Abstract
The performance of seven different correlation functions applied in Digital Image Correlation has been investigated using simulated and experimentally acquired laser speckle patterns. The correlation functions were constructed as combinations of the pure intensity correlation function, the gradient correlation function and the Hessian correlation function, respectively. It was found that the correlation function that was constructed as the product of all three pure correlation functions performed best for the small speckle sizes and large correlation values, respectively. The difference between the different functions disappeared as the speckle size increased and the correlation value dropped. On average, the random error of the combined correlation function was half that of the traditional intensity correlation function within the optimum region.
Highlights
Digital image correlation (DIC), or Particle Image Velocimetry (PIV), has since its introduction in the 1980s evolved into one of the most versatile and widespread techniques in experimental mechanics [1,2,3,4,5,6]
The purpose of this paper is to investigate the performance of correlation functions based on derivatives of intensity images as a function of feature size and image degradation
It is sufficient to vary only the speckle size to capture the general behavior of the different correlation functions
Summary
Digital image correlation (DIC), or Particle Image Velocimetry (PIV), has since its introduction in the 1980s evolved into one of the most versatile and widespread techniques in experimental mechanics [1,2,3,4,5,6]. The deformation fields can be generated as Lagrangian fields (typically used in DIC) or Eulerian fields (common in PIV), depending on which images that are compared. It has been shown that the random error in the deformation calculation roughly scales with average feature size, subimage width and correlation value [12]. The quotient between subimage width and feature size defines in principle the number of independent contributions to the correlation and relates to the reliability of the calculation. For a laser speckle pattern, the decay of the correlation value is almost completely dominated by speckle decorrelation, while for a white-light pattern algorithm dependent features such
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