Research On Phase Unwrapping Algorithm Based On Digital Grating Projection

With the progress of the times and the development of the information technology,three-dimensional(3D)information of objects has presented important value and played a great role in many fields,such as,object detection,digital model,object replication,reverse engineering,rapid prototyping,product inspection and quality control.In recent decades,3D shape measurement technology has developed rapidly.The current focus on 3D measurement is how to obtain the 3D shape of objects quickly and accurately.Fringe-projection profilometry is a well-developed technique and powerful tool.in current 3D shape measurement for its non-contact nature,full-field measurement capability,high profile sampling density and low environment vulnerability,which has been an extensively studied research area due to the diversity of potential application.As the phase obtained by phase demodulation methods is wrapped within the(-?,?)interval,phase-unwrapping is necessary to recover the object shape.Although there are many phase unwrapping algorithms,many algorithms are found to be effective only for certain situations,and there are limitations in terms of speed and accuracy.Therefore,the development of a fast and reliable phase unwrapping algorithm is still a difficult and focal point in the research of 3D profilometry.This paper studies the problem of phase unwrapping from both speed and accuracy.The main research contents are as follows:(1)Based on the analysis of Gdeisat's algorithm,a simple spatial domain algorithm to increase the residues of wrapped phase maps is presented.This algorithm eliminates Fourier transform,inverse Fourier transform and frequency selection,while achieving the frequency shift using a simple multiply operation in the spatial domain.As a result,the method can save a large amount of processing time.(2)In order to solve the problem of limited range of G in Servin's two-step temporal phase unwrapping algorithm,an iterative two-step temporal phase-unwrapping algorithm is presented,which can expand the range of sensitivity G by adding a fringe pattern with an intermediate sensitivity.(3)In order to take into account both the speed and accuracy of 3D shape measurement,an one shot profilometry using iterative two-step temporal phase-unwrapping is proposed by combining the composite fringe projection and the iterative two-step temporal phase unwrapping algorithm.(4)Conventional dual-frequency fringe projection algorithm often suffers from phase unwrapping failure when the frequency ratio between the high frequency and the low one is too large.Zhang et.al.proposed an enhanced two-frequency phase-shifting method using geometric constraints of digital fringe projection(DFP)to reduce the noise impact due to the large frequency ratio.However,this method needs to calibrate the DFP system,which is relatively complex and more time-consuming.To solve this problem,an improved phase-unwrapping method using geometric constraints is proposed,which eliminates the system calibration in Zhang's method,meanwhile does not need to use the low frequency fringe pattern.This method can simplify the procedure and improve the speed.(5)Above algorithms are achieved using MATLAB R2014a and a lot of experiments are presented to verify the performance of the proposed phase unwrapping method in the paper.The experimental results demonstrate the validity and reliability of the various phase unwrapping algorithms proposed in this paper.