2010 TRI/PRINCETON CONFERENCE 91 the image processing (~5–10s). The orientation image is then visualized. Different tools allow statistical analysis in regions of interest (ROI) in the image. The resolution of our imaging system permits to discriminate a single hair fi ber, i.e. one pixel corresponds to approximately 80–100 micron on the hair fi ber plane. This will al- low our simple model to be valid. EXPERIMENTAL VALIDATION OF THE CONCEPT We proceed to two basic experiments to validate the concept of the measurement: Birefringence measurement (extraction of the sinusoidal signal over a region of interest and measurement of the angle of orientation) Evaluation of the angle measurement precision Figure 8. (a) Intensity images in the visible spectrum for tresses of various shades (from left to right: black, dark brown, medium brown, dark brown with red dye, blond, bleached, grey 10%–90%). (b) Corresponding images in the NIR region.
JOURNAL OF COSMETIC SCIENCE 92 Figure 9. Photo of set-up. Figure 10. Signal versus the angle of the polarizer ϕ. BIREFRINGENCE MEASUREMENT We are using two hair tresses (blond and dark). Figure 10 shows the intensity I (a.u.) versus the angle of the polarizer ϕ, in a region of interest where the orientation of the hair is constant, for three orientations of the hair tress = −10°, 0°, and 10°).
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