the autofocusing performance of recent mobile phone cameras, it is necessary to determine the peak position of the center field MTF (Modulation Transfer Function), -known as the through focus MTF- of the module. However, the MTF peak position found by conventional methods deviates from the ideal position due to the focus scanning resolution of mobile phone cameras. This inaccurate peak position results in false judgements of the optical performance, leading to yield losses or customer complaints. An increase in the focus scanning resolution can address this problem, but the manufacturing UPH (Unit per Hour) level will also unfortunately increase as well, resulting in a loss of manufacturing capabilities. In this paper, several fitting models are studied to find an accurate MTF peak position within a short period of time. With an analysis of a large amount of manufacturing data, it is demonstrated that the fitting methods can reduce false judgements and simultaneously increase the capabilities of the manufacturing system.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.4
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• pp.316-319
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• 2018

To detect the ground moving target, forward-looking SAR images obtained from the FMCW radar can be exploited. However, the quality of the SAR image is deteriorated due to the turbulence or fluctuation because of the flight path condition during the missile movement. We herein propose an entropy-minimizing autofocus method to compensate the motion error of forward-looking SAR. In particular, owing to the geometry of the forward-looking SAR, the motion error affects the SAR image in the two-dimensional (2D) form (azimuth and time axis). Therefore, we suggest a 2D autofocus method for the motion compensation.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1993.10a
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• pp.255-260
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• 1993

This study proposed a new autofocusing method for a high resolution microscope with a depth of focus of a submicron range. The experimental setup was characterized by nulling method for bi-cell prhotodiode which had two active areas on sensor surface. The optical systems used in this method had was very simple and was easily matched to microscopes which had used widely. It was shown that the resolution was very high (about 20 nm) by experimental results. This method can be used in the semiconduct industry because it can find defects on the silcon wafer.

• Proceedings of the Korean Information Science Society Conference
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• 2003.10b
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• pp.514-516
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• 2003

고배율 렌즈를 장착한 3차원 비접촉 측정 장비에서 컴퓨터 비전을 이용한 정밀도 높은 형상의 측정을 위해서는 선명한 영상 획득을 위한 정확한 초점 위치 결정이 선행되어야 한다. 본 논문에서는 정초점 위치를 찾기 위하여 수동형 초점 조절 방법을 사용한다. 각각의 렌즈 위치에서의 입력 영상에 대해 초점 위치 추적의 척도가 되는 초점값을 변형된 LoG 방법을 이용하여 측정하고, 측정된 초점값들의 렌즈 위치에 따른 분포 곡선에 대한 가우시안 정합을 적용한 정초점 위치 검색을 통해 최적의 초점 위치를 결정하는 기법을 제안한다.

• Smart Structures and Systems
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• v.15 no.4
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• pp.1121-1137
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• 2015

This study presents probabilistic-based damage identification technique for highlighting damage in metallic structures. This technique utilizes distributed piezoelectric transducers to generate and monitor the ultrasonic Lamb wave with narrowband frequency. Diagnostic signals were used to define the scatter signals of different paths. The energy of scatter signals till different times were calculated by taking root mean square of the scatter signals. For each pair of parallel paths an error function based on the energy of scatter signals is introduced. The resultant error function then is used to estimate the probability of the presence of damage in the monitoring area. The presented method with an autofocusing feature is applied to aluminum plates for method verification. The results identified using both simulation and experimental Lamb wave signals at different central frequencies agreed well with the actual situations, demonstrating the potential of the presented algorithm for identification of damage in metallic structures. An obvious merit of the presented technique is that in addition to damages located inside the region between transducers; those who are outside this region can also be monitored without any interpretation of signals. This novelty qualifies this method for online structural health monitoring.

• Journal of the Semiconductor & Display Technology
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• v.14 no.1
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• pp.7-11
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• 2015

In this paper, an automatic focusing method has been proposed for speedy and reliable measurement and inspection in industry. It is very difficult to determine focusing step size and moving direction in one camera autofocusing. The proposed method can improve speed and accuracy of focusing by using the optical axis interval of two cameras, which is automatically set up as focusing step size. Also, it can determine moving direction from focus value comparisons of two cameras, and then solve ambiguity of one camera focusing. Its performance is verified by experiments. It is expected that it can apply to optical system for measurement and inspection in industry fields.

• Journal of the Optical Society of Korea
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• v.14 no.2
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• pp.104-108
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• 2010

We proposed an axis transformation technique which reveals a distance parameter directly from optical scanning holography (OSH). After synthesis of a real-only spectrum hologram and power fringe adjusted filtering, we transform an original frequency axis to a new frequency axis using interpolation. In the new frequency axis, the filtered hologram has a single frequency which is linearly proportional to the distance parameter. Thus, the inverse Fourier transformation of the filtered hologram gives a delta function pair in the new spatial axis. Finally, we extract the distance parameter by detecting the location of the delta function pair.

• Journal of the Korean Society for Precision Engineering
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• v.14 no.10
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• pp.28-34
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• 1997

This paper describes an automatic measurement method for the in-line inspection of assembly tolerances of cathod ray electron guns. The method uses an optical microscope with a CCD camera as a probe. An automatic gap recognition algorthm with digital image processing and a new software autofocus algorithm based on using an optimal edge detector have been developed to improve the measuring accuracy. An inspection system has been proposed and practically implemented for in-line inspection to a real factory automation line. The inspection system consists of a gap inspection part and an eyelet. Total time consumed for inspecting all measuring items is about 10 seconds and the repeatability is below .+-. 5 .mu. m

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.12
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• pp.3759-3766
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• 1996

In this paper a new gefchmique to measaure the creater wear using image processing and automatic focusing is presented. The contour detection algorithm, which can adopt ina noisy image, is suggested. It is suitable for eliminating high frequency noses with lower processing time and without blurring. An automatic focusing technique is applied to measure a createrwear depth with a one-dimensional search algorithm for finding the bestfocus. This method is implemented in the tool microscope driven by a servo motor. The results show that the countour and depth of crater wear can be measured reliably.