AUTHOR=Blaksley Carl , Udodaira Kumiko , Nicolas Alexandre , Casolino Marco 

TITLE=A new method for the evaluation of makeup coverage using hyperspectral imaging

JOURNAL=Frontiers in Chemistry

VOLUME=12

YEAR=2024

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2024.1400796

DOI=10.3389/fchem.2024.1400796

ISSN=2296-2646

ABSTRACT=<sec><title>Introduction</title><p>The <italic>coverage</italic> 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 begun exploring new parameters and analysis methods made available by 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.</p></sec><sec><title>Methods</title><p>As a starting point to unravelling this complex topic, we define a homogeneity factor <inline-formula id="inf1"><mml:math id="m1" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> 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 <inline-formula id="inf2"><mml:math id="m2" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>β</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> which indicates the degree of spectral change after product application. To test these new parameters and the overall analysis method, we applied them to the HSI validation dataset which contains data for three makeup foundation products of different coverage levels applied to 9 models.</p></sec><sec><title>Results</title><p>We find that <inline-formula id="inf3"><mml:math id="m3" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> correlates with the sensory ranking of coverage. Similarly, the parameter <inline-formula id="inf4"><mml:math id="m4" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>β</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> 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 <inline-formula id="inf5"><mml:math id="m5" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> and <inline-formula id="inf6"><mml:math id="m6" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>β</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">S</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula>.</p></sec><sec><title>Discussion</title><p>Nevertheless, the homogeneity factor <inline-formula id="inf7"><mml:math id="m7" xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mrow><mml:mi>α</mml:mi></mml:mrow><mml:mrow><mml:mi mathvariant="normal">H</mml:mi><mml:mi mathvariant="normal">F</mml:mi></mml:mrow></mml:msub></mml:math></inline-formula> 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.</p></sec>