Towards a colorimetric characterization of the human iris

We propose a new approach to the quantitative determination of the iris col our through the spectroradiometric measurement of a set of 72 artificial in ises under controlled illumination and geometry. The spread of these sample s in the CIELAB colour space indicates no clearly distinguished groups with in the set analysed. Colour measurements for different points of these iris es and for the overall irises (pupil and specular image of the light source included) are well correlated. Complementary colour measurements were also performed for the irises of 25 ocular prostheses and 40 real observers. Al l these colour measurements appear to be quite consistent, the average stan dard deviation of any of the three a*, b*, L* co-ordinates being lower than 1.0 units. In a visual experiment where 11 normal observers matched the 25 ocular prostheses using the 72 artificial irises, the results indicate tha t a simple criterion based on the lowest colour-difference agreed with the observers' judgements in only 18% of the cases. This result suggests that, although colour appears to be a major parameter in the overall characteriza tion of the human iris, additional factors such as patterns or textures sho uld also be considered. (C) 2000 The College of Optometrists. Published by Elsevier Science Ltd.