Quality assessment of speckle patterns for digital image correlation by Shannon entropy

Digital image correlation (DIC) is a digital-image-based whole-field deformation measuring technique. For use of the technique, the test surface of object has to be covered with random speckle pattern to ensure reliable and accurate matching. In practice, the quality of the speckle pattern has an important influence on the measurement accuracy of DIC. In this paper, an easy-to-compute parameter, called Shannon entropy which is from information theory, is employed for quality assessment of speckle patterns. Two sets of numerical translated tests are performed on three types of speckle patterns and five artificial speckle patterns with different Shannon entropies, respectively. Then, another test is performed on the computer-generated speckle patterns with nonuniform displacement field. All the results show that the measurement accuracy of DIC is related on the Shannon entropy of speckle pattern. Therefore, the speckle pattern with large Shannon entropy should be a so-called good quality speckle pattern. (C) 2015 Elsevier GmbH. All rights reserved.