OPTIMIZATION OF FRINGE PATTERN CALCULATION WITH DIRECT CORRELATIONS IN SPECKLE INTERFEROMETRY

A direct correlation technique is used to calculate correlation fringe patterns from consecutive speckle patterns acquired with a dual-beam electronic speckle interferometer. Although more calculations are requ ired than in standard image differencing routines, an advantage of the method is that the illumination over the surface of the object need n ot be uniform. In the method, Pearson's coefficient of correlation bet ween the intensities within a set of adjacent pixels is calculated. Th is has the added advantage of being directly related to the theoretica l phase-dependent correlation. A mapping of this measure of correlatio n results in the correlation fringe pattern. Laboratory tests were car ried out with in-plane translations ranging from 5 to 45 mu m. The cor relation calculations were carried out by using cells (square sets of pixels) in the raw speckle images with dimensions ranging from 2 pixel s x 2 pixels to 19 pixels x 19 pixels. Both cell dimension and transla tion magnitude dependent decorrelation effects influence the quality o f the correlation hinge patterns. (C) 1997 Optical Society of America.