Carl J. Blaksley ^1* Kumiko Udodaira ¹ Alexandre Nicolas ¹ Marco Casolino ^2,3,4

• ¹ L’Oréal Research & Innovation, Kawasaki, Japan
• ² RIKEN, Saitama, Saitama, Japan
• ³ National Institute of Nuclear Physics of Roma Tor Vergata, Roma, Italy
• ⁴ Department of Physics, University of Rome Tor Vergata, Roma, Lazio, Italy

The coverage of a makeup foundation is a perceived attribute which is not captured by opacity or any other single optical property. As previous instrumental measurements do not allow us to consistently compare one product to another, we have worked on new analysis methods employing hyperspectral imaging. Presumably, the coverage of makeup comes from the change in color, homogeneity, and evenness over the face after application, and the ability of the product to hide spots and other blemishes. As a starting point to unravelling this topic, we define a homogeneity factor α HF which measures the change in the homogeneity of the spectra using the distribution of spectral angles in the face. We likewise define a spectral shift factor β SF which indicates the degree of spectral change after product application. To test these new parameters and the overall analysis method, we applied them to a dataset containing hyperspectral images of three makeup foundation products of different coverage levels applied to 9 models, and find that α HF correlates with the sensory ranking of coverage. Similarly, the parameter β SF correlates with the visible color change induced by the product, and we can map the three products into distinct categories based on their effect on α HF and β SF . Nevertheless, the homogeneity factor α HF does not fully describe coverage, and in the variability in the product effect from model to model we find evidence that we must also account for the relative color difference between the model's skin tone and the product shade among other factors.