• Title, Summary, Keyword: 공간 필터

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Acquisition of River Velocity Data Using Acoustic Doppler Current Profiler (ADCP를 이용한 하천 유속 자료의 추출)

  • Lee, Chan Joo;Lee, Du Han;Kim, Myoung Hwan
    • Proceedings of the Korea Water Resources Association Conference
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    • pp.365-370
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    • 2004
  • 본 연구에서는 ADCP를 이용하여 수집된 3차원적 하천 유속 자료를 기기 특성상 오류, 운용상 오류 등을 고려하여 검토하였으며, 원시 자료의 편차를 보정하는 공간평균기법을 적용하여 필터링함으로써 유속 자료를 추출하였다 공간평균기법으로 추출된 자료는 원시 자료에 비해 유속 편차가 감소되어 매끄러운 유속 분포를 보여주었을 뿐만 아니라 원시 자료에 의한 유량 계산 결과와 거의 일치하여 유속 분포를 적절하게 필터링하는 것으로 파악되었다. 또한 공간평균된 유속 자료를 이용하여 하천의 흐름장을 일목요언하게 제시할 수 있는 평면적 유속 벡터와 단면상 유속 벡터를 제시하였다. 차후 다른 유속계를 이용한 결과와 적절히 비교된다면 공간평균된 자료는 원시 자료에 비해 보다 유용할 것으로 예상되며 하천 흐름 해석 및 수치 모의에 기초 자료로 이용될 수 있을 것으로 기대된다.

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Current Control for an AFE Rectifier Using Space Vector PWM (공간벡터변조방식에 의한 AFE정류기의 전류제어)

  • Jeon, Cheol-Hwan;Hur, Jae-Jung;Yoon, Kyoung-Kuk;Yoo, Heui-Han;Kim, Sung-Hwan
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.25 no.4
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    • pp.498-503
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    • 2019
  • Electric propulsion ships are gaining widespread interest in the marine industry owing to extreme air pollution concerns. Consequently, several studies are actively being conducted for improving the power quality. Various methods have been developed that incorporate passive filters, notch filters, and active filters for reducing the harmonic content in the input current of a conventional diode front end rectifier. Among such filters, the active front end (AFE) rectifier is considered as an excellent technology. In this paper, current control for an AFE rectifier employing space vector PWM (Pulse Width Modulation) is proposed. Conventional current control methods for the AFE rectifier, hysteresis, SPWM (Sinusoidal Pulse Width Modulation), and SVPWM (Space Vector Pulse Width Modulation) were simulated by employing the PSIM software tool for analysis and comparisons. The results corroborate that SVPWM has the simplest structure and provides the best performance.

Image Magnification Using Median Filter and Spatial Variation (메디안 필터와 공간 변화량을 이용한 영상 확대)

  • Kwak, Nae-Joung
    • The Journal of the Korea Contents Association
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    • v.7 no.9
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    • pp.72-80
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    • 2007
  • Image magnification is the estimation of a few pixel in images with high quality from a pixel of an image with low resolution and there have been studied many techniques to make images with high quality. In this paper, we propose an image interpolation method using median filter and spatial information. The proposed method makes an interpolating pixel using an average value of a median filtered value and an average value of two pixels correlated with an interpolating pixel tightly. Also we make the magnified image with improved quality to add the directional information of surrounding pixels and the characteristic of ones using average value and max value of spatial variation. We evaluate the performance using PSNR in the quality of enlarged image comparing the proposed method with existing methods. The results show the proposed method improves PSNR than the existing methods and make images preserving the characteristic of original imges.

Change of Contrast Sensitivity Induced by Tinted Spectacle Lens (칼라필터 렌즈에 따른 대비감도의 변화)

  • Seo, Jae-Myoung
    • Journal of Korean Ophthalmic Optics Society
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    • v.21 no.1
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    • pp.47-51
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    • 2016
  • Purpose: The purpose of this study was to investigate the change of contrast sensitivity by prescribing tinted lenses and to provide the clinical manual. Methods: Contrast sensitivity was measured for twenty adults with normal vision while they wore yellow, orange and green tinted lenses. To measure contrast sensitivity, the 5 spatial frequencies (2, 4, 6, 8 and 10 cpd) were used for 33 ms and 233 ms, respectively. Results: The contrast sensitivity was overall higher with 233 ms than 33 ms (p<0.05). The peaks of contrast sensitivity with 33 ms and 233 ms were 1.75 log unit with the yellow lens and 1. 85 log unit without the color respectively. However, there was no significance between the yellow and orange tinted lens (p>0.64) Conclusions: Yellowish tinted lens that reduces chromatic aberration and the scattering is prescribed for the various purposes to improve visual functions. Before prescribing tinted lens, identifying characteristic of user and tinted lens for cut off wavelengths is recommended.

Spatial Frequency Adaptive Image Restoration Using Wavelet Transform (웨이브릿 변환을 이용한 공간주파수 적응적 영상복원)

  • 우헌배;기현종;정정훈;신정호;백준기
    • Journal of Broadcast Engineering
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    • v.8 no.2
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    • pp.204-208
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    • 2003
  • In this paper, a new matrix vector formulation for a wavelet-based subband decomposition is introduced. This formulation provides a means to compute a regular multi-resolution analysis over many levels of decomposition. With this approach. any single channel linear space-invariant filtering problem can be cast into a multi-channel framework. This decomposition Is applied to the linear space-invariant image restoration problem and propose a frequency-adaptive constrained least squares(CLS) filter. In the proposed filter, we use different parameters adaptively according to subband characteristics. Experimental results are presented for the proposed frequency-adaptive CLS filter These experiments show that if accurate estimates of the subband characteristics are available, the proposed frequency adaptive CLS filter provides significant improvements over the traditional single channel filter.

Comparative Analysis and Accuracy Improvement on Ground Point Filtering of Airborne LIDAR Data for Forest Terrain Modeling (산림지형 모델링을 위한 항공 라이다 데이터의 지면점 필터링 비교분석과 정확도 개선)

  • Hwang, Se-Ran;Lee, Im-Pyeong
    • Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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    • v.29 no.6
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    • pp.641-650
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    • 2011
  • Airborne LIDAR system, utilized in various forest studies, provides efficiently spatial information about vertical structures of forest areas. The tree height is one of the most essential measurements to derive forest information such as biomass, which can be estimated from the forest terrain model. As the terrain model is generated by the interpolation of ground points extracted from LIDAR data, filtering methods with high reliability to classify reliably the ground points are required. In this paper, we applied three representative filtering methods to forest LIDAR data with diverse characteristics, measured the errors and performance of these methods, and analyzed the causes of the errors. Based on their complementary characteristics derived from the analysis results, we have attempted to combine the results and checked the performance improvement. In most test areas, the convergence method showed the satisfactory results, where the filtering performance were improved more than 10% in maximum. Also, we have generated DTM using the classified ground points and compared with the verification data. The DTM retains about 17cm RMSE, which can be sufficiently utilized for the derivation of forest information.

Geometrical Analysis and Implementation of the Real-Time Tuning Structure Using Spatial Light Modulator in Photorefractive Tunable Filter (광굴절 가변 필터에서 공간광학변조기를 이용한 실시간 튜닝 구조의 기하학적 해석 및 구현)

  • An, Jun-Won;Kim, Seong-Goo;Kim, Nam
    • Journal of the Korean Institute of Telematics and Electronics D
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    • v.36D no.12
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    • pp.43-52
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    • 1999
  • We propose a new method for tuning of center wavelength in photorefractive filter using $LiNbO_3$ crystal doped with 0.015Wt.% Fe. through the filter bandwidth property analysis using the geometrical method, a new wavelength selectivity theory was presented. In this scheme, the tuning of the center wavelength can be achieved by the real time incident angle control of the received heam, which was gotten by the spatial light modulator. So, tuning time depend on the response time of the SLM and results in the high speed turing. Because the use of thermally fixed grating in our filter, it has uniform diffraction property to the all filtering wavelength. Designed tunable filter has 4nm bandwidth and composed of the three channel with 10nm space. From the optical experiment, we get the 4.5nm, 4.25nm, 4nm bandwidth and 1530.5nm, 1540.5nm, 1549.5nm center wavelength respectively.

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A Spatial Filtering Neural Network Extracting Feature Information Of Handwritten Character (필기체 문자 인식에서 특징 추출을 위한 공간 필터링 신경회로망)

  • Hong, Keong-Ho;Jeong, Eun-Hwa
    • Journal of the Institute of Electronics Engineers of Korea CI
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    • v.38 no.1
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    • pp.19-25
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    • 2001
  • A novel approach for the feature extraction of handwritten characters is proposed by using spatial filtering neural networks with 4 layers. The proposed system first removes rough pixels which are easy to occur in handwritten characters. The system then extracts and removes the boundary information which have no influence on characters recognition. Finally, The system extracts feature information and removes the noises from feature information. The spatial filters adapted in the system correspond to the receptive fields of ganglion cells in retina and simple cells in visual cortex. With PE2 Hangul database, we perform experiments extracting features of handwritten characters recognition. It will be shown that the network can extract feature informations from handwritten characters successfully.

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Volume holographic correlator for fingerprint recognition (지문 인식을 위한 체적 홀로그래픽 광상관기)

  • 이승현;김은수
    • Korean Journal of Optics and Photonics
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    • v.9 no.6
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    • pp.385-389
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    • 1998
  • In this paper, we propose an optical correlator system using volume holograms for database of matched filters. Optical correlator has high speed and parallel processing characteristics of optics. Matched filters are recorded into a volume hologram that can store data with high density, transfer them with high speed, and select a randomly chosen data element. The multiple reference images of database are prerecorded in a photorefractive crystal in the form of Fourier transform images, simply by passing the image displayed in a spatial light modulator through a Fourier transform lens. The angular multiplexing method for multiple holograms of database can be achieved by rotating the crystal by use of a step motor. Experimental results show that the proposed system can be used for the fingerprint recognition.

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