Deducing ink-transmittance spectra from reflectance and transmittance measurements of prints

M. Hébert and R.D. Hersch

IS&T/SPIE Electronic Imaging Symposium, Color Imaging XII: Processing, Hardcopy and Applications, SPIE Vol. 6493, pp. 649314-1-13

The color of prints is mainly determined by the light absorption of the inks deposited on top of paper. In order to predict the reflectance spectrum of prints, we use a spectral prediction model in which each ink is characterized by its spectral transmittance. In the present paper, we consider two classical reflectance prediction models: the Clapper-Yule model and the Williams-Clapper model. They rely on a same description of multiple reflection-transmission of light, but use a different description of the attenuation of light by the inks. In the Clapper-Yule model (non-orientational ink attenuation), the orientation of light traversing the ink is not taken into account. In the Williams-Clapper model, it is taken into account (orientational ink attenuation). In order to determine experimentally which of these two models is the more suitable for a given type of print, we propose a method using the reflectance and the transmittance of prints. We introduce a bimodal model, enabling spectral reflectance and transmittance predictions. Depending whether the direction of light into the ink is taken into account, we obtain a non-orientational bimodal model or an orientational bimodal model. Using these two models, we deduce the ink transmittance spectrum from various reflectance and transmittance measurements performed on a same print, and compare the different deduced spectra. The model which is the most adapted to the considered print is the one where the deduced spectra best match each other.

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