To control printers so that the mixture of inks results in specific color under defined visual environment requires a
spectral reflectance model that estimates reflectance spectra from nominal dot coverage. The topic of this paper is to
investigate the dependence of the Yule-Nielsen modified spectral Neugebauer (YNSN) model accuracy on ink amount. It
is shown that the performance of the YNSN model strongly depends on the maximum ink amount applied. In a cellular
implementation, this limitation mainly occurs for high coverage prints, which impacts on the optimal cell design.
Effective coverages derived from both Murray-Davis (MD) and YNSN show large ink spreading. As ink-jet printing is a
non-impact printing process, the ink volume deposited per unit area (pixel) is constant, leading to the hypothesis that
isolated ink dots have lower thickness that the full-tone ink film. Measured spectral reflectance curves show similar
trend, which supports the hypothesis. The reduced accuracy of YNSN can thus be explained with the fact that patches
with lower effective coverage have a mean ink thickness very different from that of the full-tone patch. The effect will be
stronger for small dot coverage and large dot gain and could partially explain why the Yule-Nielsen n-factor is different
for different inks. The performance of the YNSN model could be improved with integration of ink thickness variation.
The paper aims to develop a method for multichannel halftoning based on the Direct Binary Search (DBS) algorithm.
We integrate specifics and benefits of multichannel printing into the halftoning method in order to further improve
texture quality of DBS and to create halftoning that would suit for multichannel printing. Originally, multichannel
printing is developed for an extended color gamut, at the same time additional channels can help to improve individual
and combined texture of color halftoning. It does so in a similar manner to the introduction of the light colors (diluted
inks) in printing. Namely, if one observes Red, Green and Blue inks as the light version of the M+Y, C+Y, C+M
combinations, the visibility of the unwanted halftoning textures can be reduced. Analogy can be extent to any number of
ink combinations, or Neugebauer Primaries (NPs) as the alternative building blocks. The extended variability of printing
spatially distributed NPs could provide many practical solution and improvements in color accuracy, image quality, and
could enable spectral printing. This could be done by selection of NPs per dot area location based on the constraint of the
desired reproduction. Replacement with brighter NP at the location could induce a color difference where a tradeoff
between image quality and color accuracy is created. With multichannel enabled DBS haftoning, we are able to reduce
visibility of the textures, to provide better rendering of transitions, especially in mid and dark tones.
Multichannel printer modeling has been an active area of research in the field of spectral printing. The most commonly
used models for characterization of such systems are the spectral Neugebauer (SN) and its extensions. This work
addresses issues that can arise during calibration and testing of the SN model when modelling a 7-colorant printer. Since
most substrates are limited in their capacity to take in large amount of ink, it is not always possible to print all colorant
combinations necessary to determine the Neugebauer primaries (NP). A common solution is to estimate the nonprintable
Neugebauer primaries from the single colorant primaries using the Kubelka-Munk (KM) optical model. In this
work we test whether a better estimate can be obtained using general radiative transfer theory, which better represents
the angular variation of the reflectance from highly absorbing media, and takes surface scattering into account. For this
purpose we use the DORT2002 model. We conclude DORT2002 does not offer significant improvements over KM in
the estimation of the NPs, but a significant improvement is obtained when using a simple surface scattering model. When
the estimated primaries are used as inputs to the SN model instead of measured ones, it is found the SN model performs
the same or better in terms of color difference and spectral error. If the mixed measured and estimated primaries are used
as inputs to the SN model, it performs better than using either measured or estimated.