To enhance the applicability and measurement accuracy of phase-based optical flow method using complex steerable pyramids in structural displacement measurement engineering applications, an improved method of optimizi...To enhance the applicability and measurement accuracy of phase-based optical flow method using complex steerable pyramids in structural displacement measurement engineering applications, an improved method of optimizing parameter settings is proposed. The optimized parameters include the best measurement points of the Region of Interest (ROI) and the levels of pyramid filters. Additionally, to address the issue of updating reference frames in practical applications due to the difficulty in estimating the maximum effective measurement value, a mechanism for dynamically updating reference frames is introduced. Experimental results demonstrate that compared to representative image gradient-based displacement measurement methods, the proposed method exhibits higher measurement accuracy in engineering applications. This provides reliable data support for structural damage identification research based on vibration signals and is expected to broaden the engineering application prospects for structural health monitoring.展开更多
Rainbow particle image velocimetry(PIV)can restore the three-dimensional velocity field of particles with a single camera;however,it requires a relatively long time to complete the reconstruction.This paper proposes a...Rainbow particle image velocimetry(PIV)can restore the three-dimensional velocity field of particles with a single camera;however,it requires a relatively long time to complete the reconstruction.This paper proposes a hybrid algorithm that combines the fast Fourier transform(FFT)based co-correlation algorithm and the Horn–Schunck(HS)optical flow pyramid iterative algorithm to increase the reconstruction speed.The Rankine vortex simulation experiment was performed,in which the particle velocity field was reconstructed using the proposed algorithm and the rainbow PIV method.The average endpoint error and average angular error of the proposed algorithm were roughly the same as those of the rainbow PIV algorithm;nevertheless,the reconstruction time was 20%shorter.Furthermore,the effect of velocity magnitude and particle density on the reconstruction results was analyzed.In the end,the performance of the proposed algorithm was verified using real experimental single-vortex and double-vortex datasets,from which a similar particle velocity field was obtained compared with the rainbow PIV algorithm.The results show that the reconstruction speed of the proposed hybrid algorithm is approximately 25%faster than that of the rainbow PIV algorithm.展开更多
The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an...The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an inaccurate pose estimation or failed tracking.To address the challenge above,a new method of feature point matching is proposed in this paper,which combines the variable velocity model with the reverse optical flow method.First,the constant velocity model is extended to a new variable velocity model,and the expanded variable velocity model is used to provide the initial pixel shifting for the reverse optical flow method.Then the search range of feature points is accurately determined according to the results of the reverse optical flow method,thereby improving the accuracy and reliability of feature matching,with strengthened interframe tracking effects.Finally,we tested on TUM data set based on the RGB-D camera.Experimental results show that this method can reduce the probability of tracking failure and improve localization accuracy on SLAM(Simultaneous Localization and Mapping)systems.Compared with the traditional ORB-SLAM2,the test error of this method on each sequence in the TUM data set is significantly reduced,and the root mean square error is only 63.8%of the original system under the optimal condition.展开更多
Because of its characteristics of simple algorithm and hardware, optical flow-based motion estimation has become a hot research field, especially in GPS-denied environment. Optical flow could be used to obtain the air...Because of its characteristics of simple algorithm and hardware, optical flow-based motion estimation has become a hot research field, especially in GPS-denied environment. Optical flow could be used to obtain the aircraft motion information, but the six-(degree of freedom)(6-DOF) motion still couldn't be accurately estimated by existing methods. The purpose of this work is to provide a motion estimation method based on optical flow from forward and down looking cameras, which doesn't rely on the assumption of level flight. First, the distribution and decoupling method of optical flow from forward camera are utilized to get attitude. Then, the resulted angular velocities are utilized to obtain the translational optical flow of the down camera, which can eliminate the influence of rotational motion on velocity estimation. Besides, the translational motion estimation equation is simplified by establishing the relation between the depths of feature points and the aircraft altitude. Finally, simulation results show that the method presented is accurate and robust.展开更多
A modification of Horn and Schunk's approach is investigated, which leads to a better preservation of flow discontinuities. It improves Horn-Schunk model in three aspects: (1) It replaces the smooth weight coeffic...A modification of Horn and Schunk's approach is investigated, which leads to a better preservation of flow discontinuities. It improves Horn-Schunk model in three aspects: (1) It replaces the smooth weight coefficient in the energy equation by the variable weight coefficient. (2) It adopts a novel method to compute the mean velocity. The novel method also reflects the effect of the intensity difference on the image velocity diffusion. (3) It introduces a more efficient iterative method than the Gauss-Seidel method to solve the associated Euler-Lagrange equation. The experiment results validate the better effect of the improved method on preserving discontinuities.展开更多
It is very important for underwater robots to accurately detect and locate target objects. However,under many circumstances,it is difficult to clearly observe the target object due to the existence of bubble noise. In...It is very important for underwater robots to accurately detect and locate target objects. However,under many circumstances,it is difficult to clearly observe the target object due to the existence of bubble noise. In this paper,we proposed a method to solve this problem. First,we used the LK optical flow algorithm to calculate the motion vector of the image background and compensate for the background motion.Then,the optical flow field of the bubbles was calculated by the HS optical flow algorithm,and the area where the bubble existed was obtained by binarizing the image. Finally,we used the adjacent frame image to repair the bubble area. We carried out a bubble noise removal experiment. The results show that this method can effectively remove the bubble noise in the image.展开更多
Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical inte...Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical intensity fluctuations by the variety of particle concentration in stack gas flow. This paper also gives the primary theoretical explanation of the measurement results in the stack of coal-fired utility boilers. Meanwhile, the cross-correlation formula is given as the theoretical basis of velocity measurement by using particle concentration scintillation.展开更多
In the process of human behavior recognition, the traditional dense optical flow method has too many pixels and too much overhead, which limits the running speed. This paper proposed a method combing YOLOv3 (You Only ...In the process of human behavior recognition, the traditional dense optical flow method has too many pixels and too much overhead, which limits the running speed. This paper proposed a method combing YOLOv3 (You Only Look Once v3) and local optical flow method. Based on the dense optical flow method, the optical flow modulus of the area where the human target is detected is calculated to reduce the amount of computation and save the cost in terms of time. And then, a threshold value is set to complete the human behavior identification. Through design algorithm, experimental verification and other steps, the walking, running and falling state of human body in real life indoor sports video was identified. Experimental results show that this algorithm is more advantageous for jogging behavior recognition.展开更多
BACKGROUND Optical coherence tomography angiography(OCTA)is a new and reliable machine used to evaluate retinal structure and macular perfusion in children.The use of OCTA under bad condition such as high altitude,low...BACKGROUND Optical coherence tomography angiography(OCTA)is a new and reliable machine used to evaluate retinal structure and macular perfusion in children.The use of OCTA under bad condition such as high altitude,low atmospheric oxygen,and low humidity,in children is rarely.AIM To quantify the macular micro-vasculature in healthy children of various ages using OCTA in Qamdo.METHODS Design:Prospective cross-sectional,school-based study.Three hundred and fortyseven normal students from 9 schools in 4 different areas in Qamdo were included.OCTA was performed on a 3 mm×3 mm area centered on the macular region and macular cube 512×128 showed details in macular.Early treatment of diabetic retinopathy study Vessel Flow Density(VD)of the macular central vascular plexus density(CVD),inner vascular plexus density(IVD),full vascular plexus density(FVD),and the size of the foveal avascular zone(FAZ)were measured.All these results corrected by t/s=3.382×0.01306×(axial length-1.82).The differences were compared among various ages,sexes and living environments.RESULTS The mean FAZ area in all eyes was 0.27 mm^(2)±0.12 mm^(2).The mean foveal thickness(MFT)in the macular cube was 227.64μm±23.51μm.Compared with girls,boys had a lager FAZ(P=0.0029).Among the different age groups,MFT(P<0.001)and FVD(P<0.0001),IVD(P<0.0001),and CVD(P=0.0050)increased with age.FAZ areas were not correlated with age(P=0.8853)or others(MFT,area).CONCLUSION OCTA can use to evaluate macular perfusion in children.Our data bridge the gap between structural OCT and perfusion density in children in high altitude.Even though these were not a longitudinal study,it may provide us with hints about retina development during puberty and clinical implications of OCTA in children.展开更多
Doppler Optical Coherence Tomography(DOCT)is a noninvasive optical diagnostic technique,which is well suited for the quantitative mapping of microflow velocity profiles and the analysis of flow-vessel interactions.The...Doppler Optical Coherence Tomography(DOCT)is a noninvasive optical diagnostic technique,which is well suited for the quantitative mapping of microflow velocity profiles and the analysis of flow-vessel interactions.The noninvasive imaging and quantitative analysis of blood flow in the complex-structured vascular bed is required in many biomedical applications,including those where the determination of mechanical properties of vessels or the knowledge of the mechanic interactions between the flow and the housing medium plays a key role.The change of microvessel wall elasticity could be a potential indicator of cardiovascular disease at the very early stage,whilst monitoring the blood flow dynamics and associated temporal and spatial variations in vessel’s wall shear stress could help predicting the possible rupture of atherosclerotic plaques.The results of feasibility studies of application of DOCT for the evaluation of mechanical properties of elastic vessel model are presented.The technique has also been applied for imaging of sub-cranial rat blood flow in vivo.展开更多
To improve the detection accuracy and robustness of crowd anomaly detection,especially crowd emergency evacuation detection,the abnormal crowd behavior detection method is proposed.This method is based on the improved...To improve the detection accuracy and robustness of crowd anomaly detection,especially crowd emergency evacuation detection,the abnormal crowd behavior detection method is proposed.This method is based on the improved statistical global optical flow entropy which can better describe the degree of chaos of crowd.First,the optical flow field is extracted from the video sequences and a 2D optical flow histogram is gained.Then,the improved optical flow entropy,combining information theory with statistical physics is calculated from 2D optical flow histograms.Finally,the anomaly can be detected according to the abnormality judgment formula.The experimental results show that the detection accuracy achieved over 95%in three public video datasets,which indicates that the proposed algorithm outperforms other state-of-the-art algorithms.展开更多
A closed form solution to the problem of segmenting multiple 3D motion models was proposed from straight-line optical flow. It introduced the multibody line optical flow constraint (MLOFC), a polynomial equation relat...A closed form solution to the problem of segmenting multiple 3D motion models was proposed from straight-line optical flow. It introduced the multibody line optical flow constraint (MLOFC), a polynomial equation relating motion models and line parameters. The motion models can be obtained analytically as the derivative of the MLOFC at the corresponding line measurement, without knowing the motion model associated with that line. Experiments on real and synthetic sequences were also presented.展开更多
As one of the important sea state parameters for navigation safety and coastal resource management, the ocean wave direction represents the propagation direction of the wave. A novel algorithm based on an optical flow...As one of the important sea state parameters for navigation safety and coastal resource management, the ocean wave direction represents the propagation direction of the wave. A novel algorithm based on an optical flow method is developed for the ocean wave direction inversion of the ocean wave fields imaged by the X-band radar continuously. The proposed algorithm utilizes the echo images received by the X-band wave monitoring radar to estimate the optical flow motion, and then the actual wave propagation direction can be obtained by taking a weighted average of the motion vector for each pixel. Compared with the traditional ocean wave direction inversion method based on frequency-domain, the novel algorithm is fully using a time-domain signal processing method without determination of a current velocity and a modulation transfer function(MTF). In the meantime,the novel algorithm is simple, efficient and there is no need to do something more complicated here. Compared with traditional ocean wave direction inversion method, the ocean wave direction of derived by using this proposed method matches well with that measured by an in situ buoy nearby and the simulation data. These promising results demonstrate the efficiency and accuracy of the algorithm proposed in the paper.展开更多
The amount of computation for detecting moving objects by the optical flow algorithm is large. The optical flow information in the smooth region cannot be detected by the optical flow algorithm, and it is susceptible ...The amount of computation for detecting moving objects by the optical flow algorithm is large. The optical flow information in the smooth region cannot be detected by the optical flow algorithm, and it is susceptible to noise in a complicated environment. In this study, an optimized Horn-Schunck (HS) optical flow algorithm based on motion estimation is proposed. To detect Harris corner in the image, the proposed algorithm is used in combination with the motion estimation algorithm based on macroblock to determine the region of interest (ROI) [1]. The ROI is then used as the initial motion vector for HS calculation to obtain the optical flow information. Filtering is conducted to eliminate the background noise. Experimental result shows that the application of the proposed algorithm improves the computational speed, avoids the interference of background noise, and enhances the robustness of HS. Moreover, the algorithm solves the problem rooted in the inability of the HS algorithm to detect the smooth part of optical flow information [2].展开更多
This paper presents a new method for robust and accurate optical flow estimation.The sig- nificance of this work is twofold.Firstly,the idea of bi-directional scheme is adopted to reduce the model error of optical flo...This paper presents a new method for robust and accurate optical flow estimation.The sig- nificance of this work is twofold.Firstly,the idea of bi-directional scheme is adopted to reduce the model error of optical flow equation,which allows the second order Taylor's expansion of optical flow equation for accurate solution without much extra computational burden;Secondly,this paper establishs a new optical flow equation based on LSCM (Local Structure Constancy Model) instead of BCM (Brightness Constancy Model),namely the optical flow equation does not act on scalar but on tensor-valued (ma- trix-valued) field,due to the two reason:(1) structure tensor-value contains local spatial structure information,which provides us more useable cues for computation than scalar;(2) local image structure is less sensitive to illumination variation than intensity,which weakens the disturbance of non-uniform illumination in real sequences.Qualitative and quantitative results for synthetic and real-world scenes show that the new method can produce an accurate and robust results.展开更多
The optical flow analysis of the image sequence based on the formal lattice Boltzmann equation, with different DdQm models, is discussed in this paper. The Mgorithm is based on the lattice Boltzmann method (LBM), wh...The optical flow analysis of the image sequence based on the formal lattice Boltzmann equation, with different DdQm models, is discussed in this paper. The Mgorithm is based on the lattice Boltzmann method (LBM), which is used in computational fluid dynamics theory for the simulation of fluid dynamics. At first, a generalized approximation to the formal lattice Boltzmann equation is discussed. Then the effects of different DdQm models on the results of the optical flow estimation are compared with each other, while calculating the movement vectors of pixels in the image sequence. The experimental results show that the higher dimension DdQm models, e.g., D3Q15 are more effective than those lower dimension ones.展开更多
The velocity and direction of internal waves(IWs) are important parameters of the ocean,however,traditional observation methods can only obtain the average parameters of IWs for a single location or large area.Herein,...The velocity and direction of internal waves(IWs) are important parameters of the ocean,however,traditional observation methods can only obtain the average parameters of IWs for a single location or large area.Herein,a new method based on optical flow is proposed to derive the phase velocity vectors of IWs from X-band marine radar images.First,the X-band marine radar image sequence is averaged,and ramp correction is used to reduce the attenuation of gray values with increasing radial range.Second,the average propagation direction of the IWs is determined using the two-dimensional Fourier transform of the radar images;two radial profiles along this direction are selected from two adjacent radar images;and then,the average phase velocity of the IWs is estimated from these radial profiles.Third,the averaged radar images are processed via histogram equalization and binarization to reduce the influence of noise on the radar images.Fourth,a weighting factor is determined using the average phase velocity of a reference point;the phase velocities on the wave crest of the IWs are subsequently estimated via the optical flow method.Finally,the proposed method is validated using X-band marine radar image sequences observed on an oil platform in the South China Sea,and the error of the phase velocity is calculated to be 0.000 3–0.073 8 m/s.The application conditions of the proposed method are also discussed using two different types of IW packets.展开更多
文摘To enhance the applicability and measurement accuracy of phase-based optical flow method using complex steerable pyramids in structural displacement measurement engineering applications, an improved method of optimizing parameter settings is proposed. The optimized parameters include the best measurement points of the Region of Interest (ROI) and the levels of pyramid filters. Additionally, to address the issue of updating reference frames in practical applications due to the difficulty in estimating the maximum effective measurement value, a mechanism for dynamically updating reference frames is introduced. Experimental results demonstrate that compared to representative image gradient-based displacement measurement methods, the proposed method exhibits higher measurement accuracy in engineering applications. This provides reliable data support for structural damage identification research based on vibration signals and is expected to broaden the engineering application prospects for structural health monitoring.
基金the National Natural Science Foundation of China(Grant Nos.51874264 and 52076200)。
文摘Rainbow particle image velocimetry(PIV)can restore the three-dimensional velocity field of particles with a single camera;however,it requires a relatively long time to complete the reconstruction.This paper proposes a hybrid algorithm that combines the fast Fourier transform(FFT)based co-correlation algorithm and the Horn–Schunck(HS)optical flow pyramid iterative algorithm to increase the reconstruction speed.The Rankine vortex simulation experiment was performed,in which the particle velocity field was reconstructed using the proposed algorithm and the rainbow PIV method.The average endpoint error and average angular error of the proposed algorithm were roughly the same as those of the rainbow PIV algorithm;nevertheless,the reconstruction time was 20%shorter.Furthermore,the effect of velocity magnitude and particle density on the reconstruction results was analyzed.In the end,the performance of the proposed algorithm was verified using real experimental single-vortex and double-vortex datasets,from which a similar particle velocity field was obtained compared with the rainbow PIV algorithm.The results show that the reconstruction speed of the proposed hybrid algorithm is approximately 25%faster than that of the rainbow PIV algorithm.
基金This work was supported by The National Natural Science Foundation of China under Grant No.61304205 and NO.61502240The Natural Science Foundation of Jiangsu Province under Grant No.BK20191401 and No.BK20201136Postgraduate Research&Practice Innovation Program of Jiangsu Province under Grant No.SJCX21_0364 and No.SJCX21_0363.
文摘The ORB-SLAM2 based on the constant velocity model is difficult to determine the search window of the reprojection of map points when the objects are in variable velocity motion,which leads to a false matching,with an inaccurate pose estimation or failed tracking.To address the challenge above,a new method of feature point matching is proposed in this paper,which combines the variable velocity model with the reverse optical flow method.First,the constant velocity model is extended to a new variable velocity model,and the expanded variable velocity model is used to provide the initial pixel shifting for the reverse optical flow method.Then the search range of feature points is accurately determined according to the results of the reverse optical flow method,thereby improving the accuracy and reliability of feature matching,with strengthened interframe tracking effects.Finally,we tested on TUM data set based on the RGB-D camera.Experimental results show that this method can reduce the probability of tracking failure and improve localization accuracy on SLAM(Simultaneous Localization and Mapping)systems.Compared with the traditional ORB-SLAM2,the test error of this method on each sequence in the TUM data set is significantly reduced,and the root mean square error is only 63.8%of the original system under the optimal condition.
基金Project(2012CB720003)supported by the National Basic Research Program of ChinaProjects(61320106010,61127007,61121003,61573019)supported by the National Natural Science Foundation of ChinaProject(2013DFE13040)supported by the Special Program for International Science and Technology Cooperation from Ministry of Science and Technology of China
文摘Because of its characteristics of simple algorithm and hardware, optical flow-based motion estimation has become a hot research field, especially in GPS-denied environment. Optical flow could be used to obtain the aircraft motion information, but the six-(degree of freedom)(6-DOF) motion still couldn't be accurately estimated by existing methods. The purpose of this work is to provide a motion estimation method based on optical flow from forward and down looking cameras, which doesn't rely on the assumption of level flight. First, the distribution and decoupling method of optical flow from forward camera are utilized to get attitude. Then, the resulted angular velocities are utilized to obtain the translational optical flow of the down camera, which can eliminate the influence of rotational motion on velocity estimation. Besides, the translational motion estimation equation is simplified by establishing the relation between the depths of feature points and the aircraft altitude. Finally, simulation results show that the method presented is accurate and robust.
文摘A modification of Horn and Schunk's approach is investigated, which leads to a better preservation of flow discontinuities. It improves Horn-Schunk model in three aspects: (1) It replaces the smooth weight coefficient in the energy equation by the variable weight coefficient. (2) It adopts a novel method to compute the mean velocity. The novel method also reflects the effect of the intensity difference on the image velocity diffusion. (3) It introduces a more efficient iterative method than the Gauss-Seidel method to solve the associated Euler-Lagrange equation. The experiment results validate the better effect of the improved method on preserving discontinuities.
基金Sponsored by the National Natural Science Foundation of China(Grant No.61673138)the National Key Basic Research Development Plan Project(Grant No.2013CB035502)the Self-Planned Task of State Key Laboratory of Robotics and System(HIT)(Grant No.SKLRS201804B)
文摘It is very important for underwater robots to accurately detect and locate target objects. However,under many circumstances,it is difficult to clearly observe the target object due to the existence of bubble noise. In this paper,we proposed a method to solve this problem. First,we used the LK optical flow algorithm to calculate the motion vector of the image background and compensate for the background motion.Then,the optical flow field of the bubbles was calculated by the HS optical flow algorithm,and the area where the bubble existed was obtained by binarizing the image. Finally,we used the adjacent frame image to repair the bubble area. We carried out a bubble noise removal experiment. The results show that this method can effectively remove the bubble noise in the image.
文摘Based on the analysis of spectrum characteristics of intensity fluctuations while light beams pass through stack gas flow in an industrial setting, this paper puts emphasis upon discussing the spectrum of optical intensity fluctuations by the variety of particle concentration in stack gas flow. This paper also gives the primary theoretical explanation of the measurement results in the stack of coal-fired utility boilers. Meanwhile, the cross-correlation formula is given as the theoretical basis of velocity measurement by using particle concentration scintillation.
文摘In the process of human behavior recognition, the traditional dense optical flow method has too many pixels and too much overhead, which limits the running speed. This paper proposed a method combing YOLOv3 (You Only Look Once v3) and local optical flow method. Based on the dense optical flow method, the optical flow modulus of the area where the human target is detected is calculated to reduce the amount of computation and save the cost in terms of time. And then, a threshold value is set to complete the human behavior identification. Through design algorithm, experimental verification and other steps, the walking, running and falling state of human body in real life indoor sports video was identified. Experimental results show that this algorithm is more advantageous for jogging behavior recognition.
基金Supported by the National Natural Science Foundation of China,No.81870650,No.81570832,and No.81300794Science and Technology Program Chongqing,China,No.2018GDRC008.
文摘BACKGROUND Optical coherence tomography angiography(OCTA)is a new and reliable machine used to evaluate retinal structure and macular perfusion in children.The use of OCTA under bad condition such as high altitude,low atmospheric oxygen,and low humidity,in children is rarely.AIM To quantify the macular micro-vasculature in healthy children of various ages using OCTA in Qamdo.METHODS Design:Prospective cross-sectional,school-based study.Three hundred and fortyseven normal students from 9 schools in 4 different areas in Qamdo were included.OCTA was performed on a 3 mm×3 mm area centered on the macular region and macular cube 512×128 showed details in macular.Early treatment of diabetic retinopathy study Vessel Flow Density(VD)of the macular central vascular plexus density(CVD),inner vascular plexus density(IVD),full vascular plexus density(FVD),and the size of the foveal avascular zone(FAZ)were measured.All these results corrected by t/s=3.382×0.01306×(axial length-1.82).The differences were compared among various ages,sexes and living environments.RESULTS The mean FAZ area in all eyes was 0.27 mm^(2)±0.12 mm^(2).The mean foveal thickness(MFT)in the macular cube was 227.64μm±23.51μm.Compared with girls,boys had a lager FAZ(P=0.0029).Among the different age groups,MFT(P<0.001)and FVD(P<0.0001),IVD(P<0.0001),and CVD(P=0.0050)increased with age.FAZ areas were not correlated with age(P=0.8853)or others(MFT,area).CONCLUSION OCTA can use to evaluate macular perfusion in children.Our data bridge the gap between structural OCT and perfusion density in children in high altitude.Even though these were not a longitudinal study,it may provide us with hints about retina development during puberty and clinical implications of OCTA in children.
文摘Doppler Optical Coherence Tomography(DOCT)is a noninvasive optical diagnostic technique,which is well suited for the quantitative mapping of microflow velocity profiles and the analysis of flow-vessel interactions.The noninvasive imaging and quantitative analysis of blood flow in the complex-structured vascular bed is required in many biomedical applications,including those where the determination of mechanical properties of vessels or the knowledge of the mechanic interactions between the flow and the housing medium plays a key role.The change of microvessel wall elasticity could be a potential indicator of cardiovascular disease at the very early stage,whilst monitoring the blood flow dynamics and associated temporal and spatial variations in vessel’s wall shear stress could help predicting the possible rupture of atherosclerotic plaques.The results of feasibility studies of application of DOCT for the evaluation of mechanical properties of elastic vessel model are presented.The technique has also been applied for imaging of sub-cranial rat blood flow in vivo.
基金National Natural Science Foundation of China(61701029)。
文摘To improve the detection accuracy and robustness of crowd anomaly detection,especially crowd emergency evacuation detection,the abnormal crowd behavior detection method is proposed.This method is based on the improved statistical global optical flow entropy which can better describe the degree of chaos of crowd.First,the optical flow field is extracted from the video sequences and a 2D optical flow histogram is gained.Then,the improved optical flow entropy,combining information theory with statistical physics is calculated from 2D optical flow histograms.Finally,the anomaly can be detected according to the abnormality judgment formula.The experimental results show that the detection accuracy achieved over 95%in three public video datasets,which indicates that the proposed algorithm outperforms other state-of-the-art algorithms.
基金The National Natural Science Foundation of China (No. 60675017) The National Basic Research Program (973) of China (No. 2006CB303103)
文摘A closed form solution to the problem of segmenting multiple 3D motion models was proposed from straight-line optical flow. It introduced the multibody line optical flow constraint (MLOFC), a polynomial equation relating motion models and line parameters. The motion models can be obtained analytically as the derivative of the MLOFC at the corresponding line measurement, without knowing the motion model associated with that line. Experiments on real and synthetic sequences were also presented.
基金The National Key Research and Development Program of China under contract No.2016YFC0800405the Shanghai Municipal Science and Technology Project of China under contract No.15DZ0500600the Specialized Research Fund for the Doctoral Program of Higher Education of China under contract No.2014212020203
文摘As one of the important sea state parameters for navigation safety and coastal resource management, the ocean wave direction represents the propagation direction of the wave. A novel algorithm based on an optical flow method is developed for the ocean wave direction inversion of the ocean wave fields imaged by the X-band radar continuously. The proposed algorithm utilizes the echo images received by the X-band wave monitoring radar to estimate the optical flow motion, and then the actual wave propagation direction can be obtained by taking a weighted average of the motion vector for each pixel. Compared with the traditional ocean wave direction inversion method based on frequency-domain, the novel algorithm is fully using a time-domain signal processing method without determination of a current velocity and a modulation transfer function(MTF). In the meantime,the novel algorithm is simple, efficient and there is no need to do something more complicated here. Compared with traditional ocean wave direction inversion method, the ocean wave direction of derived by using this proposed method matches well with that measured by an in situ buoy nearby and the simulation data. These promising results demonstrate the efficiency and accuracy of the algorithm proposed in the paper.
文摘The amount of computation for detecting moving objects by the optical flow algorithm is large. The optical flow information in the smooth region cannot be detected by the optical flow algorithm, and it is susceptible to noise in a complicated environment. In this study, an optimized Horn-Schunck (HS) optical flow algorithm based on motion estimation is proposed. To detect Harris corner in the image, the proposed algorithm is used in combination with the motion estimation algorithm based on macroblock to determine the region of interest (ROI) [1]. The ROI is then used as the initial motion vector for HS calculation to obtain the optical flow information. Filtering is conducted to eliminate the background noise. Experimental result shows that the application of the proposed algorithm improves the computational speed, avoids the interference of background noise, and enhances the robustness of HS. Moreover, the algorithm solves the problem rooted in the inability of the HS algorithm to detect the smooth part of optical flow information [2].
基金Supported by the National Natural Science Foundation of China(No.60672153)the Shenzhen Science & Technology Project (No.200424).
文摘This paper presents a new method for robust and accurate optical flow estimation.The sig- nificance of this work is twofold.Firstly,the idea of bi-directional scheme is adopted to reduce the model error of optical flow equation,which allows the second order Taylor's expansion of optical flow equation for accurate solution without much extra computational burden;Secondly,this paper establishs a new optical flow equation based on LSCM (Local Structure Constancy Model) instead of BCM (Brightness Constancy Model),namely the optical flow equation does not act on scalar but on tensor-valued (ma- trix-valued) field,due to the two reason:(1) structure tensor-value contains local spatial structure information,which provides us more useable cues for computation than scalar;(2) local image structure is less sensitive to illumination variation than intensity,which weakens the disturbance of non-uniform illumination in real sequences.Qualitative and quantitative results for synthetic and real-world scenes show that the new method can produce an accurate and robust results.
基金Project supported by the National Natural Science Foundation of China(Grant No.40976108)the Shanghai Leading Academic Discipline Project(Grant No.J50103)the Innovation Program of Municipal Education Commission of Shanghai Municipality(Grant No.11YZ03)
文摘The optical flow analysis of the image sequence based on the formal lattice Boltzmann equation, with different DdQm models, is discussed in this paper. The Mgorithm is based on the lattice Boltzmann method (LBM), which is used in computational fluid dynamics theory for the simulation of fluid dynamics. At first, a generalized approximation to the formal lattice Boltzmann equation is discussed. Then the effects of different DdQm models on the results of the optical flow estimation are compared with each other, while calculating the movement vectors of pixels in the image sequence. The experimental results show that the higher dimension DdQm models, e.g., D3Q15 are more effective than those lower dimension ones.
基金The National Natural Science Foundation of China under contract Nos 41620104003 and 42027805the National Natural Science Youth Foundation of China under contract No.41506199。
文摘The velocity and direction of internal waves(IWs) are important parameters of the ocean,however,traditional observation methods can only obtain the average parameters of IWs for a single location or large area.Herein,a new method based on optical flow is proposed to derive the phase velocity vectors of IWs from X-band marine radar images.First,the X-band marine radar image sequence is averaged,and ramp correction is used to reduce the attenuation of gray values with increasing radial range.Second,the average propagation direction of the IWs is determined using the two-dimensional Fourier transform of the radar images;two radial profiles along this direction are selected from two adjacent radar images;and then,the average phase velocity of the IWs is estimated from these radial profiles.Third,the averaged radar images are processed via histogram equalization and binarization to reduce the influence of noise on the radar images.Fourth,a weighting factor is determined using the average phase velocity of a reference point;the phase velocities on the wave crest of the IWs are subsequently estimated via the optical flow method.Finally,the proposed method is validated using X-band marine radar image sequences observed on an oil platform in the South China Sea,and the error of the phase velocity is calculated to be 0.000 3–0.073 8 m/s.The application conditions of the proposed method are also discussed using two different types of IW packets.