A Hybrid Frequency-Space Approach for Shape Measurement by Shadow Moirè Technique with Carrier Fringe Pattern

In this paper, a novel methodology to process fringe pattern is presented. The core of the signal processing technique is the use of the direction information, a modulo 2π quantity that locally informs about the direction along which fringes grow with maximum rate. By using this information, it was possible to perform adaptive, direction - and orientation-based operations on fringe images in order to remove unwanted effects, to enhance the contrast and to extract the phase information encoded. The method has been applied on shadow moiré interferograms with carrier fringes in order to measure the surface of small objects. The developed algorithm allows to process fringes whose phase information is not monotonically increasing everywhere and to more accurately estimate the phase itself. Results from two experimental fringe patterns are presented. Results are compared with measurements performed by means of a conoscopic system used as a reference. Hence, it was possible to calculate the uncertainty of the performed measurements. Besides the possibility to decode fringe patters presenting closed fringes, the proposed method provides measurements characterized by an uncertainty more than halved compared to Fourier-based methods.