Research On The Basic Characteristics Of Optical Flow Methods In Displacement Measurement

With the continuous progress of scientific research,optical displacement measurement technology has been unprecedented development.Optical displacement measurement technology is widely used in many fields,such as material analysis and detection,motion observation tracking and trajectory analysis,mechanical manufacturing,life science engineering and so on,because of its advantages of high precision,high sensitivity,non-contact,simple structure,easy operation,fast measurement speed and low cost.After the concept of optical flow was put forward in the 1950s,with the introduction of mathematical expression of optical flow and the research and development of various optical flow algorithms,optical flow has been active in the field of computer vision for a long time,and has been widely used in the detection,analysis,tracking,matching and so on of moving objects.In the fringe image,after a certain period of time,every pixel in the image will produce plane motion,forming the fringe optical flow field.The fringe optical flow field can be used to measure the plane displacement field,restore the height of the object and so on.Because only one shot of the deformed fringe pattern is needed in the measurement,optical flow is suitable for dynamic measurement.However,as a new fringe analysis tool,some basic characteristics of optical flow algorithm have not been found,such as the necessary measurement range and resolution in displacement measurement are not very clear.Therefore,we focus on the basic characteristics of the typical optical flow algorithm,global H-S optical flow algorithm and local L-K optical flow algorithm.Through numerical simulation,we analyze the basic characteristics of the typical optical flow algorithm.The main contents of this paper are as follows:1.The measurement range of optical flow displacement measurement method based on fringes is studied.The mathematical expression of optical flow,the mathematical principle of typical optical flow algorithm and the basic principle of displacement measurement based on fringes are introduced.Through the displacement measurement experiment based on Michelson interference light path,the possibility of displacement measurement by optical flow method is illustrated.The simulation process of numerical simulation experiment of typical optical flow algorithm measurement range is introduced.Through the regular parallel fringe simulation experiment without noise,it is found that when the relative error is less than 2%,the root mean square error is less than 0.03,and the measurement range of H-S optical flow algorithm and L-K optical flow algorithm is about?/6 and?/2,respectively,which reveals the fact that the measurement range of L-K optical flow algorithm is larger than that of H-S optical flow algorithm.The measurement range of H-S optical flow algorithm and L-K optical flow algorithm under different noise conditions is further analyzed through the regular parallel stripes with noise.When the noise intensity increases,the measurement range will narrow.At the same time,compared with H-S optical flow algorithm,L-K optical flow algorithm has higher robustness.2.The resolution of optical flow displacement measurement based on fringes is studied.The simulation process of the numerical simulation experiment of the resolution of typical optical flow algorithm is introduced.When the displacement is zero,the typical optical flow algorithm can calculate the zero displacement exactly as the phase shift method.Through the regular parallel fringe simulation experiment without noise,the minimum measurable phase change obtained by H-S optical flow algorithm and L-K optical flow algorithm is 10^-13and the relative error is less than 0.4%.Compared with the four-step phase-shifting method,it is found that the typical optical flow algorithm has higher resolution,but its accuracy is slightly lower than that of the four-step phase-shifting method.It is found that the resolution of H-S optical flow algorithm and L-K optical flow algorithm is greatly increased by using the regular parallel fringes loaded with 40d B Gaussian noise.3.The influence of smoothing factor in H-S algorithm on displacement measurement is analyzed.This paper introduces the basic concept of smoothing factor and the simulation process of smoothing factor numerical simulation experiment.Through the simulation experiment,the influence of smoothing factor in the process of optical flow calculation is analyzed.Under the premise of H-S optical flow algorithm measurement range,the range of smoothing factor that can meet the requirements of displacement calculation is[0.5,1.5].