Chapter 9 307 and crossed polarized light, are shown in Figure 6. The resulting plot of luminosity versus optical viewing angle (see Figure 7) is utilized to calculate luster. While such an experiment may be carried out with a standard DSLR camera, the most popular commercial luster device utilizes a polarized camera which almost instantaneously takes parallel and crossed polarized images.26 The use of DSLR cameras requires that polarization be accomplished manually. The plot shown in Figure 7 is analogous to one that could be obtained with a goniophotometer. The curve resulting from the image of parallel polarizers is indicated by S for specular reflection. On the other hand, D represents the diffuse reflection plot obtained using crossed polarizers. Often, the width of the peak at one-half its maximum (w 1/2 ) is also calculated. Normally, S and D represent the area under the specular and diffuse reflection curves, respectively, and these values are utilized to calculate a luster parameter. Leading to much discordance, research groups at various institutions employ their own method for determining the boundaries of these two factors. For example, in some cases the diffuse reflection plot is not even utilized for analysis. Instead, a straight line is extrapolated from the two end-points of the specular reflection curve to obtain an estimated diffuse plot (D Reich-Robbins ). This idea was first proposed by Reich and Robbins in goniophotometric studies and later adapted by McMullen and Jachowicz for imaging work.20,24 Lefaudeux et al. proposed deconvolution of the specular Figure 6. Images of a dark brown hair tress mounted on a luster measurement apparatus utilizing (a) parallel and (b) crossed polarized light