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The aspect of manufactured objects gives rise to increasing attention in the industrial world. Because of the concurrence, aspect becomes an essential commercial criteria like technical performances or cost. To fulfill the necessary aspect control, industry tries to replace traditional visual control by systematic procedures and dedicated measurement apparatus. Our work deals with that domain of metrology. This paper describes a brightness measurement method working on rough surfaces with a skin profile (or waviness) from 50 to 500 micrometers deep. In such a case, the skin profile visibility is not due to height distribution of the surface and depth sensitivity of eye, but it is due to the amount of light that each point of the surface scatters toward the observer eye. Our eye discerns the skin profile through the contrast level of the image it catches. So the brightness (or the scattering properties) measurement of surfaces is essential for evaluating the aspect quality of product surfaces. Our method predicts the scattering properties of surfaces by the scattering theory developed by Beckmann and Spizzichino and from roughness measurement. Confocal microscopy is used for profiling surfaces within two different roughness ranges. The skin profile is measured with low magnification objectives and that data is used to compute the local slope of the surface. High magnification objectives allow us to measure microroughness superimposed on the local shape. After high pass filtering, the statistical roughness parameters are used to compute the reflection coefficient of the material from the Beckmann and Spizzichino model. Then the contrast of the image that an observer catches under any illumination and observation configurations is computed from the knowledge of both the skin profile and the brightness.
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