Real-Time Shadow Moire Measurement by Two Light Sources

For accurate measurement, phase-shifting technique is usually adopted to the shadow moire measurement system. Accurately introducing the amount of phase shift is required in order to extract the phase properly. However, the specimen or system may be moved during the time of image capture, and not suitable for real-time measurement. In order to overcome this drawback and make an in-line measurement, a shadow moire system consisted of two light source of different colors 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 moire fringe patterns are captured by the color CCD camera, and are processed by a fringe analysis scheme using spiral phase transform (SPT) and optical flow techniques. The proposed fringe analysis scheme was applied to a simulated surface and a real specimen. The test results are reported and the validity of the scheme is investigated.