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An Improved double-threshold method Based on Gradient Histogram

Wuhan University Journal of Natural Sciences 2004年第4期9卷 473-476页

作者： YANGShen CHENShu-zhen ZHANGBing SchoolofElectronicInformation WuhanUniversityWuhan430072HubeiChina TheSecondEngineeringLimitedCompanyofChinaRailwayElectrificationBureauGroup Xiangfan441003HubeiChina SchoolofElectronicInformation WuhanUniversityWuhan430072HubeiChina

This paper analyzes the characteristics of the output gradient histogram and shortages of several traditional automatic threshold methods in order to segment the gradient image better. Then an improved double-threshold method is proposed, which is combined with the method of maximum classes variance, estimating-area method and double-threshold method. This method can automatically select two different thresholds to segment gradient images. The computer simulation is performed on the traditional methods and this algorithm and proves that this method can get satisfying result. Key words gradient histogram image - threshold selection - double-threshold method - maximum classes variance method CLC number TP 391. 41 Foundation item: Supported by the National Nature Science Foundation of China (50099620) and the Project of Chenguang Plan in Wuhan (985003062)Biography: YANG Shen (1977-), female, Ph. D. candidate, research direction: multimedia information processing and network technology.

关键词： gradient histogram image threshold selection double-threshold method maximum classes variance method

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A method to avoid the cycle-skip phenomenon in time-of-flight determination for ultrasonic flow measurement

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Journal of Zhejiang University-Science A(Applied Physics & Engineering) 2021年第9期22卷 695-706页

作者： Cheng-wei LIU Ze-hua FANG Liang HU Yong-qiang LIU Rui SU Wei-ting LIU State Key Laboratory of Fluid Power and Mechatronic Systems Zhejiang UniversityHangzhou 310027China

The double-threshold method has been widely used in ultrasonic flow measurement to determine time-of-flight(TOF)due to its low cost and ease of *** of this method is negatively affected by the cycle-skip phenomenon which occurs frequently under inconstant working conditions,especially varied fluid *** paper proposes a method to suppress the phenomenon to facilitate reliable determination of TOF in ultrasonic flow ***,the double-threshold method is used to generate a feature point to segment the ***,based on the correlation coefficient and signal power,judgement factors of individual signal periods are calculated to determine signal ***,a valid zero crossing which has a constant lag from the onset is selected to determine the ***,the cycle-skip phenomenon is *** additional modifications are proposed to eliminate the influence of varied signal frequency and low sampling *** proposed method was validated by an experiment based on an ultrasonic water flow *** showed that the frequently appearing cycle-skip phenomenon can be successfully suppressed by the proposed method.

关键词： Ultrasonic flow measurement Time-of-flight(TOF) Correlation coefficient Signal power double-threshold method

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