Intensity-modulated moire topography

Moire topography has the advantage of requiring only a single image to obta in 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 a bsolute phase and an absolute depth range. It is therefore difficult to dis cern the relation between fringes in the cases in which the fringes are dis continuous or the objects are isolated. An intensity-modulated moire topogr aphy method is presented. By modulation of the transmission factors of the projection and the observation gratings by exponential functions a new moir e pattern whose fringe intensity changes with its order can be produced. Th e fringe order can be extracted easily from the fringe intensity, and the a bsolute range of the skeleton line can be obtained solely from its intensit y. 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 n o need for interaction with the user. (C) 1999 Optical Society of America.