Analyzing the reflections from single ommatidia in the butterfly compound eye with Voronoi diagrams

This paper presents a robust method for the automated segmentation and quantitative measurement of reflections from single ommatidia in the butterfly compound eye. Digital pictures of the butterfly eye shine recorded with a digital camera are processed to yield binary images from which single facet centers can be extracted using a morphological image analysis procedure. The location of the facet centers is corrected by fitting in-line facet centers to a second-order polynomial. Based on the new centers a Voronoi diagram is constructed. In the case of the eye shine images, the Voronoi diagram defines a hexagonal lattice that overlaps with the original facet borders, allowing instantaneous quantification of the reflections from single ommatidia. We provide two typical examples to demonstrate that the developed technique may be a powerful tool to characterize in vivo the heterogeneity of butterfly eyes and to study the dynamic control of the light flux by the pupil mechanism.