Speckle deflectometry based on digital image correlation

Digital image correlation (DIC) is a widely used non-contact measurement method for the deformation of a diffused object surfaces in the experimental solid mechanics. In specular surface figure measurement, the rapidly developing deflectometry using sinusoidal fringes can achieve a sub-micron level accuracy. The fringe pattern used in the phase shift algorithm is sensitive to noise, but the speckle image used in the DIC technique is robust against noise. In this paper, three kinds of speckle deflectometry methods, which are speckle pattern defletometry(SPD), speckle pattern shifting deflectometry(SPSD) and dynamic speckle deflectometry(DSD), are introduced to measure the figure of specular surface. The principles of the three methods are introduced in detail, and the experimental results are given in order to illustrate the measurement accuracy.