pigmented colorants: dependence on media and time - Cornell ...

In summary, our implementation provides a powerful tool in visualization. Pro-
vided is a simple method for laying down paint of varying pigment concentrations
to see how they react under different conditions–all of the variables can be modi-
fied in real time. As computer processing improves, more wavelengths can be used
in the lighting computation to better simulate the spectral reflectance. As display
technology improves, the gamut of displayable colors will also expand, improving
the conditions for which the colors are viewed.
7.1.3 Implementation issues
While this model is effective and can be computed in real time, there are some lim-
itations to this theory of pigment modeling [Fis83, CAS + 97]. The model assumes
the paint is homogeneous. In fact, pigment particles tend to clump into aggregates
and often contain inclusions or impurities. Also, the scattering assumptions in the
transport theory were based on uniformly sized spherical particles. This is rarely
the case for pigment particles as they are often of widely varying shapes and sizes.
Further, all colorant layers are immersed in media of the same refractive index.
This assumption is violated at the interface between the air and paint and paint
to substrate. A fairly simple correction term for reflection and refraction at the
paint’s surface has been proposed [JW75] that could be used to increase accuracy.
While reasonably accurate, Kubelka Munk theory is only as good as the mea-
surements behind it. Therefore, for more accurate prediction of color mixtures,
many more mixtures of multiple pigments of varying concentrations are necessary
to obtain better absorption and scattering coefficients.
In our work, only constant volume ratios of pigment-to-media are studied. In
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paint, artists often manipulate the amount of binder and vehicle (as well as the