A modified regularized scheme for isochromatic demodulation in RGB photoelasticity

Red-Green-Blue (RGB) photoelasticity has become popular recently owing to its ability for determining the isochromatic fringe orders by processing a single photoelastic color image. This technique employs an a priori calibrated RGB look-up table (LUT) for demodulation of colors in the analyzed image based on an error function. The demodulation is based on the minimization of the error function, which sometimes produce ambiguous fringe orders. Therefore, the initially proposed error function was improved by regularized (or refined) schemes for ambiguity-free isochromatic demodulation. The simplest regularized scheme employs horizontal scanning and left pixel fringe order continuity to remove ambiguity. This particular scheme cannot produce noise-free fringe maps in the presence of color abberations (discontinuities or noise) at the starting pixels of the rows. The available literature mostly deals with the removal of ambiguities produced due to minimization of the error function. This paper highlights the noise produced in the fringe maps due to the presence of color abberations at the starting pixels. To address this issue, an alternative scheme is proposed, wherein a modified regularized algorithm and an improved LUT calibration have been employed in tandem. Moreover, two other schemes, which are meant for ambiguity removal, have been explored for removing the color noise. The present work is observed to produce smooth and accurate fringe maps without any manual intervention to the fringe map.