Multi-pass banded printing

Details Multi-pass banded printing Multi-pass banded printing

1998-02-05

2001-09-18

Le, N. (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

C347S015000, C347S041000

Reexamination Certificate

active

06290328

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ink jet printing systems for printing rasterized pixel data. In particular, the present invention relates to an ink jet printing system using multiple printing passes to print rasterized pixel data at a resolution greater than an available ink jet nozzle resolution.
2. Description of the Related Art
Conventional ink jet printing systems utilize ink jet print heads for printing pixels upon a recording medium. Ink jet print heads contain ink jet nozzles, which eject ink droplets onto the recording medium during a printing pass over the recording medium. Ink jet nozzles are separated from each other on an ink jet print head by a fixed vertical distance. The fixed vertical distance determines a nozzle resolution, which is the maximum vertical pixel resolution that can be printed by the ink jet print head in one printing pass. Accordingly, conventional printing systems cannot print pixels in one printing pass at a resolution greater than the nozzle resolution.
In addition, conventional ink jet systems often utilize multiple printing passes to reduce “banding” within printed image data. Banding usually occurs when, for example, rasters 1 to 24 are printed, followed by rasters 25 to 48, and so on. As a result, gaps may appear between rasters 24 and 25. Conversely, printed rasters 24 and 25 may overlap due to misalignment, resulting in a dark region at the area of overlap. “Multi-pass” printing attempts to address this problem by printing pixels of each raster using at least two different nozzles.
More specifically, multi-pass printing systems utilize a multi-pass mask to identify pixel data to be printed on a first printing pass and to identify pixel data to be printed on a second printing pass. Printed data resulting from such a mask is shown in FIG.
1
. For discussion hereinbelow, the printed data in
FIG. 1
is shown superimposed onto thirty-six {fraction (1/720)} inch×{fraction (1/720)} inch square regions.
With reference to
FIG. 1A
, pixels centered around a numeral “1” were printed during a first printing pass, and pixels centered around a numeral “2” were printed during a second printing pass. Moreover, the numerals are placed at the exact positions toward which their respective ink droplets were ejected. Accordingly, after converting input pixel data to an available nozzle resolution, conventional systems apply a mask to the data in order to indicate pixels which should be printed during a first printing pass, and apply a second mask to the data to indicate pixels which should be printed during a second pass.
Printed output resulting from multi-pass masking is significantly affected by horizontal misalignment between the first and second printing passes. For example,
FIG. 1B
shows printed output on a recording medium resulting from multi-pass masking in which a one pixel horizontal misalignment exists between the first and second printing passes. As shown, pixel coverage over the recording medium suffers. Moreover,
FIG. 1C
shows a two pixel misalignment between pixels of a first pass and a second pass. As shown, ink coverage of the recording medium is greatly decreased, in
FIG. 1C
, from the ideal situation illustrated in FIG.
1
A.
Accordingly, what is needed is a system for printing rasterized data at a vertical resolution greater than an available ink jet nozzle resolution, and in which print output is less susceptible to horizontal misalignment than in conventional systems.
SUMMARY OF THE INVENTION
The present invention addresses the foregoing by printing pixel data of a first set of rasters on a first printing pass, and by printing data of a second set of rasters on a second printing pass, wherein the second rasters are interleaved between the first set of rasters. As a result, the present invention provides output of a higher vertical resolution than can be obtained on a single printing pass, and which is less susceptible to horizontal misalignments than conventional multi-pass printing.
Thus, according to one aspect, the present invention concerns a system for printing raster data on a recording medium using a plurality of ink jet nozzles. The system includes assignment of first raster data of a first set of rasters to the plurality of ink jet nozzles for printing during a first printing pass and second raster data of a second set of rasters to the plurality of ink jet nozzles for printing during a second printing pass, printing of the first raster data during the first printing pass, advancement of the recording medium a particular distance, printing of the second raster data during the second printing pass, and advancement of the recording medium the particular distance, wherein the system repeats in order to print a first region of raster data on the recording medium.
Preferably, ink limitation processing is performed on the rasterized data to create ink-limited raster data, wherein the ink limitation processing is performed in accordance with a maximum absorbency of the recording medium and an ink droplet size. In this regard, the system also preferably provides an option of printing using small ink droplets or large ink droplets.
By virtue of the foregoing multi-pass printing of selected rasters, the present invention provides an output image having a higher-resolution than a provided nozzle resolution. Moreover, the output image is less affected by horizontal print head misalignment than those images produced by conventional multi-pass systems. In addition, the foregoing provides a mechanical advantage of utilizing a single feed distance of the recording medium during multi-pass printing.
In another aspect, the present invention also includes a system to determine whether a nozzle usage to print of a next region of raster data is different from a nozzle usage to print the first region of raster data, and to print the second raster data of the second set of rasters and third raster data of a third set of rasters of the next region during the second printing pass in a case that it is determined that the nozzle usage to print the next region of raster data is different from the nozzle usage to print the first region of raster data. According to this aspect, the present invention reduces banding at a boundary between regions printed using different ink jet nozzle usages.
This brief summary has been provided so that the nature of the invention may be understood quickly. A more complete understanding of the invention can be obtained by reference to the following detailed description of the preferred embodiments thereof in connection with the attached drawings.


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