Hewlett-Packard Company

Nathan M Moroney

Josep Maria Serra

An inkjet printing system uses high-resolution printheads holding different color inks to produce true 600 dpi color printing with a single pass of the printheads. By achieving a smaller drop size in the range of 25-50 picoliters for each printhead having a separate ink color (yellow, cyan, magenta, black), a full range of high-resolution color print-quality modes is possible. In an exemplary embodiment with a carriage scan speed of 25 ips, a two-pass draft mode uses a 7.5 kHz firing frequency, a four-pass normal mode uses a 4 kHz firing frequency, and an eight-pass best mode uses a 2 kHz firing frequency. In all of these print modes, each printhead can provide color inkdrop placement on every pixel row during a single pass.

High-resolution inkjet printing using color drop placement on every pixel row during a single pass

Gray component or undercolor in an input image is quantitatively determined, and reduced in amounts nonlinearly related to the quantity of undercolor. The reduced and added signals are applied to control printing by, preferably, scanning inkjet printheads. The total undercolor inking is a substantially monotonic function of the quantity of undercolor. Preferably the reducing and adding are performed in a subtractive-colorant color space, e.g. CMYK space. Preferably image data is initially accepted or generated in terms of additive RGB signals, and these are converted into the subtractive domain. Preferably the reducing and adding means operate only above an undercolor threshold of about twenty to thirty-five percent; and total inking is made between one hundred fifty and two hundred fifty percent when the signals are all gray component. Initial very gradual increases from a threshold are important, for consistent, smooth, regularized dynamic-response in tonal gradations. Preferably these increases follow a spline function. The system works in virtually the same way for black input as chromatic input. Corresponding method and apparatus modules characterize the invention. Automatic operating instructions for the apparatus (or method) modules are stored. Results include minimizing ink usage, consistent with an optimal black, and nearly linearizing composite grays.

Thresholded undercolor removal and black replacement in a thermal-inkjet

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.

Growing community of inventors

Barcelona, Spain

Nathan M Moroney