Correction of illumination fluctuations in phase-shifting technique by use of fringe histograms.

Abstract

With phase-shifting technique, the illumination fluctuations may decrease measurement accuracy. This paper presents a simple method for solving this problem by use of fringe histograms. A fringe pattern containing bright and dark fringes is recognized as an image having two classes of pixels following a bimodal histogram, and the optimal threshold for segmenting this pattern enables maximizing its intervariance between the two classes. Using this optimal threshold, some statistics of the segmented classes, that is, their means, keep stable during phase shifting. Using these means of classes as nodes allows us to determine a linear transformation function by which the fluctuations of the fringe patterns in background intensities and modulations are corrected. Numerical simulation and experimental results demonstrate this method to be efficient and effective in improving the phase measuring accuracies with phase-shifting technique.