Mixing overprinting and underprinting of inks in an inkjet printer to speed up the dry time of black ink without undersirable hue shifts

摘要

A black printhead (24) is installed in a scanning carriage (20) with at least one primary color printhead (22, 26) on both sides of the black printhead. To reduce the drying time of a printed black ink pattern and to achieve other benefits, a first one of the primary color inks (C) underprints the black ink (K) in a first scan direction, and a second one of the primary color inks (M) underprints the black ink (K) in an opposite second scan direction. To minimize hue shifts due to the different underprinted colors, the black ink is overprinted, during the same scan that printed the underprinted ink and black ink, by a color ink that is different from the underprinted ink, so that the resulting black image printed in both scan directions will contain the same three color components. In one embodiment, the order of print cartridges in the scanning carriage, as viewed from the front of the printer, is cyan (22), black (24), magenta (26), and yellow (28). Other orders may also be used, and additional colors may be used. The invention is also applicable to a color printer using a single printhead with multiple sets of nozzles, each set printing a different color ink.