Green noise digital halftoning

Digital color halftoning with generalized error diffusion and multichannel green-noise masks

“…The parameter is the cluster radius and is related to as (5) where is the area covered by a circle with radius . Lau et al [2] note the is most apparent in when the variation in cluster size is small as increasing the variation leads to a "whitened" dither pattern where the peaks and valleys of become blurred. The term "green" refers to the resulting patterns' predominantly mid-frequency spectral components with the blue-noise model a limiting case ( ).…”

“…point process, the statistical properties of are invariant to rotation, and therefore, for an isotropic process is written as and is referred to as the pair correlation. is explicitly defined as (2) the ratio of the expected number of minority pixels located in the ring (Fig. 1) under the condition that is a minority pixel to the unconditional expected number of minority pixels located in .…”

“…Point process statistics have a long history in stochastic geometry [11]- [13] and were recently introduced to digital halftoning by Lau et al [2] for the study of periodic dither patterns. In this framework, is a stochastic model governing the location of points in .…”

“…Typically, FM halftones are produced by the process of error diffusion which creates a stochastic arrangement of dots. Besides avoiding moiré, FM halftoning, by isolating minority pixels, maximizes the spatial resolution of the printed image relative to the printer [2], but this distribution also maximizes the perimeter-to-area ratio of printed dots [3]-making FM halftones more susceptible to printer distortions such as dot-gain, the increase in size of a printed dot. Whether a function of the printing process (mechanical dot-gain) or of the optical properties of the paper (optical dot-gain), dot-gain causes the printed halftone to appear darker than the original ratio of white-to-black pixels [4].…”

“…Studied by Lau et al [2], Levien's technique creates patterns described in terms of their spectral content as green-noise-containing no low or high frequency spectral components. This green-noise model is presented in accordance with Ulichney's [6] blue-noise model which describes the spectral characteristics of the ideal error-diffused halftone patterns as having no low-frequency content.…”