Quality assessment of speckle patterns for digital image correlation

Digital image correlation (DIC) is an optical–numerical full-field displacement measuring
technique, which is nowadays widely used in the domain of experimental mechanics. The
technique is based on a comparison between pictures taken during loading of an object. For an
optimal use of the method, the object of interest has to be covered with painted speckles. In the
present paper, a comparison is made between three different speckle patterns originated by the
same reference speckle pattern. A method is presented for the determination of the speckle size
distribution of the speckle patterns, using image morphology. The images of the speckle
patterns are numerically deformed based on a finite element simulation. Subsequently, the
displacements are measured with DIC-software and compared to the imposed ones. It is
shown that the size of the speckles combined with the size of the used pixel subset clearly
influences the accuracy of the measured displacements.