Abstract: Apparatus and method establish two or more selectable colorimetrically equivalent printmasks, and—from among those—select masks for use. An image-processing stage assigns inking spatially among pixels; each mask sets temporal assignments, among print passes, of the spatially assigned inking. Selected masks are used, for successive pixels, in a randomized sequence. The image is defined as an array of input colorimetric levels, each one selectably mapped to any one of plural colorimetrically equivalent masks. Plural colorimetrically equivalent levels are defined, and then assigned (through a randomized procedure) to particular masks. The image is prepared using a pixel grid coarser than the available printer resolution; and the plural equivalent masks formed by varying allocation of printer passes among pixels of the coarser grid.