Statistical Characterization of Face Spectral Reflectances and Its Application to Human Portraiture SpectralEstimation

©2002, IS&T—The Society for Imaging Science and Technology outer thin layer, epidermis, and an inner, relatively thick layer, dermis. For normal human skin, the absorption of the epidermis is dominated by a black pigment called melanin, though there are five different pigments in the skin.6 The spectral characteristics of different races or different individuals are due only to variation in the amount of melanin present.7,8 Buckley and Grum,9 and Kollias and Baqer8 indicated that the spectral reflectance of melanin monotonically increases across the visible range. The inner layer, dermis, is rich with blood vessels that contain hemoglobin. Hemoglobin has marked absorption bands around 575 nm, 540 nm and 410 nm.10,11 Brumsting and Sheard4,5 indicated that the marked absorption bands of hemoglobin occur only when it bonds with oxygen within living skin. Heavily pigmented skin will present a less pronounced effect of hemoglobin absorption because of the masking effect of the greater amount of melanin pigmentation. Human lips, on the other hand, are in rich of blood vessels and will present hemoglobin absorption bands. Optically, the epidermis is a strongly forward scattering layer and, for all wavelengths considered, scattering is much more important than absorption.12 Details of skin biology are beyond the scope of this research. The skin is not the only part of the human body that differs in color from one individual to another. The eyes have the same elements affecting their coloring. In dealing with an individual’s eye color one is referring to the pigmentation of the iris. The iris, from the standpoint of color, consists of the anterior layer together with its underlying stroma and the posterior pigmented epithelium.13 In the eye, as in the skin, melanin is the dominant pigment material. However, in this case, the location of the melanin is as important as the amount.6 Eye color also depends partly on optical phenomena. Introduction