Patent US 5,107,331

A metthod of generating a set of half-tone screens for color printing using a digital computer and an x-y plotter, including the steps of generating and storing a separate and unique screen function matrix for each of the half-tone screens, each matrix comprising a set of light intensity level values in increments going from zero to a maximum, the sequence of numbers being a predetermined pattern that is different for each matrix, gnerating and storing a picture matrix of values representing the pixel portions and desired levels of color intensity of each basic color at the positions in the picture to be printed, creating each screen by dividing each screen area into a plurality of cells, each cell being formed as a binary matrix of elemental areas that are selectively either clear or opaque, assigning one of said converted numerical values from each of said basic colors from said set to each of said cells in the corresponding screens being created; and setting the binary values for the elemental areas within a cell by comparing the converted intensity level value for the particular basic color with each of the values in the associated screen function matrix, the binary value for each elemental area being set to one value or the other depending on whether the intensity level value is greater or less than the compared value stored in the cell function matrix. The screens are positioned to superimpose the basic colors over each other in partially overlapping fashion at the same screen angle. The spots of the color screens are shifted rectilinearly from each other.