Human skin color correlated with optical characteristics of the skin tissue and local blood regions such as erythemas, tumors, internal bleedings, port-wine stains, and veins. Blood is originally red or dark red, but the local blood region usually looks bluish on the human skin surface. Since the bluish appearance of veins may reflect the physiological condition such as the depth and diameter of veins, quantitative understanding of the bluish appearance is expected to be useful for the diagnosis of the various skin diseases.
In this research projects, we have proposed a simple approach for evaluating this bluish appearance based on the well-known CIEXYZ colorimetric system. The color of an object can be expressed by tristimulus values X, Y, and Z which are derived from a visible reflectance spectrum. We have investigated experimentally and numerically the relations of bluish appearance of veins and their depth, diameters and oxygen saturation, with xy chromaticity diagram.