Roughness measurements are of main importance in characterizing the optical properties of papers and prints. However, there is a lack of knowledge concerning the surface size and the spacing of the measures to be optically representative of the surface structure. Paper is a multiscale medium, and the roughness parameters extracted from the three-dimensional (3D) surface mapping depend on both the size and the step of discretization. Ray tracing, based on optical geometry, could be a tool to model the light reflection on a paper surface. Ray-tracer software was therefore developed. A new optical device was used to measure paper surface topographies at various scales. Ray tracing simulations were then performed on the 3D mapping and compared to the scattering indicatrix obtained with a classical goniometer. Hence it was possible to identify a magnification for various types of paper grades that is optically representative of the specular gloss.
(c) 2008 Optical Society of America