Two methods for determining the absolute order of moire fringe have been developed. The first one is for shadow type moire typography and capable of automatic measurement in real-time. Light source moves with constant speed, and intensity variations on the object surface are analyzed by FFT. Experimental results show that the method can be successfully applied to shadow moire topography and does not need the continuity of the object surface. Measurement time is less than 9 s, and the accuracy of measuring absolute depth is better than 1% for measuring range.
The other one is for projection type moire topography. It uses gratings in which color lines are inserted so that the absolute order of a fringe can be determined even if some discontinuities exist on the object. The increasing or decreasing of fringe orders is easily distinguished.
The visibility of additive type moire fringe was enhanced to that of subtractive moire in real-time by using computer image processing technique. The enhanced moire was applied to the moire topography to show the possibility of practical use. A noise reduction technique that can be used for uneven background level is also suggested.
