Image Analysis Tools to Quantify Visual Properties of Hair Fiber Assemblies 306 light and detector. Several parameters are determined from the goniophotometric curves and include the area under the specular (S) and diffuse (D) reflection curves as well as peak width at half of its maximum (w 1/2 ). Together, these values are utilized in empirical equations for the calculation of hair luster (discussed in a subsequent section in this chapter). Image analysis-based measurement techniques: Many luster evaluation apparatuses are based on digital imaging technology. Using a macro lens, a photograph is taken of a hair tress wrapped around a cylinder, or sometimes of a full head, and image analysis measurements provide light intensity as a function of distance, or more appropriately viewing angle. A diagram is provided in Figure 5 for a typical image analysis-based luster evaluation system. As many as several hair tresses are wrapped around a cylindrical mounting stage allowing illumination of the tress and resulting in a visible specular reflection band. A DSLR (digital single-lens reflex) camera is used to collect the data and image analysis is carried out on the resulting photographs. Typical photographs, obtained with parallel Figure 5. Diagram of a typical imaging system employed for luster measurements