A Method to Separate Ink/Paper Interaction Effects from Halftone Effects in the Study of Inkjet Prints

Abstract

The development of analytical models that predict measured reflectance spectra of halftoned printing has progressed for over half a century. Most of the published work has focused on the contribution of the halftone pattern to the measured reflectance, either through the development of the halftoning algorithm itself, or through the optical and physical dot gain resulting from the process. However, the non-ideality of the ink/paper interaction is also a key contributor to the measured reflectance. This non-ideality is partially addressed by perturbations to existing models, such as the cellular Neugebauer equations, or more directly with Kubelka-Munk descriptions. These effects can be especially large in inkjet printing, as the round ink dots require overlap and therefore variable ink laydowns across even a single-color nominally constant density patch, something that is not true of graphic arts printing. This work illustrates the contribution of the ink/paper interactions to the measured reflectance, and describes a workable method to separate the ink/paper effects from the halftone effects, to allow the direct study of the ink/paper interaction. The inks are applied in continuous layers using hand-coating rollers, and the ink laydowns are quantified by weighing under carefully controlled conditions. Finally, we demonstrate with reflectance measurements that the half-tone effects are removed, and the remaining unusual spectral features reproduce those seen in inkjet prints.