Patent ID: 8467103

Claim:
A moiré-free halftone image forming method for reproducing an image using a different halftone screen with hexagonally tiled clusters for each colorant associated with an image rendering device, the method comprising: a) defining a first colorant halftone screen with hexagonally tiled clusters having a first fundamental frequency vector V c1 , a second fundamental frequency vector V c2 , and a third fundamental frequency vector V c3 , where V c3 =V c1 −V c2 , A ( V c2 , V c1 ) is substantially 60° and A ( V c1 , V c3 ) is substantially 60°; b) defining a second colorant halftone screen with hexagonally tiled clusters having a first fundamental frequency vector V m1 , a second fundamental frequency vector V m2 and a third fundamental frequency vector V m3 , where V m3 =V m1 −V m2 , A ( V m2 , V m1 ) is substantially 60° and A ( V m1 , V m3 ) is substantially 60°; c) selecting the values of the fundamental frequency vectors V c1 , V c2 , V c3 , V m1 , V m2 , V m3 such that |V c1 | is substantially equal to |V c2 | which is substantially equal to |V c3 |, |V m1 | is substantially equal to |V m2 | which is substantially equal to |V m3 |, V c1 and V m1 are separated by substantially 30° , V c2 and V m2 are separated by substantially 30°; and V c3 and V m3 are separated by substantially 30°; d) generating the first colorant halftone screen, and the second colorant halftone screen; e) applying the first colorant halftone screen to the image to produce a first colorant halftone output, and applying the second colorant halftone screen to the image to produce a second colorant halftone output; and f) overlaying the first colorant halftone output and the second colorant halftone output to reproduce the image with a moiré-free halftone image.