We used the same skin model and the same parameters that were used in the previous studies1,9 as follows: a two-layered model of the epidermis with uniform melanin and an underlying dermis with uniform oxygenated and deoxygenated hemoglobin was used; the thicknesses of the epidermis and dermis were 0.06 and 4.94 mm, respectively. The refractive indices were assumed to be 1.4, independent of wavelength and layer. The refractive index of the external area was set to 1. The absorption coefficients of the epidermis and dermis were assumed to be and , respectively. Here, , , and are the concentrations of melanin, oxygenated hemoglobin, and deoxygenated hemoglobin in each layer. For , we used the average absorption coefficient of a monomer melanosome with a concentration of ; this was approximated as , where the unit of is nanometers.18 For and , we used the extinction coefficients of oxygenated and deoxygenated hemoglobin, respectively, converted to the concentration of 45 hematocrit in blood.19 The scales of , , and were the ratios of the concentrations to those under which , , and , respectively, were derived. To characterize the scattering, a reduced scattering coefficient is required; this is derived from , using the scattering coefficient and anisotropy , which are the primitive parameters of scattering.20,21 The value of for both the epidermis and dermis was ; the first term represents Mie scattering, the second one represents Rayleigh scattering,20–22 and the unit of is nanometers.