Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1998-05-29
2002-10-22
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06467866
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a print control method and print control apparatus for controlling a printer which prints an image on a print medium by using a printhead, and a printer using the same.
Specific examples on density unevenness generated by an ink-jet printer will be described with reference to
FIGS. 12A
to
12
C and
FIGS. 13A
to
13
C, taking a single color ink-jet head
91
as an example.
In
FIG. 12A
, reference numeral
91
denotes an ink-jet head. To simplify the explanation, the drawing shows a case where the ink-jet head
91
comprises eight nozzles
92
. Reference numeral
93
denotes ink droplets discharged by each of the nozzles
92
. It is ideal when the ink droplets, each having a uniform discharge amount, are discharged in the same direction as shown in FIG.
12
A. If such discharge operation is realized, dots having a uniform size are formed on a print paper as shown in
FIG. 12B
, achieving an image as shown in
FIG. 12C
in which there is no density unevenness in the nozzle array direction of the ink-jet head
91
.
However, in the ink-jet head
95
(
FIG. 13A
) used in reality, the shape and ink discharge characteristic of each of the nozzles vary. If the ink-jet head
95
is driven similarly to the case of
FIG. 12A
to perform printing, the size and direction of ink droplets discharged by each of the nozzles varies as shown in FIG.
13
A. Therefore, the dots formed on a print paper by the discharged ink droplets are not uniform as shown in FIG.
13
B. More specifically, as can be seen from
FIG. 13B
, high and low density portions appear periodically in the main-scanning direction of the ink-jet head
95
, or plural dots unnecessarily overlap with each other, or a white line (non-printed portion) is generated as shown in the central portion of FIG.
13
B. The aggregated dots formed in such condition have the density distribution shown in
FIG. 13C
, which corresponds to the nozzle array direction of the ink-jet head
95
. In this case, density unevenness is clearly visible by human eyes. Moreover, such conspicuous line is attributable not only to the ink-jet head
95
but also to an uneven paper-conveyance amount.
To reduce such density unevenness and a white omission line between adjacent raster lines, Japanese Patent Application Laid-Open (KOKAI) No. 60-107975 proposes the following method adopted to a monochrome ink-jet printer.
The method is now briefly described with reference to
FIGS. 14A
to
14
C and
FIGS. 15A
to
15
C. According to this method, the ink-jet head
95
is scanned three times to print the area shown in
FIGS. 12A
to
12
C or
FIGS. 13A
to
13
C. The area corresponding to four pixels, which is printed by half of the nozzles of the ink-jet head
95
, is printed by scanning twice. In other words, the eight nozzles of the ink-jet head
95
are divided into two groups: four nozzles in the upper side and four nozzles in the lower side. In the first scanning operation, the four nozzles in the lower side of the ink-jet head
95
are used to print every other pixels, and in the second scanning operation, the four nozzles in the upper side of the ink-jet head
95
are used to scan the same area and print dots in the portion skipped by the first scanning operation, whereby completing printing of the area of interest. The above-described printing method is called fine printing. Adopting the fine printing method to the ink-jet head
95
shown in
FIG. 13A
enables to reduce the influence of uneven nozzles over a printed image. Therefore, as shown in
FIG. 14B
, the printed image does not have conspicuous black lines or white lines which are generated in FIG.
13
B. Also in this case, density unevenness is relatively reduced as shown in
FIG. 14C
, as compared to FIG.
13
C.
When performing printing in the foregoing manner, image data is divided so as to complement each other in accordance with a predetermined arrangement in the first and second scanning operations.
FIGS. 15A
to
15
C show the examples of image data arrangement (masked pattern). The image data arrangement in
FIGS. 15A
to
15
C shows a checker pattern in which image data is divided to print every other pixels in the vertical and horizontal directions. Therefore, to complete print operation of a unit area (a unit of four pixels in this case), a checker pattern is printed in the first scanning and a reverse checker pattern is printed in the second scanning operation.
FIGS. 15A
to
15
C show how the print operation of a predetermined area is completed when a checker mask pattern and a reverse checker mask pattern are alternatively used, by utilizing an ink-jet head having eight nozzles similarly to the case of
FIGS. 12A
to
12
C-
14
A to
14
C.
In the first scanning operation, the checker pattern is printed by using the four nozzles in the lower side of the ink-jet head (FIG.
15
A). In the second scanning operation, the print paper is conveyed for a distance corresponding to four pixels and the reverse checker pattern is printed by using all the nozzles of the ink-jet head (FIG.
15
B). Note that in
FIGS. 15A
to
15
C, the dots (circles) indicated by hatching represent the dots printed by the checker pattern (FIGS.
15
A and
15
C), while the dots without hatching represent the dots printed by the reverse checker pattern (FIG.
15
B). Further in the third scanning operation, the print paper is conveyed again for a distance corresponding to four pixels (½ of all nozzles) and the checker pattern is printed again by using the four nozzles in the upper side of the ink-jet head (FIG.
15
C). By alternately performing the sequential paper conveyance in units of four pixels and the printing operation of a checker pattern or a reverse checker pattern as described above, printing an area in units of four pixels is completed per one scanning.
In a case of performing printing by the aforementioned multi-scanning, various mask patterns are used to remove pixel data in each scanning operation. Examples thereof are the aforementioned checker pattern and reverse checker pattern type, horizontal-line type, vertical-line type, or a type where the mask pattern (image-correspondence type mask) changes in accordance with image data and so forth. The image-correspondence type mask is a pattern in which printing orders are predetermined in raster units. For example, assuming a case of performing printing by scanning twice, in the first scan, the first dot of the first raster line is printed (shown as white circle in FIG.
16
); the second dot of the first raster line is not: printed (shown as black circle in FIG.
16
); and this is repeated for the third and subsequent dots of the first raster line. Then, the first dot of the second raster line is not printed (shown as black circle in FIG.
16
); the second dot of the second raster line is printed (white circle in FIG.
16
); and this is repeated for the third and subsequent dots of the second raster line. The arrangement of dots to be printed in the first scan (pass) is determined in this manner.
Next, in the second scan, the first dot of the first raster line is not printed (shown as white circle in FIG.
16
); the second dot of the first raster line is printed (black circle in FIG.
16
); and this is repeated for the third and subsequent dots of the first raster line. Then, the first dot of the second raster line is printed (black circle in FIG.
16
); the second dot of the second raster line is not printed (white circle in FIG.
16
); and this is repeated for the third and subsequent dots of the second raster line.
By setting the arrangement of dots to be printed in each raster, the checker mask pattern and reverse checker mask pattern are printed as shown in FIG.
16
. The mask data used in this case is determined in accordance with, for instance, the image shown in FIG.
17
.
FIG. 17
shows an image in which only the first dot of the second raster is apart from other dots. In the image in
FIG. 17
, dots of the second raster are printed from the first dot in the order of “not print”, “
Kato Masao
Nagoshi Shigeyasu
Barlow John
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Stewart Jr. Charles W.
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