Chapter 9 311 exposure settings, ISO values, white balance, and image type captured (e.g. RAW, JPEG, TIF, GIF, etc.). Hair with varying degrees of geometry: Most of the experimental techniques used to determine luster rely on measurements of straight hair. Of equal importance is the luster of hair fiber assemblies containing geometries other than straight alignment, such as frizzy, curly, very curly, extremely curly (e.g. African), and wavy hair. Analysis of luster for these hair types is not feasible using traditional methodologies. In a previous publication, the practicality of image analysis in the determination of luster for frizzy, curly, very curly, and African hair was demonstrated.25 In this account, we illustrate the effect of treatment with a styling gel on frizzy hair. Prior to treatment, the frizzy hair contains multiple specular reflection sites throughout the hair fiber assembly due to its geometric arrangement. As shown in Figure 8, treatment with the styling gel aligns the fibers and reveals the underlying curvature of the hair fiber assembly. Alternating convex and concave regions along the tress result in intense specular reflection bands that are adjacent to dark diffuse regions of well-aligned hair fibers. Such a treatment reduces the number of scattering centers in the fiber assembly and provides a clear dividing line between specular and diffuse reflection. Measurement of luminosity along the fiber axis provides plots analogous to the specular curves shown in Figure 7. The untreated frizzy hair Figure 8. Images of (a) untreated frizzy-curly hair and (b) the same hair after treatment with a commercial hair styling gel. Treatment reduces frizz and exposes the natural underlying curvature of hair.