The varying intensity of the diffraction halo affects the positions of the fringe maxima and minima in speckle photography. Significant fringe shifts appear if this background is not removed prior to fringe spacing evaluation. A logarithm method is used to simplify data acquisition of speckle fringe patterns, so that recording of diffraction halos for each point on the specklegram is not necessary. Experimental results show the accuracy of the processing method.
G. H. Kaufmann,
"New Developments In Digital Processing Of Speckle Photography Fringes", Proc. SPIE 0397, Applications of Digital Image Processing V, (26 October 1983); doi: 10.1117/12.935323; https://doi.org/10.1117/12.935323