Study On Optical Flow Shape Measurement Technique

With the development of science and technology,3D shape measurement technology is widely used in 3D sensing,target detection,product detection,quality control,industrial monitoring,biomedical engineering,heritage restoration and other fields.The commonly used three-dimensional surface measurement system is the structural light lighting system,which has the advantages of simple hardware configuration,non-contact,high measurement accuracy,high speed and low cost.However,in the process of measurement,there may be shadow,phase truncation,spatial discontinuity and other problems.Optical flow has been a major activity in computer vision,which is widely used in tracking,stereo matching,object classification,rigid and elastic motion,fluid propagation and driver assistance.The fringe optical flow is the planar motion of the pixel points that make up the fringe in the image plane,which is used for deformation measurement.Therefore,we propose a surface shape measurement technique which is completely different from the traditional three-dimensional surface shape measurement method,which mainly calculates the fringe distortion caused by the object modulation through optical flow,and then obtains the surface shape distribution of the object.The research contents of this paper are as follows:1.An object shape measurement method based on fringe optical flow is proposed.In this paper,the principle of optical flow field calculation and the principle of fringe optical flow method for measuring three-dimensional surface shape of objects are introduced.From the perspective of optical flow,the changes of two projected fringe patterns before and after object modulation are analyzed,and the theoretical relationship between the optical flow and the phase and height distribution of the measured surface under the condition of parallel optical projection is established.Through the simulations and experiments of rules fringe patterns and irregular fringe patterns,the proposed is verified by optical flow method measuring the fringe pattern face form the height of the feasibility and accuracy,and the light stripe flow measurement by projection of the object surface shape when the stripe image without strict requirements,namelythrough the projection of irregular stripe images can also measure the object surface shape.The resolution of measuring object profile height by fringe optical flow method is simulated and analyzed by building a stepped plane model.Combined with the height measurement of the keyboard,the feasibility of the fringe optical flow method to measure the height of the object with rapid surface change is verified.Also the experimental results show that the proposed method is robust to the noise in the experiment.2.In this paper,a method of optical-flow-based coordinate profilometry by using the capture line is proposed to measure object surface shape.Through the intersection coordinates of the projection ray and the line of sight(observation ray),the three-dimensional profile height distribution of the measured object is directly calculated by combining the optical flow method.The principle of the method is introduced,and the calibration method of each parameter in the measurement system is given.Simulation and experiment show that this method can accurately recover the height of the measured object.3.The fringe optical flow method and optical-flow-based coordinate method were compared with phase-shift method and Fourier profilometry.In the experiment,the same object and projection fringe were selected to calculate the shape distribution of the object,and the cross-sectional data were compared.Through the comparison experiment of fringe optical flow method and phase-shift method,it is shown that fringe optical flow method has a higher accuracy in measuring the phase of the object surface.In addition,compared with the phase shift method,the fringe optical flow method is more robust to the noise introduced at the edge of the object cavity region.By comparing the optical flow spatial line-of-sight coordinate method with Fourier profilometry,it can be seen that the proposed method is also accurate in measuring the height of objects.