Reduction of periodic artifacts in incremental printing, through use of asymmetric randomized superpixels

Abstract

Periodic inking artifacts are reduced by randomness introduced into an image-processing stage. 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 is selected, essentially at random, from a plurality of superpixels—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 or some other reason for using superpixels (and starting with a coarse grid) is not present, the randomness-introduction approach preferably includes preparing the image using a pixel grid that is coarser than the available printer resolution. The selected superpixel 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, downstream and distinct from the image-processing stage, is used to establish temporal assignments of inking into the plural passes. Because most or many printing systems already employ superpixels anyway for various purposes, the simple tactic of selecting superpixels randomly achieves major gains in artifact reduction but adds little complexity, apparatus, processing time or cost.