A comparison between local and global phase unwrapping algorithms in a modified Fourier Transform Profilometry Method

Abstract

This work present a modified Fourier Transform Profilometry method, in particular, the development of local and global phase unwrapping algorithms has been considered, because this is one of the major challenges when this method is applied. The basic idea is to project a sinusoidal fringe pattern with a known spatial frequency on the object to digitize, and then a vision system captures and processes the image to obtain the object's depth information. First, the fringe pattern is projected on a reference plane then an image is acquired, later the object to digitize is placed in front of the reference plane and then another image is acquired. The fringe pattern is distorted due to the object's irregular shape. One of the main difficulties to face is the high frequency content in the unwrapping process. This effect can be minimized by knowing the spatial frequency and its multiples. Here, we propose to implement global and local phase unwrapping algorithms to overcome the high frequency problems. These algorithms are part of the modified Fourier Transform Profilometry Method (FTP), where the resulting phase difference of the acquired and processed images have the information of the object's depth. Some tests with computer generated and real objects with different geometries are carried out to verify the proposed methodology, considering the factors that mostly affect the method.