Pre-modulated Phase-Shifting Coding Absolute Phase Retrieval Method

Absolute phase retrieval is an important part of 3D measurement. The conventional phase-unwrapping algorithm requires the projection of extra patterns to retrieve the absolute phase, which reduces the measurement speed. Based on the theory of phase domain modulation, the phase is pre-modulated in the form of a specific code embedded into the phase shift method to reduce the number of projected images for improving the speed. To improve the number of codewords and for the accurate determination of the fringe order, the coding strategy of segmented quantization is adopted at the time of coding. When decoding, the original wrapped phase is obtained by solving the wrapped phase map based on the wrapped phase map with the corresponding fringe order for absolute phase retrieval. The experimental results reveal that this method requires only one set of phase-shift modes to realize absolute phase retrieval. This feature improves the measurement speed and simultaneously maintains an accuracy that is consistent with that of the phase-coding method.