In this study, we present a quantitative characterization of skin pigmentation through the analysis of 1005 diffuse reflectance spectra associated with Fitzpatrick skin phototypes (I-VI) of Hispanic individuals. Complementary metrics such as the Structural Similarity Index (SSIM), the percentage of spectral overlap, and the Individual Typology Angle (ITA), obtained from objective colorimetric measurements, were used. SSIM results ranged from 0.42 to 0.94, showing high structural similarity between adjacent phototypes (especially V and VI) and marked differences between extreme phototypes (I vs. VI). The spectral overlap analysis confirmed this trend, with percentages between 0.00% and 52.05%, indicating significant overlap in closely related phototypes and no overlap in more distant ones. Meanwhile, the average ITA values showed a decreasing progression from (51.76 ± 6.40) • in phototype I to (-33.63 ± 15.91) • in phototype VI, confirming the inverse correlation between the typological angle and the degree of skin pigmentation. The intra-phototype variability, more pronounced in dark skin, suggests chromatic heterogeneity that should be considered in clinical and technological applications. Likewise, the volumetric fraction of melanosomes (f me ) was estimated using a quadratic relationship of the chromaticity coordinate (L * ) with an RMSE of 0.0016 and a residual difference of 0.11%. This allowed the determination of the total melanin content in µg/mg from f me with a correlation coefficient of ρ = 0.996.
Jimenez et al. (Fri,) studied this question.