Topography and reflectance analysis of paper surfaces using a photometric stereo method

This paper describes a fast photometric stereo method, useful for the deter mination of surface-topography and reflectance. First we show how the irrad iance in two images of a surface, illuminated from the left and right, resp ectively, can be used to determine the inclination of the surface elements. This requires a model for the light scattering properties of the surface. The model used divides the scattered light into a bulk-scattered, Lambertia n part and a surface-scattered, specular part. The specular part is elimina ted with the help of crossed polarizers. The inclinations are integrated to give a surface height function with the help of a Wiener filter, which sup presses frequencies with an expected poor signal-to-noise ratio. Profiles m easured with this method show good agreement with profiles obtained both wi th optical and mechanical scanning methods. The standard deviation between surface height measured with the different methods was about 1 mu m. The ab ility of this method to study reflectance and topography at the same time m akes it suitable for studies of the coupling between print result and surfa ce topography. As an example, a gravure-printed paper surface with missing dots has been studied. It was found that missing dots occur at depressions, or pores, in the surface. (C) 2000 Society of Photo-Optical Instrumentatio n Engineers. [S0091-3286(00)00109-4].