Use of polarized light in image analysis: Application to the analysis of fish eye color during storage

• Image analysis is an objective method the measure changes in the color of fish eyes during chilled storage.
• Measurements on discrete circular regions of the eye give better results than the whole eye.
• If eyes don't touch ice during storage their color does not get whiter and cloudier.

The evaluation of the eye is one method to determine the state of the fish: it is expected that the eye will start as black, transparent, and convex, and during storage it will become progressively lighter in color, more opaque, and will be sunken. Image analysis is an objective method to measure color. In this study, a method was developed to define a region of interest within the image of the eye, and to analyze its color. The effects of using polarized or non-polarized illumination, the dry or wet condition of the fish, and the eye touching ice during storage or being only exposed to air were determined. The L* values of the eye of the fish on the side touching the ice behaved as expected: L* values increased during storage for 7 or 11 days. However, the eye exposed only to air during storage on ice had significantly lower L* values. Wet or dry conditions did not affect L* values, however the eyes illuminated by non-polarized light had higher L* values than those illuminated by polarized lighting. These results should be considered when developing subjective or automated methods to evaluate fish by examination of their eyes.