This paper proposes an absolute phase unwrapping method for 3D measurement that uses two cameras and one projector. On the left camera image, each pixel has one wrapped phase value which corresponds to multiple projector candidates with different absolute phase values. We use geometric relationship of the system to map projector candidates into right camera candidates. By applying a series of candidate rejection criteria, a unique correspondence pair between two camera images can be determined. Then the absolute phase is obtained by tracing the correspondence point back to projector space. Experimental results demonstrate that the proposed absolute phase unwrapping algorithm can successfully work on both complex geometry and multiple isolated objects measurement.
This paper proposes a method that does not require to change exposure time of the camera for high-quality surface measurement when the surface contrast is large. The idea is that three phase-shifted inverted fringe patterns are used to complement regular three phase-shifted fringe patterns for phase retrieval. For saturated pixels, the inverted fringe patterns will be used in lieu of the original patterns for phase computation. Though not as robust as some of previously proposed time-consuming methods, experimental data showed that the proposed method can substantially increase measurement quality for high-contrast surfaces.