FM (Frequency modulation) halftoning (aperiodic and dispersed-dots) is increasingly popular with traditional analog offset lithographic printing. There is a desire from customers in the commercial market to use this capability with high-end digital presses based on electrophotographic printing (EP) technologies. However, the inherent instability of the EP process challenges the achievement of satisfactory print quality with dispersed-dot, aperiodic halftoning. The direct binary search (DBS) algorithm is widely considered to represent the gold standard of dispersed-dot, aperiodic halftone image quality. In this paper, we continue our previous efforts to adapt DBS from dispersed-dots to clustered-dots to use with the Indigo liquid EP printing technology; we present a new screen design algorithm for aperiodic, clustered-dot halftoning based on Direct Bineary Search. Our screen design has a very good detail rendering capability and very stable halftone frequency overall. The halftone texture after applying screen is even better than directly using our previous work, clustered-dot halftoning.
In this paper, we propose a novel error diffusion halftoning algorithm for the conversion of cyan, magenta and yellow (CMY) ink amounts to a multi-bit halftone image. We adopt the idea of allowing multiple drops of colorants in order to achieve print results with better saturation, which is implemented by modifying the classic Floyd-Steinberg error diffusion algorithm. For better halftone texture and more efficient use of colorants, we add a dot-off-dot feature to the classic Floyd-Steinberg error diffusion. Blending-in the original input image with its DBS screened multilevel halftone image as a preprocessing step to dot-off-dot error diffusion is proposed as a measure to reduce halftone artifacts. Digitally simulated halftone images will be presented to illustrate the better halftone texture that can be achieved by applying the proposed algorithm.