Sinusoidal phase-shifting symmetrically combined with cyclic code is
one of the most important encoding methods in the field of 3D
measurement. Due to the modulation of the object surface and the
influence of the noise of the image acquisition system, the periods of
the cyclic code and the sinusoidal phase-shifting in the intensity
image do not coincide completely, and they lead to large absolute
phase decoding errors near the cycle boundaries, which are called
cycle dislocation errors. In order to eliminate these errors in
principle, the concept and method of region encoding for four-step
sinusoidal phase-shifting are proposed, and the sinusoidal
phase-shifting is combined with cyclic code asymmetrically. Under the
premise that the cyclic code and the region code change at different
times, the cycle dislocation error is reduced from one cycle of cyclic
code to one pixel by the dual constraint of cyclic code and region
code. The simulation measurement results of 3 ds max and the
physical measurement results show that the asymmetric combination
encoding method effectively eliminates the cycle dislocation errors;
the maximum measurement error is reduced by an order of magnitude, and
the root mean square measurement error is reduced by 70%.
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