2010 TRI/PRINCETON CONFERENCE 95 positive charges and begin to repel from the rest of hair. Figure 15 shows the intensity im- age of three bleached hair tress (a) and their corresponding orientation measurements (b). The computation of the angular distributions in the selected regions of interest (ROI) permits to quantify the fl yaway as shown in Figure 16. Subtracting the histogram of the ROI2 to the histogram of the ROI1 gives the angular distribution of the fl yaway. The distribution is mostly homogeneous across the range of angles, which is translated by an offset of the histogram in the ROI2 compared to the ROI1. However, the distribution of the fl yaway shows a little bump around 10–15 deg, which shows that the fl yaway has a greater tendency to repel from the rest of the hair tress at this orientation in the environmental conditions of the measurement. Single fi ber reso- lution measurement with this technique not only permits to easily detect fl yaway hair, but also to add information by giving the orientation of the fl yaway relatively to the rest of the hair tress. Figure 14. Image of a single hair fi ber in the NIR (a) and its corresponding orientation image (b). Figure 15. Intensity image of three bleached hair tresses (a) and their corresponding orientation measurement (b).

JOURNAL OF COSMETIC SCIENCE 96 MEASUREMENT OF DEGREE OF CURL AND STYLE LONGEVITY In Figure 17 below, three bleached hair tresses with different degrees of curl are imaged (a) intensity and (b) orientation. The computation of the histogram (Figure 18) for each hair tress shows different pat- terns according to the degree of curl. As a matter of fact, as the degree of curl increases (from tress 1 to tress 3), the angular distribution becomes wider (standard deviation increases). The computation of the standard deviation of the histograms (parameter W) shows that the higher the degree of curl is, the greater the W is, as shown in Table I. The angular distribution widens as the degree of curl increases to eventually tend towards a fl at distri- bution for a very high degree of curl. Such analysis can allow the evaluation of the style longevity under high humidity condi- tions for example or allow the classifi cation of tresses according to their degree of curl. Figure 16. (a) Selection of two regions of interest for the center part of the hair tress (ROI 1) and the com- plete image (ROI2), histograms in the respective ROIs (b). Figure 17. Intensity image of three bleached hair tresses (a) and the corresponding orientation (b).