Research On Phase Measurement Algorithm For Fringe Projection Profilometry

With the advancement of technology,fringe projection profilometry has a wide range of application in the fields of medical,cultural relics repair,industrial detection and target recognition.The study can be summarized as:(1)The stair phase coding method is studied,and a series of improvement methods are discussed.The first method is called a stair phase coding method based on arc cosine with only four patterns.The method projects and captures a set of three-step phase-shift sinusoidal fringe patterns and a cosine pattern encoding stair phase,and then compute the wrapped phase and background light from the three-step phase-shift sinusoidal fringe patterns,normalized cosine pattern can be estimated via background light,and the cosine pattern encoding stair phase.Arc cosine calculation is applied to the normalized cosine pattern to obtain the stair phase,then the fringe order is determined from the stair phase.A semi-periodic fringe order correction algorithm based on the dilation image processing technique is proposed to ensure the accuracy of fringe order.The continuous phase is obtained from the wrapped phase and the fringe order.Experiments results show that the method can achieve accurate three-dimensional measurement with only four patterns.The second method is called phase unwrapping method based on the stair phase coding of the Fourier transform,the method captures a high-frequency carrier fringe pattern and a composite high-frequency carrier fringe pattern embedded stair phase,the Fourier transform profile is used for the two pictures,the corresponding phase of the fundamental frequency component is obtained,and then the difference operation is performed to obtain the stair phase and the unwrapping phase.The number of captured images is reduced and the measurement speed is increased.(2)The paper proposes a direct gamma estimation method.Theoretical derivation shows that the gamma factor is related to the three-step phase-shifted fringe patterns and the ideal unwrapped phase.The gamma factor is used to inverse gamma correct the captured fringe patterns,and then the gamma-corrected unwrapped phase is obtained by phase demodulation and phase untangling from the inverse gamma corrected fringe patterns.The method only needs to project and collect three frames of fringe pattern,which meets the high-speed measurements requirement.The result shows that the method can effectively reduce the nonlinear phase errors.