Detection of Secondary Reflections Using Morphology

This paper discusses very simple but effective one-dimensional morphological techniques for the identification of primary and secondary peak locations associated with reflected light patterns from glass surfaces. A common optical technique for measuring glass thickness and related properties is to observe light reflected from the glass surfaces. Two reflections can be observed when an appropriate structured light source is used to illuminate a glass surface. A very bright primary reflection associated with the reflection from the front surface will be observed along with a much fainter secondary reflection from the back surface. The secondary reflection is difficult to detect reliably given the large difference in magnitude between the two peaks, the presence of noise, and the varying amounts of overlap between the two peaks that can occur. The methods described in the paper have been implemented successfully for two vision applications using images acquired using standard matrix and linear cameras. The signal is pre-processed using onedimensional morphological and linear methods to normalize the background and remove noise. Further morphological operations are performed to identify the peaks associated with primary and secondary reflections.