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Model-based Analysis and Design of Color Screen Sets for Clustered-Dot Periodic Halftoning and Design of Monochrome Screens Based on Direct Binary Search for Aperiodic Dispersed-Dot Halftoning
Periodic clustered-dot halftones are widely used in electrophotographic printers due to the relatively poor print stability of this class of printers. It is important to analyze the nature and the causes of perceived fluctuation in order to understand the factors that prevent the high-end digital presses from achieving the same print quality as the commercial offset presses. In order to better approximate the screen sets used for the commercial offset presses, irregular screen sets can be considered. We start by developing a set of candidate screen tile-vectors that best fit the specified screen frequency, screen angle, and printer resolution. We then perform Fourier-based analysis of regular and irregular periodic, clustered-dot halftone textures in order to understand how perceived fluctuation relates to the halftoning technology. After exploring the search for the best single separation geometry, we consider the superposition of multiple periodic clustered-dot halftones, and propose to apply HVS-based model, which assists us in finding the best color assignments to the superimposed halftones. It turned out that the choice of the best color assignments depends on different combinations of colorant absorptance values, hence we propose to apply different color assignments within the image depending on the local color and content of the image. Next, we propose a step-by-step screen design for standard and high resolution periodic irregular clustered-dot halftones. Finally, we presented monochrome DBS-based screen design with overlapping clusters of 2 × 2 or 3 × 3 pixels, which can also be used in electrophotographic printers.