Use of very small advances of printing medium for improved image quality in incremental printing

This invention relates generally to machines and procedures for printing text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to incremental machines and methods that construct text or images from individual ink spots formed progressively on a printing medium, in a pixel array-as for example by a scanning inkjet printer, or most other forms of matrix printing. The invention is directed to mitigation of several kinds of printing artifacts. A printhead scans to form marks in a multirow swath on the medium. A mechanism gives relative motion between the head and medium, orthogonal to the scan. Normal advance of the mechanism is at least several rows. There are variants or preferences: in one, the mechanism steps about a row or less to deliberately misalign successive swaths. There is best no associated data shift or normal advance. In another, the step roughly equalizes graininess between image regions with and without normal advance-e.g. between scans near at least one end of a page, to roughly equalize graininess as to swaths near and far from the end. The step best equals different fractions of a row, respectively, between successive swath pairs; these fractions progressively decrease-as e.g. programmed:Preferably Amplitude is 7; Frequency is 0.2244; nPasses are increments from zero through 7; and Phase is zero. Another variant/preference: steps deliberately misalign successive swaths as to scans far from both page ends. Another has small-amplitude reciprocation-as a vibration or successive alternating-direction offsets. An oscillatory signal is injected into the scan or medium-advance drive signals.