• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.3
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• pp.265-271
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• 2015

In this study, optical design for small satellite camera equipped with online optical compensation movements has been conducted. Satellite camera equipped with compensation movements at M2 mirror and focal plane can guarantee the MTF performance through the focal plane image stabilization and the on-orbit optical alignment. The designed optical system is schmidt-cassegrain type that has M1 mirror of a diameter 200mm, GSD 3.8m at an altitude of 700km, and 50 % MTF performance. The performance of the designed optical system has been analyzed through the method of ray aberration curve, spot diagram, and MTF. It has been found by the optical performance analysis that the designed optical system satisfies the optical requirements of satellite camera equipped with online optical compensation movements.

• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.67-75
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• 2012

Purpose : We studied enhanced method to view the vessels in the brain using Magnetic Resonance Angiography (MRA). Noticing that Maximum Intensity Projection (MIP) image is often used to evaluate the arteries of the neck and brain, we propose a new method for view brain vessels to stereo image in 3D space with more superior and more correct compared with conventional method. Materials and Methods: We use 3T Siemens Tim Trio MRI scanner with 4 channel head coil and get a 3D MRA brain data by fixing volunteers head and radiating Phase Contrast pulse sequence. MRA brain data is 3D rotated according to the view angle of each eyes. Optimal view angle (projection angle) is determined by the distance between eye and center of the data. Newly acquired MRA data are projected along with the projection line and display only the highest values. Each left and right view MIP image is integrated through anaglyph imaging method and optimal stereoscopic MIP image is acquired. Results: Result image shows that proposed method let enable to view MIP image at any direction of MRA data that is impossible to the conventional method. Moreover, considering disparity and distance from viewer to center of MRA data at spherical coordinates, we can get more realistic stereo image. In conclusion, we can get optimal stereoscopic images according to the position that viewers want to see and distance between viewer and MRA data. Conclusion: Proposed method overcome problems of conventional method that shows only specific projected image (z-axis projection) and give optimal depth information by converting mono MIP image to stereoscopic image considering viewers position. And can display any view of MRA data at spherical coordinates. If the optimization algorithm and parallel processing is applied, it may give useful medical information for diagnosis and treatment planning in real-time.

• Journal of Dental Rehabilitation and Applied Science
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• v.30 no.2
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• pp.93-101
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• 2014

Purpose: The aim of this study is to investigate the typical shape of the curve of Spee in Korean and analyze the curve of Spee according to gender, age, and left and right. Materials and Methods: Among the patient of Wonkwang University Sanbon Dental Hospital taking cone beam computerized tomography, the images of 500 Koreans (311 males and 189 females) who qualifies the criteria of this study were selected and their curve of Spee were analysed in sagittal plane. Results: The mean radius of curve of Spee in Korean was 91.4 mm. There was statistically significant difference between male (94.6 mm) and female (86.1 mm) by gender, but not significant differences by age and between right and left side. Conclusion: Within the limitation of this study, the smaller radius (91.4 mm) of Korean than the 4-inch (101.6 mm) value advocated by Monson was meaned that it would be need to reconsider the application of the curve of Spee in all cases when occlusal plane is reconstructed in Korean.

• Journal of Korean Ophthalmic Optics Society
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• v.17 no.3
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• pp.305-309
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• 2012

Purpose:This study was conducted to research any effect on aided distance visual acuity and refractive error changes by using smartphone at near for long term. Methods: 20($20.6{\pm}0.9$ years) young adults subjects with no ocular diseases, over 0.8 of aided distance visual acuity, normal amplitude of accommodation and normal accommodative facility agreed to participate in this study. The subjects were divided into two group, Group 1 (15 cm fixation distance) included 10 subjects and Group 2(40 cm fixation distance) included 10 subjects. Aided distance visual acuity and refractive error were measured before and after using smartphone for 30 minutes by auto-chart project (CP-1000, Dongyang, Korea), phoropter (VT-20, Dongyang, Korea), auto refractor-keratometer (MRK-3100, Huvitz, Korea). After then, the subjects looked at distance with wearing spectacles. Refractive error was measured at 5 minutes, 10 minutes, and 15 minutes later, respectively. Results: After using smartphone at 15 cm for 30 minutes, there was statistically significant reduction of aided distance visual acuity (p=0.030) and increasing myopia (p=0.001). The increased myopia was not statistically significant after 5 minutes rest (p${\geq}$0.464). However there was no statistically significant changes in aided distance visual acuity (p=0.163) and refractive error (p=0.077) after using smartphone at 40 cm for 30 minutes. Conclusions: It is recommend to keep 40 cm off the smartphone from eyes to avoid any aided distance visual acuity and refractive error changes. If smartphone is used closer than 40 cm, a rest for 5 minutes is also recommend after every 30 minutes use with smartphone to avoid any aided distance visual acuity and refractive error changes.

• Journal of the Institute of Electronics Engineers of Korea CI
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• v.45 no.3
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• pp.160-174
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• 2008

In this paper, we propose new coding techniques for photometry data of three-dimensional(3-D) mesh models. We make a good use of geometry and connectivity information to improve coding efficiency of color, normal vector, and texture data. First of all, we determine the coding order of photometry data exploiting connectivity information. Then, we exploit the obtained geometry information of neighboring vortices through the previous process to predict the photometry data. For color coding, the predicted color of the current vertex is computed by a weighted sum of colors for adjacent vortices considering geometrical characteristics between the current vortex and the adjacent vortices at the geometry predictor. For normal vector coding, the normal vector of the current vertex is equal to one of the optimal plane produced by the optimal plane generator with distance equalizer owing to the property of an isosceles triangle. For texture coding, our proposed method removes discontinuity in the texture coordinates and reallocates texture image segments according to the coding order. Simulation results show that the proposed compression schemes provide improved performance over previous works for various 3-D mesh models.

• Journal of the Korea Convergence Society
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• v.9 no.9
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• pp.183-189
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• 2018

This study deals with the design and development of imaging optics having 24mm focal length for MWIR ($3{\sim}5{\mu}m$) with two symmetrical lenses facing each other. We used CodeV in our optical design, and we performed the optimization process to have the resolution and angle of view satisfying the user's requirements. The materials of lenses were limited to two types, including KCIR035 with a refractive index of 1.7589, developed in Korea. The optical system designed in this way consists of two aspherical lenses made of KCIR035 material having the same shape and one spherical lens made of Si. Here, the arrangement of the two aspherical lenses is characterized by having a symmetrical structure facing each other. And this optical system has a resolution of MTF value of 0.35 or more at a line width of 20 lp / mm. Therefore, it is considered that this optical system has the capability to be applied to a thermal imaging camera using a $206{\times}156$ array MWIR detection device having a pixel size of $25{\mu}m$.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.8 no.2
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• pp.185-196
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• 1997

By considering the definition and application of resolution as well as the concept and theory of SAR, the essential contents of the SAR design and analysis are described. This paper is to compare and analyze the resolution performance capability of three techniques for achieving azimuth resolution such as the real aperture, the unfocused and the focused techniques, through the simulation. Simulation is performed to make the restricted conditions for the unfocused technique that can be implemented by the less commputing load of signal processingand the lower cost. Through the mission analysis, the use of SAR image can be applied for estimation of whole situation at the regional area in the field of military demands for tactical purpose as well as civilian demands for the damage of disaster. RPV and sall or medium aircraft are selected to carry the SAR for these purposes and the proper resolution turns ou 5~15 m. The trade-off study of variables through the simulations results in the proper conditions such that range is less 3, 000 m, Wavelength is 1~10 m, and the raw signals and results processed by three techniques for two point targets are exhibited undr such conditions. Therefore, at some points, the result of this paper si proposed for useful applications of unforcused technique in the restricted conditions except the identification of the small target at a long range re- quired for high resolution.

• Korean Journal of Optics and Photonics
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• v.28 no.3
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• pp.108-115
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• 2017

We report the assembly procedure and performance evaluation of a visible and near-infrared spectrometer in the wavelength region of 400-900 nm, which is later to be combined with fore-optics (a telescope) to form a f/2.5 imaging spectrometer with a field of view of ${\pm}7.68^{\circ}$. The detector at the final image plane is a $640{\times}480$ charge-coupled device with a $24{\mu}m$ pixel size. The spectrometer is in an Offner relay configuration consisting of two concentric, spherical mirrors, the secondary of which is replaced by a convex grating mirror. A double-pass test method with an interferometer is often applied in the assembly process of precision optics, but was excluded from our study due to a large residual wavefront error (WFE) in optical design of 210 nm ($0.35{\lambda}$ at 600 nm) root-mean-square (RMS). This results in a single-path test method with a Shack-Hartmann sensor. The final assembly was tested to have a RMS WFE increase of less than 90 nm over the entire field of view, a keystone of 0.08 pixels, a smile of 1.13 pixels and a spectral resolution of 4.32 nm. During the procedure, we confirmed the validity of using a Shack-Hartmann wavefront sensor to monitor alignment in the assembly of an Offner-like spectrometer.