ABSTRACT--New algorithms are proposed for processing wrapped isochromatic and isoclinic fringe data generated by the digital photoelastic technique of phase-stepping. The new algorithms are based on processing areas rather than individual pixels to demodulate the data and employing quality assessments of the data to guide the unwrapping procedure. Comparisons with an existing algorithm, manual analysis, and finite element modeling have been used to demonstrate that the new approach is more robust without any reduction in speed or accuracy. This represents a significant advance for processing complex fringe patterns, which are often encountered in the aerospace industry from which the exemplars are drawn.KEY WORDS--Photoelasticity, phase-stepping, finite element analysis Nomenclature A(j) = current area for processing A(j + 1) = next area for processing H = threshold height used in spike removal process applied to partial derivative data il. 9 9 i6 = intensity measured in polariscope orientated as shown in Table 1 im ---intensity term to account for stray light entering the polariscope iv = intensity observed in a polariscope when the fast axes of all the elements are alignedn, m = coordinates of pixel of interest N, M = number of pixels in x, y direction in data map Qo(n, m) = quality value for the pixel located at (n, m) wl = window dimension used in evaluating quality map w2 = window dimension used in reducing number of areas to be processed = relative retardation Atpx (i, j), Aqry (i, j) = difference in partial derivative of the phase data with respect to the x, y directions P. Siegmann is a Research Associate and E.A. Patterson (SEM member," eann @egr.msu.edu) is a Professor,
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