Using Anti-aliasing Camera Filters for DIC: Does It Make a Difference?

Abstract

Aliased speckle patterns are a known problem for digital image correlation (DIC). By definition, aliased speckles are smaller than the resolution limit of the camera and add “noise” to images via the spatially-aliased frequency content. Aliased speckles occur quite frequently in practical DIC applications, especially when using spray paint to speckle a surface, where control of the speckle size is difficult at best. This paper compares DIC results from aliased speckle patterns imaged with typical machine cameras with and without physical anti-aliasing filters applied to the camera detectors. Additionally, physical anti-aliasing filters are compared with post-processing, digital low-pass filters of aliased images to quantify the influence of the two types of filters on the quality of DIC results. A key result from this work is that the loss of contrast associated with the addition of physical anti-aliasing filters is generally more detrimental to DIC results than the noise resulting from aliased speckles.