Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-05-01
2002-01-15
Barlow, John (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000
Reexamination Certificate
active
06338538
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a printing system with a head, which forms at least two different dots having different densities per unit area on an object, for recording multi-tone images by the dots formed by the head, as well as to a method of recording such images.
BACKGROUND ART
Color printers, in which a plurality of color inks are discharged from a head, are widely used as an output device of a computer that records a multi-color, multi-tone image processed by the computer. Several methods are applicable to print a multi-color, multi-tone image with three color inks, cyan, magenta, and yellow (CMY). One method is a technique adopted in the conventional printers. This technique expresses the tone of a printed image by the density of dots (frequency of appearance of dots per unit area) while fixing the size of dots formed on a sheet of paper by a spout of ink. Another method adjusts the diameter of dots formed on a sheet of paper, in order to vary the density of dots per unit area. Although the advanced processing of the head for forming ink particles has been improving the density of dots formable per predetermined length or the variable range of the dot diameter, the printers have only the limited printing density (resolution) to 300 through 720 dpi and the limited particle diameter to several ten microns. The resolution of printers is significantly lower than the resolution of silver photography, which has reached several thousand dpi on the film.
Dots are sparsely formed in an area of low image density, that is, in an area of low density of dots to be printed. This increases the degree of granularity and makes the dots conspicuous. A printing system and a method utilizing inks of different densities have been proposed to improve the printing quality. The proposed technique utilizes a high-density ink and a low-density ink for a certain color and regulates discharge of these inks, thereby realizing print with an excellent tone expression. By way of example, a method of and an apparatus for recording multi-tone images are disclosed in JAPANESE PATENT LAYING-OPEN GAZETTE No. 61-108254. The disclosed technique provides a head for forming deep dots and light dots for a specific color and regulates the number and overlap of deep dots and light dots formed in a predetermined dot matrix according to the density information of an input image, so as to record a multi-tone image.
The proposed printing system utilizing inks of different densities, however, does not give any specific idea on the allocation of high-density ink and low-density ink to the input tone signals of an original image. Inks of different densities are simply allocated in the order of densities to the input tone signals of the image (for example,
FIG. 9
in JAPANESE PATENT LAYING-OPEN GAZETTE No. 2-215541).
In a printing system for forming at least two different dots having different densities per unit area (for example, dots by at least two inks of different densities), the object of the present invention is to enable the at least two different dots to be appropriately mapped to tone signals of an original image, thereby improving the quality of a resulting recorded image.
Disclosure of the Invention
The present invention applies the following structures, in order to realize at least part of the above and the other related objects. The present invention is directed to a first printing system with a head, which forms at least two different dots having different densities per unit area on an object, for recording a multi-tone image by a distribution of the dots, the first printing system including:
input means for successively receiving a tone signal of each target pixel included in an image to be printed;
recording density setting means for specifying a recording density to be realized by at least a selected one of a dot having a higher density per unit area, that is, a higher-density dot, and a dot having a lower density per unit area, that is, a lower-density dot, which are both included in the at least two different dots having different densities per unit area, based on the input tone signal;
first dot formation determination means for carrying out a multivaluing operation based on the specified recording density, and determining whether or not the selected one of the higher-density dot and the lower-density dot is to be formed;
second dot formation determination means for making a result of the multivaluing operation by the first dot formation determination means reflect upon a recording density to be realized by the other one of the higher-density dot and the lower-density dot, causing the other one of the higher-density dot and the lower-density dot to be subjected to a multivaluing operation according to the reflected recording density, and determining whether or not the other one of the higher-density dot and the lower-density dot is to be formed; and
head driving means for driving the head based on results of the determination by the first dot formation determination means and the second dot formation determination means, in order to form the at least two different dots having different densities per unit area.
In the first printing system of the present invention, the recording density setting means specifies a recording density to be realized by at least a selected one of a higher-density dot and a lower-density dot, which are both included in the at least two different dots having different densities per unit area. The first dot formation determination means carries out a multivaluing operation based on the specified recording density, and determines whether or not the selected one of the higher-density dot and the lower-density dot is to be formed. The multivaluing operation may be binary coding, ternary coding, or higher-value coding. In case that the at least two different dots having different densities per unit area consist of only two different dots, the first dot formation determination means carries out the determination for either one of the two different dots. In case that the head can form four different dots, however, the first dot formation determination means may carry out the multivaluing operation simultaneously for two or more different dots. The second dot formation determination means makes the result of the multivaluing operation by the first dot formation determination means reflect upon a recording density to be realized by the other one of the higher-density dot and the lower-density dot. The second dot formation determination means then causes the other one of the higher-density dot and the. lower-density dot to be subjected to a multivaluing operation according to the reflected recording density, and determines whether or not the other one of the higher-density dot and the lower-density dot is to be formed. The head driving means drives the head based on the results of the determination by the first dot formation determination means and the second dot formation determination means, in order to form the at least two different dots having different densities per unit area.
This structure enables a density error due to formation of the selected one of the higher-density dot and the lower-density dot to be reduced by formation of the other one of the higher-density dot and the lower-density dot, so that the tone of an original image is reproduced by a combination of the at least two different dots.
This printing system may be carried out by a variety of embodiments. By way of example, the recording density setting means may specify only a recording density to be realized by the selected one of the higher-density dot and the lower-density dot, or alternatively may specify a recording density to be realized by the selected one of the higher-density dot and the lower-density dot as well as a recording density to be realized by the other one of the higher-density dot and the lower density dot, based on the input tone signal. In the latter case, the first printing system further includes recording density correcting means for computing correction data, which is
Barlow John
Do An H.
Seiko Epson Corporation
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