Electronic speckle photography: increased accuracy by nonintegral pixel shifting

Electronic speckle photography offers a simple and fast technique for measuring in-plane displacement fields in solid and fluid mechanics. An improved algorithm is presented and analyzed by use of both computer-simulated speckle patterns and real experiments. The idea of the improved algorithm is to maximize the correlation between correlated subimages from different images by shifting one of them by nonintegral pixel values. The improved algorithm was found to determine displacement components with an uncertainty of less than 1% of a pixel and with negligible systematic errors in ideal experimental conditions.