Moiré 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 fringe 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 moiré topography method is presented. By modulation of the transmission factors of the projection and the observation gratings by exponential functions a new moiré 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 moiré pattern by its fringe order. For every segment the absolute phase and the absolute depth range of every point of the moiré pattern can be obtained solely from its intensity with no need for interaction with the user.
A new pattern projection technique for measuring three-dimensional topography is presented, called the optimal intensity-modulation projection technique. The proposed technique dramatically shortens the measurement time and improves stripe detection accuracy compared with previous methods. Furthermore, the method deals reliably with discontinuous patterns and multiple objects.
The Monochrome-Projection Color-Analysis (MPCA) technique is proposed in order to measure the three-dimensional shape of an object having a complicated surface color, to shorten the measurement time and to improve measurement accuracy. An optimal color channel is chosen, and a single channel image for intensity calculation is compounded so that the greatest amount of information from an observation image is used and the effect of object color on the measurement is mitigated. By combining MPCA and the Optimal Intensity-Modulation Projection (OIMP) technique, approximately 100 stripes are reliably detectable in a single pattern projection and double image capture.
A new projection pattern control technique is presented in an attempt to solve the problem whereby an image having an ideal intensity distribution cannot be photographed when measurement conditions, such as object color or object surface reflection, change. The proposed technique can adjust the intensity distribution of a projection pattern automatically, according to changes in the measurement conditions. An image with an ideal intensity distribution can then be obtained in a short time, approximately three projections on average. Thus, the speed, robustness, and practicality of 3-D image measurement can be improved.
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