Intensity-modulated moire topography

Moire topography has the advantage of requiring only a single image to obtain a three-dimensional measurement, but it cannot discern the fringe order. Because there is an ambiguity problem when calculating the depth range by use of hinge intensity or phase unwrapping, it is impossible to obtain an absolute phase and an absolute depth range. It is therefore difficult to discern the relation between fringes in the cases in which the fringes are discontinuous or the objects are isolated. An intensity-modulated moire topography method is presented. By modulation of the transmission factors of the projection and the observation gratings by exponential functions a new moire pattern whose fringe intensity changes with its order can be produced. The fringe order can be extracted easily from the fringe intensity, and the absolute range of the skeleton line can be obtained solely from its intensity. At the same time, we can segment the moire pattern by its fringe order. For every segment the absolute phase and the absolute depth range of every point of the moire pattern can be obtained solely from its intensity with no need for interaction with the user. (C) 1999 Optical Society of America.