Dr. XiaoLei Li Profile

Dr. XiaoLei Li

at Xi'an Univ. of Technology

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Publications (4)

Proceedings Article | 17 April 2020 Paper

Comparative study on double-step phase-shifting algorithm for nonlinear phase error compensation

Canlin Zhou, Zhenkun Lei, XiaoLei Li

Proceedings Volume 11455, 114553F (2020) https://doi.org/10.1117/12.2564637

KEYWORDS: Phase shifts, Fringe analysis, Error analysis, Phase shifting, 3D metrology, Phase measurement, Cameras, Calibration

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The phase-shifting method is widely used in fringe projection profilometry (FPP),The digital light projector (DLP) and charge coupled device (CCD) are generally nonlinear devices.The captured fringes do not have a good sinusoidal property,which leads to errors in the retrieved phase map.The methods to calibrate the nonlinear response of a FPP and compensate for the associated error can be classified into active methods(correction before pattern projection) and passive methods(correction after pattern projection).The basic idea of the active method to precisely obtain the input output relation function of the projector. The passive method compensates the error in phase domain by the post-processing algorithms. Huang et. al. presented the double three-step phase shifting algorithm to reduce the nonlinear phase error by projecting two groups of three-step phase-shifting fringe with an initial phase offset of 60 degree.Subsequently,some scholars improved this method. Zheng et.al. presented a method that combined the two wrapped phases to obtain the combination of the wrapped phase,it is simpler than Huang’s method because only one time phase unwrapping procedure is needed. Lei et. al. combined double-step phase-shifting method and multifrequency temporal phase unwrapping algorithm, proposed a multi-frequency inverse-phase method to realize the 3D shape measurement of the complicated objects. Mao proposed a similar approach.The main difference between Lei and Mao is that the operation order of double-step phase-shifting algorithm for error compensation is different. In Mao’s method,error compensation is performed in the wrapped phase map while it is done with the unwrapped phase map in Lei’s method.This paper compares double-step phase-shifting algorithm, its variational algorithm (Zheng's method, Lei’ s method, Mao's method) and phase shift algorithm with twice the number of steps for nonlinear error compensation, our study finds that these algorithms have similar effect in reducing nonlinear phase error. Phase shift algorithm with twice the number of steps is simpler and more direct than double-step phase-shifting algorithm.In variational algorithm, Zheng’s method reduces the number of phase unwrapping by half compared with traditional double-step phase shifting algorithm,Mao’s method is essentially the same as Lei’s method,it was by introducing multi-frequency temporal phase unwrapping algorithm that Lei and Mao's method can measure the complex object. Experimental results are presented to demonstrate the rationality of this analysis.

Proceedings Article | 17 April 2020 Paper

Dynamic 3D shape measurement based on the phase-shifting moire algorithm

Canlin Zhou, Shuchun Si, XiaoLei Li

Proceedings Volume 11455, 114553G (2020) https://doi.org/10.1117/12.2564641

KEYWORDS: Fringe analysis, 3D metrology, Phase shifts, Fourier transforms, Moire patterns, 3D modeling, Optical filters, Composites, Phase shifting

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Structured-lighting projection methods are the important parts of the optical three-dimensional (3D) measurement. Phase-shifting profilometry has a higher accuracy,however it requires multiple phase-shifting sinusoidal patterns’ projection,it can only be used for static measurement. The 3D shape measurement of dynamic objects is a challenging issue and attracts many scholars’ attention. The single frame 3D reconstruction technique (such as the Fourier transform, color-encoded or composite coded grating method and single frame Moiré retrieval method) can meet the requirements of dynamic measurement well since only one-frame deformed pattern is required to obtain the 3D information of the object, but there are still issues in the stability and accuracy when using these methods. Recently, Wang et. al. [26] presented a high-speed Moiré-based phase retrieval method. However, it is used only to measure the thin objects. Inspired by reference 27, we combined phase-shifting, moire algorithm and reconstruction algorithm of complex Fast Fourier Transform (FFT), proposed a dynamic three-dimensional (3D) measurement based on four-step phase-shifting Moiré algorithm. Only one fringe pattern of the object was required to reconstruct the 3D shape of the tested object after the four fringe patterns with a π /2 phase shift of the reference plane were captured in advance. Only a single Fourier transform of a complex fringe composed of two multiplexed fringe patterns is calculated,the calculation time of the inverse 2D FFT is decreased due to the smaller calculated data matrix. First, four sinusoidal fringe patterns with a π/2 phase-shift are projected on the reference plane and acquired four deformed fringe patterns of the reference plane. Then single-shot deformed fringe pattern of the tested object is captured in measurement process. Four Moiré fringe patterns can be obtained by numerical multiplication between the the AC component of the object pattern and the alternating components(AC) of the reference patterns respectively. The four low-frequency components corresponding to the Moiré fringe patterns are calculated by the complex encoding FT (Fourier transform) ,spectrum filtering and inverse FT. Thus the four phase-shifting Moiré fringe patterns can be retrieved. Then the wrapped phase of the object can be determined in the tangent form from the four phase shifting Moiré fringe patterns using the four-step phase shifting algorithm.The continuous phase distribution can be obtained by the phase unwrapping algorithm.The 3D shape distribution can be reconstructed according to the phase-to height mapping relation after the calibration of the system. Finally, experiments are conducted to prove the validity of the proposed method. The results demonstrate that our method not only can expand the measurement scope, but also can improve accuracy and speed.

Proceedings Article | 20 December 2019 Paper

One-shot common-path phase-shifting holography based on micropolarizer camera and large-shearing Wollaston Prism

Canlin Zhou, Shuchun Si, XiaoLei Li, Zhenkun Lei, YanJie Li

Proceedings Volume 11209, 112091W (2019) https://doi.org/10.1117/12.2547690

KEYWORDS: Holograms, Digital holography, Phase shifts, Cameras, Prisms, Holography, Polarization, 3D image reconstruction, Beam splitters, Image processing

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Proceedings Article | 24 July 2018 Paper

Simple tilt compensation algorithm for off-axis digital holography

Canlin Zhou, XiaoLei Li, Shuchun Si, Zhenkun Lei, YanJie Li

Proceedings Volume 10827, 108270Q (2018) https://doi.org/10.1117/12.2500462

KEYWORDS: Holograms, Fourier transforms, Digital holography, Computer simulations, Phase measurement, Microscopes, Fringe analysis

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