Generating stochastic dispersed and periodic clustered textures using a composite hybrid screen

Abstract

In electrophotographic printing, a periodic clustered-dot halftone pattern is preferred for a smooth and stable result. In addition, the screen frequency should be high enough to minimize the visibility of the halftone textures and to ensure good detail rendition. However, at these frequencies, the halftone cell may contain too few pixels to provide a sufficient number of distinct gray levels. This will result in contouring and posterization. The traditional solution is to grow the clusters asynchronously within a repeating block of clusters known as a supercell. The growth of each individual cluster is governed by a microscreen. The order in which the clusters grow within the supercell is determined by a macroscreen. Typically, the macroscreen is a recursive pattern due to Bayer. In highlights and shadows, this ordering results in visible artifacts. Replacing the Bayer screen by a stochastic macroscreen eliminates these artifacts, but results in new artifacts. In this paper, we propose a new composite screen architecture that employs multiple microscreens and multiple macroscreens in the highlights and shadows. These screens are jointly designed by using the direct binary search (DBS) algorithm.

Halftone Blending Between Smooth and Detail Screens to Improve Print Quality With Electrophotographic Printers

“…Gradually, the large-size smooth halftone dots are transformed to the small-size detail halftone dots. This digital dot structure still remains in the printed Image [4,2]. Therefore, by the combination of proper screen selection and boundary blending, we can significantly reduce the boundary artifacts.…”

“…We need a more general criterion for selecting the two halftone screens. Figure 4 shows the results for blending according to (2), using a single low frequency halftone pattern, but two different possible high frequency halftone patterns. In Fig.…”

“…We earlier discussed how to compute d from the original input continuous-tone image f (x, y); so we know a and d at pixel location (x, y). If this pixel belongs to a transition region, we choose (a (S) , a (D) ) from the blending LUT, based on the values for a and d, and get the final value g(x, y) from (1) and (2). If this pixel does not belong to a transition region, we do normal object-oriented halftoning at (x, y) based on the object map o(x, y).…”

“…11 to obtain the absorptance values a (S) and a (D) (2 operations) that will be applied to (1) to obtain the smooth and detail halftone PWM values (2 operations). Finally, these values are applied to (2) to yield the final blended halftone (7)-(14) is performed off-line only to determine the contents of the LUTs.…”