2008 TRI/PRINCETON CONFERENCE 157 Polarization imaging provides the profi le of intensity, specular and diffused light, as well as the corresponding images. These come from a direct measurement of a different phys- ical property of light. Goniophotometric measurements only gives the profi le of the in- tensity of light. Several methods like deconvolution and curve fi tting allow extracting specular and diffused light from goniophotometric measurement. The results obtained are very similar but also show some small difference. For instance, deconvolution or curve fi tting methods usually consider the specular light to be zero outside of the main specular peak. Polarization shows that it is not always the case. Having this physical separation allows better understanding of the effect of treatments. For instance, as specular light is considered to be zero outside of the main peak, a gonio- photometric method will attribute a decrease in the edges of the intensity light distribu- tion to a decrease of diffused light (meaning a darkening of the hair). Polarization meaurement allows saying if it comes from a decrease of the specular light outside of the Figure 4. (a) Sample positioned on the cylinder. (b) Complete angular distribution with a single image. Figure 5. Three images are acquired: an intensity image showing the normal view of the hair, a specular image showing only the refl ections (shine and chroma) and a diffused light image showing the diffused light only.

JOURNAL OF COSMETIC SCIENCE 158 main peak (meaning a reduction of the extreme surface defects that put specular light far from the main peak) or from a decrease of the diffused light (darkening of the hair). Further processing on the specular profi les using RGB information allows separating the shine band from the chroma band (Figure 7). This separation is based on the fact that the shine band is white. This fi nal separation allows complete characterization of the hair visual appearance. It shows that for light blond hair chroma totally dominates shine (Figure 8). In the case of light blond hair, the luster sensation comes mainly from chroma as the shine is negligible. It also shows that some treatment to increase shine overlaps shine and chroma which cause an increse of what is visually considered as the shine band but is actu- ally shine and chroma. It has been considered for a long time that only the fi rst surface refl ection was playing a role in hair luster. However these results as well as other recent research (16) show the Figure 6. Angular profi les computed from the images acquired by averaging along the width of the region of interest (ROI). (a) Specular. (b) Diffused. Figure 7. Extraction of the shine and chroma bands from the specular profi le for a red hair. This separation is based on the fact that the shine band is white while the chroma band is colored.