Scattering from Printed Paper Surfaces

The primary function of printed paper is to visually communicate information and its quality depends on how it scatters light. Printed paper is ultimately assessed subjectively when it is seen and experienced by humans. The Visual Interfaces group at Acreo is developing a model for print quality based on the three-dimensional structure of printed paper and the sensitivity of the human visual system. Our goal is to virtually assess the quality rating of simulated printed paper samples.
Surface scattering from printed paper surfaces is of particular interest since it predominantly affects the angular dependence of the reflected light. Paper surfaces are rough, non-isotropic, and often show structural variations ranging from a few micrometers to a few centimetres. Taking this into account is not trivial.
Acreo¿s Grace model is a Monte-Carlo simulation program for calculating light scattering from printed paper. It describes paper as a three-dimensional structure including rough surfaces and a statistical description of the paper components such as fibres or fillers. There are several ways to describe surface topography, either geometrically, statically, or by means of modelling. Today Grace uses topographical data obtained from confocal laser scanning microscopy (CLSM) and microroughness measurements obtained from atomic force microscopy (AFM). Surface scattering is treated as a combination of geometrical optics and diffuse scattering due to microroughness. The model shows good agreement with experimental data such as angle-resolved scattering (ARS) measurements and gloss variation measurements (reflection uniformity) over 1mm2 areas. There is a need for simulating larger samples, i.e. 5×5 cm2, whose print quality will be assessed by a panel of judges. However it is almost impossible to measure such large areas with high resolution and a huge amount of memory and computational time would be required to simulate these structures with the current model. Therefore a new surface description combining statistics, topographical and microroughness data is needed.

Goal
The objective is to develop a model of the paper surface based on a statistical distribution of surface properties. It should be feasible to generate 5×5 cm2 paper-like surfaces. The performance will then be compared to the current surface model implemented in Grace.

Activities
- Project background and literature study
- Look for algorithms to be used for distributing surface parameters (normal, roughness...)
- Implement a solution
- Evaluate solution, test against current model
- Documentation and report


Background in physics with interest in optics, electromagnetism and programming (Matlab, C++) is needed for this project.