Optimizing HANS Color Separation: Meet the CMY Metamers

HANS – the Neugebauer Primary based color separation and halftoning print control approach – was presented in broad terms at CIC18. The present paper provides an in–depth look at how HANS color separation can be optimized, what level of variety it provides access to and how it can be used for direct optimization of print attributes. The results show that even in the case of having only three colorants – CMY, where current approaches lead to unique solutions, HANS provides significant metamer sets that lead to variety in print attributes such as the 12.7% ink use range show in the results. Introduction Print has many uses, each of which has different requirements in terms of print attributes. Professional photographers tend to focus on image quality, color accuracy and color gamut while print service providers pay close attention to cost and throughput. Architects and engineers care more about line and small text quality for their drawings, while looking for pleasing appearance in prints made of rendered work. The level at which each of a print’s attributes is achieved then depends on the materials used (inks, toners, substrates, varnishes, etc.), on the imaging technology and also on the color separation and halftoning algorithms used. Direct optimization of print attributes and their explicit trading–off is highly desirable, since color resources need to be tuned to individual substrate types and since a single printer model is typically aimed at more than one target use case. Having to tune resources by hand becomes costly and unreliable and also has to deal with the challenges of transitioning between individually chosen colorant combinations (Morovic, 2007). A solution to this problem is the Halftone Area Neugebauer Separation (HANS) approach presented at CIC18 (Morovic et al., 2010), which both gives access to a larger set of printable halftone patterns and allows for explicit optimization of print attributes. While the HANS approach was sketched out previously (Morovic et al., 2011), details of its color separation optimization will first be presented here. A brief summary of HANS will be followed by a detailed exposition of its optimization framework and the paper will conclude with results for the simple case of a printer with CMY inks and a bi–level halftoning mechanism.