Abstract: Method and apparatus enabling color or black/white bi-level or multi-level halftone images to be displayed or printed on various raster output devices, in particular on display devices (cathode ray tubes, plasma displays, liquid crystal displays) or on printing devices (printers, telefaxes). The originality of the present invention is found in the dither matrix R.sup.c*n which is obtained by applying on a c-fold replication of a well-dispersed threshold matrix D.sup.n a one-to-one discrete rotation of Pythagorean angle .alpha.=arctan(b/a) or .beta.=arctan(a/b) around an arbitrary point, where {a,b,c} are Pythagorean triplets satisfying Diophantine equation a.sup.2 +b.sup.2 =c.sup.2 and n is an integer. The images produced using the disclosed method are visually pleasing due to the absence of visible artifacts and to the small typical structure size. In addition, this method offers very smooth intensity gradations throughout the dynamic range.

Abstract: The invention relates to a method and apparatus for automatic high-speed generation of digital angled halftone screens, specially suited for obtaining screens approximating the irrational angles which are generally required by high-quality color reproduction. The method enables color separations to be generated which minimize Moire effects, interferences and artifacts by applying discrete one-to-one rotations to digital halftone screens of the required period in order to reach the final screen angle. Dither tiles incorporating assemblies of the basic screen element are rotated by one-to-one discrete rotation and transformed into a new type of dither array, the scanning dither array. The scanning dither array is composed both of dither thresholds and of displacement vectors, providing the means to scan the dither array at image generation time.