• 한국정보통신학회:학술대회논문집
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• 한국정보통신학회 2021년도 추계학술대회
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• pp.118-120
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• 2021

현대 사회는 IoT 기술의 발달에 따라 CCTV, 탐사로봇 등 폭넓은 분야에서 다양한 디지털 장비들이 보급되고 있다. 이에 데이터처리의 중요성이 커지고 있으며, 영상 분야에서도 데이터를 수신하는 과정에서 발생하는 잡음을 제거하기 위한 다양한 연구들이 진행되고 있다. 대표적인 잡음으로 AWGN(additive white Gaussian noise)이 있으며, 잡음을 제거하기 위한 기존의 필터로는 평균필터(AF : average filter), 알파 트림드 평균필터(A-TAF : alpha trimmed average filter), 메디안필터(MF : median filter) 등이 있다. 하지만 기존의 필터들은 고주파영역에서의 잡음 제거 특성이 다소 미흡한 성능을 보이는 단점이 있다. 따라서 본 논문에서는 고주파영역에 존재하는 AWGN을 효과적으로 제거하기 위해 표준편차를 기반한 거리에 따른 가중치필터를 제안한다.

• 대한원격탐사학회지
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• 제23권4호
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• pp.273-285
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• 2007

대부분의 스테레오 정합 방법은 두 점간의 대응점을 측정하는데 있어 밝기값을 사용하며 잡음의 영향을 받은 화소가 정합에 사용될 경우 정합 성능이 저하된다. 따라서 잡음은 정합 성능을 결정짓는 중요한 역할을 한다. 본 논문에서는 고해상도 위성영상에서 정합 성능을 향상시키기 위해 잡음에 강건한 밝기 필터와 에지 필터를 이용하여 정합하는 방법을 제안한다. Mean, Median, Midpoint, Gaussian 필터와 같은 밝기 필터와 Gradient, Roberts, Prewitt, Sobel, Laplacian 필터와 같은 에지 필터를 사용하였다. 에지필터와 밝기 필터의 성능 평가를 위해 균일 잡음 또는 가우시안 잡음이 첨가된 합성 영상과 위성 영상에 대해 실험을 수행하였고 필터들은 성능에 따라 순위를 정하였다. 밝기 필터와 에지 필터들 중에서 Median 필터와 Sobel 필터가 가장 우수한 성능을 나타낸 반면에 Midpoint 필터와 Laplacian 필터는 가장 저조한 성능을 나타내었다. Ikonos 스테레오 위성영상을 실험 영상으로 사용하였으며 Median 필터와 Sobel 필터를 이용한 정합 방법이 다른 필터 조합을 이용한 정합 방법보다 향상된 정합 결과를 나타내었다.

• ETRI Journal
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• 제38권3호
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• pp.579-588
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• 2016

To improve the ability to determine a vehicle's movement information even in a challenging environment, a hybrid approach called non-Gaussian square rootunscented particle filtering (nGSR-UPF) is presented. This approach combines a square root-unscented Kalman filter (SR-UKF) and a particle filter (PF) to determinate the vehicle state where measurement noises are taken as a finite Gaussian kernel mixture and are approximated using a sparse Gaussian kernel density estimation method. During an outage-free GPS period, the updated mean and covariance, computed using SR-UKF, are estimated based on a GPS observation update. During a complete GPS outage, nGSR-UPF operates in prediction mode. Indeed, because the inertial sensors used suffer from a large drift in this case, SR-UKF-based importance density is then responsible for shifting the weighted particles toward the high-likelihood regions to improve the accuracy of the vehicle state. The proposed method is compared with some existing estimation methods and the experiment results prove that nGSR-UPF is the most accurate during both outage-free and complete-outage GPS periods.

• 한국광학회지
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• 제9권3호
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• pp.151-155
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• 1998

회절손실을 줄이기 위해 별도로 빔의 크기를 제한하기 위한 부품이나 정렬용 부품을 사용하지 않고도 공극이 10um이 상인 새로운 구조의 Fabry-Perot형 파장가변 필터를 제작하였다. 이를 위해서 FP 공진기를 이루는 두 광섬유중 수신용 광섬유의 단면을 1차측 광섬유에서 나오는 Gaussian 빔 파면의 곡률과 같은 곡률의 곡면으로 가공하였다. Cleaved된 광섬유 단면 곡면가공된 광섬유 단면에 고반사율 유전체 코티을 수행한 후 단일모드 광섬유-곡면가공 단일모드 광섬유로 배치한 Fprhdwlsrl형 필터를 제작하였으며, 제작된 필터의 통과파장폭, free spectral range, 삽입손실은 각각 1.47nm, 52nm, 그리고 5.6dB이었다.

• Journal of information and communication convergence engineering
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• 제15권2호
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• pp.131-136
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• 2017

Chest X-ray image cannot be focused in the same manner as optical lenses and the resultant image generally tends to be slightly blurred. Therefore, appropriate methods to improve the quality of chest X-ray image have been studied in this paper. As the frequency domain filters work well for slight blurring and moderate levels of additive noises, we propose an algorithm that is particularly suitable for enhancing chest image. First, the chest image using Gaussian high pass filter and the optimal high frequency emphasis filter shows improvements in the edges and contrast of the flat areas. Second, as compared to using histogram equalization where each pixel of chest image is characterized by a loss of detail and much noises, in using fuzzy logic, each pixel of chest image shows the detail preservation and little noise.

• 대한전기학회논문지
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• 제40권9호
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• pp.929-936
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• 1991

An estimator for a discrete nonlinear system is derived in the sense of minimum mean square error. An optimal estimator for nonlinear system is very difficult to find and it will be infinite dimensional even if it is found. It has been known that the statistical linearization technique makes it possible to obtain a finite dimensional estimator. In this paper, the procedure of its derivation using the statistical linearization technique that gives an exact mean and variance information is introduced in the sense of minimum mean square error. The derived estimator cannot be clainmed to be globally optimal estimator because it uses the Gaussian assumption to the non-Gaussian distributed nonlinear output. However, the proposed filter exhibits a better performance compared to extended Kalman filter. Simulation results of a simple example present the improvement of the proposed filter in convergent property over the extended Kalman filter.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2004년도 ICCAS
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• pp.223-226
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• 2004

This paper analyzes the accuracy of free space path loss and matched filter gain approximated by using a passband rectangular pulse for ultra wideband (UWB) radio systems. The example causal signal, a modulated Gaussian pulse with the same center frequency and frequency bandwidth of the passband rectangular pulse, is used to consider the accuracy. The path loss and matched filter gain of the modulated Gaussian pulse are simulated for the reference results. The UWB free space path loss is shown and is compared with that obtained from simulation and Friis' transmission formula. The UWB matched filter gain is shown and compared with simulation results. From the results, we can see that the UWB path loss formula is more accurate than the Friis' transmission formula. The results from the UWB free space path loss and matched filter gain formulas agree with the simulation. Then, these free space path loss and matched filter gain formulas approximated by using a passband rectangular pulse are appropriate for UWB system.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권11호
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• pp.5491-5505
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• 2017

Use of the Gaussian inverse Wishart PHD (GIW-PHD) filter has demonstrated promise as an approach to track an unknown number of extended targets. However, the partitioning approaches used in the GIW-PHD filter, such as distance partition with sub-partition (DP-SP), prediction partition (PP) and expectation maximization partition (EMP), fails to provided accurate partition results when targets are spaced closely together and performing maneuvers. In order to improve the performance of a GIW-PHD filter, this paper presents a cooperation partitioning (CP) algorithm to solve the partitioning issue when targets are spaced closely together. In the GIW-PHD filter, the DP-SP is insensitive to target maneuvers but sensitive to the differences in target sizes, while EMP is the opposite. The proposed CP algorithm is a fusion approach of DP-SP and EMP, which employs EMP as a sub-partition approach after DP. Therefore, the CP algorithm will be sensitive to neither target maneuvers nor differences in target sizes. The simulation results show that the use of the proposed CP algorithm will improve the performance of the GIW-PHD filter when targets are spaced closely together.

• Nuclear Engineering and Technology
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• 제52권10호
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• pp.2328-2333
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• 2020

The filter technique was applied to noise images, as noise is the significant factor that cause poor image quality due to lower photon counting. The purpose of this study is to confirm that image quality can be improved using the median modified Wiener filter (MMWF) technique; this is achieved via a National Electrical Manufacturers Association International Electrotechnical Commission body phantom with four large spheres that are filled with the ^99mTc radioisotope when evaluating the image quality. Conventional filters such as Wiener, Gaussian, and median filters were designed, and signal to noise ratio, coefficient of variation, and contrast to noise ratio were used as the evaluation parameters. The improvement in the image quality was in the following order, from the least to the highest improvement, in all cases: Wiener filter, Gaussian filter, median filter, and the MMWF technique. The results show that the image quality was improved from 20.6 to 65.5%, 7.4-40.3%, and 12.7-44.7% for the SNR, COV, and CNR values, respectively, when using the MMWF technique, compared with the use of conventional filters. In conclusion, our results demonstrated that the MMWF technique is useful for reducing the noise distribution in gamma camera images.

• 한국정보통신학회논문지
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• 제17권5호
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• pp.1227-1232
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• 2013

현재, 디지털 시대의 급속 발전과 함께 디지털 장치에 대한 수요가 급격히 성장되면서 영상의 화질에 대한 기대가 증가되고 있다. 그러나 영상은 여러 가지 원인에 의해 훼손되며, 그 주요원인은 잡음에 의한 것이다. 따라서 잡음제거에 대한 필요성이 대두되고 있으며, 잡음제거를 위한 활발한 연구가 진행되고 있다. 영상은 AWGN(additive white Gaussian noise)에 의해 많이 훼손되며, 평균 필터(mean filter) 등 기존의 방법들은 잡음제거 특성이 다소 미흡하다. 본 논문에서는 AWGN을 효과적으로 제거하기 위하여, 공간 가중치와 변형된 적응 가중치를 결합한 알고리즘을 제안하였다. 시뮬레이션 결과, 제안한 방법은 우수한 잡음제거 특성을 나타내었다.