US Patent 7513589 Multipass printing

A multi-pass printing system and a corresponding method are provided for printing an image, which includes a plurality of continuous-tone values, based on halftone matrices having threshold values. The printed image is composed of sub-images, each of which includes dots printed in a respective pass. The sub-images present independent dot patterns at corresponding places. The printing system is arranged to obtain the sub-images by splitting the continuous-tone values into at least two pass values, an individual pass value indicating an intensity to be printed in a respective pass. Then, in one pass a first halftone matrix for printing the respective pass values, and in another pass one or more second halftone matrices are used, which are obtained by positionally shifting the threshold values of the first halftone matrix, for printing all pass values of the other pass, or at least those pass values above a highlight threshold.