Incremental printing of symbolic information – Ink jet – Controller
Reexamination Certificate
1999-06-01
2002-05-07
Hallacher, Craig A. (Department: 2853)
Incremental printing of symbolic information
Ink jet
Controller
C347S043000
Reexamination Certificate
active
06382757
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a printer having a head, which provides inks of different densities with respect to at least one hue and may create at least two different types of dots having different ink quantities with respect to each of the different density inks, and enabling a multi-tone image to be printed with inks spouted from the head. The present invention also pertains to a method of printing as well as a recording medium for implementing the method.
2. Description of the Related Art
Color printers that spout multiple colors of inks from a head are widely used as an output device of a computer, which prints images processed by the computer in a multi-color, multi-tone manner. In order to further improve the printing quality in an area of low image density, that is, a highlighted area, a printer and a printing method using higher density and lower density inks have been proposed. This technique provides both a higher density ink and a lower density ink for an identical hue and controls the spout of these inks, so as to attain printing of the excellent tone expression.
Another proposed printer for multi-tone expression creates two different types of dots having different ink densities and ink quantities and thereby changes the density per unit area in multiple stages (for example, JAPANESE PATENT LAID-OPEN GAZETTE No. 59-201864). In this printer, one pixel consists of four dots. The technique applied to this printer changes the frequency of appearance of the higher-density dots and the lower-density dots in the pixels and thereby enables an image to be printed with multiple densities.
In the printer that spouts ink and creates dots, the quantity of ink per unit area, that is, the ink duty, should be controlled not to exceed a preset level, which depends upon the type of printing paper. The spout of ink exceeding this preset level causes the printing paper to be readily broken and makes ink stains on the printing paper, thereby lowering the picture quality of resulting printed images.
In the prior art printer that enables creation of two different types of dots having different ink densities and ink quantities, there is no specific consideration for the ink duty. The prior art printer simply creates these two different types of dots according to the input tones of the respective pixels based on a preset pattern, and does not take into account the restriction of ink duty nor attain the well-balanced regulation of the quantities of inks having different densities to create the different types of dots.
SUMMARY OF THE INVENTION
The object of the present invention is thus to provide a technique applicable to a printer, which enables at least two different types of dots having different ink densities and ink quantities to be utilized effectively when there is a requirement in regulation of the ink quantities for dot creation, for example, when there is a restriction of ink duty.
At least part of the above and the other related objects is attained by a printer that creates a plurality of dots and thereby prints an image on a printing medium. The printer includes: an input unit that inputs image data for each of pixels included in an original image; a head that provides a plurality of inks, which include at least two inks of different densities with respect to at least one hue, and enables creation of at least two different types of dots having different quantities of ink for each of the plurality of inks; an expected ink quantity setting unit that sets an expected quantity of ink, which is to be spouted for creation of a dot, in each pixel based on the image data, with respect to each of the plurality of inks; a multi-valuing unit that sets an on-off state of each of the at least two different types of dots in each pixel, based on the expected quantity of ink, with respect to each of the plurality of inks; and a dot creation unit that creates dots set in the on state.
In the printer of the present invention, the technique sets the expected quantity of ink used for creation of a dot in each pixel, with respect to each of a plurality of inks, which include at least two inks having different densities provided for at least one hue, and determines the type of the dot to be created in each pixel. This arrangement enables the quantities of ink used for creation of dots to be regulated appropriately.
The expected quantity of ink here represents an ideal quantity of ink to be spouted in each pixel for expression of the tone value included in the input image data. In the printer of the present invention, the quantities of ink used for creation of dots are practically restricted to several values. The expected quantities of ink are, however, not restricted to these several values but may take any continuous values in a specific range. Although the expected value is a term generally used in the field of probability, the term ‘expected value or quantity’ in this specification means a value or quantity of ink expected to spout in each pixel.
The expected quantity of ink may not coincide with a quantity of ink actually required for expressing the tone value of the image data but may be determined by taking into account the characteristics of the nozzles, from which ink is spouted, and other related factors. The expected quantity of ink may be greater than or less than the quantity of ink actually required for expressing the tone value of the image data. By way of example, the expected quantity of ink may be set greater for some tone values and set smaller for other tone values.
In accordance with one preferable application of the printer, the image data includes tone values with respect to at least one color component in a color space. The expected ink quantity setting unit includes: an expected values storage unit that stores expected quantities of inks corresponding to combinations of tone values regarding a plurality of color components in the color space in the form of a table; and a unit that refers to the table, which is stored in the expected values storage unit, and reads an expected quantity of ink in each pixel corresponding to the input image data.
The expected quantities of inks to be spouted in the respective pixels are determined according to the combinations of the tone values regarding the plurality of color components in the color space and stored in the form of a table. The arrangement discussed above enables the expected quantity of ink to be set in each pixel, based on this table.
In the printer of the above configuration, it is preferable that the table stored in the expected values storage unit specifies expected quantities of each color ink, which are determined by taking into account expected quantities of the other color inks irrespective of the hue, corresponding to the combinations of the tone values regarding the plurality of color components in the color space.
In the table stored in the expected values storage unit, the expected quantities of each color ink are determined by taking into account the expected quantities of the other color inks. This arrangement ensures regulation of the total quantity of ink and improves the picture quality of a resulting image. There is typically an upper limit in quantity of ink to be spouted per unit area. For example, it is assumed that the printer records an area of a specific density with two inks of different densities, that is, the light ink and the deep ink, for cyan. When the expected quantities of inks are small for the other hues, there is a sufficient margin to the upper limit. In this case, the expected values are set to use a large quantity of the light ink, which makes cyan dots relatively inconspicuous. When the expected quantities of inks are large for the other hues, on the other hand, there is an insufficient margin to the upper limit. In this case, the expected values are set to decrease the quantity of the light cyan ink and increase the quantity of the deep cyan ink.
A variety of methods may be applied to the multi-valuing unit in the printer of the
Hallacher Craig A.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Seiko Epson Corporation
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