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The evaluation of skin surface contours can be carried out by various techniques, including the use of a stylus profilometer, a laserprofilometer and a conventional optical profilometer (COP). But these methods have some drawbacks because their data are basically obtained from two-dimensional algorithms. So a new technique has been developed based on a new concept: a stereo image processing technique which is considered in this paper. Since a pair of stereo images contains depth information, the 'disparity', or the difference between the left and right images, enables the production of three-dimensional coordinates. This study was performed to evaluate the change of skin surface contours according to the ageing process. The stereo image optical topometer (SOT) is a new instrument used for the three-dimensional evaluation of skin surface contours. Thus. five new parameters have to be developed, such as mean surface roughness (S(a)), mean depth of roughness (S(z)), three-dimensional length (S(L)), three-dimensional area (S(A)), and three-dimensional volume (S(V)). S(a), S(L) and S(A) have shown a statistically significant increase in the seventies age group. S(z) has also shown a significant increase in the twenties and over-sixties age groups. The coefficient variation of the height of the skin surface using a COP varies between 14.76 and 6.57, but that using a SOT is between 2.18 and 2.69, according to age variation. In conclusion, the SOT system is a more reliable and useful method for evaluating skin surface contours than the COP system. Among the three-dimensional parameters which were made in this study, S(A), S(L) and S(a) seem to be useful as reliable parameters for evaluating skin surface contours in the ageing process.

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