Automated Shadow Moiré Fringe Analysis Using Two Light Sources

Abstract

Introduction. Shadow moiré method is an effective optical technique for surface profile measurement of diffusely reflecting objects. For accurate measurement, phase-shifting technique is usually adopted to the shadow moiré measurement system. However, the specimen or system may be moved during the time of image capture, and not suitable for in-line measurement. In order to overcome this drawback and make an automated in-line measurement, a shadow moiré system consisted of two light source of different color, and a color CCD camera is proposed. The phase shift is introduced by using two light sources illuminate the grating from different position simultaneously. The two moiré fringe patterns captured by the color camera are processed by an automated fringe analysis scheme using spiral phase transform (SPT), optical flow and digital filtering techniques. The proposed automated fringe analysis scheme was applied to simulated surface profile and real specimen. The principles and test results are presented.