Duan-Jun Chen, Fu-Pen Chiang
Optical Engineering, Vol. 29, Issue 11, (November 1990) https://doi.org/10.1117/12.55730
TOPICS: Fringe analysis, Diffraction, Photography, Speckle, Fourier transforms, Convolution, Digital signal processing, Signal to noise ratio, Cameras, Visibility
A new technique for fully automatic diffraction fringe measurement
in pointwise analysis of speckle photographs is presented. The fringe
orientation and spacing are initially estimated with the help of a 1-D fast
Fourier transform (FFT). A 2-D convolution filter is then applied to enhance
the estimated image. A fringe pattern with high signal-to-noise ratio is
achieved, which makes feasible precise determination of the displacement
components. The halo effect is also optimally eliminated in a new way by
a halo-division technique. High reliability and accurate determination of
displacement components are achieved over a wide range of fringe densities,
with the computation time comparing favorably with those for the
2-D autocorrelation method and the iterative 2-D FFT method.