Green-noise digital halftoning

In this paper, we introduce the concept of green noise-the mid-frequency co mponent of white noise-and its advantages over blue noise for digital halft oning. Unlike blue-noise dither patterns, which are composed exclusively of isolated pixels, green-noise dither patterns are composed of pixel-cluster s making them less susceptible to image degradation from nonideal printing artifacts such as dot-gain. Although they are not the only techniques which generate clustered halftones, error-diffusion with output-dependent feedba ck and variations based on filter weight perturbation are shown to be good generators of green noise, thereby allowing for tunable coarseness. Using s tatistics developed for blue noise, we closely examine the spectral content of resulting dither patterns. We introduce two spatial-domain statistics f or analyzing the spatial arrangement of pixels in aperiodic dither patterns because green-noise patterns may be anisotropic, and therefore spectral st atistics based on radial averages may be inappropriate for the study of the se patterns.