Digital moir  by a diffractive optical element for deformation analysis of ancient paintings

In this paper we propose a digital projection moiré system for full-field measurement of out-of-plane deformation of cultural heritage objects. The method is based on a new fringe generator realized by a diffractive optical element illuminated by a spherical wave phase. Two grating patterns on an object before and after deformation are captured by a CCD camera and stored in a computer. With the aid of fast Fourier transform, signal demodulating techniques and a robust and fast phase-unwrapping algorithm, a 3D mapping of deformation can be visualized. The simplicity of the system and the fact that only readily available and unsophisticated equipment is required characterize the proposed method. The theoretical basis of the device is presented. Furthermore, experimental results made with a test object and a real ancient wooden panel painting are presented to demonstrate the validity of the technique.