Printing system, print controller, printing apparatus,...

Incremental printing of symbolic information – Ink jet – Fluid or fluid source handling means

Reexamination Certificate

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C347S100000

Reexamination Certificate

active

06592212

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technique of forming an adequate distribution of ink dots of respective colors on a printing medium, so as to print an image expressed in a wide range of natural colors.
2. Description of the Related Art
In a printing apparatus that ejects ink droplets of various color inks from a print head and thereby expresses an image of natural colors on a printing medium, four color inks, that is, cyan (C), magenta (M), yellow (Y), and black (K), are basically used to create ink dots and print an image. The printing apparatus regulates the hue and the lightness, which are indexes representing the color, so as to print an image expressed in a wide range of natural colors. The hue, that is, the ‘color’ or ‘tint’, such as red or blue, is regulated by changing the ratio of dots of the C, M, and Y inks ejected from the print head. The lightness is, on the other hand, regulated by changing the density of dots. Regulating the ratio and the density of dots created with the respective color inks on the printing medium enables a printed image to have a wide range of natural colors.
Some recently developed printing apparatus use light cyan (LC) ink and light magenta (LM) ink, (additionally light yellow (LY) ink in some cases) in addition to the above four basic color inks, so as to significantly improve the picture quality in an area of high lightness. In the case where an image in the area of high lightness (that is, the highlighted area) is printed with only four color inks, C, M, Y, and K, a sparse distribution the C and M dots undesirably makes these dots conspicuous and thereby lowers the picture quality of the printed image. The phenomenon of making the dots conspicuous to worsen the picture quality is expressed by the term ‘poor granularity’. It is difficult to reproduce the image information with regard to a fine part with the sparsely distributed dots. This is also the reason of the poor picture quality of the resulting printed image with only the four color inks, C, M, Y, and K. The dots of the LC and LM inks (additionally LY ink in some occasions) are, on the other hand, not so conspicuous as the dots of the C and M dots and thereby do not lower the picture quality of the highlighted area. The LC and LM inks enable the dots to be formed at a higher density than the C and M inks. This accordingly enables reproduction of the image information with regard to the fine part and further improves the picture quality. Because of these reasons, the printing apparatus using the six color inks including the LC and LY inks (or the seven color inks further including the LY ink) improves the picture quality of the highlighted area.
The prior art printing apparatus including those using the light inks, however, can not sufficiently improve the picture quality in an area of low lightness (that is, the shadow area), because of the reasons discussed below. Especially the printing apparatus using the light inks have an insufficient improvement in picture quality in the shadow area, while significantly improving the picture quality in the highlighted area.
This problem is explained with an example of a gradation pattern from red to black with a gradual decrease in lightness. The color ‘red’ is reproduced by mixture of magenta dots and yellow dots. The lightness is lowered by addition of cyan dots or black dots. Formation of black dots on red dots makes the black dots extremely conspicuous in an area supposed to have a homogeneous color. This results in the poor granularity. The dots of cyan, which is complementary to red, are also rather conspicuous on the red dots, although the degree of conspicuousness is lower than that of the black dots. Formation of cyan dots on red dots thus also results in the rather poor granularity. As in the case of the highlighted area, the use of the light cyan ink effectively improves the granularity. From the viewpoint of the improvement in granularity, the light cyan ink is most preferable over the cyan ink and the black ink to form dots over the red dots. Addition of the cyan dots or the black dots on the red dots having a sufficiently low lightness, however, does not make the cyan dots or the black dots so conspicuous but keeps the granularity at a fair level.
There is a restriction of total quantity of ink ejected per unit area on the printing medium, and it is impossible to heighten the density of dot formation limitlessly. This restriction is referred to as the restriction of ink duty. Ejection of ink over the allowed density of dots causes blots or wrinkles on the printing medium. In order to avoid such problems, each printing medium has a preset maximum density of dots (restriction of ink duty). The total density of dots created with the respective inks should not exceed this restriction of ink duty.
When the gradation pattern from red to black is printed, it is required to add the light cyan dots or the cyan dots. The color ‘red’ is originally expressed by a large number of yellow dots and magenta dots as mentioned previously. Formation of even a small number of light cyan dots or cyan dots thus causes the total quantity of ink to reach the restriction of ink duty. In the course of the gradation, there is accordingly a prohibition of further addition of the light cyan dots or the cyan dots. In the practical operation, when there is some margin for the restriction of ink duty, light cyan dots are added to red dots to lower the lightness. When the total quantity of ink reaches the restriction of ink duty, even if the cyan dots may have adverse effects on the granularity of the resulting printed image, the cyan dots instead of the light cyan dots should be formed to further decrease the lightness. When the total quantity of ink again reaches the restriction of ink duty under the condition of the perfect replacement of the light cyan dots with the cyan dots, even if the black dots are conspicuous, the black dots instead of the cyan dots should be formed to further decrease the lightness. In the shadow area (the area of low lightness) having the gradation from red to black, the cyan dots and the black dots are often used irrespective of their conspicuousness, because of the restriction of ink duty. This naturally results in the poor granularity.
The above description regards the example of printing the gradation pattern from red to black. The formation pattern of ink dots should be specified under the various limitations including the improvement in granularity and the restriction of ink duty. The design of the optimum dot formation pattern accordingly requires a lot of time and labor with the trial and error.
SUMMARY OF THE INVENTION
The object of the present invention is thus to enhance the degree of freedom in specification of dot on-off conditions with regard to a plurality of different inks and thereby improve the picture quality in a specific area including a low lightness area (shadow area).
At least part of the above and the other related objects is actualized by a printing system, which includes a printer that creates dots with a plurality of different inks, so as to print an image on a printing medium, and a print controller that supplies control information to the printer, so as to control the creation of dots with the plurality of different inks. The print controller includes: a dot on-off condition specification unit that specifies dot on-off conditions with regard to a plurality of basic color inks and a dark ink based on input image data, the plurality of basic color inks being combined with one another to express achromatic color, the dark ink having a main wavelength region of light absorption substantially identical with that of one basic color ink selected out of the plurality of basic color inks but a lower lightness than that of the selected basic color ink; and a control information output unit that outputs the specification of the dot on-off conditions with regard to the plurality of basic color inks and the dark ink to the printer as the control information. Th

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