Combined defocusing triangular pulse width modulation fringe pattern and Gray code for absolute phase measurement

Wenbin Deng; Jeh Won Lee

doi:10.1117/1.OE.58.3.034110

27 March 2019 Combined defocusing triangular pulse width modulation fringe pattern and Gray code for absolute phase measurement

Wenbin Deng, Jeh Won Lee

Author Affiliations +

Optical Engineering, Vol. 58, Issue 3, 034110 (March 2019). https://doi.org/10.1117/1.OE.58.3.034110

Abstract

Projecting defocused binary pattern method can overcome the nonlinear gamma effect of the projector, as well as filter high harmonics, but it is sensitive to defocus levels. Therefore, it makes it difficult to generate both comparable performance to ideal sinusoidal fringe patterns and good quality Gray code when only a small number of phase shift patterns are used. To overcome this problem, a phase unwrapping approach combined Gray code with phase-shifting fringe patterns generated by triangular pulse width modulation (TPWM) technique based on slight defocusing is proposed. The phase is retrieved using a four-step phase-shifting method, and the corresponding phase order is obtained by Gray-code patterns. Because of defocusing projection, the boundaries of two adjacent Gray-code patterns become blurred, which make the recovery of accurate Gray-code patterns difficult. To solve this problem, we propose to project an all-white pattern and an all-black pattern to obtain threshold values, which are used to execute the binarization of Gray-code patterns. This approach is robustness to different defocus levels of projector. Experiments are submitted to verify that the proposed technique can be utilized to high-accuracy three-dimensional shape measurement of complex and/or discontinuous objects.

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Wenbin Deng and Jeh Won Lee "Combined defocusing triangular pulse width modulation fringe pattern and Gray code for absolute phase measurement," Optical Engineering 58(3), 034110 (27 March 2019). https://doi.org/10.1117/1.OE.58.3.034110

Received: 22 October 2018; Accepted: 13 March 2019; Published: 27 March 2019

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