From fringe phases or from pixel shifts: a comparative study of depth-measuring modes in fringe projection profilometry

Abstract

In fringe projection profilometry, by taking the projector as a camera, depth measurement has the similar principle with binocular vision. The matching of feature points carrying depth information plays an important role in measurement. Due to the existence of difficultly-corrected projector errors, the measurement results of using a fixed point in camera corresponding to the points in the projector or of conversely using a fixed point in projector corresponding to the points in the camera is not exactly same. According to fringe projection system, a function representing the relationship between the depths and the corresponding fringe phases is introduced for measurement. This traditional method usually requires three or more known reference planes to calibrate parameters determined by the measurement system. However, another way is also feasible. Based on the measurement system, a generic function representing the relationship between the depths and the corresponding pixel shifts are also presented in this paper. Using these two functions allows us to recover the depth information of the object. Theoretical analyses are carried out to investigate the performances of these two methods. Comparative experiments are implemented, and their results demonstrate that the depth measurement method from pixel shifts is immune to the influence of high order harmonics as a little expense of efficiency, being better than the method from fringe phases having high measurement efficiency regardless of the low accuracy.