A novel methodology for enhancing the contrast of correlation fringes obtained by ESPI

Abstract

Electronic speckle pattern interferometry (ESPI) has been used to elucidate the in-plane and out-of-plane displacements of an object. It is a method for measuring the deformation or displacement of the surface of an object by recording at least two speckle patterns, one before and one after the object is deformed. By adding, subtracting or multiplying the speckle patterns, correlation fringe patterns with poor signal to noise ratios are obtained. In general, the contrast of the correlation fringe patterns is enhanced using digital filter methods. However, digital filter methods cannot remove the speckle noise efficiently and sometimes leads to inaccurate digital filtering when the noise is intense. This paper describes a methodology for adjusting the intensity (normalizing the interferogram) to enhance the contrast of the correlation fringe patterns. It is a trigonometric operation and differs from digital filter methods. A comparison is also made with previously proposed digital filters. Normalization outperforms digital filters. Finally, deformation phase map with the novel methodology is shown.