Variable scale grating projection method based on from-coarse-to-fine progressive refinement

In terms of the calculation of absolute phase in conventional grating projection methods, the unwrapping algorithm is applied. Due to the demand upon spatial phase continuity from the unwrapping algorithm, it is not suitable for the measurement of objects with step-height. A multi-scale fringe projection measurement was put forward to tackle this problem, and the absolute phase of high-density fringe projection could be directly gained. Through the experiment upon the quadratic fitting curve of the high-density 64 periods fringes phase measurement, within the variation range -201,201 of the absolute phase, the fitting standard deviation reaches the precision of 0.096 63 rad.