Image recording method

Details Image recording method Image recording method

2001-01-11

2002-06-18

Nguyen, Thinh (Department: 2861)

Incremental printing of symbolic information

Ink jet

Controller

C347S043000

Reexamination Certificate

active

06406117

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image recording method for recording color images on a recording medium by using a plurality of colored inks that have different densities of the same color, to express a specific basic color.
2. Description of Related Art
In recent years, color printers have come into broad distribution as image recording devices for recording computer-processed images in different tones and with a plurality of colors. Such color printers eject different colors of ink from a recording head. Generally, color printers reproduce images using ink of four basic colors of cyan (C), magenta (M). yellow (Y), and black (K), which will be referred to as “normal inks” hereinafter.
SUMMARY OF THE INVENTION
In order to improve image quality, it is conceivable that color printers use “light ink” together with normal ink in order to reproduce a single specific color such as cyan (C) or magenta (M). Each light ink has a density lower than its corresponding normal ink. In other words, light ink and, normal ink are different inks that have different densities of the same basic color.
FIG. 1
represents how images can be reproduced using both normal and light inks for some basic color, such as cyan (C) or magenta (M). As shown in
FIG. 1
, when color data, inputted from a computer or the like, has a small tone value, then the basic color is reproduced using the light ink only. Variations in the tone value of the color data can be reproduced by changing the dot density of the light ink. Once the tone value of the color data reaches a predetermined reference tone value (“100” in this example), then normal ink starts being used together with light ink. As the tone value of the color data increases further from the reference tone value, the dot density of the light ink is gradually reduced, while the dot density of the normal ink is gradually increased to reproduce the desired tone of the basic color.
In order to form an image on a recording medium using light and normal inks in the manner described above, it is conceivable that a light ink conversion table and a normal ink conversion table are prepared in advance for each of the basic colors, such as cyan (C) and magenta (M), as shown in FIGS.
2
(
a
) and
2
(
b
).
In order to produce the light ink conversion table and the normal ink conversion table, the reference tone value, which indicates when to start using normal ink, should be first determined. It is conceivable that the reference tone value be determined in a manner described below.
A plurality of color patches are outputted onto a recording medium based on a plurality of tone values that differ from one another in stepwise increments. Then, normal ink is ejected in a predetermined dot density (for example, 1%) onto each color patch. An operator visually observes the color patches, and selects one or more allowable color patches where the normal ink does not give a highly noticeable dot “rough” appearance. The operator then selects one color patch that has been produced by the smallest tone value among the selected one or more allowable color patches. The operator sets, as the reference tone value, the tone value of his/her finally-selected color patch.
Then, the conversion tables of FIGS.
2
(
a
) and
2
(
b
) are prepared to represent the input/output characteristics of FIG.
1
. Based on the thus obtained conversion tables, color data inputted, from a computer or the like, will be converted into ink data for light ink and ink data for normal ink. Light ink and normal ink will be selectively ejected, based on the thus obtained ink data, to form an image on the recording medium.
It is noted, however, that the density level actually outputted onto a recording medium changes according to various printer characteristics, such as the type or model of the printer, the resolution, the type of ink used, and the type of recording medium. For example, it is assumed that dot “roughness” or light ink “bleeding (blurring)” do not appear noticeable when a basic color is reproduced by outputting light ink and normal ink under some condition onto a particular kind of recording medium. However, when printing is performed onto another kind of recording medium with different shade, different quality, or different absorbency, even if the printing is performed under the same condition, dot “roughness” and/or light ink “bleeding” will possibly appear noticeable. It therefore becomes impossible to always record images under optimum conditions.
Additionally, when reproducing a basic color using light ink and normal ink, as shown in
FIG. 3
, a point of inflection tends to occur in the output density level of the basic color at the reference tone level, that is, at the tone level where normal ink starts being used. At the inflection point, the first derivative of the output density level changes discontinuously. Such an inflection point can result in pseudo contours in the recorded image.
It is conceivable that, in order to suitably reproduce colors based on color data inputted from a computer or similar source, color correction and tons correction be performed onto the inputted color data using previously-prepared color correction table and tone correction table. Each of the color correction table and tone correction table is generally provided with correction values for some tone values, which are arranged at a fixed interval, rather than for all the tone values. Interpolation is therefore employed to calculate approximate correction values for tone values with no corresponding correction values. Color correction and tone correction are performed using the approximate correction values. However, precision of the interpolation process drops when the output density level for input color data includes the inflection point as described above with reference to FIG.
3
. It becomes impossible to determine a suitable approximate correction value, and consequently impossible to perform suitable color correction or suitable tone correction.
It is therefore a first objective of the present invention to provide an image recording method that enables always recording images in a suitable condition, regardless of changes in printer characteristics, when expressing a basic color using different inks that have different densities of the same color.
It is a second objective of the present invention to provide an image recording method that enables performing suitable correction operation, without generation of pseudo contours in the image recorded on the recording medium, when expressing a basic color using different inks that have different densities of the same color.
In order to attain the above and other objectives, the present invention provides a method for recording a color image on a recording medium by expressing at least one basic color using a plurality of inks that have different densities of the corresponding color, the method comprising the steps of: preparing a plurality of conversion tables, each for converting color data of at least one basic color into converted color data of the plurality of inks that have different densities of the corresponding color, each conversion table matching one of a plurality of sets of printer characteristics; selecting a set of printer characteristics, with which printing operation is desired to be performed; selecting one conversion table from the plurality of conversion tables in accordance with the selected set of printer characteristics: converting, based on the selected conversion table, the color data of each of the least one basic color into converted color data of the plurality of inks that have different densities of the corresponding color; and performing printing operation to record a color image on a recording medium based on the converted color data with the selected set of printer characteristics.
As used with respect to the present invention, “printer characteristics” refers to various conditions that influence recorded images. Representative examples of the printer characteristics include;

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