Multilevel screen design using direct binary search

Abstract

Screening is an efficient halftoning algorithm that is easy to implement. With multilevel devices, there is a potential to improve the overall image quality by using multilevel screening, which allows us to choose among multiple native tones at each addressable pixel. We propose a methodology for multilevel screen design using direct binary search (DBS). We refer to one period of the screen as a multitone cell. We define a multitone schedule, which for each absorptance level specifies the fraction of each native tone used in the multitone cell. Traditional multitoning uses only one native tone in smooth areas corresponding to absorptance values near the native tones, an approach that introduces contouring artifacts. To reduce contouring, we employ schedules that use more than one native tone at each absorptance level. On the basis of the multitone schedule, multitone patterns are designed level by level by adding native tones under the stacking constraint. At each level the spatial arrangement of the native tones is determined by a modified DBS search. We explore several different multitone schedules that illustrate the image-quality trade-offs in multitone screen design.

Blue-Noise Multitone Dithering

“…26. Here, patches of intensity 236, 19, and 127 are multitoned with DBS as presented in Section III-C2 and with DBS as initially introduced in [33]. The algorithms use the same HVS Fig.…”

“…26. Combination of stacking blue-noise halftone patterns to generate bluenoise multitones and final result compared with multitone DBS as in [33]. model and the same ink concentrations: 90% for the majority pixels and 5% for each one of the other two.…”

“…plots show a multitone generated with DBS for multitoning as in [33]. The pattern looks more uniform but presents clustering of minority pixels (white pixels for and black pixels for .…”

“…For example, the error diffusion algorithm was modified by replacing the binary thresholding by a multilevel quantizer (Gentile et al [34]), correlated error diffusion was applied to channels that represented the available inks (Faheem et al [35]), screening was extended to multitoning using Bayer dither arrays [34] and clustered-dot dither [36]. Iterative algorithms for multitoning have been proposed based on neural networks [37] or as an extension of DBS [33]. The latter is also applied to the design of a multitoning dither array.…”

Multilevel halftoning using multiscale error diffusion

“…Compared with conventional binary halftoning, 1 MH can improve the rendition quality of a continuous-tone image. [2][3][4] In theory, MH can be accomplished by an error diffusion algorithm equipped with a multilevel quantizer. However, when the number of quantization levels is small, typically 3 to 5, undesirable banding artifacts occur, as all signal levels close to an intermediate quantization level are quantized to a single output level, such that gradation reproducibility cannot be maintained.…”