Quality Map Guided Phase Unwrapping Methods For Fringe Projection Profilometry

3-D shape measurement technique based on fringe projection has been one of the research hot spots, because of its characteristics of non-contact, high speed and high precision. How to extract the unwrapped phase fast and accurately is one of the most important problems of fringe projection technique. First of all, a variety of mainstream phase unwrapping algorithms are introduced in detail. Then two novel quality map algorithms used in Fourier transform profilometry and wavelet transform profilometry are presented to improve the deficiencies of the mainstream algorithms.In this paper, the fundamental principle and theory of Fourier transform algorithm are introduced and then the quality map is derived according to modulation depth. The quality map is divided into two parts by the pre-set threshold. The scan-line algorithm and flood-fill algorithm are used to this two parts to unwrap phase respectively. The proposed method is verified by static experiments and dynamic experiments. While the limitations of phase unwrapping algorithm used in Fourier transform profilometry are discussed.Second, a novel quality map algorithm used in wavelet transform profilometry is presented to improve the accuracy and speed of the phase unwrapping. The wrapped phase and the instantaneous frequency of a deformed fringe pattern can be obtained by applying wavelet transform to it. Then the quality map is derived according to two aspects. One is the absolute difference between the instantaneous frequency and fringe carrier frequency. And the other is the instantaneous frequency change over adjacent pixels. The value of the quality map determines the quality of the wrapped phase. The quality map can precisely indicate the areas where noise, shadows or fringe abrupt changes exist. Our experiments demonstrate that the proposed algorithm outperforms the flood-fill phase unwrapping algorithm in terms of accuracy and computational time. The proposed algorithm is suitable for dynamic measurements where a large number of fringe patterns require accurate phase unwrapping.