An absolute depth range measurement of 3-D objects based on modulation Moire topography

It is the foundation that the absolute fringe order is discerned in 3-D image measurement methods, such as spatial pattern projection technique and Moire topography. The reason is that the depth range of the object is computed from the correspondence relation between the fringe order of a reflective pattern and the depth of an object. Multiple images are need by the conventional method for discerning the fringes order. Moreover, it has a problem of phase unwrapping in the phase analysis method of a Moire pattern or other interfering pattern. So it is difficult to calculate the absolute phase or to discern the relation between the fringes, especially in cases of which the fringes are discontinuous or the objects are isolated, and so forth. The technique of using modulation projection with 3-D information is presented. A new fringes pattern whose fringe intensity or color changes with its order is produced. Thus the fringe order can be extracted easily from the fringe intensity or color, and then the absolute phase and the absolute depth range can be obtained also. This technique needs only a single image or double images.