Abstract: As is well known, the spatial coherence in a speckle field is limited to an area called the mean speckle size. Throughout this area, the coherence decays smoothly from the center to the margin of a speckle, and the degree of coherence between two points (x$-1$/,y$-1$/) and (x$-2$/,y$- 2$/) determines the probable amount of deviations between their intensities I$-1$/, I$-2$/ and phases. These deviations are of special importance when spatial phase shifting is applied in electronic speckle pattern interferometry. We demonstrate that the knowledge about the intensity and phase gradients in the object speckle pattern can be used to reduce the noise in measured deformation maps significantly.!14
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