Depending on the needs, different approaches can be used. The most used models, given in order of their increasing complexity, are customised extensions of the Kubelka-Munk model, Discrete Ordinate Radiative Transfer (DORT), and Monte-Carlo techniques. Monte-Carlo simulations allow simulating virtually any physical process. They can use a very detailed description of the paper structure, simulating the light reflection from surfaces, fibres, and filler materials for instance.

 

One drawback of these techniques is that they can be time-consuming. However they allow a full 3-D description of the printed paper structure and simulate the spatial- and angle-resolved light reflection. In addition any kind of light source and detector can be simulated.

 

Innventia has developed a simulation tool, Grace, that enables setting up different Monte Carlo simulation models. Simulated images can then be further processed to estimate print quality attributes with methods such as STFI-Mottle.

 

Mottle simulation from a perfect ideal raster on a coated paper. Structure based simulations help in separating the influence of the paper from the influence of the printed film.		Simulated CIE whiteness for a multi-layer board for layers with diffferent optical properties. The image shows an example of simulated white-top mottle.

Many of the methods available were developed by Innventia and provide unique possibilities for a deeper insight into the optical properties of paper and board. We can also modify and customise models for specific applications.