Performance of gradient operators in algorithm of gradient-based subpixel registration

Surface displacement measurement is important in experimental solid mechanics. Algorithm of gradient-based subpixel registration as one of the DIC methods is introduced to measure subpixel displacement, because of its high efficiency and precision. But different gradient operators in this algorithm have different performances. First, several existed gradient operators are illustrated and two gradient operators are deduced through cubic spline interpolation of five neighboring pixels. Then computer-simulated speckle images are used to verify the sensitivities of all the six gradient operators. The calculated error and relative error are presented. The algorithm is also calibrated using rigid body translation and uniform uniaxial tension test of metal specimen to examine the precision and stability. The final results show that the algorithm of gradient-based subpixel registration using Barron gradient operator stably gets the highest precision and is a practicable subpixel registration method.