Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
2000-01-31
2001-12-11
Nguyen, Thinh (Department: 2861)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000, C358S001200
Reexamination Certificate
active
06328404
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printing apparatus that enables dots to be created in pixels arranged in a two-dimensional array and thereby prints an image on a printing medium. More specifically the invention pertains to a printing apparatus that significantly varies the maximum dimensions of the dot in two different directions that define the two-dimensional array.
2. Description of the Related Art
Ink jet printers, which create dots with several color inks ejected from a plurality of nozzles formed in a print head and thereby record an image, have been proposed as the output apparatus of the computer. The ink jet printers are widely used to print images processed by the computer in a multi-color, multi-tone expression. This printer generally allows expression of only two levels, that is, the dot on level and the dot off level, with regard to each pixel. The printer accordingly expresses the various tones of original image data by dispersion of dots.
One proposed technique reduces the weight of ink to create each dot, in order to ensure rich tone expression and high-quality printing in binary dot printers having only two levels with regard to each pixel. Creation of each dot by a reduced weight of ink enables an increase in number of dots possibly formed per unit area. This increases the number of tones expressible per unit area. The binary dot printer of this proposed technique, however, has the lowered printing speed, while enabling the rich tone expression.
Multilevel printers that enable tone expression of three or greater levels have been proposed as the technique of ensuring the rich tone expression as well as the improved printing speed. Examples of such multilevel printers include a printer that varies the quantity of ink or the density of ink to enable expression of three or more different densities with regard to each dot and a printer that enables a plurality of dots to be created in an overlapping manner in each pixel for multi-tone expression.
In the case of printing an image by a two-dimensional array of dots, the ideal shape of the dot is a circle to equalize the granularity of a resulting printed image in every direction. The quantity of ink ejected to form a substantially circular dot is rather fixed for each nozzle. In the case of formation of the substantially circular dots, there is accordingly a restriction in variation of the tone value expressible in each pixel by varying the quantity of ink ejected from the nozzle. In the binary dot printer using a single type of dot, there is a restriction in variation of the area of the dot formed according to the printing mode.
SUMMARY OF THE INVENTION
One object of the present invention is thus to provide a printing apparatus that enables expression of densities in a wide range and thereby attains high quality printing with excellent tone expression.
Another object of the present invention is to provide a printing apparatus that enables an adequate dot selected among various types of dots to be created in each pixel according to the purpose of printing.
At least part of the above and the other related objects is attained by a printing apparatus that forms dots at a preset resolution in pixels arranged in a two-dimensional array, thereby printing an image on a printing medium. The printing apparatus includes: a print head that creates a flat dot having a significantly smaller maximum dimension in a first direction of the two-dimensional array than a maximum dimension in a second direction of the two-dimensional array; a data setting unit that sets image data at the preset resolution; and a dot creation unit that drives the print head based on the image data set by the data setting unit, and creates dots at the preset resolution. The resolution is set in the first direction to satisfy a condition that an interval between adjoining dots in the first direction does not exceed the maximum dimension of the flat dot in the first direction, and is set in the second direction to satisfy a condition that an interval between adjoining dots in the second direction does not exceed the maximum dimension of the flat dot in the second direction and that the resolution in the second direction is lower than the resolution in the first direction.
The printing apparatus of the present invention intentionally adopts the flat dot, which is explicitly different in shape from the substantially circular dot. This arrangement enables a greater number of different types of dots to be used for printing, compared with the prior art printing apparatus. For example, the large dot having a greater quantity of ink than the allowable quantity for the substantially circular dot may be formed in the printing mode of the improved printing speed. In the case where the quantity of ink is extremely large, the ejected ink droplet from the nozzle may be split to hit at two different positions on the printing medium. The printing apparatus of this embodiment allows formation of such dots. The arrangement of the invention also allows misplacement of hitting positions of ink droplets in the case of ejecting a plurality of ink droplets in each pixel.
The printing apparatus of the present invention uses the flat dot, which is clearly different in shape from the substantially circular dot, in order to increase the possible options of dot type applicable for printing. This arrangement enables the adequate type of dot to be used according to the purpose of printing. The technique of the invention increases the number of different printing modes provided in the printing apparatus and enables a single print head to be used for plural printing apparatuses of different purposes.
The flat dot is defined by the dimensions of the whole shape formed by the total quantity of ink ejected in each pixel on the printing medium. For example, when the ejected ink droplet is split to hit at two different positions as shown in
FIG. 19
, each split of the ink droplet may form a dot of substantially circular shape. A dimension WDS in one direction of the whole shape formed by the total ink droplet is, however, significantly different from a dimension WDM in the other direction. The whole shape is accordingly regarded as the flat dot. Another technique called the area tone expression divides one pixel into a plurality of pixel divisions and varies the number of dots of substantially circular shape formed in the respective pixel divisions, in order to enable expression of plural tones in the pixel.
FIG. 20
shows one example of this technique. In this case, the maximum dimension of the whole shape in one direction is significantly different from that in the other direction, so that the whole shape is regarded as the flat dot.
In the specification hereof, the pixels are defined according to the image data that specify the dot on-off levels. In the case of the area tone expression shown in
FIG. 20
, the pixel divisions shown by the dotted lines may be treated as individual pixels. The dot on-off level in each of these pixel divisions is set according to each piece of data included in the image data. In the specification hereof, a set of such pixel divisions, that is, a part shown by the solid line in
FIG. 20
, is referred to as the pixel. In a similar manner, even when a plurality of ink droplets are formed in one pixel, the whole shape formed by the total quantity of ink ejected in the pixel is referred to as the dot.
The printing apparatus of the present invention carries out the printing operation at the resolution set according to the shape of the flat dot defined as discussed above. The printing apparatus of the present invention using the flat dot ensures the high quality printing as well as the rich tone expression without causing the banding due to the clearance between adjoining dots, as described below in detail.
The following describes the conventional method of setting the resolution in a prior art printing apparatus and the effects of the present invention.
FIG. 16
shows a prior art method of setting the reso
Nguyen Lamson D.
Nguyen Thinh
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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