Halftoning by Rotating Non-Bayer Dispersed Dither Arrays

V. Ostromoukhov, R.D. Hersch

Int. Symposium on Electronic Imaging: Science and Technology, Proc. Conf. Human Vision, Visual Processing and Digital Display VI, SPIE Vol. 2411, 1995,

In a recent contribution, published in the SIGGRAPH'94 Conference Proceedings, the authors proposed a new dither technique for digital halftoning: rotated dispersed-dot dither. It is based on the discrete one-to-one rotation of a Bayer dispersed-dot dither array. Discrete rotation has the effect of rotating and splitting a significant part of the frequency impulses present in Bayer's halftone arrays into many low-amplitude distributed impulses. The halftone patterns produced by the rotated dither method therefore incorporate fewer disturbing artifacts than the horizontal and vertical components present in most of Bayer's halftone patterns. In grayscale wedges produced by rotated dither, texture changes at consecutive gray levels are much smoother than in error diffusion or in Bayer's dispersed-dot dither methods, thereby avoiding contouring effects. This paper explores rotated dispersed dither matrices whose dispersion patterns differ from Bayer's. The paper especially studies the cases of self-similar matrices with self-similarity factors 2 and 3, hexagonal dispersed dither matrices, as well as their combinations. After application of discrete one-to-one rotation, new rotated dispersed dither matrices of improved quality are obtained. Their spectral characteristics are briefly explored. Due to their semi-clustering behavior, some rotated dispersed-dot dither methods show an improved tone reproduction behavior on printers having a significant dot gain, while maintaining the high detail rendition capabilities of dispersed-dot halftoning algorithms.

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