Multipass inkjet printmodes with randomized dot placement, to minimize

Abstract

Color inkdrops form on a print medium in at least partly overlapping swaths. Apparatus holds and provides--or generates in real time--data defining a generally randomized printmask, which is applied to control working parts of an inkjet printer. Preferably the apparatus establishes an elemental pixel subgrid of rows and columns, used in determining inking patterns essentially throughout the image; and stores in the pixel subgrid a previously generated, generally randomized selection of pixel columns for printing of an inkdrop, in each subgrid pixel row--and conversely an analogous selection of pixel rows for printing a drop in each subgrid pixel column. Also preferably the generally randomized selection is subjected to location rules as to pixels above and to at least one side of each pixel. Numerous specific masks are specified as pass-number patterns, including an eight-by-eight 'knight' array, two sixteen-by-five arrays, a sixteen-by-ten array, and several four-by-four arrays. Another form of the invention includes apparatus for minimizing directional and other patterns in a printed color image, and coalescence and puddling of ink. A method of creating and using a printmask includes generating, as a row-and-column array, a series of essentially randomized numbers for use in defining rows or columns, or both, of a pixel subgrid; and storing the array in a tangible medium.