• 지구물리와물리탐사
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• 제16권4호
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• pp.211-216
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• 2013

일반적으로 평활화 필터는 주변값들과의 차이를 감소시켜 함수를 정규화하는 역할을 한다. 따라서 완전파형역산에 평활화 필터를 적용하면 역산 해를 정규화 할 수 있으며 실제 지하 구조에 가까운 영상을 얻을 수 있다. 다만 단일 평활화 계수를 사용했을 때는 지층 형태나 속도변화에 관계없이 동일하게 평활화가 이루어지므로 지층간 경계면이나 단층 등의 구조가 불명확해지는 단점이 있다. 본 논문에서는 이러한 문제를 해결하기 위해 단일 평활화 계수가 아닌 역산 반복 과정에 따라 선택적으로 평활화 계수를 조정하는 정규화 기법을 개발하였다. 먼저 파형역산에 적합한 탐사자료의 주파수 대역과 그에 대응하는 파수 범위를 분석하였다. 분석한 파수 범위에 적합한 평활화 계수를 선정하기 위해 평활화 필터의 파수 스펙트럼에서 99백분위수에 해당하는 파수를 유효최대파수로 결정하였다. 선정된 평활화 계수를 반복역산에 따라 다르게 적용하여 여러 주파수를 동시에 이용하는 멀티-스케일 완전파형역산을 구현하였다. 암염 모델과 같은 속도대비가 큰 지질구조에 대해 성공적인 역산결과를 얻음으로써 본 연구에서 개발한 평활화 계수 선택기법이 효과적인 정규화 과정을 구현한다는 것을 알 수 있었다. 또한 무작위 잡음이 더해진 인공합성 음원모음 자료에 대한 수치예제를 통해 현장 자료에 대한 적용 가능성도 확인할 수 있었다.

• 한국정보과학회논문지:소프트웨어및응용
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• 제33권1호
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• pp.95-104
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• 2006

Gradient vector flow(GVF) snake 또는 active contour 모델은 영상 분할에서 훌륭한 성능을 보여준다. 그러나 기존의 snake 모델에는 제한된 캡쳐 영역과 요면으로의 느린 진행과 같은 문제점들이 존재한다. 본 논문은 주변의 필드로부터 외부장(external force field)을 확장시키고 변형된 평탄화기법을 이용하여 확장된 필드를 정규화 함으로서 GVF snake 모델의 성능을 개선시키는 새로운 방법을 제시한다. 시뮬레이션을 위해 사용된 U자 모양 이미지에서의 결과는 제안된 방법이 좀 더 큰 캡쳐 영역을 갖고 기존의 GVF snake 모델에 비하여 요면으로 빠르게 진행하는 것이 가능함을 보여준다.

• 대한전자공학회논문지
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• 제20권6호
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• pp.11-17
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• 1983

본 연구는 explicit M.K.A.C. 알고리즘으로 마이크로프로세서를 사용하여 직류전동기 속도 제어를 하였다. 실험에 사용된 적응 제어 알고리즘으로는 먼저 지수함수적 가중 최소사승법 (exponentially wighted least square method: E.W.L.S) 알고리즘의 계산상의 불안정과 수행시간을 최소로 하기 위하여 시간 지연이 있는 E.W.L.S.알고리즘에 EDUt-_인수화법을 도입한 UDUt-인수화법 알고리즘을 사용하였고, 또한 gradient-type의 알고리즘으로도 초기에 dtatl-zollr을 갖는 직류전동기를 효과적으로 제어하기 위하여 gradient-type의 알고리즘에 smoothing polynomal과 상수ℓ을 사용한 SM gradient-쇼pe의 알고리즘을 제안하였다. UDTt인수화법 알고리즘을 적용한 결과 수행시간이 단축되었으며, SM gradient-type의 알고리즘의 경우는 dead-zone을 위한 기동전압을 사용하지 않고도 효과적인 속도제어를 할 수 있음을 확인하였다.

• 한국정밀공학회지
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• 제20권7호
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• pp.138-146
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• 2003

A critical issue in area-based stereo matching lies in selecting a fixed rectangular window size. Previous stereo methods doesn't deal effectively with occluding boundary due to inevitable window-based problems, and so give inaccurate and noisy matching results in areas with steep disparity variations. In this paper, a variable window approach is presented to estimate accurate, detailed and smooth disparities for three-dimensional structure reconstruction. It makes the smoothing of depth discontinuity reduced by evaluating corresponding correlation values and intensity gradient-based similarity in the three-dimensional disparity space. In addition, it investigates maximum connected match candidate points and then devise the novel arbitrarily shaped variable window representative of a same disparity to treat with disparity variations of various structure shapes. We demonstrate the performance of the proposed variable window method with synthetic images, and show how our results improve on those of closely related techniques for accuracy, robustness, matching density and computing speed.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.284-287
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• 2003

Previous stereo methods doesn't deal effectively with depth discontinuity due to inevitable window-based problems, and so give inaccurate and noisy matching results in areas with steep disparity variations. In this paper. a variable window approach is presented to estimate accurate, detailed and smooth disparities with three-dimensional disparity space. It makes the smoothing of depth discontinuity reduced by evaluating corresponding correlation values and intensity gradient-based similarity in the space. In addition, it devises the novel arbitrarily-shaped variable window to treat with disparity variations of various structure shapes. We show how our results improve on those of closely related techniques for accuracy, robustness. matching density and computing speed.

• Journal of Mechanical Science and Technology
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• 제14권5호
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• pp.518-529
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• 2000

A detailed and thorough parametric study of digital image correlation method is presented. A theoretical background and development of the method were introduced and the effects of various parameters on the determination of displacement outputs from the raw original and deformed image information were examined. Use of the normalized correlation coefficient, the use of 20 to 40 pixels for a searching window side, 6 variables searching, bi-cubic spline sub pixel interpolations and the use of coarse-fine search are some of the key choices among the results of parametric studies. The displacement outputs can be further processed with two dimensional curve fitting for the data noise reduction as well as displacement gradient calculation.

• Interaction and multiscale mechanics
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• 제6권2호
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• pp.237-255
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• 2013

In this paper, a meshfree-enriched finite element method (ME-FEM) is introduced for the large deformation analysis of nonlinear path-dependent problems involving contact. In linear ME-FEM, the element formulation is established by introducing a meshfree convex approximation into the linear triangular element in 2D and linear tetrahedron element in 3D along with an enriched meshfree node. In nonlinear formulation, the area-weighted smoothing scheme for deformation gradient is then developed in conjunction with the meshfree-enriched element interpolation functions to yield a discrete divergence-free property at the integration points, which is essential to enhance the stress calculation in the stage of plastic deformation. A modified variational formulation using the smoothed deformation gradient is developed for path-dependent material analysis. In the industrial metal forming problems, the mortar contact algorithm is implemented in the explicit formulation. Since the meshfree-enriched element shape functions are constructed using the meshfree convex approximation, they pose the desired Kronecker-delta property at the element edge thus requires no special treatments in the enforcement of essential boundary condition as well as the contact conditions. As a result, this approach can be easily incorporated into a conventional displacement-based finite element code. Two elasto-plastic problems are studied and the numerical results indicated that ME-FEM is capable of delivering a volumetric locking-free and pressure oscillation-free solutions for the large deformation problems in metal forming analysis.

• 한국방송∙미디어공학회:학술대회논문집
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• 한국방송공학회 2013년도 하계학술대회
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• pp.315-318
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• 2013

A novel foveation filter method is proposed in DCT domain. For countering the blocking and ringing artifacts, we devise the tools measuring the signal gradient, the block signal variations in the DCT domain. Each measurement is properly applied to each enhancement region and smoothing region. The proposed method optimally adapts the enhancement factors to the characteristics of the underlying signals and so maximizes the enhancement performances with significantly suppressing the artifacts. The subjective and objective evaluations verify that the proposed method sustains producing the improved video qualities for various sequences without tuning any parameters to individual sequences.

• 한국멀티미디어학회논문지
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• 제18권10호
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• pp.1164-1171
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• 2015

The edge preserving method is important for image storage and geometric transformation. In this paper, we propose a new edge preserving method using HOG-Guide filter for image segmentation. In our approach, we extract edge information using gradient histogram to set HOG guide line. Then, we use HOG guide line to smooth image. With two to four iterations of smoothing operations, we finally obtain desirable edge preserved image. Our experimental results showed good performances showing that our proposed method is better than other methods.

• 디지털산업정보학회논문지
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• 제11권4호
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• pp.155-164
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• 2015

In this paper, we propose a new color interpolation method based on trilateral filter approach, which not only preserve the high-frequency components(image edge) while interpolating the missing raw data of color image(bayer data pattern), but also immune to the image noise components and better preserve the detail of the low-frequency components. The method is the trilateral filter approach applying a gradient to the low frequency components of the image signal in order to preserve the high-frequency components and the detail of the low-frequency components through the measure of the freedom of similarity among adjacent pixels. And also we perform Gaussian smoothing to the interpolated image data in order to robust to the noise. In this paper, we compare the conventional demosaicing algorithm and the proposed algorithm using 10 test images in terms of hue MAD, saturation MAD and CPSNR for the objective evaluation, and verify the performance of the proposed algorithm.