Synopsis

Objective
Hair shine is one of the most desirable attributes for consumers, influencing the overall perception of hair health. The interaction of light with hair is complex, consisting of reflection, absorption and scattering all which contribute to its shine or lustre. The overall visual appearance of hair is a combination of lustre, colour and shape. Instrumental shine measurements commonly involve fixing hair tresses onto a cylinder in an aligned configuration, with lustre calculated based on the reflected specular and diffused light. Whilst these methods yield reproducible and robust measurements of technical shine, they are limited to aligned geometries. Hair shape is a principal factor in shine perception, as fibre alignment and hair curvature influence how light is reflected. To address this, we have developed an integrated image-based instrumental method which presents tresses in an unconstrained geometry and enables the measurement of shine across all hair types, textures and styles.

Method
This work presents the development of an Unconstrained Shine Index (USI), a physics-based optical metric. Spectral polarisation imaging is used to separate reflected light into specular, diffuse, chromatic and intensity components. Normalized reflectance components are combined with hair alignment data to generate a single shine parameter.

Results
Shine evaluations were conducted on different hair types with and without a shine enhancing formulation and styling aids. These datasets were explored to evaluate USI results under varying alignment states and natural configurations. The results showed a strong relationship between fibre alignment and high shine. The optical appearance of the hair was reconstructed from the diffuse, specular, chromatic, and intensity components.

Conclusion
This work presents a new unconstrained shine index measurement approach to evaluate shine across all hair types with relevance for textured and highly curled hair where traditional shine methods are limited.