Chapter 9 319 distribution appears demonstrating that fibers are beginning to exhibit a repeating pattern. In the fully relaxed hair, the distribution becomes even more narrow and intense, indicating fiber alignment along a principle axis. Since the Fourier transform images are symmetrical, only half of the image needs to be quantified. A 180-degree arc is drawn circumferentially from one axis of the Fourier transform image to another, allowing us to measure light intensity (luminosity) along the arc. From the plot of luminosity versus arc angle, we observe a peak corresponding to fiber alignment distribution. In the case of untreated African hair, the peak is very wide (177 degrees) however, the partially and fully relaxed hair samples had peak widths of 35 degrees and 18 degrees, respectively. The utility of two-dimensional Fourier transform is demonstrated for relaxer treatments of African hair. It may also be applied to quantify other chemical treatments of hair, or even to characterize hair styling configurations such as brading. In addition, we utilize this method in the analysis of eyelash treatments, which is discussed in a section below. Hair Curliness It is often desirable to measure the degree of hair curliness to evaluate the efficacy of cosmetic treatments, or just to investigate how curly is a given hair type. Using a method proposed by Loussouarn et al., the length of the hair is measured at rest then fully stretched to calculate the curl index (CI):50 Eq. 10 In the original method, fiber measurements are conducted without the aid of image analysis or imaging equipment. In this study, we obtain images of hair with a flatbed scanner, which is calibrated with a measuring scale. Images of three hair types, African, artificially curled, and frizzy, are provided in Figure 11. Representative fibers are shown in the relaxed and stretched state. Applying equation 8 to the distance measurements yields