Skin translucency: what is it and how is it measured?

Objective: Translucency is the most nebulous attribute that describes ideal skin appearance. Physics would define an object as translucent if light can partially pass through it. However, skin translucency is not only about light passing through the skin. P&G research shows that the perception of skin translucency is a holistic term that involves the integration of skin color, glow and texture. I set out to develop new methods to simultaneously measure the integration of these parameters and develop a technical model for translucency. Methods: A panel of 30 judges visually evaluated facial images of 32 female subjects to determine translucent skin and dull skin clinically. The images were captured using dual-polarized imaging system. It captures facial images including and excluding specular components simultaneously at RGB color channels. Specular rate defined from the specular and non-specular images was calculated as a numerical index for skin translucency. Relevancy of specular rate to visual translucency was examined statistically. Tri-ring spectrophotometer which is designed to measure internal skin color at different three depths was used to investigate internal colorimetric structure of translucent skin and dull skin for technical modeling. Results: Specular rate mean and standard deviation distinguished translucent skin from dull skin with statistical significance. Translucent skin has lower mean and standard deviation at blue and green channel while the mean of red channel was greater than dull skin. The upper layers of translucent skin is less-colored than dull skin. The deeper layers of translucent skin are, on the contrary, more-colored than dull skin. Conclusion: The sensorial perception of skin translucency was successfully translated into numerical descriptions using dual-polarized imaging system. Translucent skin is structured in multi-layers having larger color gradation from the surface to the deeper layers. Dull skin has rather mono-layered or uniformly colored structure from the surface to the deeper layers. Introduction Translucent skin is one of ideal skin appearances that look radiant, fair, smooth and even younger. The appearance is originated in the physics occurred across multi-layered skin structure that involves transmittance, reflectance, absorbance and scattering. However, perception of translucent skin includes psychological elements on top of the physics. A visual evaluation study conducted by P&G showed significant correlation between translucent skin appearance and glow (r = 0.932), skin fairness (r = 0.929) and fine texture (r = 0.939). How can we evaluate such a perceptional translucency with objective measurement? Human eyes are not directly sensing the physical transmittance of the light that passes through the skin layers but recognize it as tone, glow and texture. The method for perceptional skin