Color-difference formula for evaluating color pairs with no separation: ΔENS.

All color-difference formulas are developed to evaluate color differences for pairs of stimuli with hairline separation. In printing applications, however, color differences are frequently judged between a pair of samples with no separation (NS) because they are printed adjacently on the same piece of paper. A new formula, ΔENS, has been developed for pairs of stimuli with NS. An experiment was conducted to investigate the effect of different color-difference magnitudes using sample pairs with NS. 1012 printed pairs with NS were prepared around 11 CIE recommended color centers. The pairs, representing four color-difference magnitudes of 1, 2, 4, and 8 CIELAB units were visually evaluated by a panel of 19 observers using the gray-scale method. Comparison of the present data based on pairs with NS, and previously generated data using pairs with hairline separation, showed a clear separation effect. A new color-difference equation for the NS viewing condition (ΔENS) is proposed by modifying the CIEDE2000 formula. The separation effect can be well described by the new formula. For a sample pair with NS, when the CIEDE2000 color difference is less than 9.1, a larger color difference leads to a larger lightness difference, but has no effect on the chromatic difference. When the CIEDE2000 color difference is greater than 9.1, the effect is the opposite. The new formula is recommended for future research to evaluate its performance in appropriate applications.

Direct Pattern Control Halftoning of Neugebauer Primaries.

Halftoning is a key stage of any printing image processing pipeline. With colorant-channel approaches, a key challenge for matrix-based halftoning is the co-optimization of the matrices used for individual colorants, which becomes increasingly complex and over-constrained as the number of colorants increases. Both choices of screen angles (in clustered-dot cases) or structures, and control over how individual matrices relate to each other and result in over-versus side-by-side printing of the colorants, impose challenging restrictions. The solution presented in this paper relies on the benefits of a halftone area Neugebauer separation pipeline, where local Neugebauer Primary use is specified at each pixel and where halftoning can be performed using a single matrix, regardless of the number of colorants. The provably complete plane dependence of the resulting halftones will be presented among the solution's benefits.

Large color gamut displays with diffraction gratings.

The ability to display a broad variety of colors has great benefits not only in the context of entertainment but also as a means to streamline design in prototyping and manufacturing processes. Displays that use RGB filters or backlights cannot span all colors that occur in nature. To improve the accuracy of color reproduction, there have been attempts to include additional color primaries in displays. Existing solutions, however, have an impact on cost, scalability, and spatial resolution and are predominantly applicable to projection systems. We propose an approach based on combining diffraction grating extractors and the HANS imaging pipeline initially developed for printing. This combination offers unprecedented potential to attain large color gamuts with the same backlights commercially used today.

HANS: controlling ink-jet print attributes via Neugebauer primary area coverages.

Ink-jet print attributes such as color gamut, grain, and cost are consequences of the materials and printing technology used and of choices made during color management, color separation, and halftoning operation. Traditionally, color separation determines what amounts of the available inks to use for each reproducible color, and halftoning deals with the spatial distribution of inks that also results in the nature of their overprinting. However, using an ink space as a means of communication between color separation and halftoning gives access only to some of the printed patterns that a printing system is capable of and, therefore, only to a reduced range of print attributes. Here, a method, i.e., Halftone Area Neugebauer Separation, is proposed to gain access to all possible printable patterns by specifying relative area coverages of a printing system's Neugebauer primaries instead of only ink amounts. This results in delivering prints with more optimal attributes (e.g., using less ink and giving rise to a larger color gamut) than is possible using current methods.

Sampling optimization for printer characterization by greedy search.

Printer color characterization, e.g., in the form of an ICC output profile or other proprietary mechanism linking printer RGB/CMYK inputs to resulting colorimetry, is fundamental to a printing system delivering output that is acceptable to its recipients. Due to the inherently nonlinear and complex relationship between a printing system's inputs and the resulting color output, color characterization typically requires a large sample of printer inputs (e.g., RGB/CMYK) and corresponding color measurements of printed output. Simple sampling techniques here lead to inefficiency and a low return for increases in sampling density. While effective solutions have been proposed to this problem very recently, they either do not exploit the full possibilities of the 3-D/4-D space being sampled or they make assumptions about the underlying relationship being sampled . The approach presented here does not make assumptions beyond those inherent in the subsequent tessellation and interpolation applied to the resulting samples. Instead, the tradeoff here is the great computational cost of the initial optimization, which, however, only needs to be performed during the printing system's engineering and is transparent to its end users. Results show a significant reduction in the number of samples needed to match a given level of color accuracy.