Coaxial projection profilometry based on speckle and fringe projection

In a coaxial projection-imaging system, there exists weak triangulation for retrieving depth information. The triangulation is due to the angular difference between the projection and imaging light, which causes deformation of a projected pattern with depth change of an object. A speckle projection and a fringe projection method are proposed to retrieve the surface profile of an object evaluated under such a system. In speckle projection, local displacement of the pattern is recorded in one image and is calculated by digital image correlation. In fringe projection, the displacement is recorded in two sets of images. A phase-tracking method is applied to recover the displacement. Several experiments on two system implementations are conducted. Based on the results, strength and weakness of the coaxial speckle and fringe projection methods are discussed.