A method of ink jet printing comprising the steps of: (a) conveying a print medium in a first direction; (b) scanning a printhead in the first direction; and (c) printing on the print medium while the printhead is scanning in the first direction and the print medium is moving in the first direction.

A test pattern is scanned to find ideal print-medium advance for a pen (or other marking device). The pattern has a medium; and, marked on it, image patches each with overlapped swaths stepped by different distances. At best there are different-color pens; and for each distance a set of patches, each with a patch for each color (preferably area fills at sensitive tones by color). All patches in a set are best adjacent along a scan direction, with alignment lines above each set across the whole pattern, and a nozzle-conditioning patch at each image patch. A processor prints the pattern, operates a sensor and uses its signals to find optimum advance. The system finds and prints with ideal advance for a most-active pen; or weighs pen activity to find an optimum for all pens based on certain statistical and/or prospective choices.

The center-to-center spacing of pens containing a "problematic" combination of inks is increased to introduce a relatively small additional time-delay in which those particular constituents are applied to the same or adjacent areas during a single pass, thereby providing a substantial improvement in print qualities (such as Halo or Bleed) on plain (untreated) and special purpose (matt, glossy, transparent) print media, without substantially increasing the throughput rate. The center-to-center spacing of a critical combination of pens is substantially greater than the width of a single pen, thereby providing an increased delay that is equal to the increased spacing divided by the traverse speed. Different delays are provided for different combinations of ink by arranging at least three pens in a fixed sequence with different fixed spacings between different combinations of pens, such that a greater spacing and thus a longer delay is associated with one or more combinations of inks which interact adversely on print quality, and a shorter delay with at least one combination of inks which interacts less adversely on print quality. In particular, if a particular pair of two pens is a "problematic" combination requiring a longer delay and other pairs are "safe" combinations requiring a shorter delay, the pair requiring the longer delay may be held in two non-adjacent compartments, possibly separated by one or more other pens. In one particular example, the order is KMCY, which provides an effective center-to-center spacing of 2 pen widths for the two "problematic" combinations of KC and YM, and a center-to-center spacing of at least 1 pen width for the four safe combinations, thereby providing an economic solution to improve print qualities such as Halo and Bleed by increasing the center-to-center spacing of the pens associated with one or more "problematic" combinations of inks, without any noticeable change in throughput rate.

Non-black ink jet printheads are arranged in a printer carriage such that the printhead nozzle arrays are non-overlapping in the carriage swath direction. A fixer printhead is positioned such that the print medium is first advanced past the fixer printhead prior to reaching any of the other printheads. The printheads are selectively driven during each direction of a bi-directional carriage movement, and the print medium is incrementally advanced before each change in carriage movement direction. The order of laying down droplets of different colors is the same during the movement in each direction, thereby eliminating bi-directional hue shifting print artifacts.

A wet-dye hard copy apparatus includes a scanning carriage selectively movable along a scan axis and a plurality of ink-jet writing instruments on the carriage for printing on adjacent print media transported along an orthogonal axis. The writing instruments are offset a predetermined distance in the direction of media travel to increase throughput and to allow simultaneous multiple page printing.