• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.12
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• pp.2503-2510
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• 2002

Since the first shape-form-shading technique was developed by Horn in the early 1970s, many different approaches have been continuously emerging in the past three decades. Some of them improve existing techniques, while others are completely new approaches. Using the image reflectance equation, they estimate the 3-D shape of an object utilizing adequate constraints. Each algorithm applies different constraints such as brightness, smoothness, and integrability to solve the shape-from-shading problem. Especially for symmetric objects, a symmetry constraint is proposed to improve the performance of existing shape-from-shading algorithm in this paper. The symmetry constraint is imposed to a conventional algorithm and then the improvement in the performance of 3-D shape reconstruction is proved by quantitatively comparing the depth and gradient errors.

• Korean Journal of Remote Sensing
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• v.2 no.2
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• pp.117-131
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• 1986

The purpose of this study was to develop techniques acquiring hydrologic parameters that affect runoff conditions from Landsat imagery. Runoff conditions in a study area were analyzed by employing the U.S. Soil Conservation Service(SCS) Method. SCS runoff curve numbers(CN) were estimated by the computer analysis of Landsat imagery and digiral terrain model(DTM) data. The SCS Method requires land use/cover and soil conditions of the area as input parameters. A land use/cover map of 5 hydrological classes was produced from the Landsat multi-spectral scannerr imagery. Slope-gradient and contour and contour maps were also made using the DTM topographic data. Inundation areas depending on reservoir levels were able to be mapped on the Landsat scene by combining the contour data.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.11a
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• pp.29-30
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• 2012

본 논문은 고해상도의 깊이맵을 얻기 위해서 대응되는 색상 영상의 최대 변화도를 이용한 깊이맵 업샘플링 기술을 제안한다. 기존 알고리즘들이 인접한 화소의 깊이 값을 참조할 때 거리에 따른 가중치를 부여하는 것과 달리, 제안한 방법은 현재 화소와 참조 화소 사이의 최대 색차 변화도를 이용하여 가중치를 부여한다. 이런 접근 방법은 비슷한 색상의 물체가 서로 붙어 있거나 큰 크기의 객체가 존재할 경우에도 모두 올바른 가중치를 부여할 수 있다는 장점을 갖는다. 먼저, 색상 영상의 색차 성분에 대한 변화도 영상을 계산하고, 업샘플링하고자 하는 화소와 참조 화소 사이의 최단 경로 위에서 가장 큰 변화도를 취한다. 변화도가 클수록 다른 객체에 존재할 확률이 높기 때문에 변화도가 큰 참조 화소에는 작은 가중치를 부여하고, 이들의 가중합을 통해 최종 깊이 값을 계산한다. 제안한 방법을 이용하여 깊이맵을 업샘플링한 결과가 기존 알고리즘들에 비해 우수한 결과를 보였다.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.165-172
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• 2002

We presents an hazard zonation mapping technique in karst terrain and its assessment. From the detailed engineering geological mapping. Controlling factors of sink hole and limestone cave formation were discussed and 4 main hazard factors affecting hazard potential are identified as follows: prerequisite hazard factor(distributions of pre-existing sink holes and cavities), geomorphological hazard factors(slope gradient, vegetation, and drainage pattern etc.) geological hazard factors(lithology, fracture patterns and geological structures etc.) and hydraulic conditions(hydraulic head, annual fluctuation of ground water table and composition of g/w water). From the construction of hazard zonation map along the Jecheon-Maepo area, and vertical cross-sectional hazard zonations specific tunnel site we suggest hazard zonation rating systems.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2016.06a
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• pp.306-308
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• 2016

신호등 검출은 지능형 교통 시스템에서 매우 중요하며 최근 신호등 검출 관련한 연구가 활발히 진행 중이다. 하지만 기존의 신호등검출 알고리듬의 문제점은 조명의 변화에 민감하다는 문제점이 있다. 이러한 문제점을 해결하기 위하여 본 논문에서는 다음과 같은 신호등 검출 알고리듬을 제안한다. 먼저 제안하는 색상지도와 HSV(Hue-Saturation-Value)를 이용하여 신호등의 후보를 검출한다. 검출한 신호등의 후보로부터 HOG(Histogram of Oriented Gradient) 서술자를 이용하여 특징을 추출한 다음 최종적으로 선형 SVM(Support Vector Machine)을 이용하여 신호등을 검출하는 알고리듬을 제안한다.

• Proceedings of the Korean Society of Broadcast Engineers Conference
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• 2012.07a
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• pp.314-316
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• 2012

본 논문에서는 의료영상 영역화 기법으로 이용되는 레이블 융합 기법을 기반으로, 정합 기법을 이용했을 시 빈번하게 발생하는 경계에서의 오차를 크게 줄여줄 수 있는 기법을 제안한다. 패치 기반 레이블 융합 기법은 패치 간의 밝기 값의 유사도를 기반으로 융합 가중치를 계산하였지만 이는 밝기의 분포가 상대적으로 다른 자기공명영상에 적합하지 못한 경우가 많았다. 본 논문에서는 밝기 값과 함께 밝기 값의 경사도 유사도를 추가적으로 계산하여 융합 가중치를 얻어내는 기법을 제안한다. 밝기의 분포가 다른 영역에서도 밝기의 경사도 분포는 대부분 유사하기 때문에, 오차가 많은 모호한 경계에서 향상된 결과를 얻을 수 있었다. 제안하는 기법의 성능평가를 위해 50 개의 SKI10 무릎 관절 데이터 셋 내에서 대퇴골을 영역화 하였다. 실험 결과를 통해 제안하는 기법이 밝기 값 유사도 정보만을 이용했던 기법에 비해 개선된 성능을 보이고 있음을 확인할 수 있다.

• Journal of the Korea Computer Graphics Society
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• v.11 no.1
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• pp.40-49
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• 2005

Several optimization techniques have been proposed for volume ray casting, but these cannot achieve real-time frame rates. In addition, it is difficult to apply them to some applications that require perspective projection. Recently, hardware-based methods using 3D texture mapping are being used for real-time volume rendering. Although rendering speed approaches real time, the larger volumes require more swapping of volume bricks for the limited texture memory. Also, image quality deteriorates compared with that of conventional volume ray casting. In this paper, we propose a data structure for real-time volume ray casting named PERM (Precomputed dEnsity and gRadient Map). The PERM stores interpolated density and gradient vector for quantized cells. Since the information requiring time-consuming computations is stored in the PERM, our method can ensure interactive frame rates on a consumer PC platform. Our method normally produces high-quality images because it is based on conventional volume ray casting.

• Investigative Magnetic Resonance Imaging
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• v.1 no.1
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• pp.119-124
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• 1997

Purpose: To assess the utility of magnetic resonance(MR) cerebral blood volume (CBV) map in the evaluation of brain tumors. Materials and Methods: We performed perfusion MR imaing preoperatively in the consecutive IS patients with intracranial masses(3 meningiomas, 2 glioblastoma multiformes, 3 low grade gliomas, 1 lymphoma, 1 germinoma, 1 neurocytoma, 1 metastasis, 2 abscesses, 1 radionecrosis). The average age of the patients was 42 years (22yr -68yr), composed of 10 males and S females. All MR images were obtained at l.ST imager(Signa, CE Medical Systems, Milwaukee, Wisconsin). The regional CBV map was obtained on the theoretical basis of susceptibility difference induced by first pass circulation of contrast media. (contrast media: IScc of gadopentate dimeglumine, about 2ml/sec by hand, starting at 10 second after first baseline scan). For each patient, a total of 480 images (6 slices, 80 images/slice in 160 sec) were obtained by using gradient echo(CE) single shot echo-planar image(EPI) sequence (TR 2000ms, TE SOms, flip angle $90^{\circ}$, FOV $240{\times}240mm,{\;}matrix{\;}128{\times}128$, slice-thick/gap S/2.S). After data collection, the raw data were transferred to CE workstation and rCBV maps were generated from the numerical integration of ${\Delta}R2^{*} on a voxel by voxel basis, with home made software (${\Delta}R2^{*}=-ln (S/SO)/TE). For easy visual interpretation, relative RCB color coding with reference to the normal white matter was applied and color rCBV maps were obtained. The findings of perfusion MR image were retrospectively correlated with Cd-enhanced images with focus on the degree and extent of perfusion and contrast enhancement. Results: Two cases of glioblastoma multiforme with rim enhancement on Cd-enhanced Tl weighted image showed increased perfusion in the peripheral rim and decreased perfusion in the central necrosis portion. The low grade gliomas appeared as a low perfusion area with poorly defined margin. In 2 cases of brain abscess, the degree of perfusion was similar to that of the normal white matter in the peripheral enhancing rim and was low in the central portion. All meningiomas showed diffuse homogeneous increased perfusion of moderate or high degree. One each of lymphoma and germinoma showed homogenously decreased perfusion with well defined margin. The central neurocytoma showed multifocal increased perfusion areas of moderate or high degree. A few nodules of the multiple metastasis showed increased perfusion of moderate degree. One radionecrosis revealed multiple foci of increased perfusion within the area of decreased perfusion. Conclusion: The rCBV map appears to correlate well with the perfusion state of brain tumor, and may be helpful in discrimination between low grade and high grade gliomas. The further study is needed to clarify the role of perfusion MR image in the evaluation of brain tumor.

• Korean Journal of Remote Sensing
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• v.39 no.6_3
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• pp.1721-1730
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• 2023

As awareness of the problem of global warming emerges around the world, the role of carbon sinks in settlement is increasingly emphasized to achieve carbon neutrality in urban areas. In order to manage carbon sinks in settlement, it is necessary to identify the current status of carbon sinks. Identifying the status of carbon sinks requires a lot of manpower and time and a corresponding budget. Therefore, in this study, a map predicting the location of trees was created using already established tree location information and Sentinel-2 satellite images targeting Seoul. To this end, after constructing a tree presence/absence dataset, structured data was generated using 16 types of vegetation indices information constructed from satellite images. After learning this by applying the Extreme Gradient Boosting (XGBoost) model, a tree prediction map was created. Afterward, the correlation between independent and dependent variables was investigated in model learning using the Shapely value of Shapley Additive exPlanations(SHAP). A comparative analysis was performed between maps produced for local parts of Seoul and sub-categorized land cover maps. In the case of the tree prediction model produced in this study, it was confirmed that even hard-to-detect street trees around the main street were predicted as trees.

• Proceedings of the Korean Vacuum Society Conference
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• 2013.08a
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• pp.99-99
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• 2013

In this talk, I will present two research works in progress, which are: i) mapping of piezoelectric polarization and associated charge density distribution in the heteroepitaxial InGaN/GaN multi-quantum well (MQW) structure of a light emitting diode (LED) by using inline electron holography and ii) in-situ observation of the polarization switching process of an ferroelectric Pb(Zr1-x,Tix)O3 (PZT) thin film capacitor under an applied electric field in transmission electron microscope (TEM). In the first part, I will show that strain as well as total charge density distributions can be mapped quantitatively across all the functional layers constituting a LED, including n-type GaN, InGaN/GaN MQWs, and p-type GaN with sub-nm spatial resolution (~0.8 nm) by using inline electron holography. The experimentally obtained strain maps were verified by comparison with finite element method simulations and confirmed that not only InGaN QWs (2.5 nm in thickness) but also GaN QBs (10 nm in thickness) in the MQW structure are strained complementary to accommodate the lattice misfit strain. Because of this complementary strain of GaN QBs, the strain gradient and also (piezoelectric) polarization gradient across the MQW changes more steeply than expected, resulting in more polarization charge density at the MQW interfaces than the typically expected value from the spontaneous polarization mismatch alone. By quantitative and comparative analysis of the total charge density map with the polarization charge map, we can clarify what extent of the polarization charges are compensated by the electrons supplied from the n-doped GaN QBs. Comparison with the simulated energy band diagrams with various screening parameters show that only 60% of the net polarization charges are compensated by the electrons from the GaN QBs, which results in the internal field of ~2.0 MV cm-1 across each pair of GaN/InGaN of the MQW structure. In the second part of my talk, I will present in-situ observations of the polarization switching process of a planar Ni/PZT/SrRuO3 capacitor using TEM. We observed the preferential, but asymmetric, nucleation and forward growth of switched c-domains at the PZT/electrode interfaces arising from the built-in electric field beneath each interface. The subsequent sideways growth was inhibited by the depolarization field due to the imperfect charge compensation at the counter electrode and preexisting a-domain walls, leading to asymmetric switching. It was found that the preexisting a-domains split into fine a- and c-domains constituting a $90^{\circ}$ stripe domain pattern during the $180^{\circ}$ polarization switching process, revealing that these domains also actively participated in the out-of-plane polarization switching. The real-time observations uncovered the origin of the switching asymmetry and further clarified the importance of charged domain walls and the interfaces with electrodes in the ferroelectric switching processes.