Abstract
To evaluate skin color and skin tone exactly, we developed a new instrument, Skin Tone Analyzer (STA), which applys an image-processing system on the polarized images of skin.
The insertion of two polarized filters into the CCD camera in STA made the observation of clear images without interference from the diffuse reflections originating on the surface of the skin. The 20 times magnified images of the skin surface (1×1cm) are resolved into 400×400 points and transfered to a digital computer. To measure the color difference value, calculate the L, a and b values of each point from their respective R, G and B values, using conversion equations determined from the measurement of two hundred pieces of standard color papers with the STA and general spectrophotometric colorimeter (CMS-1200). Then, the color differences determined by STA are indicated as average values of L, a and b values for a finite set of points. Further, their standard deviation values (s. d.) which may represent the degree of skin tone (irregularity in the lavel of skin color) are obtained. In fact, we found that the s. d. of b values (s. d. b) among the three components, L, a and b, reflects appropriately the degree of skin tone caused by delocalization of melanin. Thus we now propose that the s. d. b is a good parameter for the evaluation of skin tone. Moreover, a designated part of images can be analyzed and STA will be a useful tool for the study of pigmentation spots.
Based on the above assumption, we examined the effect of seasons and aging on the skin color and skin tone of the cheek (exposed skin) and the inside of the upper arm (non-exposed skin) in healthy Japanese females (N=62, 19-75y) with STA. From the analyses of skin tone during periodical measurements, the degree of skin tone in the cheek was found to be worse than the arm's. The former becoming worse owing to aging, but the later exhibiting no change. Also the degree of skin tone in the cheek in October (after the summer) was worse than in February (in the winter). In addition, L and b values for the cheek also increased owing to aging, but these values for the arm did not so change.
It is known that daily exposure to ultraviolet rays (UV) can influence colory skin. We now also confirm that UV promotes a change for the worse in the skin tone. Next, we propose to study the effects of UV on localized pigmentation using STA.
