Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-06-07
2002-04-02
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S016000
Reexamination Certificate
active
06364446
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a printing method and printing apparatus and, more particularly, to a printing method and printing apparatus for printing in accordance with, e.g., an ink-jet printing method.
BACKGROUND OF THE INVENTION
In a conventional serial printer and, more particularly, an ink-jet printer, head shading for measuring a variation in printed image density corresponding to each ink discharge nozzle (to be simply referred to as nozzles hereinafter) and correcting image data is performed to reduce a phenomenon (to be referred to as “deviated discharge” hereinafter) in which droplets are discharged while being deviated in different directions in units of nozzles of a printhead, generation of stripes (to be referred to as “undesirable stripes” hereinafter) at a boundary portion for printing corresponding to one printhead scanning due to a variation in conveyance amount of a printing medium such as a printing paper sheet, or density unevenness due to the difference in amount of discharged droplet between nozzles.
FIG. 16
is a block diagram showing head shading processing in a conventional serial printer. The processing shown in
FIG. 16
assumes so-called multipass printing in which a printhead scans one region plural times to complete printing in that region.
For this processing, first, before execution of actual head shading processing, a patch is printed without executing head shading, and the relationship between the density of input data used for the printing and the density of an image printed by the printer is measured in units of nozzles. Next, the input data density correction coefficient for each nozzle is obtained from the measurement result. This relationship is stored in a table (shading data table
102
in
FIG. 16
) as shading data in a table format. If the input data resolution does not coincide with the printing resolution of the printer, the correction coefficient is determined in accordance with the input data resolution.
After this preparation, the actual head shading processing is executed.
As shown in
FIG. 16
, density data input from an input terminal
101
is input to the shading data table
102
and shading correction unit
103
. The shading data table
102
outputs a correction coefficient corresponding to the input density value to the shading correction unit
103
. The shading correction unit
103
corrects the input density value on the basis of the correction coefficient and outputs the corrected density value to a binarization unit (which is sometimes called bi-level conversion unit)
104
.
The binarization unit
104
generates output data (bitmap data) of the printer by well-known binarization processing method and outputs the data to a printing buffer
107
. The printing buffer
107
has a capacity to store bitmap data corresponding to printing for one scanning of a printhead+paper feed amount and constructs a ring buffer in units of paper feed amounts. A printing buffer control unit
106
controls input/output to/from the printing buffer
107
. When bitmap data of one scanning of the printhead is stored in the printing buffer
107
, the printing buffer control unit
106
activates a printer engine (not shown), reads out the bitmap data from the printing buffer
107
and outputs the data to a masking unit
109
as the printhead moves. When bitmap data is input from the binarization unit
104
, the printing buffer control unit
106
controls and makes the printing buffer
107
store the data in a free area (area where data already printed is stored) of the printing buffer
107
.
When the printer engine is activated, a pass number detection unit
105
detects the pass number (the sequence number of scanning cycle in one region in multipass printing) from the position of a nozzle corresponding to the bitmap data read out from the printing buffer
107
and outputs the pass number to an address generation unit
108
. The address generation unit
108
generates a read address for a mask generation unit
110
on the basis of the pass number and printhead position.
The mask generation unit
110
is constructed by a lookup table (to be referred to as an “LUT” hereinafter) and outputs mask data corresponding to the address generated by the address generation unit
108
to the masking unit
109
. The masking unit
109
calculates the logical-product (AND operation) of the bitmap data read out from the printing buffer
107
and the mask data from the mask generation unit
110
and transfers the calculation result to a printhead
111
. Thus, the bitmap data is divided into data to be used in units of a plurality of passes.
In a conventional ink-jet printer, multipass printing for dividing an image corresponding to one scanning of a printhead into a plurality of scanning cycles and forming the image is also performed to reduce generation of stripes (to be referred to as “stripes due to a discharge position error” hereinafter) or density unevenness in the printed image, which occurs when the discharge position on the printing medium deviates from a predetermined position because of deviated discharge or a variation in conveyance amount of the printing medium.
FIG. 17
is a block diagram showing the outline of multipass printing control of a conventional ink-jet printer.
Bitmap data input from an input terminal
1111
is stored at a predetermined address of a printing buffer
1113
under the control of a buffer control unit
1112
. The printing buffer
1113
has a capacity to store bitmap data corresponding to one scanning of a printhead+paper feed amount and constructs a ring buffer in units of paper feed amounts.
When the buffer control unit
1112
controls the printing buffer
1113
to store bitmap data corresponding to one scanning of the printhead in the printing buffer
1113
, a printer engine (not shown) is activated. The bitmap data is read out from the printing buffer
1113
and output to a masking unit
1117
as a printhead
1001
moves. When bitmap data is input from the input terminal
1111
, the printing buffer
1113
is controlled to store the data in a free area (area where data already printed is stored) of the printing buffer
1113
.
When the printer engine is activated, a pass number detection unit
1116
detects the pass number from the position of a nozzle of the printhead
1001
corresponding to the bitmap data read out from the printing buffer
1113
and outputs the pass number to an address generation unit
1115
. The address generation unit
1115
generates a read address for a mask generation unit
1114
on the basis of the pass number and printhead position.
The mask generation unit
1114
is constructed by a lookup table (LUT) and outputs mask data corresponding to the address generated by the address generation unit
1115
to the masking unit
1117
. The masking unit
1117
calculates the logical-product of the bitmap data read out from the printing buffer
1113
and the mask data read out from the mask generation unit
1114
, thereby masking the bitmap data such that printing is completed by scanning (passing) the printhead plural times. The masked bitmap data is transferred to the printhead
1001
by a head driver
1705
.
In the above-mentioned conventional art, shading correction is performed for multivalued data before binarization. If print data and a nozzle of the printhead are not made to correspond to each other at this time, correction does not consider the discharge characteristics of each nozzle. However, actual printing is performed on the basis of binary data. Since the input data does not take the discharge characteristics of each nozzle into consideration, no accurate correction is performed.
To solve this problem, it is necessary to grasp the correspondence between each nozzle number of the printhead and each bit of the bitmap data obtained from binarization. However, always grasping such correspondence increases the load on a printer driver, which is a program installed in a personal computer or the like to perform printer control, and is actually almost impossible.
As desc
Edamura Tetsuya
Inoue Hiroo
Ishikawa Hisashi
Kawatoko Norihiro
Konno Yuji
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen Thinh
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