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.

The hybrid screen: improving the breed

“…This is known to have a maze-like artifact in the bilevel output case. 3,4 The other one has a 2 × 2 core, so the dispersed-dot pattern is achieved by both the DBS macrocell growing sequence and the randomization of the microcell growing sequence of the first four dots in each microcell, which is also chosen via a DBS-like algorithm.…”

“…Even if we adopt a carefully designed macrocell growing sequence, e.g, the sequence that reflects blue noise characteristics, a maze-like artifact still remains if every microcell follows the same growing sequence and the first dot placement is the same for all microcells. 3,4 This rigid structure does not allow enough freedom to make the frequency spectrum of the screen similar to that of blue noise in highlights.…”

“…3,4 In the hybrid screen, a small region in each microcell is defined as a core. Inside the core, the original microcell growing sequence is ignored and the sequence can be randomized.…”

Halftone blending between smooth and detail screens to improve print quality with electrophotographic printers

“…First in (a), the screens are selected arbitrarily. The smooth part is (2,5), (5, −3); and the detail part is (4, 0), (0, 4). They are not matched according to the screen condition described in Sec.…”