Practical 3D computer vision techniques and applications in measurement and NDT

Abstract

This paper describes two computer-aided full-field optical techniques for measurement of surface shapes, inspection of surface quality, and nondestructive flaw detection. The first technique is for diffuse surfaces and the second technique is for specularly reflective surfaces. The technique for diffuse surfaces involves projecting onto the surface a computer- generated fringe pattern, whereas the technique for specularly reflective surfaces involves reflecting the fringe pattern from the mirror-like surface. In both techniques, the fringe pattern is perturbed in accordance with the object surface with fringe- phase bearing information on the depth (for diffuse surfaces) or the slope (for specularly reflective surfaces) of the surface. The fringe-phase is determined by a phase extraction algorithm using digitally-controlled four-frame phase-shifting, and the relationship between the fringe-phase distribution and the depth/slope is obtained by calibration. The techniques are applicable in an industrial setting and can be fully automated.