Banding reduction in incremental printing, by spacing-apart...

Details Banding reduction in incremental printing, by spacing-apart... Banding reduction in incremental printing, by spacing-apart...

2001-11-02

2003-02-25

Nguyen, Thinh (Department: 2861)

Incremental printing of symbolic information

Ink jet

Ejector mechanism

Reexamination Certificate

active

06523936

ABSTRACT:

RELATED PATENT DOCUMENTS
A closely related document is another, coowned U.S. utility-patent application filed in the United States Patent and Trademark Office substantially contemporaneously with this document. It is in the name of Askeland, identified as Hewlett Packard Company docket number PD-10982166-1 and entitled “BANDING REDUCTION IN INCREMENTAL PRINTING, THROUGH VARIATION OF NOZZLE COMBINATIONS AND PRINTING-MEDIUM ADVANCE”—subsequently assigned utility-patent-application Ser. No. 09/1516.815. That document, and other related documents cited or discussed in it, are hereby incorporated by reference in their entirety into this document.
Other related documents also wholly incorporated by reference herein are other, coowned U.S. utility-patent applications filed in the United States Patent and Trademark Office generally contemporaneously with this document. One such document, pertinent for its introduction of print-medium-axis directionality (“PAD”) error, is in the name of Doval and identified as Hewlett Packard Company docket number PD-60980081H95, under the title “COMPENSATION FOR MARKING-POSITION ERRORS ALONG THE PEN-LENGTH DIRECTION, IN INKJET PRINTING”. It was later assigned utility-patent-application Ser. No. 09/693,524. Another such document of Doval, U.S. patent-application Ser. No. 09/408,407, issued as U.S. Pat. No. 6,408,407, shows that extremely tiny (i. e. a pixel row or less) imprecisions or variation in print-medium advance can be helpful, whereas repetitive somewhat larger advance errors are more often troublesome.
Other such documents, pertinent for their introduction of printing-element selection generally (and swath-height manipulation to accommodate such selection), are in the name of Askeland. They are identified as Hewlett Packard docket numbers PD-10982150Z111, entitled “ADAPTIVE INCREMENTAL-PRINTING MODE THAT MAXIMIZES THROUGHPUT WHILE MAINTAINING INTERPEN ALIGNMENT BY NOZZLE SELECTION”, and PD-10982151Z112, entitled “ADAPTIVE INCREMENTAL-PRINTING MODE THAT MAXIMIZES THROUGHPUT BY SHIFTING DATA TO PRINT WITH PHYSICALLY UNALIGNED NOZZLES”—and subsequently assigned respective patent-application Ser. Nos. 09/492,564 and 09/492,929.
Still another such document is in the name of Gil, and is pertinent for its introduction of printmode techniques that enable printers to develop printmasks in the field, from factory-supplied kernels or algorithms, very efficiently and quickly. This document is identified as Hewlett Packard Company docket PD-60990032Z21, intended for filing shortly after the present document—and subsequently assigned utility-patent-application Ser. No. 09/ 516,323, and issued as U.S. Pat. No. 6,312,098.
FIELD OF THE INVENTION
This invention relates generally to machines and procedures for printing text or graphics on printing media such as paper, transparency stock, or other glossy media; and more particularly to a scanning thermal-inkjet machine and method that construct text or images from individual nal pixel array. The invention employs print-mode techniques to optimize image quality.
BACKGROUND OF THE INVENTION
(a) Spatial-frequency effects in banding—A persistent problem in incremental printing is conspicuously visible banding or patterning, which arises from a great variety of causes. Generally these causes are associated with repetitive phenomena that are inherent in the swath-based natured of such printing.
Joan Manel Garcia, in U.S. utility-patent applications Ser. No. 09/150,321 through '323, particularly addresses problems of patterning in the lateral or transverse dimension, i. e. parallel to the scan axis. He points out that such patterning is especially objectionable when it occurs at spatial periodicities to which the human eye is particularly sensitive.
Garcia shows that such banding can be rendered very inconspicuous at normal reading distances by moving its periodicity to roughly 3 cm (1 inch), or preferably a bit longer. This can be accomplished by tiling printmasks of those widths.
Unfortunately that technique is not now readily applicable to the longitudinal dimension—i. e. to the direction parallel to the print-medium advance axis. The reason is that, generally, largest current-day printheads are only about 2½ cm (1 inch) long in that direction.
Within the corresponding available range of spatial frequencies, banding in the lower three-quarters of that range (used in single-pass through four-pass printmodes) is quite conspicuous. Unfortunately the current trend toward reducing the number of passes used for printing each image segment—to enhance overall printing throughput—militates toward use of precisely that part of the range.
(b) Swath-interface effects—Some banding along the print-medium advance axis arises at the interfaces between swaths—due to the advance errors and “PAD” errors mentioned above, and due to ink-media interactions such as coalescence or print-medium expansion. Earlier documents such as Doval's have pointed out that repetitive, small failures of abutment themselves introduce banding (though extremely tiny imprecisions or variations in abutment can be helpful).
Swath-abutment irregularities may represent the single most conspicuous form or type of banding effect. When one swath edge is closely abutted to another, the abutment is almost always imperfect—leading to either a shallow gap between swaths or a shallow overprint where they overlap.
Also the two swaths are generally not exactly the same in darkness or color saturation, adding another element of contrast along the interface. Such problems are aggravated by a high or abrupt gradient of wetness along the edge of a just-deposited swath, when an abutting swath is formed soon after.
(c) Internal effects—Not all banding problems, however, occur at swath boundaries. Some result simply from nozzle PAD problems and these can be entirely internal to the swath.
Internal patterns can be formed by repetitive coincidences of nozzle irregularities. Prior systematic procedures placed particular irregularly-performing pairs (or other groups) of printhead elements into conjunction—with respect to the printing medium—over and over.
As an example, the Hewlett Packard Company printer product known as the Model 2000C uses two-pass bidirectional printmodes—each pixel row being printed by two separate nozzles. At 24 rows per millimeter (600 dots per inch, dpi), a 12.7 mm (half inch) pen, has 300 nozzles.
Ordinarily nozzles number
1
and
151
contribute drops to the same image row—using a 6⅓ mm (quarter inch) advance and, again, a two-pass, 300-nozzle printmode. Every 6⅓ mm these same two nozzles are paired (see FIG.
7
and the Table).
If nozzles
1
and
151
when used in combination form a noticeable band effect, this effect is highly visible to the user—because it is present in a repeating pattern, roughly every 6 mm or quarter inch. For example, if both nozzles happen to be directed well away from their nominal target pixel row, then that pixel row will appear unprinted (at least in the particular color in which the head in question prints), rather than the nominal double-printed.
Another kind of band effect can be caused by an interaction of nozzles that are adjacent or nearby. For example assume that nozzle number
5
is aimed “low” (toward the nominal target row for nozzle
6
). If nozzle
6
is aimed accurately, its target row will be double-printed.
If in addition nozzle
156
is also aimed accurately but nozzle
157
is aimed “high” (i. e. both toward the target row for nozzle
156
), then in the printed image the common pixel row for nozzles
6
and
156
will be quadruple-printed—while the adjacent rows above and below will each be single-printed rather than the nominal (double printed).
In short, banding within swaths results from repetitive coincidences between irregularly printing elements within each combination. Patterning arises from repetitive, systematic operation.
Objectionable patterning is subject to quantitative effects. Thus some printmasking approaches to patterning in effect simply dilute repetition withi

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