• 비파괴검사학회지
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• 제26권3호
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• pp.162-168
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• 2006

Speckle interferometry with phase-shifting method has been applied to measurement of micro-scale displacement through optical signal processing. Four-step phase-shifting method by PZT is used to measure out-of-plane displacement in spot-welded cantilever and results of optical experiments are comparable to those of FEM. Phase-shifting method using Fourier transform by PZT is applied to measurement of in-plane displacement on rectangular steel plate with a circular hole. The results of optical experiment agree well with theoretical calculation. New phase-shifting method in speckle interferometry has been implemented with a quarter wave plate. In-plane displacement of specimen is measured by the new phase-shifting method. Results of optical experiment show that the quarter wave plate can be used for phase-shifting method that is cheap and easy to use in speckle interferometry.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2009년도 추계학술대회
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• pp.329-332
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• 2009

Speckle noise reduction for ultrasound CT image using morphological adaptive median filtering based on edge preservation is presented in this paper. Speckle noise is multiplicative feature and causes ultrasound image to degrade widely from transducer. An input image is classified into edge region and homogeneous region in preprocessing. The speckle is reduced by morphological operation on the 2D gray scale by using convolution and correlation, and edges are preserved. The adaptive median is processed to reduce an impulse noise. As the result the proposed method enhances the image to about 20% in comparison with Winer filter by Edge Preservation Index and PSNR.

• 대한전자공학회:학술대회논문집
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• 대한전자공학회 2000년도 하계종합학술대회 논문집(2)
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• pp.119-122
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• 2000

스페클 패턴은 광섬유의 모드 간섭 때문에 발생하는 현상으로, 광섬유에 인가된 미세 외압으로 인해서 발생하는 스페클 패턴의 변화를 이용해 외부압력의 인가여부 및 그 크기를 알 수 있다. 이를 이용하여 본 연구에서는 미세 압력을 외부에서 인가하며 스페클 패턴의 변화에 따른 광 강도의 변화를 측정하였으며, 그 신호는 증폭기와 필터를 거쳐 오실로스코프로 관찰하였다. 그 결과 우리는 이 신호를 관찰하여 부하인가에 대한 응답특성을 실시간에 정확히 확인할 수 있었다. 본 연구에서 제작된 센서는 기존의 센서에 비해 매우 높은 감도를 가지고 넓은 영역을 실시간에 감시할 수 있으며, 저 비용으로 센서를 설계·제작이 가능하므로 범용의 방재용 센서 및 침입 센서에 응용 가능할 것으로 기대된다.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 1998년도 춘계학술대회 논문집
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• pp.239-244
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• 1998

ESP(Electronic Speckle Pattern Interferometry) is an optical technique to measure deforamtion of engineering components and materials in industrial areas. ESPI, a non-contact and non-destructive measuring method, is capable of providing full-field results with high spatial resolution and high speed. One of important application aspects using electronic speckle pattern interferometry is to generate contours of a diffuse object in order to provide data for 3-D shape analysis and topography measurement. The electronic speckle contouring is suitable for providing measurement range from millimeters to several centimeters. In this study, we introduce the contouring method by modified dual-beam speckle pattern interferometer and a shift of the two illumination beams through optical fiber in order to obtain the contour fringe patterns. Before the experiments, we performed the geometric analysis for dual-beam-shifted ESPI contouring. And by this geometric analysis, we performed the electronic speckle contouring experiment. We used 4-frame phase shifting method with PZT for quantitative analysis of contour fringes. Finally, we showed good agreements between the geometric analysis and experimental results.

• 한국광학회지
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• 제5권1호
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• pp.138-143
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• 1994

거친 표면을 가진 물체의 미소변위를 1차원 CCD소자와 레이저 스펙클(laser speckle) 방법을 이용하여 측정하였다. 거친 표면에서 산란된 레이저 광이 이루는 스펙클 무늬를 물체의 이동 전후에 얻고, 그것의 상호상관함수(cross-correlation)를 계산하여 스펙클 변위를 계산한다. 1차원 CCD소자를 이용하여 물체이동 전후의 스펙클 무늬를 측정하고, 레이저 스펙클 변위값을 386 PC로 인터페이스하여 PC에서 계산한다. 사용한 CCD 소자의 화소 간격은 $15\mu\textrm{m}$이고, 화소의 개수는 1728개이다. 스펙클 변위와 물체의 이동거리와는 비는 레이저 빔의 파면의 곡률에따라 1.03으로부터 5.20까지 변화한다. CCD 픽셀의 간격이 $15\mu\textrm{m}$이므로 물체의 $3\mu\textrm{m}$ 이동을 감지해 낼 수 있다.

• 전기전자학회논문지
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• 제12권3호
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• pp.158-166
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• 2008

의용 초음파 장비는 X-Ray, CT, MRI 등 다른 의료 장비보다 휴대성과 안전성면에서는 장점이 있지만 진단 시 해상도와 화질 저하를 유발하는 스펙클이 생기는 단점이 있다. 그러나 단순한 스펙클 잡음의 제거는 경계선 정보의 손실을 발생시킬 수도 있다. 이에 본 논문에서는 효과적인 스펙클 제거와 손실 없는 경계선 검출을 위해 뉴럴네트워크와 퍼지 클러스터링을 이용한 뉴로-퍼지 스펙클 제거 방법을 제안하였다. 제안된 방법은 입력된 의용 초음파 영상에 대해 먼저 퍼지 클러스터링을 적용하여 세 영역으로 나누고 이후 각 영역별로 별도의 뉴럴 네트워크를 적용하는 방법이다. 실제 실험 및 기존 방법들과의 정성적?정량적 비교 분석을 통해 제안 방법의 유용성을 검증하였다.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 1999년도 Proceedings of International Symposium on Remote Sensing
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• pp.144-147
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• 1999

The objective of this study is to quantitatively evaluate the effects of various SAR speckle reduction methods for multisource land-cover classification by backpropagation neural network, especially over the coastal region. The land-cover classification using neural network has an advantage over conventional statistical approaches in that it is distribution-free and no prior knowledge of the statistical distributions of the classes is needed. The goal of multisource land-cover classification acquired by different sensors is to reduce the classification error, and consequently SAR can be utilized an complementary tool to optical sensors. SAR speckle is, however, an serious limiting factor when it is exploited for land-cover classification. In order to reduce this problem. we test various speckle methods including Frost, Median, Kuan and EPOS. Interpreting the weights about training pixel samples, the “Importance Value” of each SAR images that reduced speckle can be estimated based on its contribution to the classification. In this study, the “Importance Value” is used as a criterion of the effectiveness.

• 대한의용생체공학회:의공학회지
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• 제29권2호
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• pp.122-131
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• 2008

For B-mode ultrasound images, we propose an image enhancement algorithm based on a multi-resolution approach, which consists of edge enhancing and noise reducing procedures. Edge enhancement processing is applied sequentially to coarse-to-fine resolution images obtained from wavelet-transformed data. In each resolution, the structural features of each pixel are examined through eigen analysis. Then, if a pixel belongs to an edge region, we perform two-step filtering: that is, directional smoothing is conducted along the tangential direction of the edge to improve continuity and directional sharpening is conducted along the normal direction to enhance the contrast. In addition, speckle noise is alleviated by proper attenuation of the wavelet coefficients of the homogeneous regions at each band. This region-based speckle-reduction scheme is differentiated from other methods that are based on the magnitude statistics of the wavelet coefficients. The proposed algorithm enhances edges regardless of changes in the resolution of an image, and the algorithm efficiently reduces speckle noise without affecting the sharpness of the edge. Hence, compared with existing algorithms, the proposed algorithm considerably improves the subjective image quality without providing any noticeable artifacts.

• Journal of the Korean Wood Science and Technology
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• 제35권4호
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• pp.45-51
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• 2007

로진을 이용하여 제조된 천연도료의 건조거동을 확인하기 위해 건조가 진행하는 동안의 천연도료의 질량변화와 스펙클 이미지(speckle image)를 통한 광학적 변화를 측정하였고, 두 측정방법 사이의 상관관계를 조사하였다. HORUS를 통해 측정된 스펙클 이미지에서는 선형 스케일에서 질량변화는 건조시간과 깊은 상관관계가 있으며, Log 스케일에서는 질량변화에 따른 영향뿐만이 아니라 건조거동에 따라 나타났다. 그러므로 HORUS를 이용하여 도료의 건조시간과 건조거동을 조사하는 하나의 방법으로 추천될 만한 것으로 검토되었다.

• Journal of the Optical Society of Korea
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• 제12권3호
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• pp.126-130
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• 2008

We propose and experimentally demonstrate an effective method to reduce near-field speckle noise at the output of a 50 ${\mu}m$ graded index multimode fiber using a short cylindrical piezoelectric transducer(PZT) vibrating in the radial direction. The fiber was coiled as tightly as possible around the mandrel of the PZT and a periodic stretching effect was caused by the radial oscillations of the actuator. The output of the optical fiber using the He-Ne laser source was intensively observed by a CCD camera. By counting all the pixels corresponding to relative intensity graded into 256 levels in the selected area and by calculating standard deviation and mean value of the intensity, we could measure the speckle contrast and vibration effect quantitatively with reduction ratio of pixels and line profile of the illuminated region. It was clearly observed that the characteristics of the speckle pattern in the vibration-on state were significantly improved over that of the vibration-off state due to time-averaged smoothing.