Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-03-01
2002-08-27
Barlow, Jr., John E. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C358S001900, C358S296000
Reexamination Certificate
active
06439682
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing method, which creates at least three different types of dots and thereby enables printing of a multi-tone image, as well as a printing apparatus to actualize the printing method. The invention also pertains to a recording medium on which a program for actualizing the printing method is recorded.
2. Description of the Related Art
An ink jet printer proposed as an output apparatus of the computer creates dots with inks of different colors spouted from a plurality of nozzles mounted on a head and thereby records a multi-color image. The ink jet printer has widely been used to print an image processed by the computer in a multi-color, multi-tone manner. In this printer, each pixel typically has only two tones, that is, the dot-on state and the dot-off state. An image is accordingly printed after the halftone processing, which is the image processing performed to enable the tone of the original image data to be expressed by the dispersibility of dots.
In order to enrich the tone expression, the recently proposed ink jet printer is a multi-valuing printer that enables the tone expression of each pixel in three or a greater number of values. One example of the multi-valuing printer varies the dot diameter and the ink density and thus enables three or a greater number of different densities for each dot. Another example of the multi-valuing printer creates a plurality of dots in each pixel in an overlapping manner to enable the multi-tone expression. In these printers, the halftone processing is required since the tone of the original image data can not be expressed sufficiently in each pixel unit.
Typical methods applicable for the halftone processing include the dither method and the error diffusion method. The dither method determines the on-off state of the respective dots based on the results of the comparison between a threshold value corresponding to each pixel read from a dither matrix and the tone value of the image data. The error diffusion method diffuses a density error arising due to the determination for the on-off state of the dot with respect to a certain pixel into peripheral pixels and corrects the tone data of these peripheral pixels. The error diffusion method then determines the on-off state of the respective dots based on the results of the comparison between the corrected tone data and a predetermined threshold value. The advantage of the dither method is the high-speed processing, whereas the advantage of the error diffusion method is the excellent picture quality.
In the multi-valuing printer that enables tone expression in three or a greater number of values, a plurality of different types of dots can be created for an identical hue. The halftone processing generally determines the on-off state of the respective dots individually. In order to enable the smooth expression of multiple tones and realize the printing of high picture quality, it is desirable to prevent the dots of the identical hue from being created in the same pixel in an overlapping manner. The technique of halftone processing that takes into account this point is, for example, described in JAPANESE PATENT LAID-OPEN GAZETTE No. 10-157167.
The proposed technique of halftone processing adopts the dither method in the following manner to determine the on-off state of the deep dot having a higher density and the light dot having a lower density. A recording ratio of the deep dot and a recording ratio of the light dot corresponding to the tone data of each pixel are read from a table provided in advance. The determination for the on-off state is carried out in the sequence of the deep dot and the light dot, based on the result of the comparison between a threshold value read from an identical dither matrix and the recording ratio. The result of the comparison between the threshold value and the sum of the recording ratio of the deep dot and the recording ratio of the light dot is used in the determination for the on-off state of the light dot. The light dot is set in the off state in the pixel where the deep dot has been set in the on state. This technique enables the deep dot and the light dot to be recorded in different pixels while maintaining the required recording ratios of the deep dot and the light dot.
There has been, however, little consideration on the sequence of making the dots subjected to the determination for the on-off state and the selection of the adequate method for the halftone processing in the multi-valuing printer that is provided with at least two inks having an identical hue but different densities and enables at least two different types of dots having different ink weights to be created. One example of the multi-valuing printer is provided with two inks of different densities, that is, the deep ink and the light ink, and enables at least two different types of dots having different ink weights to be created by each ink.
In order to realize the printing of high picture quality, it is desirable to create the dots of the identical hue in a sufficiently dispersing manner. The dots of the identical hue, however, often require different dispersibilities. The dots created by the inks of different densities are generally formed by separate heads. Creation of these dots in an identical pixel thus does not significantly affect the printing speed. Creation of the dots having different ink weights by an identical ink in an identical pixel, on the other hand, requires the head to be driven twice or more times for the same pixel, thereby significantly lowering the printing speed. The requirement for the sufficient dispersibility of the dots is thus especially high for the dots created by the identical ink.
An increase in number of different dots subjected to the determination for the on-off state in each pixel results in the longer time required for the halftone processing. Application of the dither method for the halftone processing does not ensure the high picture quality, while enabling the high-speed processing. The primary object of the multivaluing printer enriches the tone expression and realizes the printing of high picture quality. The deterioration of the picture quality is thus not a negligible problem in the multi-valuing printer. Application of the error diffusion process for the halftone processing ensures the sufficient picture quality, but undesirably lengthens the time required for the processing.
There has been no proposed technique that selectively applies the adequate method for the halftone processing of the respective dots created by the multi-valuing printer and specifies the sequence of making the respective dots subjected to the halftone processing, by taking into account these advantages and disadvantages. The problems discussed above arise not only in the printers but in a variety of printing apparatuses that can express the density of each pixel in three or a greater number of values by the inks of different densities and the dots having different ink weights.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique that determines the on-off state of the respective dots in an adequate sequence and enables the printing of high picture quality in the multi-valuing printer that is provided with at least two inks having an identical hue but different densities and enables at least two different types of dots having different ink weights to be created by at least one ink among the at least two inks.
At least part of the above and the other related objects is realized by a first method of printing a multi-tone image as a distribution of dots created with a head wherein the head is provided with at least two different inks that have an identical hue but different densities and enables at least three different types of dots, which include at least two different types of dots that have different ink weights and are created by at least one ink among the at least two different inks, to be created on a printing medium. The first method in
Barlow Jr. John E.
Mouttet Blaise
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
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