A Separation Method of Superimposed Gratings in Double-Projector Fringe Projection Profilometry Using a Color Camera

Abstract

Fringe projection profilometry has been intensively studied for several decades. However, due to the limitation of the field range of a single projector, when measuring objects with complex surfaces, there are always shadow areas in the captured images, resulting in missing measurement data in the dark areas. To solve this problem, systems with double projectors and single camera were employed. Not only were the shadow areas reduced, but system recalibration and multiple measurements were not needed, improving measuring efficiency. Nevertheless, separating the corresponding projection pattern from the superimposed fringe presented a difficult problem. A color camera has RGB three color channels. When the color camera is applied to fringe projection profilometry, the information obtained is three times as much as that of the monochrome camera. Due to the small overlap between the red- and blue-light spectra response of color cameras, the channel color crosstalk can be ignored. This paper proposes a method to project red and blue fringe patterns from two projectors and utilize the characteristics of the red and blue channels of the color camera to separate the superposition grating pattern. The original patterns can be recovered integrally and easily. To explain the effectiveness of superimposed fringe separation, a simulation and experiments were carried out. Both of them showed that the superimposed fringe can be separated correctly, proving that our method is feasible.