Turning blue sound into blue noise [image halftoning]

Because binary representation of images fit VLSI constraints well, the bilevel rendition of continuous tone pictures, referred to as the halftoning problem, is likely to play an important role in robot vision soon. In the present work, the author explains (in 1-D) and puts in evidence (in 2-D) an important limitation of the most familiar high-quality technique, i.e., error diffusion. By extending earlier work of B.M. Gray (1989), it is shown that the full propagation of the error on uniform images may generate a significant amount of low-frequency spectral energy, which corresponds to the appearance of undesirable textures and artifacts on the halftoned image. Disagreeing with results presented by R.A. Ulichney (1988), the author concludes that error diffusion is a bad `blue noise´ generator. Relaxing the DC constraint through an optimization approach solves the difficulty