Patent ID: 6985262

Claim:
A method of generating a plurality of non-orthogonal halftone screens for substantially moiré-free four-color halftoning, comprising: locating non-orthogonal halftone cells suitable for tiling an image plane that are substantially specified by two frequency vectors F n 1 =(fx n 1 , fy n 1 ) and F n 2 =(fx n 2 , fy n 2 ), where n=color indices a, b, c, d of four different colors; identifying combinations of four of the non-orthogonal halftone cells which simultaneously satisfy: F a 1 +F b 1 +F c 1 =0, and F a 2 +F b 2 +F c 2 =0 and F a 1 +F b 2 +F d 1 =0, and F a 2 +F b 1 +F d 2 =0 where, F d 1 ≠F c 1 , F d 1 ≠F c 2 , F d 2 ≠F c 1 , and F d 2 ≠F c 2 , and | F n x ±F m y |>M where, M=minimum acceptable two-color moiré frequency n=a, b, c, d m=a, b, c, d n≠m x=1, 2, y=1, 2; selecting one of the identified combinations of four non-orthogonal halftone cells; and associating each non-orthogonal halftone cell of the selected identified combination with one or more color separations of a color halftone printer.