How to detect object-caused illumination effects in 3D fringe projection

摘要

3D measurement of the shape of rough structures can be realised with structured light illumination techniques. Several problems can arise while measuring complex object geometries with these techniques. Complex objects are characterized, f.e. by deep holes, walls, concave and convex corner-like shaped surface structures. When illuminating the object, one part of the object can "illuminate" another one, yielding locally spurious fringe patterns. Due to these spurious fringe patterns the phase values are strongly distorted significantly increasing the measurement noise locally. Here we propose methods how to detect and to avoid these spurious fringe patterns. The idea is to use the overestimated information which is contained in the graycode and the sinusoidal intensity distribution. On the basis of this procedure, an operator is defined which results in a mask operation. With this new method we can reduce the noise amplitude. In this paper, the detection and reduction of the illumination effect using this operator will be demonstrated while measuring different object geometries.