Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2001-12-13
2003-03-25
Nguyen, Thinh (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
Reexamination Certificate
active
06536862
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an inkjet printing apparatus and image data generation method of said apparatus, and more particularly, to an inkjet printing apparatus and image data generation method of said apparatus, which can effectively prevent occurrence of cockling while performing printing with an inkjet printhead which discharges ink based on information transmitted by an external apparatus.
BACKGROUND OF THE INVENTION
A printing apparatus serving as a printer, copying machine, facsimile apparatus or the like, or a printing apparatus serving as an output apparatus of a work station or composite electronic device including a computer or word processor or the like, is configured to print an image on a print medium, such as paper or a plastic sheet, based on image data. Printing apparatuses of this type are categorized by the printing methods they adopt: an inkjet method, wire-dot method, thermal method, laser method and so on.
An inkjet printer adopting the inkjet method performs printing with the use of a printhead serving as printing means, which discharges ink on a print medium. The inkjet printer has the following advantages: easy to downsize printing means, the ability to print high-definition images at high speed, ability to print on regular paper without requiring special processing, low running cost, low-noise operation because of its non-impact method, easy to print color images with multiple colors of ink, and so forth.
Particularly a printhead having high-density fluid passages (discharge orifices), employed in the inkjet method for discharging ink by utilizing heat energy, can easily be manufactured by the semiconductor manufacturing processes of etching, deposition and sputtering. Therefore, the entire printing apparatus can be further downsized. In the similar sense, a printing apparatus adopting the thermal method can be further downsized similar to the inkjet printer.
The recent trend in such inkjet printer is a system in which a host apparatus transmits a printing command to a printer in the page description language (PDL) so as to share the transmitting data irrespective of the resolution of printers.
Steps of generating printing image data to be used in printing based on an image drawing command written in the PDL are described with reference to the block diagram in FIG.
5
. An image drawing command
501
, transmitted by the host computer, is transferred to the inkjet printer through a communication cable or the like. The inkjet printer interprets and processes the received command at a command interpretation unit
502
to generate various printing image data, and stores the generated data in image memory
510
.
The image drawing command
501
represents a group of image drawing commands.
FIG. 6
shows the format of each command. Each image drawing command consists of image shape information
601
, image position/size information
602
, image density information
603
, and fill-in information
604
. The image shape information
601
indicates a shape, such as a circle, square, and so on. The image position/size information
602
indicates, for instance if the image is a circle, X and Y coordinates of the center and the radius of the circle. The image density information
603
indicates a color, e.g., red, blue, or green, and density thereof in a specified range (e.g., 0 to 255). The fill-in information
604
indicates whether or not the image is just a line of circle with no fill-in patterns or a circle whose circumference and inside the circle are filled in.
Among these information, the image shape information
601
and image position/size information
602
, which are related to the image drawing position, are processed by an image shape interpretation unit
503
, then the drawing position is determined by an image position interpretation unit
504
, and outputted by a memory control unit
505
as the memory address information of actual image memory
510
. Meanwhile, the image density information
603
is subjected to &ggr; conversion, which is unique to the printing apparatus, by an image density conversion unit
507
, and outputted as color data of the image to the image memory
510
. A fill-in control unit
506
interprets the fill-in information
604
to determine existence/absence of filled-in areas, and controls a value outputted to the image density conversion unit
507
based on the information of the memory control unit
505
.
In inkjet printers, there is an important relation between print paper and the amount of ink droplets discharged per unit area (also called a discharge amount).
When a large amount of ink droplets is discharged onto print paper, cellulose which constitutes paper swells in the print paper. In particular, when ink having a characteristic of low permeability into print paper is used, the ink droplet discharged by a printhead hardly permeates through the print paper, thus remains on the print paper surface. As a result, the aforementioned phenomenon of cellulose swelling takes place only on the face of the print paper surface, resulting in different surface areas on the face and back of the print paper. Ultimately, a corrugation phenomenon, called cockling, occurs in the portion of the print paper surface on which a large amount of ink droplets is discharged. Furthermore, in a case where a large amount of ink droplets is discharged on the entire page of print paper, a curling phenomenon of the print paper takes place.
When the cockling phenomenon occurs, the spaces between print paper and a printhead become unstable. Variations of the ink droplet discharging direction cause to lose stability in the ink droplet discharging position on the print paper surface, resulting in image quality deterioration. Furthermore, when the curling phenomenon occurs, it is difficult to align print paper in case of printing plural pages, imposing inconvenient handling. In addition, the curling phenomenon can cause snagging of paper or malfunction in the printer.
In order to prevent the above-described cockling or curling, methods have been proposed to limit the ink discharge amount based on actual printing image data or halftone image data, which is the pre-stage data of the actual printing image data.
However, according to the proposed methods, data processing must be performed on each pixel data. Therefore, processing a high-resolution image increases the number of times of operation. This processing requires hardware with high processing speed, and also is time consuming. Furthermore, it is difficult to control the ink discharge amount in accordance with each print medium used.
SUMMARY OF THE INVENTION
The present invention has been proposed to solve the conventional problems, and has as its first object to provide an inkjet printing apparatus, which can effectively prevent the occurrence of cockling without largely increasing a load imposed upon hardware.
The second object of the present invention is to provide an image data generation method of the inkjet printing apparatus, which can effectively prevent the occurrence of cockling without largely increasing a load imposed upon hardware.
Another object of the present invention is to provide a computer program and storage medium storing the program, which implements the image data generation method of the inkjet printing apparatus.
According to the present invention, the first object is attained by providing an inkjet printing apparatus for printing on a print medium based on a drawing command with the use of an inkjet printhead for discharging ink, said apparatus comprising: calculation means for calculating an area of a graphic to be drawn based on the drawing command; first determination means for determining whether or not the calculated area exceeds a predetermined value; second determination means for determining based on the drawing command whether or not a density value of the graphic exceeds a predetermined density value; and density conversion means for converting the density value in accordance with determination results of the first and second determi
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