Novel absolute phase measurement method with few-patterns

Abstract

The temporal phase unwrapping method can obtain the absolute phase of an object with large discontinuities and isolated objects in phase measuring profilometry. But it needs many frames fringe patterns, which may consume a significant amount of time in 3D surface measurement. In the light of this problem, we proposed a novel absolute phase measurement method with few-patterns. 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 calculate the wrapped phase, divide the whole measurement region into many sub-regions, correct the surface reflectivity of the tested object. A frame of half-period gray-coded pattern and the index number of the sub-region are 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. To verify the effectiveness of the proposed method, we measured two isolated masks and compared the result with Chen's method [1]. The result shows that the accuracy of our method is similar to Chen's method, but our method has two images less than Chen's method, which improves the measurement speed. Then we measured two complex isolated sculptures. The result shows that our method is also effective for complex surfaces.