Average surface roughness evaluation using 3-source photometric stereo technique

Abstract

Copyright © The Authors and EDP Sciences, 2016. This paper presents a technique for measuring surface roughness (Ra), using photometric stereo method. The method utilizes three or more images of the measured surface from the same viewpoint, taken sequentially under different illumination conditions. The scenes captured by the camera were reconstructed by the least square method to obtain surface normal from surface topography. Three-dimensional surface textural patterns were recovered from those surface normal. The system was validated with five standard surface roughness specimens. The Ra calculated from the recovered surface was compared with the values measured from contacting roughness measurement (stylus instrument). The best coefficient of the slant angles can also be determined through the linear regression. The experimental results indicate that the technique can be applied to well recover standard surface roughness.