• 응용통계연구
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• 제16권2호
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• pp.305-319
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• 2003

본 연구에서는 바이어스 필드에 의해 왜곡된 MRI 영상에 대한 분할을 위해 확장된 EM 알고리즘을 기반으로 한 통계적 접근법을 제시한다. 영상의 명암값을 자료로 하는 분할기법들은 고주파 성분의 잡음 뿐만 아니라 영상을 불균질하게 만드는 바이어스 필드라는 저주파 성분의 왜곡에 특히 취약하다. 이 문제를 해결하기 위해 본 논문에서는 잡음을 효과적으로 제어하기 위해 마코프랜덤필드가 적용된 정규혼합모형을 고려하며, 효과적인 바이어스 필드의 보정을 위해 페널티-우도를 도입하여 추정하는 방법으로 고안되었다.

• 비파괴검사학회지
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• 제32권3호
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• pp.296-301
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• 2012

This paper describes an analytic method for infrared thermography to detect surface cracks in thin plates. Traditional thermographic method uses the spatial contrast of a thermal field, which is often corrupted by noise in the experiment induced mainly by emissivity variations of target surfaces. This study developed a robust analytic approach to crack detection for thermography using the holomorphic function of a temperature field in thin plate under steady-state thermal conditions. The holomorphic function of a simple temperature field was derived for 2-D heat flow in the plate from Cauchy-Riemann conditions, and applied to define a contour integral that varies depending on the existence and strength of singularity in the domain of integration. It was found that the contour integral at each point of thermal image reduced the noise and temperature variation due to heat conduction, so that it provided a clearer image of the singularity such as cracks.

• 디지털산업정보학회논문지
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• 제7권4호
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• pp.133-139
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• 2011

In this paper, we propose a hybrid filter for noise reduction. The proposed method adjusts rational filtering direction according to an edge in the image using median filtered data. Rational filter modulates the coefficients of a linear lowpass filter to limit its action in presence of image details. By the ratio of polynomials in the input variables, rational filter reduces noise adaptively. Median filter is widely used to reduce impulse noise, but removes some details for highly corrupted images. Also, desirable details are removed when the window size is large. Our proposed algorithm combines rational filter and median filter. Thus, proposed method not only preserves edge, but also reduces noise in uniform region. Experimental results show that our proposed method has better quality than those by existing median and rational filtering methods.

• Journal of Electrical Engineering and information Science
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• 제2권5호
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• pp.79-88
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• 1997

This paper introduces a new energy function, as maximum a posteriori(MAP) estimate of binocular disparity, that can deal with both random dot stereo-gram(RDS) and natural scenes. The energy function uses phase-magnitude as features to detect only the shift for a pair of corrupted conjugate images. Also we adopted Fleet singularity that effectively detects unstable areas of image plant and thus eliminates in advance error-prone stereo mathcing. The multi-scale concept is applied to the multi laser architecture that can search the solutions systematically from coarse to fine details and thereby avoids drastically the local minima. Using mean field approximation, we obtained a compact representation that is suitable for fast computation. In this manner, the energy function satisfies major natural constraints and requirements for implementing parallel relaxation. As an experiment, the proposed algorithm is applied to RDS and natural stereo images. As a result we will see that it reveals good performance in terms of recognition errors, parallel implementation, and noise characteristics.

• 대한원격탐사학회:학술대회논문집
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• 대한원격탐사학회 2003년도 Proceedings of ACRS 2003 ISRS
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• pp.1058-1060
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• 2003

A ground control point (GCP) is a point on the surface of Earth where image coord inates and map coordinates can be identified. The GCP is useful for the geometric correction of systematic and unsystematic errors usually contained in a remotely sensed data. Especially in case of synthetic aperture radar (SAR) data, it has serious geometric distortions caused by inherent side looking geometry. In addition, SAR images are usually severely corrupted by speckle noises so that it is difficult to identify ground control points. We developed a ground point extraction algorithm that has an improved capability. An application of radargrammetry to Daejon area in Korea was studied to acquire the geometric information. For the ground control point extraction algorithm, an ERS SAR data with precise Delft orbit information and rough digital elevation model (DEM) were used. We analyze the accuracy of the results from our algorithm by using digital map and GPS survey data.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.750-753
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• 2007

다양한 멀티미디어 서비스에 대한 요구가 증가함에 따라, 영상을 정보전달의 수단으로 사용하기 위한 관련 기술들이 급격히 발전하였다. 그러나 영상의 인지도와 신호 오류에 큰 영향을 미치는 임펄스 잡음은 영상을 디지털화하거나 전송하는 과정에서 여전히 발생하고 있다. 이러한 임펄스 잡음을 제거하기 위해 일반적으로 비선형 필터를 적용하며, SM 필터가 대표적이다. 그러나 SM 필터는 에지성분의 오류로 인해 전체 영상의 품질을 저하시킨다. 따라서 본 논문에서는 임펄스 잡음에 의해 훼손된 영상을 복원하기 위해, Min-max 연산에 기반한 비선형 공간필터를 제안하였으며, 시뮬레이션을 통해 기존의 방법들과 비교하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 춘계종합학술대회
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• pp.209-212
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• 2007

디지털 영상은 획득 및 전송과정에서 다양한 잡음에 의해 훼손되며, 이러한 잡음들 중, AWGN과 임펄스 잡음이 가장 대표적이다. 기존의 영상복원 알고리즘들은 대부분 단일 잡음환경하에서 처리되며, 상이한 잡음모델에 대해서는 우수하지 못한 처리결과를 나타내었다. 따라서 본 논문에서는 임펄스 잡음과 AWGN을 분리하여 제거하기 위한 영상복원 알고리즘을 제안하였다 이때, 공간영역에서 마스크 내의 중심화소와 인접한 화소들의 크기차와 공간거리를 파라미터로 사용하여 복합적인 잡음성분을 제거하였다. 시뮬레이션 결과로부터, 제안한 방법은 임펄스 잡음과 AWGN을 제거하는 동시에 에지와 같은 영상의 상세정보를 우수하게 보존하였다.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2007년도 추계종합학술대회
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• pp.359-362
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• 2007

현재, 정보통신 기술의 급격한 발전으로 인해 디지털 영상처리 기술 분야에서도 많은 연구가 진행되고 있으며, 영상복원 분야 중에서도 임펄스 잡음과 같은 잡음 제거 기술은 우수한 품질의 영상을 얻기 위해서 필수적으로 요구된다. 이러한 임펄스 잡음을 효과적으로 제거하기 위한 방법으로 SM (standard median) 필터가 대표적이지만 영상의 에지 영역에서 오류를 나타내어 전체 영상의 품질을 저하시킨다. 따라서 본 논문에서는 임펄스 잡은 환경에서 훼손된 영상을 복원하기 위해 영상의 방향성 정보를 이용한 비선형 공간 필터를 제안하였으며, 시뮬레이션을 통해 기존의 방법들과 그 성능을 비교하였다.

• 한국통신학회논문지
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• 제33권1C호
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• pp.68-78
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• 2008

The transmission of multimedia information over error-prone channels such as wireless networks has become an important area of research. In this paper, we propose two Error Concealment(EC) schemes for wireless transmission of JPEG2000 image. The Multiple Representation(MR) is employed as the preprocessing in our schemes, whereas the main error concealing operation is applied in wavelet domain at receiver side. The compressed code-stream of several subsampled versions of original image is transmitted over a single channel with random bit errors. In the decoder side, the correctly reconstructed wavelet coefficients are utilized to recover the corrupted coefficients in other sub-images. The recovery is carried out by proposed basic(MREC-BS) or enhanced(MREC-ES) methods, both of which can be simply implemented. Moreover, there is no iterative processing during error concealing, which results a big time saving. Also, the simulation results confirm the effectiveness and efficiency of our proposed schemes.

• 대한원격탐사학회지
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• 제23권1호
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• pp.33-42
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• 2007

In this paper, an iterative MAP approach using a Bayesian model based on the lognormal distribution for image intensity and a GRF for image texture is proposed for despeckling the SAR images that are corrupted by multiplicative speckle noise. When the image intensity is logarithmically transformed, the speckle noise is approximately Gaussian additive noise, and it tends to a normal probability much faster than the intensity distribution. MRFs have been used to model spatially correlated and signal-dependent phenomena for SAR speckled images. The MRF is incorporated into digital image analysis by viewing pixel types as slates of molecules in a lattice-like physical system defined on a GRF Because of the MRF-SRF equivalence, the assignment of an energy function to the physical system determines its Gibbs measure, which is used to model molecular interactions. The proposed Point-Jacobian Iterative MAP estimation method was first evaluated using simulation data generated by the Monte Carlo method. The methodology was then applied to data acquired by the ESA's ERS satellite on Nonsan area of Korean Peninsula. In the extensive experiments of this study, The proposed method demonstrated the capability to relax speckle noise and estimate noise-free intensity.