  Compared to the error diffusion, dot diffusion provides an additional
pixel-level parallelism for digital halftoning. However, even though its
periodic and blocking artifacts had been eased by previous works, it was still
far from satisfactory in terms of the blue noise spectrum perspective. In this
work, we strengthen the relationship among the pixel locations of the same
processing order by an iterative halftoning method, and the results demonstrate
a significant improvement. Moreover, a new approach of deriving the averaged
power spectrum density (APSD) is proposed to avoid the regular sampling of the
well-known Bartlett's procedure which inaccurately presents the halftone
periodicity of certain halftoning techniques with parallelism. As a result, the
proposed dot diffusion is substantially superior to the state-of-the-art
parallel halftoning methods in terms of visual quality and artifact-free
property, and competitive runtime to the theoretical fastest ordered dithering
is offered simultaneously.
