Digital image correlation

About: Digital image correlation is a research topic. Over the lifetime, 7842 publications have been published within this topic receiving 132166 citations.

Fast, Robust and Accurate Digital Image Correlation Calculation Without Redundant Computations

Abstract: High-efficiency and high-accuracy deformation analysis using digital image correlation (DIC) has become increasingly important in recent years, considering the ongoing trend of using higher resolution digital cameras and common requirement of processing a large sequence of images recorded in a dynamic testing. In this work, to eliminate the redundant computations involved in conventional DIC method using forward additive matching strategy and classic Newton–Raphson (FA-NR) algorithm without sacrificing its sub-pixel registration accuracy, we proposed an equivalent but more efficient DIC method by combining inverse compositional matching strategy and Gauss-Newton (IC-GN) algorithm for fast, robust and accurate full-field displacement measurement. To this purpose, first, an efficient IC-GN algorithm, without the need of re-evaluating and inverting Hessian matrix in each iteration, is introduced to optimize the robust zero-mean normalized sum of squared difference (ZNSSD) criterion to determine the desired deformation parameters of each interrogated subset. Then, an improved reliability-guided displacement tracking strategy is employed to achieve further speed advantage by automatically providing accurate and complete initial guess of deformation for the IC-GN algorithm implemented on each calculation point. Finally, an easy-to-implement interpolation coefficient look-up table approach is employed to avoid the repeated calculation of bicubic interpolation at sub-pixel locations. With the above improvements, redundant calculations involved in various procedures (i.e. initial guess of deformation, sub-pixel displacement registration and sub-pixel intensity interpolation) of conventional DIC method are entirely eliminated. The registration accuracy and computational efficiency of the proposed DIC method are carefully tested using numerical experiments and real experimental images. Experimental results verify that the proposed DIC method using IC-GN algorithm and the existing DIC method using classic FA-NR algorithm generate similar results, but the former is about three to five times faster. The proposed reliability-guided IC-GN algorithm is expected to be a new standard full-field displacement tracking algorithm in DIC.

Subpixel displacement and deformation gradient measurement using digital image/speckle correlation (DISC)

Abstract: Experimental solid mechanics relies heavily on surface dis- placement and deformation gradient measurements. Digital image/ speckle correlation (DISC) uses digital image processing to resolve dis- placement and deformation gradient fields. The practical implementation of DISC involves important challenges such as computation complexity and the discrepancy of the sensitivities and accuracies claimed in previ- ous studies. We develop an iterative, spatial-gradient based algorithm, which uses only first-order spatial derivatives of the images before and after deformation. Simulated images are then used to verify this algo- rithm, as well as to study the impact of speckle size on the accuracy. Based on these simulations, the sensitivity of DISC to displacement and deformation gradient, as well as an optimal speckle size for optimal ac- curacy, is recommended. The algorithm is then calibrated using rigid body translation and rotation, and an application of DISC to thermome- chanical diagnostics of electronic packaging is also presented. © 2001