24 February 2014 Lateral light propagation and angular variation of the reflectance of paper
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The appearance of translucent materials is strongly affected by bulk (or sub surface) scattering. For paper and carton board, lateral light propagation and angle-resolved reflection have been studied extensively but treated separately. The present work aims at modelling the BSSRDF of turbid media in order to study the angular variation of the reflectance as function of the lateral propagation within the medium. Monte Carlo simulations of the spatial- and angle resolved reflectance of turbid media are performed for different scattering and absorption coefficients, phase functions and surface topographies representative for uncoated paper grades. The angle-resolved radiance factor of turbid media is found to be function of the lateral light propagation within the substrate and both the reflected radiance factor and the fluorescence emission are found to be clearly non- Lambertian, although the latter clearly depends on the light absorption at the excitation wavelength. It is also suggested that the modelling of uncoated paper should not include surface scattering. The findings impact on the appearance of turbid media at different angles and make measurements of the lateral light propagation dependent on the instrument geometry.
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Ludovic Gustafsson Coppel, Ludovic Gustafsson Coppel, "Lateral light propagation and angular variation of the reflectance of paper", Proc. SPIE 9018, Measuring, Modeling, and Reproducing Material Appearance, 90180L (24 February 2014); doi: 10.1117/12.2038260; https://doi.org/10.1117/12.2038260


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