Quality evaluation of speckle patterns used in digital image correlation by two-dimensional entropy

This Digital image correlation method is a non-contact measurement method that achieves deformation measurement by tracking speckle patterns that cover the measured surface and deform with the measured surface. The quality of speckle patterns has a significant direct impact on measurement accuracy of DIC. A global evaluation method for speckle pattern quality using a simple and easy-to-calculate parameter called two-dimensional entropy is proposed in this paper. To verify the effectiveness of the evaluation method, comparative experiments are conducted on displacement measurement accuracy using three types of speckle. The results indicate that the larger the two-dimensional entropy of the speckle, the higher the displacement measurement accuracy. In order to further validate the proposed evaluation method, measurement experiments are performed using the same type of speckle patterns with different two-dimensional entropies, and the similar conclusions are obtained. These results prove that the two-dimensional entropy of speckle pattern can be effectively used for speckle pattern quality evaluation.