Automatic analysis of speckle photographs with extended range and improved accuracy

A new algorithm for automatic analysis of Young's fringes in speckle photography, applicable to fringe numbers >0.5, is developed. In the algorithm we first divide the diffraction pattern by the corresponding diffraction halo, then integrate the result over bands in various directions for detecting the fringe orientation, and use curve fitting for determining the fringe spacing. The algorithm has enabled fully automatic analysis of double-exposure specklegrams for a wide range of speckle displacement with improved accuracy. Contours of displacement and strain fields have also been plotted using the result of the analysis.