Absolute phase recovery based on two-wavelength fringes using a defocusing technique in fringe projection profilometry

Abstract

We present an approach that combines binary structured patterns generated by tripolar pulse width modulation technique with a two-wavelength phase-shifting unwrapping method to realize absolute phase recovery at the same defocusing level. Optimized binary fringe patterns projected by a small defocusing degree projector can significantly alleviate the phase error based on fringe projection profilometry, providing the binary patterns with a similar performance to standard sinusoidal fringe patterns. With this method, a set of images using only two-wavelength fringe patterns is captured by the camera, and it is not obliged to obtain the equivalent wavelengths and their corresponding phase maps. In consequence, the error propagation is avoided, which leads to improved accuracy in the continuous phase map retrieval. Furthermore, The effectiveness of the presented phase recovery technique that can be utilized to measure discontinuous and multiple objects was also verified by experiments. And it can reach high-precision and fast three-dimensional shape measurement.