Effects of contrast and brightness on subpixel image correlation

In the past years a method that uses digital image correlation to determine the deformations of subsets of an object has been developed. In the paper an attempt is made to explore and understand the effects of changing signal amplitude on the errors associated with digital image correlation. This is important because changes in signal amplitude relate to changes in contrast and brightness between the images. The work was prompted by use of substances that change their phosphorescence under UV light as temperature varies. This results in changes in intensity amplitudes (contrast and brightness) between the initial and final images. The system components are simulated, a representative intensity pattern is chosen and then deformed (translated and strained) by known amounts under changing contrast and brightness. Pure translation, with strain set to zero and translation varied was studied first, and repeated using different intensity amplitudes for the deformed object. The absolute normalized error between the actual and calculated displacement was found by a cross-correlation. For the second study, uniform strains of 0.1%, 0.5%, 1.0% and 5.0% were imposed in addition to centerpoint translation and repeated using different intensity amplitudes