Infoscience

Thesis

Color Reproduction with Juxtaposed Halftoning

Recently, non-standard inks have begun to make their way into the world of printing. Non-standard inks are printing materials which exhibit unusual effects such as angular color dependence, texture, or fluorescence. They are made of special-effect pigments that play an increasingly important role in the paint, plastic, and cosmetic industries. In the printing industry, due to the challenges they pose, they have restricted applications. A long-held assumption in classic printing is the transparency of standard inks. This simplifies the printing process in which different layers of halftone patterns can be laid out on top of each other without much caution about their spatial interaction. However, many non-standard inks either are not transparent or counteract each other¿s effect while overprinting. Currently, these inks are used for different purposes mainly as single-ink fulltones or halftones. Non-standard multi-ink halftones could however be used together, or in combination with classic inks, to open new design spaces. The solution to the problem of opaque-ink halftoning is fairly intuitive. We can place different inks next to each other to prevent them from overlapping. There is therefore a need for a well-executed, scalable juxtaposed halftoning algorithm. In this dissertation, we propose a new juxtaposed color-halftoning method based on discrete lines. As many inks as desired can be placed within a single screen-element. Furthermore, we introduce discrete-line juxtaposed superscreens in one and two dimensions. Like classic superscreen, discrete-line juxtaposed superscreens offer a larger number of tones without decreasing the screen frequency of halftone dots. Moreover, superscreens can eliminate or reduce the automoiré¿ an artifact that is due to the interaction of the halftone dots and the device grid. Juxtaposed halftoning, however, introduces new aspects to color reproduction. It partially invalidates current assumptions about the color-reproduction workflow. For example, many of the existing color-prediction models rely on the independent superposition of different ink layers. We cannot rely on this paradigm because juxtaposed halftones prevent the colorants from being superposed. We propose the application of the two-by-two dot-centering model for the color prediction of juxtaposed halftones. We introduce an enhancement to this model by proposing a solution that significantly reduces the number of required calibration pixel-tiles with a negligible loss in prediction accuracy. In order to put the developed method into practice, we study the creation of metallic-ink prints whose contributing colorants are made of metallic inks. We study the application of the Yule-Nielsen spectral Neugebauer model on color prediction of metallic-ink halftones at multiple illumination and observation angles. We study the interaction of light and the metallic halftones and explain the differences in model accuracy and parameters at different geometries. As we do not superpose the inks, we need more inks than in a traditional printing system. This introduces new challenges especially for backward characterization of metallic-ink prints. The problem is similar to n-color separation. We therefore describe the problem of n-color separation in the context of juxtaposed halftoning. We compare different print characteristics obtained different color-separation formulations.

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