• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.1
• /
• pp.56.4-57
• /
• 2017

The Schwarzschild-Chang off-axis telescope is a "linear astigmatism-free" confocal system. The telescope comprises two pieces of aluminum-alloy freeform mirrors that are fabricated with diamond turning machine (DTM) process. We designed optomechanical structures where optical components in the telescope system can be adjustable on a linear stage. Optomechanical deformation caused by the weight of system itself and its temperature variation is analyzed by the finite element analysis (FEA). The results show that the deformation is estimated in the tolerance range. For the optic-axis alignment of telescope system, three-point alignment (TPA) method is chosen. The TPA method uses three parallel lasers and a plane mirror. Point source images were taken from collimated light and field observation. The performance of optical system was tested by point spread function and aberration measurement of the point sources.

• Journal of Astronomy and Space Sciences
• /
• v.30 no.4
• /
• pp.321-326
• /
• 2013

The modulation transfer function (MTF) is a widely used indicator in assessments of remote-sensing image quality. This MTF method is also used to restore information to a standard value to compensate for image degradation caused by atmospheric or satellite jitter effects. In this study, we evaluated MTF values as an image quality indicator for the Geostationary Ocean Color Imager (GOCI). GOCI was launched in 2010 to monitor the ocean and coastal areas of the Korean peninsula. We evaluated in-orbit MTF value based on the GOCI image having a 500-m spatial resolution in the first time. The pulse method was selected to estimate a point spread function (PSF) with an optimal natural target such as a Seamangeum Seawall. Finally, image restoration was performed with a Wiener filter (WF) to calculate the PSF value required for the optimal regularization parameter. After application of the WF to the target image, MTF value is improved 35.06%, and the compensated image shows more sharpness comparing with the original image.

• Journal of the Optical Society of Korea
• /
• v.19 no.5
• /
• pp.487-493
• /
• 2015

A wavefront coding (WFC) technique provides an extension of the depth of field for a microscopy imaging system with slight loss of image spatial resolution. Through the analysis of the relationship between the incidence angle of light at the phase mask and the system pupil function, a mixing symmetrical cubic phase mask (CPM) applied to 5X-40X micro-objectives is optimized simultaneously based on point-spread function (PSF) invariance and nonzero mean values of the modulation transfer function (MTF) near the spatial cut-off frequency. Optimization results of the CPM show that the depth of field of these micro-objectives is extended 3-10 times respectively while keeping their resolution. Further imaging simulations also prove its ability in enhancing the defocus imaging.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.27 no.1
• /
• pp.56-74
• /
• 2023

In order to obtain practical and high-quality satellite images containing high-frequency components, a large aperture optical system is required, which has a limitation in that it greatly increases the payload weight. As an attempt to overcome the problem, many multi-aperture optical systems have been proposed, but in many cases, these optical systems do not include high-frequency components in all directions, and making such an high-quality image is an ill-posed problem. In this paper, we use deep learning to overcome the limitation. A deep learning model receives low-quality images as input, estimates the Point Spread Function, PSF, and combines them to output a single high-quality image. We model images obtained from three rectangular apertures arranged in a regular polygon shape. We also propose the Modulation Transfer Function Loss, MTF Loss, which can capture the high-frequency components of the images. We present qualitative and quantitative results obtained through experiments.

• Journal of Korean Elementary Science Education
• /
• v.33 no.2
• /
• pp.273-285
• /
• 2014

Purpose of this study is to analyze eye movements of pre-service teachers and elementary students about a visual material of the change on the lunar phases. Eye-Tracker was used for analysis for eye-fixation time and eye movement at the structure, behavior, function question on the visual material. The Results were as follows. First, the pre-service teacher checked the visual materials from a holistic perspective depending on the function questions and fixed eye-fixation on the moon of the behavior question concerned. On the contrary, elementary school student only checked function of the moon located in the upper part and eye-fixation focus was spread here and there regardless of the questions. Second, the pre-service teacher gazed at the sun, earth and moon in a consecutive order depending on the questions to identify their spatial relations and checked location of the moon related to the question. On the contrary, the elementary school student did not view relations between earth, sun and moon from a spatial perspective. These findings indicate that the pre-service teacher conjures up the mechanism of the change on the lunar phases and confirms it in visual materials by visualizing change on the lunar phase model from earth's point of view while the elementary school student fails to take advantage of visual materials to visualize it from earth's point of view.

• Proceedings of the KIEE Conference
• /
• 1979.08a
• /
• pp.164-165
• /
• 1979

Two dimensional kernels which reconstruct the tomographic image from the blurred one formed by simple back-projection are investigated and their performances are compared. These kernels are derived from tile point spread function of the tomographic system and have the form of a ramp filter modified by several window functions to suppress ringing in the reconstruction. Computer simulation using a computer generated phantom image data with different correction functions(kernels) has been carried out. In this simulation, filtering in frequency domain by 2-D FFT technique or in space domain by 2-D direct convolution is considered. It is found that the-computation time required for real space convolution technique is much larger than that of Fourier 2-D filtering technique in the pratical situation.

• Transactions of the Society of Information Storage Systems
• /
• v.11 no.1
• /
• pp.1-5
• /
• 2015

The selective frequency analysis method is suggested in the holographic data storage system with the nyquist aperture to reduce the size of hologram. The image filter was designed with many different methods to improve the bit error rate caused by the nyquist aperture. In previous the methods of image restoration for HDS, an iteration time and a highly precise point spread function were necessary. In this paper, we describe the optical system with analytic method. Thereby, we expect our result help the researchers to design the filter.

• Proceedings of the Korean Society of Broadcast Engineers Conference
• /
• 2019.11a
• /
• pp.204-205
• /
• 2019

영상 보안 시스템에 사용되는 일반적인 CCTV 로 획득한 영상에서의 움직이는 피사체의 화질은 좋지 않다. 본 논문에서는 주변광을 정의하고 이를 통해 외부조명 조건하에 획득한 영상의 모션 디블러링을 위한 PSF 패턴을 최적화하여 영상의 화질을 개선하는 방법을 제안한다. 제안하는 알고리즘은 외부조명 동작 패턴에 주변광을 분석한 패턴을 더하여 영상복원을 수행하기 위한 PSF 패턴을 생성한다. 제안한 방법으로 최적화된 PSF 패턴을 사용하여 영상을 복원한 결과 기존에 사용된 방법에 비해 주관적 화질이 향상됨을 확인할 수 있다.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2002.05a
• /
• pp.187-190
• /
• 2002

Confocal microscopy is very popular technology in bio-medical inspection due to its ability to reject background signals and to measure very thin slide of thick specimens, which is called optical sectioning. But intensity of detected signal in fluorescence type confocal microscopy is so small that only 0.2% of emitted fluorescence light can be detected in the best case. In this paper, we proposed the reflecting optical system to improve the detection intensity and designed the optical system by optimal design method. At the end of the paper, we analyzed the characteristics of the proposed reflecting optical system.

• Journal of Biomedical Engineering Research
• /
• v.3 no.1
• /
• pp.35-42
• /
• 1982

The objective of this phantom study is to develop a digital method for improving the lateral resolution of B-scan ultrasonographic images irs medical application of ultrasound. By utilizing a discrete state-space modeling approach and Kalman-Buch method for analysis of the transducer's beam profile and the measurement and sampling noise, a stable recursive restoration of the object image was obtained for improved lateral resolution. The point spread function (PSF) was measured for the reflective signals after scanning the small pins located along the depth of interest. One major advantage of the present recursive scheme over the transform method is in its applicability for the space-variant imaging, such as in the case of the rotational movement of transducer.