Incremental printing of symbolic information – Ink jet – Ejector mechanism
Reexamination Certificate
1998-04-20
2001-04-10
Le, N. (Department: 2861)
Incremental printing of symbolic information
Ink jet
Ejector mechanism
Reexamination Certificate
active
06213586
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to control of a multicolor inkjet printhead as it deposits multiple ink colors on a media sheet during plural overlapping scans and, more particularly, to a method and apparatus which produces either temporally or spatially shingled images in a manner which reduces image artifacts.
BACKGROUND OF THE INVENTION
“Shingling” of ink drops to produce inkjet images is known in the prior art. In inkjet printers which produce binary colors (i.e., black/white), shingling is accomplished by causing the inkjet printhead to make at least two passes over a single swath of raster scan lines of print data. During a first scan, every other pixel site is masked and during a second scan, the complementary pixel sites are masked. Ink deposited during a first scan is thus placed at every other pixel site and is allowed to dry before ink is placed on adjacent pixel sites during the second scan.
Multi-level shingling is also known in the prior art. In such a shingling procedure, instead of firing one drop per pixel site, the inkjet printhead is enabled to fire plural drops at each pixel site. The number of overlapping drops (and their respective volumes) is dependent upon the number of drops, one on top of each other, that can be accommodated while still retaining a desired level of image quality. Such a print technique is termed “drop-on-drop”. Multi-level shingling is utilized to enable the deposition of various thicknesses of colored inks to achieve a desired level of color intensity.
Currently, inkjet printers have the capability of producing high quality images. Such printers utilize a printhead (e.g. whose nozzle plate
10
is as schematically shown in
FIG. 1
) which is capable of depositing four separate color dots, i.e., cyan (C), magenta (M), yellow (Y) and black (K). Nozzle plate
10
includes at least four columns of nozzles
11
,
12
,
13
and
14
, with each column having N nozzles devoted to the deposition of a single color. The number of nozzles in each column defines the width of a swath of pixel sites that can be printed during a scan of the printhead across a media sheet. Further, there may be plural columns of nozzles devoted to each color.
Prior art printheads, of the type shown in
FIG. 1
, are controlled such that, as each column of nozzles arrives over a pixel position, in the sequence of nozzles shown, a respective nozzle is energized to deposit a color dot of ink. Such multi-color printheads have only been enabled to deposit a single dot per pixel site, with the deposition occurring in the order in which the color nozzles are arranged across nozzle plate
10
. Thus, as shown in
FIG. 1
, if the scan direction is as shown by arrow
15
, a magenta ink dot is invariably deposited before a cyan dot is deposited. Such invariant ordering of dot placement, at times, results in image artifacts and variations from a desired color representation.
It is known that both temporal and spatial shingling can improve image representations that are produced by an inkjet printhead (e.g., improved gray level representation and half-toning). Further, as above indicated, experience has shown that if the deposition of colors onto a media sheet is restricted to a certain order of color dots, undesirable image artifacts can be created (e.g., banding). Finally, there is a requirement to improve the image reproduction capability of inkjet printers to enable image representations to be produced that are closer to high quality photographic reproductions.
Accordingly, it is an object of this invention to provide an improved method and apparatus for controlling a multicolor inkjet printer.
It is a further object of this invention to provide an improved method and apparatus for controlling a multicolor inkjet printhead, wherein either temporally or spatially shingled images are produced.
It is yet another object of this invention to provide an improved method and apparatus for control of a multicolor inkjet printhead, wherein the sequence of deposition of colored dots is selectively alterable.
It is still another object of this invention to provide a method and apparatus for control of a multicolor inkjet printhead which reduces image artifacts in a resultant printed image.
SUMMARY OF THE INVENTION
A system incorporating the invention controls ink deposition from a multi-orifice inkjet printhead. The printhead is adapted to deposit shingled dots, of plural colors, during multiple passes across a media sheet. The system includes an image buffer which stores image data, the data configured into plural color planes, each color plane including single color subpixels. Each subpixel is a multibit value that is representative of a color intensity. Multiple color plane deposition masks are stored for use with subpixel data from associated color planes, each color plane deposition mask including plural threshold values. Subpixel values from each color plane are compared with logically corresponding threshold values from an associated color plane deposition mask and print control signals are produced in accordance with the comparing action. If the subpixel value equals or exceeds an associated threshold value, a print signal is issued and if not, a no-print action occurs. A printer control procedure is responsive to the print control signals to control colored ink ejections from the respective nozzles on the inkjet printhead, during each pass across a media sheet, to either deposit a corresponding color dot on the media sheet or to inhibit deposition thereof.
REFERENCES:
patent: 5111302 (1992-05-01), Chan et al.
patent: 5473446 (1995-12-01), Perumal, Jr. et al.
patent: 5500662 (1996-03-01), Watanabe
patent: 5509085 (1996-04-01), Kakutani
patent: 5672016 (1997-09-01), Miyano
patent: 5841549 (1998-11-01), Munakata
patent: 5959646 (1999-09-01), Bates et al.
Hewlett--Packard Company
Hsieh Shih-Wen
Le N.
Potts Jerry R.
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