A morphological approach to the automatic detection of dark fringes of birefringence images obtained in a multipass rheometer

This work presents a novel approach to automatically detect the position of dark fringes in birefringence images obtained during the flow of polymers through slit dies. The determination of these positions is important for rheology, as it allows one to obtain the principal stress difference (PSD) profile along the flow centerline. The developed approach uses mathematical morphology techniques to find the patterns that characterize the birefringence fringes and to detect their center position. The proposed method was compared with other fringe center detection methods, revealing the superior accuracy of our method, and the results were compared with the semi-automated measurements obtained with the GIMP software in a previous work. In addition, the statistical analysis performed showed that the difference of the average obtained with the two methodologies can be considered irrelevant to the application at hand for most of the fringes observed in the experiments.