Fundamental Characteristics of Halftone Textures: Blue-Noise and Green-Noise

In this paper, we review the spatial and spectral characteristics of blue and greennoise halftoning models. In the case of blue-noise, dispersed-dot dither patterns are constructed by isolating minority pixels as homogeneously as possible and by doing so, a pattern composed exclusively of high frequency spectral components is produced. Blue-noise halftoning is preferred for display devices that can accommodate isolated dots such as various video displays and some print technologies such as ink-jet. For print marking engines that cannot support isolated pixels dispersed-dot halftoning is inappropriate. For such cases, clustered-dot halftoning is used to avoid dot-gain instability. Green-noise halftones are clustered-dot blue noise patterns. Such patterns enjoy the blue-noise properties of homogeneity and lack of low frequency texture, but have clusters of minority pixels on blue-noise centers. Green noise is composed exclusively of mid-frequency spectral components. In addition to the basic spatial and spectral characteristics of the halftoning models, this paper also reviews some of the earlier work done to improve error diffusion as a noise generator. Also reviewed are processes to generate threshold arrays to achieve blue noise and green noise with the computationally efficient process of ordered dither.