• Korean Journal of Optics and Photonics
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• v.20 no.4
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• pp.241-248
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• 2009

We suggest a new method to determine the off-alignment error of the composite film, together with in-plane($R_{in}$) and out-of-plane retardation($R_{th}$) of the compensation film, simultaneously. The composite film consists of a polarizing film and a compensation film for improvement of viewing angle of a liquid crystal display. We regarded the compensation film as o-plate with its optic axis along an arbitrary direction. By using an extended Jones matrix method, the polarization characteristics of the composite film are examined. The calculated Fourier constants, ($\alpha$, $\beta$) curves of the composite film as the azimuth angle is varied at the incident angles of $0^{\circ}$ and $50^{\circ}$, respectively, are used to determine the axis misalignment, the tilt angle and the azimuth angle of the compensation film by adopting the linear regressional analysis technique. Since this method can be applied for the inspection of the composite film even after laminating the polarizing film and the compensation film, it will be useful for simplifying the manufacturing process and reducing the production cost of liquid crystal display panels.

• Transactions of the Society of Information Storage Systems
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• v.3 no.1
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• pp.34-39
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• 2007

Super-REsolution Near-field Structure (Super-RENS) 재생 현상을 모델링하고 재생 신호를 계산하여 실험 결과와 비교하였다. 약 2mW 내외의 높은 광 파워로 집광된 Spot 은 디스크 내의 상변화 물질인 GST 를 용융시키므로 집광 Spot 내에는 용융 영역과 비 용융 영역이 공존하게 되고 연속적 또는 불연속적인 경계를 이루게 된다. 이러한 열 효과로부터 기인하는 집광 Spot 내에서의 물질의 광학적 특성 변화와 변화 정도의 차이를 가정하였고 변화된 광학적 특성은 집광된 Spot 의 유효 크기를 줄어들게 함으로써 회절한계 이하의 정보를 재생 가능하게 한다. 계산은 FDTD 방법과 Scalar 방법을 병행하였다. FDTD 방법으로는 위와 같은 집광 Spot 내의 물질 굴절률 (n,k) 변화로부터 회절한계 이하의 정보가 재생 가능함과 CNR 문턱 현상을 확인하였고, Scalar 방법으로는 물질 굴절률을 직접 다루지 않고 굴절률 변화로부터 기인하는 광의 Amplitude 와 Phase 변화로부터 회절한계 이하의 정보가 재생 가능함을 확인하였다. 이 때 광의 Amplitude 와 Phase 변화를 모델링하기 위하여 지름, 위치, 반사율 변화량, 위상 변화량의 네가지 변수로 정의되는 광 마스크를 도입하였다. Scalar 방법을 이용하여 재생 RF 신호 등 다양한 Super-RENS 디스크의 신호를 계산 활용 할 수 있고 다음의 두가지 광학계에 대하여 계산과 실험으로 얻은 채널 특성 및 RF 신호를 비교하여 각각 오차평균 4.2%, 4.7%로 일치함을 확인하였다. 파장 659nm, NA=0.6, Min Pit Length=173nm ROM 디스크 System, 파장 405nm, NA=0.85 Min Mark Length=75nm WORM 디스크 System.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.200-206
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• 2014

In this paper, using the value theoretically calculated to emit multidirectionally a beam coming into an optical fiber with diameter of $125{\mu}m$, we modeled and produced a cone-shaped structure at the distal end of the fiber. A numerical simulation was performed for an optical fiber tip in which all incident beams were totally reflected and emitted toward the side, as well as for an optical fiber tip from which the beams could be emitted forward and sideways simultaneously. We produced multidirectional-firing optical fiber tips based on the simulation result and model. Laser fabrication of the optical fiber was done by processing a cone-shaped structure at the distal end of an optical fiber with diameter of $125{\mu}m$ using a femtosecond pulsed laser and polishing the processed surface with a $CO_2$ laser. We also conducted an analysis to compare experimental and simulation results.

• Korean Journal of Optics and Photonics
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• v.18 no.3
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• pp.179-184
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• 2007

In order to extract more accurate skin parameters, this study was focused on the improvement of the efficiency of a previous inverse fitting algorithm based on genetic algorithms. The algorithm provides the best fitting result of the diffusion approximation model to a VRS (visual reflectance spectroscopy) curve of skin. Simplex and wavelength selection methods were applied to the previous algorithm. Nine skin parameters were inversely extracted from the modeling studies. The revised inverse fitting algorithm was determined to produce an 83% reduction of computation time and a 0.64% reduction of sum of square error, compared to the previous algorithm. In conclusion, we confirmed that the new algorithm provides faster and more accurate solutions for the diffusion approximation model.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.43 no.6 s.312
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• pp.46-56
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• 2006

In this paper, we propose an improved reproduction algorithm for a realistic image of the real scene based on the optical characteristics of the light sources and the materials at the lighting environment. This paper is continuation of the previous study to improve the modeling method of the light sources and the materials and apply this to the real rear lamp of automobile. The backward ray tracing method is first used to trace the light ray from a light source, and also considers the physical characteristics of object surfaces and geometric properties of light radiation to estimate accurately the light energy incoming toward to human eyes. For experiments and verification of the proposed method, the simulation results are compared with the measured light stimuli. Accordingly, the simulation results show that the proposed algorithm can estimate light energy well and reproduce the visually similar image with a scene incident on a sight of viewer.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.5
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• pp.472-482
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• 2008

A modulation transfer function(MTF) tree is established to estimate the overall MTF of an observation satellite and to analyze the image performance. Basic MTF models relevant to each MTF tree component are represented as mathematical relationship between optics-structural dynamics, thermal deformation, attitude and dynamic characteristics of a satellite and the effects due to the space environment. The Basic MTF models consist of diffraction limited MTF with central obscuration, aberration, defocus, line-of-sight(LOS) jitter, linear motion, detector integration, and so forth. Performance estimation is demonstrated for a virtual earth-observation satellite in order to validate the constructed modeling method. The proposed models enable the system engineers to calculate the overall system MTF and to determine the crucial design parameters that affect the image performance in the conceptual design phase of an observation satellite.

• Korean Journal of Remote Sensing
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• v.30 no.2
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• pp.173-183
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• 2014

Field survey research on damages caused by volcanic activities has plenty of difficulties due to human resources, safety and costs issues. Remote sensing application using satellite image is one of very useful tools to overcome those issues. In this study, we monitored the volcanic activities of Sinabung volcano in 2010, which is located in Sumatra island, Indonesia by using Landsat 7 ETM+ satellite images acquired on 17 April, 2009 and 30 July, 2012. We found that the area of pyroclastic flow inundation after 2010 has been tripled roughly, since extracting the pyroclastic flow inundation before and after 2010 eruption from classification. The result from modeling of pyroclastic flow inundation has been compared with the extracted pyroclastic flow inundation from Landsat 7 ETM+ images. As a result, we confirmed that the length of inundation area from the modeling was calculated to 92% accurate, but the width of inundation area was somewhat imprecisely estimated in the volcanic area having the sharp slope and only calculated to 17% accurate.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.407-407
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• 2010

본 논문에서는 확장된 히든마코브모델을 이용하여 플라즈마 식각공정에서 식각종료검출을 위한 방법을 연구하였다. 플라즈마 식각장비는 유도성 결합플라즈마 시스템을 사용하였으며, 종료점 검출을 위해 식각공정이 진행됨에 따른 플라즈마의 상태를 확인할 수 있는 광학 방사 분광기(Optical Emission Spectroscopy: OES)를 사용하였다. 식각이 진행되는 동안 여기되는 입자들은 특정한 재료에 해당하는 파장에서 빛을 방출한다. 플라즈마상태에서 여기되는 원자와 분자들에 의해서 방출되는 빛은 OES를 통해 식각되는 물질을 확인하기 위해서 특별한 파장의 빛을 선택하여 분석한다. 본 논문에서는 확장된 히든마코브모델을 이용해 산화물이 식각될 때 방출하는 고유한 파장의 빛을 분석하여 식각이 종료되는 시점을 찾는 연구를 하였다. 제안된 확장형 히든마코브 모델은 세미-마코브모델과 분절특징 히든마코브모델을 결합한 것으로, 확률적 통계기법을 통해 종료시점을 찾아내는 방법이다. OES를 통해 얻은 데이터는 식각 종료가 일어나기 전의 파장의 상태와 식각이 종료된 후의 파장의 상태로 구분되어지는데, 식각종료시점에서 파장의 상태가 변화하며 이를 감지하여 식각종료점을 검출한다. 분절특징 히든마코브모델을 이용하여 식각종료시점 전후의 파장의 상태를 모델링 하였으며, 일반적인 마코브 모델의 특정상태가 유지될 시간의 확률을 변형된 세미-마코브 모델을 이용하여 OES를 통해 얻은 데이터 내에서 식각 종료가 일어나기 전의 상태가 유지될 수 있는 확률을 모델링 하였다. 실험을 통해 얻어진 6개의 데이터중 4개를 학습을 위해 사용하여 모델링을 하였고 나머지 2개의 데이터를 검증을 위해 사용한 결과, 확장형 히든마코브모델의 식각종료시점검출에 있어 뛰어난 정확성과 우수성을 증명하였다.

• Korean Journal of Remote Sensing
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• v.38 no.6_1
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• pp.1357-1369
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• 2022

Cloud removal is an essential image processing step for any task requiring time-series optical images, such as vegetation monitoring and change detection. This paper presents a two-stage cloud removal method that combines conditional generative adversarial networks (cGANs) with regression-based calibration to construct a cloud-free time-series optical image set. In the first stage, the cGANs generate initial prediction results using quantitative relationships between optical and synthetic aperture radar images. In the second stage, the relationships between the predicted results and the actual values in non-cloud areas are first quantified via random forest-based regression modeling and then used to calibrate the cGAN-based prediction results. The potential of the proposed method was evaluated from a cloud removal experiment using Sentinel-2 and COSMO-SkyMed images in the rice field cultivation area of Gimje. The cGAN model could effectively predict the reflectance values in the cloud-contaminated rice fields where severe changes in physical surface conditions happened. Moreover, the regression-based calibration in the second stage could improve the prediction accuracy, compared with a regression-based cloud removal method using a supplementary image that is temporally distant from the target image. These experimental results indicate that the proposed method can be effectively applied to restore cloud-contaminated areas when cloud-free optical images are unavailable for environmental monitoring.

• Electronics and Telecommunications Trends
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• v.27 no.3
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• pp.12-21
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• 2012

최근 3DTV, 입체 모니터, 입체 노트북 등이 출시되고, 3D 영화, 게임 등 3D 관련 산업이 성장하면서 관련 콘텐츠의 요구사항이 증가하고 있다. 특히, 3D 콘텐츠의 주요 요소 중 하나인 인체는 전통적으로 고가의 3D 스캐너를 이용해 모델링하는 방식을 주로 사용해 왔다. 하지만 근래에는 광학 기술 및 컴퓨팅 성능의 향상으로 구조광과 같은 능동 센서나 카메라로부터 획득한 영상을 기반으로 3D 인체 외형을 복원하는 연구가 각광을 받고 있다. 이런 추세에 발맞춰 본고에서는 인체 중에서도 사용자의 민감도가 높은 얼굴의 3D 복원 기술 및 연구 동향을 살펴보고, 다양한 응용을 목적으로 ETRI에서 개발 중인 3D 얼굴 복원 기술을 소개하고자 한다.