The Nyquist criterion and its relevance in phase-stepping digital shearography: a quantitative study

The Nyquist criterion, or Nyquist sampling theorem, has been used as a gold standard in signal processing and in digital imaging. In this work, we examine its applicability and relevance in phase-stepping digital shearography, which has become a useful tool in the generation of displacement gradient maps of extended objects, and in non-destructive testing (NDT). We show, with experimental data and quantitative measurements from our digital shearography experiments, that it is not necessary to comply strictly with the Nyquist criterion in digital shearography. Operation of the digital imaging device in the sub-Nyquist domain is perfectly feasible, and even desirable, in many cases. This will suggest, to the experimentalist in shearography, the best possible ways to perform image sampling in the case of digital shearography.