Digital halftoning is essential to print or display a continuous tone with binary devices. Error Diffusion (ED) has been a major stream to produce a pictorial image on inkjet prints, but is not always acceptable for commercial printing or EP printer, because it generates the dispersed dots hard to print.This paper proposes a novel method for generating ordered dither mask using “magic square”. Magic square provides spatially balanced threshold values in row, column, and diagonal directions by the rule of “even-sum”. The proposed magic square satisfies the energy minimum criterion in the local area and is expandable to a large scale for sufficient gray scales. We selected the magic square candidates with Fourier spectra concentrated in the middle spatial frequency to produce a smoothed gradation suitable for LBP or commercial printing. The paper introduces a systematic method for expanding small mask to large mask by “master-slave” algorithm. The experimental results show the improved grayscale reproduction with reduced artifacts in comparison with the conventional Bayer dither or ED.
Hiroaki Kotera, Fugen Jin, Takahiko Horiuchi, "A Digital Halftoning Using Magic Square" in Proc. IS&T Int'l Conf. on Digital Printing Technologies (NIP21), 2005, pp 403 - 407, https://doi.org/10.2352/ISSN.2169-4451.2005.21.1.art00019_2