• 전기전자학회논문지
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• 제7권2호
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• pp.271-280
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• 2003

본 논문에서는 진단 초음파 영상에서의 스펙클 잡음의 영향을 줄여 대상물체를 효율적으로 분리하는 방법을 제안하였다. 스페클 잡음을 제거하기 위하여 전처리 과정에서 gray scale opening 연산을 실행 후 윈도우내에서 임의의 픽셀에서의 분산을 계산하여 균일 영역과 경계 영역을 구분하고, 구분된 각 영역에 대해 윈도우 크기가 다른 pseudomedian 필터를 사용하였다. (본 논문에서 적응 pseudomedian 필터라 부름.) 영역 구분 없이 같은 크기의 윈도우를 사용한 경우보다 필터링 시간이 단축되며, 스페클 잡음을 충분히 제거할 수 있었다. 필터의 성능을 평가하기 위하여, 제안한 필터를 기존의 영상처리 필터의 결과에 대한 PSNR과 비교하여 우수하다는 것을 입증하였다.

• 한국광학회지
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• 제1권1호
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• pp.12-15
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• 1990

홀로그래피 간섭법과 스펙클 사진법을 결합한 홀로스펙클 간섭법을 이용하여 3차원 변형을 측정하였다. 이 방법은 이중노출된 하나의 사진건판으로부터 종변위와 횡변위를 모두 알아낼 수 있어 3차원 변형측정에 매우 유용하게 사용되고 있다. 본 연구에서는 물체의 일부분에 밀집되어 일어나는 변형을 측정하기 위하여 image holography에 기초를 둔 광학시스템을 구성하였다. 시스템의 배율을 적절히 증가시키고 기준파의 세기를 감소시킴으로써 보통의 홀로그램에 비해 스펙클의 효과를 증대시켰다. 이로써 가시도가 높은 Young의 무늬 뿐만 아니라 확대되고 명확한 홀로 그래피 간섭무늬를 얻을 수 있어 indentor에 의한 3차원 접촉변형을 측정하였다.

• 한국통신학회논문지
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• 제22권11호
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• pp.2401-2408
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• 1997

The measured pulse shapes provided in the given data package demonstrated pulse distortions due to laser speckle. the distorted pulse shapes were carefully analyzed, modeled, and then applied to the DTTL(Digital-data Transition Tracking Loop)[1] bit synchronizer simulator to measure the mean time delay and its delay variation performance. The result showed that the maximum mean time delay variation with the modeled data was 12.5% when window size equals 1. All the data given were located within this modeled boundary and the maximum eman time delay variation was 7% in this case. The mean time delay variation was known to be smaller by reducing the window size [2][5][6]. The mitigated delay variation was 2.5% in the modeled case and 1.4% in the data set given when the windown size equals 0.1. With the digital DTTL insteal of analog DTTL, similar results was obtained.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.140-143
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• 2001

Digital shearography, a speckle pattern method is based on the superposition of two laterally sheared images. Therefore, object points which are positioned in some distance from each other are superposed in the image plane. This shearography, one of NDT methods without contact, is able to inspect defects in pipelines and pressure vessels that are used in nuclear power plants. This is can inspect whole fields and has a low sensitivity to environmental noise. Because optical setting is very simple, it has a little exhaustion of time, cost and man power. And also it can find a defect position through real time monitoring of a part. This paper, finds out the relationship among shearing quantity image quality and defect size with this method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2001년도 춘계학술대회 논문집
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• pp.195-198
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• 2001

Backside defect of plate structure may grow due to fatigue or overload to cause critical failure during operation, so it is important to detect this kind of defect in line. For this purpose, nondestructive, non-contact and highly sensitive method is required. ESPI and Shearography are considered as useful method to satisfy these requirements. In this paper, the possibility of application of ESPI and Shearography to detect the backside defect of steel plate and to quantify the defect size was tested. For the experiment, some steel plates with defect on the backside were prepared. Experimental results for these plates showed that location and size of defect could be detected correctly by both of ESPI and Shearography.

• 한국의학물리학회지:의학물리
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• 제20권2호
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• pp.62-71
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• 2009

최근에 광간섭 단층촬영은 생물학적 조직을 비 침습적으로 이미지를 얻는데 많이 사용되고 있다. 그러나, 광간섭 단층촬영은 노이즈 때문에 해석하는데 아직까지는 어려움을 갖고 있다. 본 논문에서는 인체와 토끼의 연골 이미지들의 이미지에서 잡음을 제거하는 다양한 영상처리 기술을 적용해 보았다. 또한 광간섭 단층촬영으로 얻은 이미지들을 영상 분할 방법을 통해 얻고자 하는 부위를 구별 하였으며 대부분의 이미지들이 영상분할 알고리즘에 적합함을 볼 수 있었다. 그리고, 광간섭 단층영상에 적합한 영상분할 방법을 선택한 후 영상을 재구성 하였다. 광간섭 단층촬영은 작은 깊이와 거리에 제한을 가지고 있기 때문에 영상처리장치에 단점을 가지고 있다. 광간섭 이미지가 매우 작은 공간에서 이루어 짐으로 같은 지역의 영상을 재구성 하기는 어려운 점이 있다. 그래서, 광간섭 단층영상 재구성을 할 때 좋은 매칭 알고리즘 방법이 필요하다. 본 논문에서는 챔퍼 매칭 알고리즘을 사용하여 재구성 하였다. 본 연구에서는 OCT 연골 이미지를 얻어 노이즈 제거, 영상 분할, 3D 광간섭 단층 영상을 재구성 할 수 있었다.

• 한국해양공학회지
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• 제16권4호
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• pp.13-18
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• 2002

The magnitude of the plastic zone around the crack tip of DENT(Double Edge Notched Tension) specimen and the crack growth length under cyclic loading were measured by ESPI(Electronic Speckle Pattern Interferometry) system. The measured magnitude of plastic zone was compared with the equations proposed by Irwin and calculated by a nonlinear static method of MSC/NASTRAN. The measured crack growth length by ESPI system was also compared with the obtained data by the image analysis system. From the study, it is confirmed that the plastic zone and crack growth length can be measured accurately with the high-tech equipment.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2003년도 춘계학술대회 논문집
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• pp.251-254
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• 2003

In recent years, shearogrpahy has significantly improved capabilities In the areas of unbend and separation detection in tires. Although shearography has many advantages fur qualitative evaluation, the technique remains the problem of quantitative analysis of inside defects, because shearography needs several effective factors including the amount of shearing, shearine direction and induced load, which exist as barrier for the quantitative analysis of inside defects. Since the factors are highly dependent on inspectors skill and also affect the in-situ workability. The factors were optimized and the size of cracks inside of pipeline and tire has been quantitatively determined.

• 한국공작기계학회논문집
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• 제13권6호
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• pp.119-126
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• 2004

The welding characteristics of Inconel 600 Alloy using a continuous wave Nd:YAG laser are experimentally investigated. The major process parameters studied in the present laser welding experiment were the positions of focus, laser power and travel speed of laser bean We measured the fusion zone size and its shape using an optical microscope for the observation of cross-sectional area. We performed two tests regarding the tension and the micro hardness for welding quality estimation. Then we measured residual stress in welds by electronic speckle pattern interferometry(ESPI). In conclusion the optimum butt welding process parameters were 0.5mm focus position, 1.6kW laser power, 1m/min travel speed and 5.5$\ell$/min assist gas discharge.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.476-477
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• 2009

The smallest green laser containing a built-in temperature controlling unit has been demonstrated. The device volume was just 0.5 cubic centimeters, which is nearly the same size as existing red and blue diode lasers, has an electrical-to-optical conversion efficiency of 10% and 150 mW power output. Furthermore as an alternative approach for compact green laser development, a quasi-phase matching method with wide spectral bandwidth for the reduction of speckle noise will be presented.