• 융합신호처리학회논문지
• /
• 제7권4호
• /
• pp.169-177
• /
• 2006

이 논문의 목적은 X선의 감쇠를 이용한 측정에서 발생하는 여러 종류의 잡음을 효과적으로 제거하는데 적합한 영상재구성 방법을 제안하는 것이다. 구체적으로, X선의 방출기와 검출기의 필연적인 기계적 오류에 의해 발생하는 원형모양 오류와 전반적인 관측오차와 푸리에 변환기반 재구성 과정에서 나타나는 줄무늬 모양 잡음을 효과적으로 제거하기 위해 웨이블렛 방법을 제안한다. 원형모양 오류를 프로젝션에서 제거하기 위해 해당 잡음이 각도방향으로 강한 상관관계를 가지고 있음을 이용하여, 평균화된 정보에서 해당 잡음의 강도를 추정하고 이를 웨이블렛 축소법을 통해 제거하는 방법을 제안한다. 또한, 전반적인 잡음 제거와 영상재구성을 위해 웨이블렛-배규렛 분해법을 제안한다. 제안된 방법은 기존의 푸리에 변환을 기반으로 하는 방법에 비해 원형모양 오류와 영상재구성에 있어서 우수한 영상을 제공함을 시뮬레이션을 통해 확인하였다.

• 대한전자공학회논문지
• /
• 제17권3호
• /
• pp.20-25
• /
• 1980

Singular value decomposition을 통한 pseudo-inverse를 단층영상 재구성에 이용하였다. 본 논문에서는 SVD pseudo-inverse를 이용한 truncated inverse filter와 Scalar Wiener filter에 대하여 검토하고 각각에 대하여 통계적 측면에서의 최적화가 연구되었다. 이러한 방법은 신호와 잡음문에 trade-off를 기함으로써 재구성 문제에 항상 뒤따르는 ill-conditioning 현상을 극복할 수 있다. 본 논문을 통하여 구성된 filter의 성능을 확인하기 위하여 컴퓨터를 이용한 simulation이 이루어졌으며 그 결과 재구성된 협상은 만족할 만 하였다.

• 한국분무공학회지
• /
• 제7권4호
• /
• pp.9-15
• /
• 2002

Convolution Fourier transformation tomographically reconstructs the spatially resolved spray injection rate from direct measuring cells. Asymmetric sprays generated from a twin-hole air shroud injector are tested with 12 equiangular projections of measurements. For each projection angle, line of sight integrated injection rate was measured at 35 positions with equal spacing measuring cells of 3 mm in width, 100 mm in length, 55 mm in depth and 0.5 mm thickness of separating wall. Interpolated data between the projection angles effectively increase the number of projections, which significantly enhances the signal-to-noise level in the reconstructed data. This modified convolution Fourier transformation scheme predicts well the structure of asymmetric sprays. Comparative study has been made between sprays with and without air shrouding. Tomograhpic reconstruction of injection rate from direct measuring cells obtained can be used to estimate the accuracy of volume fraction of spray from the LDPA tomographic reconstruction.

• 전자공학회논문지B
• /
• 제28B권5호
• /
• pp.318-326
• /
• 1991

A Quantizer reconstruction level control method for block artifact reduction in DCT image coding is described. In our scheme, quantizer reconstruction level control is obtained by adding quantization level step size to the optimum quantization level in the direction of reducing the block artifact by minimizing the mean square error(MSE) and error difference(EDF) distribution in boundary without the other additional bits. In simulation results, although the performance in terms of signal to noise ratio is degraded by a little amount, mean square of error difference at block boundary and mean square error having relation block artifact is greatly reduced. Subjective image qualities are improved compared with other block artifact reduction method such as postprocessing by filtering and trasform coding by block overlapping. But the addition calculations of 1-dimensional DCT become to be more necessary to coding process for determining the reconstruction level.

• 대한전기학회논문지:시스템및제어부문D
• /
• 제50권2호
• /
• pp.59-64
• /
• 2001

In this paper, we propose an alternate method for determining the uniqueness of the reconstruction of a complex sequence from its phase. Uniqueness constraints could be derived in terms of the zeros of a complex polynomial defined by the DFT of the sequence. However, rooting of complex polynomials of high order is a very difficult problem. Instead of finding zeros of a complex polynomial, the proposed uniqueness criteria show that non-singularity of a matrix can guarantee the uniqueness of the reconstruction of a complex sequence from its phase-only data. It has clear advantage over the rooting method in numerical stability and computational time.

• Journal of Information Processing Systems
• /
• 제15권2호
• /
• pp.410-421
• /
• 2019

Distributed compressed sensing (DCS) states that we can recover the sparse signals from very few linear measurements. Various studies about DCS have been carried out recently. In many practical applications, there is no prior information except for standard sparsity on signals. The typical example is the sparse signals have block-sparse structures whose non-zero coefficients occurring in clusters, while the cluster pattern is usually unavailable as the prior information. To discuss this issue, a new algorithm, called backtracking-based adaptive orthogonal matching pursuit for block distributed compressed sensing (DCSBBAOMP), is proposed. In contrast to existing block methods which consider the single-channel signal reconstruction, the DCSBBAOMP resorts to the multi-channel signals reconstruction. Moreover, this algorithm is an iterative approach, which consists of forward selection and backward removal stages in each iteration. An advantage of this method is that perfect reconstruction performance can be achieved without prior information on the block-sparsity structure. Numerical experiments are provided to illustrate the desirable performance of the proposed method.

• Nuclear Engineering and Technology
• /
• 제55권5호
• /
• pp.1533-1540
• /
• 2023

Self-Powered Neutron Detectors(SPNDs) are used to calculate core power distributions, an essential factor in the safe operation of nuclear power plants. Some detectors may fail during normal operation, and signals from failed detectors are isolated from intact signals. The calculated detailed power distribution accuracy depends on the number of available detector signals. Failed detectors decrease the operating margin by enlarging the power distribution measurement error. Therefore, a thorough reconstruction of the failed detector signals is critical. This note suggests a compressive sensing based methodology that rationally reconstructs the readings of failed detectors. The methodology significantly improves reconstruction accuracy by sorting signals and removing high-frequency components from conventional compressive sensing methodology.

• Computers and Concrete
• /
• 제20권5호
• /
• pp.555-562
• /
• 2017

The accuracy and integrity of stress data acquired by bridge heath monitoring system is of significant importance for bridge safety assessment. However, the missing and abnormal data are inevitably existed in a realistic monitoring system. This paper presents a data reconstruction approach for bridge heath monitoring based on the wavelet multi-resolution analysis and support vector machine (SVM). The proposed method has been applied for data imputation based on the recorded data by the structural health monitoring (SHM) system instrumented on a prestressed concrete cable-stayed bridge. The effectiveness and accuracy of the proposed wavelet-based SVM prediction method is examined by comparing with the traditional autoregression moving average (ARMA) method and SVM prediction method without wavelet multi-resolution analysis in accordance with the prediction errors. The data reconstruction analysis based on 5-day and 1-day continuous stress history data with obvious preternatural signals is performed to examine the effect of sample size on the accuracy of data reconstruction. The results indicate that the proposed data reconstruction approach based on wavelet multi-resolution analysis and SVM is an effective tool for missing data imputation or preternatural signal replacement, which can serve as a solid foundation for the purpose of accurately evaluating the safety of bridge structures.

• 자동차안전학회지
• /
• 제13권1호
• /
• pp.14-25
• /
• 2021

This paper presents a RLS based adaptive sliding mode observer (A-SMO) for unknown fault reconstruction in longitudinal autonomous driving. Securing the functional safety of autonomous vehicles from unexpected faults of sensors is essential for avoidance of fatal accidents. Because the magnitude and type of the faults cannot be known exactly, the RLS based A-SMO for unknown acceleration fault reconstruction has been designed with relationship function in this study. It is assumed that longitudinal acceleration of preceding vehicle can be obtained by using the V2V (Vehicle to Vehicle) communication. The kinematic model that represents relative relation between subject and preceding vehicles has been used for fault reconstruction. In order to reconstruct fault signal in acceleration, the magnitude of the injection term has been adjusted by adaptation rule designed based on MIT rule. The proposed A-SMO in this study was developed in Matlab/Simulink environment. Performance evaluation has been conducted using the commercial software (CarMaker) with car-following scenario and evaluation results show that maximum reconstruction error ratios exist within range of ±10%.

• 대한방사선기술학회지:방사선기술과학
• /
• 제40권3호
• /
• pp.385-392
• /
• 2017

본 연구는 전산화단층촬영에서 관전압과 관전류에 따른 화질과 피폭선량을 연구하고 None IR과 IR (Iterative Reconstruction)의 단계에 따른 영상의 SNR(Signal to Noise Ratio)을 비교하여 영상 화질의 개선정도에 대하여 확인해보고자 하였다. Image J를 이용하여 화질을 측정한 결과 관전압의 증가에 따라 HU (Hounsfield units)와 BN(Background Noise)은 감소하였으며, 이와 반대로 SI (Signal Intensity)와 SNR, $CTDI_{vol}$ (CT dose in dex volume)은 관전압이 높아질수록 증가하였으며, BHU(Background Hounsfield Units)의 변화는 없었다. 관전류의 증가로 인해서 BN이 감소하였고, 반대로 SNR과 CTDI은 증가하였다. 또한 IR의 단계가 높아질수록 HU와 SI, BN이 낮아지고, SNR이 약 10~60% 향상됨을 알 수 있었다. 이를 토대로 임상에서 IR 적용 시 단계적 접근 방식으로 관전압과 관전류를 미세 조정하여 점차적으로 방사선량을 줄여 나가야 할 것이다.