Absolute phase measurement method with few-patterns

Abstract

To unwrap the wrapping phase from phase measuring profilometry in 3D surface measurement, many spatial and temporal phase retrieval methods have been presented. However, spatial phase retrieval method often leads to errors because of discontinuous morphology, noise and fringe undersampling. Temporal phase retrieval method can solve this problem. But the method needs multiple frames of fringe images which would take much time. We proposed a novel absolute phase measurement method with few-patterns to overcome this problem. The proposed method combines an object reflectivity correction and a half-period gray-coded phase unwrapping algorithm. One group of precoded three-step phase-shifting fringe patterns are used to determine the wrapped phase, divide the region, and correct the surface reflectivity of the tested object, a frame of half-period gray-coded pattern is used to determine the fringe order. The proposed method can obtain a large number of codewords for fringe order without decreasing the intensity level for each stair. The result shows that our half-period gray-level coding (HGC) method is robust and efficient.