REDUCTION OF PERIODIC ARTIFACTS IN INCREMENTAL PRINTING, THROUGH USE OF ASYMMETRIC RANDOMIZED SUPERPIXELS

摘要

Periodic inking artifacts (Fig. 2) are reduced by randomness (82) introduced into an image-processing stage (73). This goes beyond providing a fixed pattern earlier derived through random processing; rather the system literally introduces randomness or at least pseudorandomness into the image-processing stage. Preferably a superpixel (87) is selected, essentially at random, from a plurality of superpixels (84) - at least for points with an intermediate tonal level, which is the part of the tonal range where dot-placement error is most conspicuous. If image scaling (78) or some other reason for using superpixels (and starting with a coarse grid) is not present, the randomness-introduction approach preferably includes preparing (86) the image (71) using a pixel grid that is coarser than the available printer resolution. The selected superpixel (87) is applied at the coarser grid to define a set of individual pixels at printer resolution. A major preference relates to printing in sequential printing passes: a printmasking stage (Fig. 8, fifth block; 74), downstream and distinct from the image-processing stage, is used to establish temporal assignments of inking into the plural passes. For printing systems that already employ superpixels, selecting superpixels randomly achieves major artifact-reduction gains but adds little complexity, apparatus, processing time or cost. IMAGE