OPTICAL MODULATION AND DIGITAL DEMODULATION OF AN INPLANE MOIRE CARRIER

A rotational mismatch of gratings is used to generate a fringe carrier of an in-plane moire pattern so that specimen deformation shows itself in the form of modulation of the carrier frequency. As both the unmodulated and modulated carriers are the patterns without fringe-loop or fringe-connection, they are automatically numbered with monotonical increasing orders by a digital image processing system without any ambiguity. The orders at every pixel of the image are determined by interpolation of the orders of the tracked fringes to establish two grey image files, from the difference of which, the orders of the in-plane displacement moire are displayed with grey-level variation.