JP2003246099A - Color image output device and method for selecting ink - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color image output device and a method for selecting ink in which gray insensitive to variation of apparatus can be outputted using smallest number of kinds of ink. <P>SOLUTION: In the color image output device, at least one brightness level is provided for each of basic colors including at least Y (yellow), M (magenta), C (cyan) and K (black) and the basic colors at respective levels are combined in color representation. The number of levels is determined for each basic color based on the difference between the lowest lightness level of respective basic colors and the lightness of white, and the number of levels for each basic color is determined to increase monotonously as the difference of lightness between respective basic colors increases. The number of levels of color K is set not smaller than the largest number of levels of respective basic colors except K and larger than the number of levels of one of respective basic colors except K. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image output apparatus for forming an image by combining inks of different colors and an ink selection method.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 4, the frequency response of the human eye is higher in light-dark than red-green or yellow-blue. For example, using halftoning (error diffusion, blue noise, dither, etc.),
When expressing an intermediate gradation, if a dark ink such as a black (K) ink is frequently used, a granular feeling is felt. Therefore, in an image output device such as a conventional inkjet printer, black ink should be used as little as possible,
By reproducing the output colors with the three color inks of cyan (C), magenta (M) and yellow (Y),
The graininess of the output image is reduced. On the other hand, in an image output device such as an inkjet printer, it is desired to output gray that is insensitive to variations in the device and to realize cost reduction with a small number of recording heads and inks.

[0003]

By the way, in recent years,
Inks with sharp spectral absorption are used to expand the range of colors to be reproduced. When such inks are used and YMC is combined to output gray, the gray light source dependency becomes high. I will end up. When the light source dependency increases, for example, when illuminating the output gray with two types of light sources that emit light that looks the same with the naked eye, one light source looks gray and the other light source becomes chromatic. It may be visible (metamerism).

Further, in the case of outputting gray by combining YMC, when various conditions of the ink jet printer at the time of printing (for example, ink state, medium, storage state, etc.) change, the output gray state also changes. It has deteriorated the quality. In other words, the image quality is usually gray stability and memory colors (colors in memory are usually brighter than actual colors, so when reproducing colors, memory colors should be selected rather than the original color reproduction. However, the gray state among them deteriorates as described above, resulting in deterioration of image quality. Also, in order to improve the gray state, a method of reproducing the color by using the K color ink as much as possible (100% U
CR, 100% GCR, Maximum Black)
When using, the graininess becomes a problem as described above.

An object of the present invention is to provide a color image output device and an ink selection method capable of outputting a gray color which is insensitive to a variation in a device with the smallest possible number of ink types.

[0006]

The invention according to claim 1 is
Each basic color including at least Y (yellow), M (magenta), C (cyan), and K (black) is provided with at least one lightness level number, and color reproduction is performed by combining the basic colors of each level. A color image output device, wherein, for each of the basic colors, the number of levels is determined based on a difference in brightness between the lowest level brightness of each of the basic colors and the brightness of white, and It is determined that the number of levels for each of the basic colors increases monotonically as the lightness difference for each color increases, and the number of levels of the K color is the same for each basic color excluding the K. And the number of levels is set to be greater than the number of levels of one of the basic colors excluding at least K.

According to the first aspect of the present invention, the number of levels is determined for each basic color based on the difference in brightness between the lowest level lightness of each basic color and the lightness of white, and It is determined that the number of levels for each basic color increases monotonically as the difference in lightness for each basic color increases, so a basic color with a larger lightness difference from white has a greater number of levels than a bright basic color. As a result, even if the color is dark, it is possible to provide a lightness level close to that of the output color. Therefore, it is easy to match the brightness of the output color, and it is possible to reduce the graininess of the output image when the color is reproduced by using many dark colors. The number of K color levels is set to be equal to or greater than the maximum level number of each basic color excluding K, and is set to be larger than at least one color level of each basic color excluding K. Therefore, even when the K color is heavily used to reproduce the color, it is possible to correspond to the brightness to be output, and it is possible to reduce the graininess of the output image.

Here, "the number of levels of each color increases monotonically" means that, for example, YMCK is used as a basic color.
In the case of four colors, the relationship of the number of levels of each color of YMCK is Y ≦ M ≦ C ≦ when it is assumed that the order of the lightness difference of the lowest level of YMCK increases in the order of YMCK. K, Y <K (color with the smallest difference in brightness (one of YMCK) has the largest number of levels (color with one of YMCK) has the largest number of levels) Good. That is, the number of K levels is at least two or more.

According to a second aspect of the present invention, in the color image output apparatus according to the first aspect, at least a basic ink that is a basic is provided for each of the basic colors, and the recording that outputs the basic ink to a recording medium. A head is provided, and the level of the brightness is at least the formation position, the number, the size, and the basic color of the dots for each of the basic colors output from the recording head within a predetermined area of the recording medium. A color image output device, characterized in that it is determined by any one of the types of ink having different lightness values provided for each.

According to the second aspect of the present invention, the lightness level is such that at least the formation position, number and size of dots for each of the basic colors output from the recording head within a predetermined area of the recording medium. , And the type of ink having different lightness provided for each of the basic colors, the level of lightness may be, for example, at least the formation position, the number, or the size of dots for each basic color. When it is determined by one of the basic colors, it is possible to output a color having a lightness corresponding to each level without increasing the type of ink for each basic color, and it is possible to reduce the cost.
When the lightness level is determined by the type of ink with different lightness provided for each basic color, the darker ink having a larger lightness difference from white has a larger number of levels than the lighter ink, Even with dark-colored ink, it is possible to select ink having a lightness level close to that of the color to be output. For this reason, it is possible to easily correspond to the brightness of the color to be output, and it is possible to reduce the graininess of the output image when the color is reproduced by frequently using dark color, for example, black ink.

Further, the ink here is basically a liquid, but it may be a solid having a dye, and the image output device is a device using ink or an ink ribbon. It is also possible to use a color toner or a color toner.

According to a third aspect of the present invention, in the color image output apparatus according to the second aspect, there is provided control means for converting the color data included in the image data into data for each basic color and determining the color. When the control means converts the main color data of the image data into data for each basic color to determine a color, the ink usage amount of the K color is set to the ink usage amount of each basic color excluding the K color. The feature is that the color is determined so that the amount of ink used is greater than the minimum amount of ink used.

According to the third aspect of the invention, when the control means determines the color by converting the main color data of the image data into data for each basic color, the ink usage amount of the K color is K
Since the color is determined so as to be larger than the minimum ink usage amount of the basic color inks other than K, when the image is output, K inks are combined in the main colors and at least K inks are combined. Ink of K is used with a larger usage amount than the lowest usage amount of each basic color except for. The K ink is spectrally stable, and by combining this K ink, it is possible to stabilize the gray balance with respect to equipment fluctuations and light source fluctuations. Further, at this time, not only the black ink but also the gray ink having high brightness is used as the K ink, so that the generation of graininess is prevented. Further, when an image of a color with low lightness is output mainly by combining inks of respective basic colors (for example, YMC) except K, each ink of YMC is used to reduce the lightness, and the ink of YMC is used. Although the amount is large, in the above configuration, the ink of K is used to reduce the lightness, and the usage amount of the three colors of YMC is reduced accordingly, so the target usage while suppressing the usage amount of the YMCK ink as a whole. It is possible to express an image with the brightness.

In general, when a gray color is formed by using K ink, for example, the characteristic of the spectral reflectance is flatter than that of the gray color formed by YMC ink, so that it becomes chromatic even if the light source changes. It becomes difficult to see (when YMC is combined to express gray, the absorption peak of the dye of YMC becomes high, and it becomes low at other points, and the wave is reflected, so that the spectral reflectance is not flat). If the spectral reflectance is completely flat, it does not affect the change of the light source, and stable printing is possible. In other words, it is desirable to select the K ink (black or gray ink) whose spectral reflectance characteristics are as flat as possible.

According to a fourth aspect of the present invention, in the color image output apparatus according to the third aspect, the resolution is 360 dpi or more and the number of K levels is 3 or more.

According to the invention of claim 4, the resolution is 3
If it is 60 dpi or more and the number of K levels is 3 or more, an output image with less graininess can be reliably obtained.

According to a fifth aspect of the present invention, in the color image output apparatus according to the second aspect, there is provided control means for determining color by converting color data included in the image data into data for each basic color. The control means divides an output image into a black-and-white image and a color image from the image data, and determines the amount of K ink used when the black-and-white image is output.
It is characterized in that the amount of ink used for the color K is larger than the amount of ink used for outputting the color image.

According to the fifth aspect of the present invention, the control means divides the output image from the image data into a black-and-white image and a color image, and determines the amount of K ink used when the black-and-white image is output. Since the amount of ink of the K color used when outputting a color image is made larger, it is possible to stabilize the gray balance with respect to a black-and-white image with respect to device variations and light source variations. Here, the color image and the monochrome image may be divided for each image file, or may be divided into a color image portion and a monochrome image portion in one image file. Is also good.

According to a sixth aspect of the present invention, a basic dark ink is provided for each of the basic colors including at least Y (yellow), M (magenta), C (cyan) and K (black). One or more colors of each of the basic colors is a kind of light color ink having a higher lightness than the dark color ink,
Alternatively, there is provided a method of selecting an ink used in a color image output device, which is provided with two or more kinds of light color inks having a lightness higher than that of the dark color ink and different in lightness from each other, and performing color reproduction by combining these inks , The number of levels indicating the number of types of ink in which the dark color ink and the light color ink are combined for each of the basic colors is based on the lightness difference between the lightness of the dark color ink and the lightness of white for each of the basic colors. And the number of levels of each basic color is determined to increase monotonically as the lightness difference in each of the basic colors increases, and the number of levels set for each color of each of the basic colors It is characterized in that the same number of inks having different lightnesses are selected for each of the basic colors.

According to the invention described in claim 6, it is possible to obtain the same effect as that of the invention described in claim 2.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings of FIGS.

The color image output device of this embodiment is
Each basic color including at least Y (yellow), M (magenta), C (cyan), and K (black) is provided with at least one lightness level number, and color reproduction is performed by combining the basic colors of each level. It is a thing. In the following, a case where each of the colors YMCK is provided as a basic color will be described as an example. Further, the color image output device has a halftoning function. An inkjet printer will be described as an example of the color image output device.

An ink selection method for determining the number of ink levels for each color of YMCK will be described below. These basic colors (Y (yellow), M (magenta), C (cyan) and K (black)) are provided with basic dark ink, and at least one of the basic colors is A kind of light color ink having a lightness higher than that of the dark color ink, or two or more light color inks having a lightness higher than that of the dark color ink but different in lightness from each other are provided. Further, here, the number of types of ink, which is a combination of the dark color ink and the light color ink for each basic color, is defined as the level number. That is, what is described below is a method of selecting the type of ink used in an inkjet printer when designing the inkjet printer.

First, YMCK reference inks (dark color inks: Y (Yellow), DM (Dark Magenta), D
The brightness of C (Dark Cyan) and DK (Dark Black) is calculated. At this time, from the tristimulus values (XYZ) obtained from the measured values of Y, DM, DC, and DK (for example, RGB values), each brightness L * (L * a determined by CIE (International Commission on Illumination)) * B * luminance value) is calculated. The calculation of the lightness L * is the formula defined by CIE.

[Formula 1] Alternatively, you can simply use Y / Y0
May be raised to 1 / 2.5, or if the background is white or black, it may be raised to 1/2 or 1/3. When the recording medium is paper, the CIE requires about 20% gray assuming that the background is white, but here, assuming that the background is white, the brightness calculation curve for the white background is calculated. It is preferable to obtain the brightness by using it. By using the brightness calculation curve for the white background, the graininess near the highlight is reduced, and the output image becomes more like a photographic image.
Further, in the present embodiment, the Y value when the paper is a white background is used for Y0, but the Y value corresponding to the perfect diffuse reflection surface may be used. The tristimulus values and the lightness L * of the dark color ink used in this embodiment are shown in Table 1.

[0025]

[Table 1]

When the lightness L * of each dark color ink is obtained, the lightness difference between the lightness of each dark color ink and the lightness of white is calculated. Here, the white lightness is the lightness of the recording medium when it is not colored, and in the present embodiment, for example, lightness L * = 100. Here, assuming that the total number of inks used in the inkjet printer 1 is a natural number N, the largest difference among the undivided lightness differences of the dark inks (K: lightness difference 77.2 in the present embodiment). ) Is selected and the brightness difference is divided into two (77.2 / 2 = 38.6). Next, of the brightness differences divided into two and the brightness differences not selected, the one having the largest brightness difference (in the present embodiment, C: 58.
2) is selected and the brightness difference is divided into two (58.2 / 2 = 2).
9.1) Hereinafter, among the brightness differences of the dark color ink and the divided brightness differences, selecting and dividing the largest brightness difference among the brightness differences not selected is referred to as the brightness difference of the dark color ink. Repeat until the total number of divided brightness differences reaches N. Note that, when repeating, if there is a value whose divided brightness difference is larger than the undivided brightness difference, the divided brightness difference is further divided. At this time, the lightness difference after M (natural number) division is multiplied by M and divided by (M + 1) to calculate the lightness difference after division.

In the dark color ink of the present embodiment, when the total number N of inks is set to 4 to 12 and the number of divisions of each dark color ink is calculated, as shown in Table 2, there is a large difference in lightness for each color of YMCK. As the number of levels increases, the number of levels for each color of YMCK monotonically increases. The right column shows the number of divisions, and the left column shows the difference in brightness. When the present invention is applied, the total number of ink types is preferably 5 or more, and more preferably 8 or more when the number of K ink levels is 3 or more. When cost is taken into consideration, it is preferable that the number of types of ink is small. Thus, for example, when cost is taken into consideration, the total number of types of ink is preferably 8 or less.

[0028]

[Table 2]

In this way, when the level number of each dark color ink is obtained, the light color ink having the lightness corresponding to the division number is selected. That is, the target lightness of the light color ink is represented by 100−lightness difference × i. (I: Natural Number Below Divided Number) Specifically, selection of K light color ink when the total number of inks is 8 will be described. At this time, 8 colors of Table 2-YMC
According to the column K, Y has a level of 1, a brightness difference of 8.4, M has a level of 2, a brightness difference of 23.1, and C has a level of 2, a brightness difference of 2.
9.1 and K have 3 levels and a brightness difference of 25.7. The ink for each color of YMCK has a target lightness of 100-8.4 × 1 = 91.6 for Y ink (Y), and a target lightness of 100-23.1 for M dark color ink (DM). ×
1 = 76.9, M light color ink (LM: Light magent)
In a), the target brightness is 100-23.1 × 2 = 53, C
In the dark ink (DC) of No. 3, the target lightness is 100-29.
1 × 1 = 70.9, C light color ink (LC: Light Cya
n), the target brightness is 100-29.1 × 2 = 41.
With 8 and K dark color ink (DK), the target lightness is 100-
25.7 × 1 = 74.3, K light color ink (LK: Light
t Black), the target brightness is 100-25.7 × 3 = 2.
2.9, Light color ink (LL with lightness between DK and LK)
K: Light Light Black), 100-25.7 x 2
= 48.6. In the present embodiment, the difference in lightness of ink levels is set at equal intervals. However, even if the difference in lightness is not evenly set, the setting of the number of levels may have a large difference in lightness as described above. Good.

That is, the number of levels for each basic color is determined based on the difference in brightness between the lowest level brightness for each basic color and the brightness of white, and the difference in brightness for each basic color becomes large. Accordingly, the number of levels for each basic color is determined to increase monotonically.

The structure of the ink jet printer 1 will be described. As shown in FIG. 1, the main configuration of the inkjet printer 1 includes a conveyance unit 2 that conveys a recording medium at the time of printing, a recording head 3 that outputs ink to the recording medium, and a carriage 4 that mounts a plurality of recording heads 3. , And a control unit (control means) 30 that controls these units. The resolution of this inkjet printer is 3
It is preferably set to 60 dpi or more.

A plurality of recording heads 3 are provided corresponding to the total number of inks (eight in this embodiment: Y, DM, LM, DC, L).
C, DK, LK, LLK).

The control unit 30 includes an interface 31, R
OM (Read Only Memory) 32, RAM (Random Acces
memory 33, CPU (Central Processing Unit)
34, etc., and controls various devices connected to the interface 31 according to the control program and control data written in the ROM 32.

The interface 31 includes a transport means 2,
The recording head 3, the carriage 4, etc. are electrically connected.

Various control programs and control data relating to the operation of each section of the ink jet printer are written in the ROM 32.

The RAM 33 is capable of storing a plurality of data input only while power is being supplied, a storage area for storing various data such as image data to be printed, and a CPU.
A work area by 34 is provided.

The CPU 34 reads out a program designated from various programs stored in the ROM 32 from the R program.
It is developed in the work area in the AM 33, and various processes according to the program are executed according to the input signal from each sensor.

The control unit 30, which controls the overall operation of the ink jet printer 1, reproduces the colors (RGB values) used in the image data by using YMCK inks and halftoning. Here, a process from input image data to ink ejection will be described with reference to FIGS. 2 and 3.

As shown in FIG. 2, the control unit 30 reads the image data of the output image from the ROM 32 (process S).
1), the output image is divided into a monochrome image region and a color image region based on the RGB value and L * a * b * value of the image data (process S2). Here, as a method for discriminating a monochrome image and a color image, for example, R of image data is used.
If the GB value is R = G = B, it is determined to be a monochrome image,
Other than that, there is a method to judge that it is a color image,
In addition to this, a method of manually setting the determination condition or setting in association with the data format may be used. Further, here, for example, one image data file is discriminated into a color image area and a monochrome image area. However, for each image data file, the image data is a color image file or a monochrome image. It may be configured to determine whether it is a file. When the output image is divided into a monochrome image and a color image, the process proceeds to step S3.

In step S3, the color data (RGB value, L * a * b * value, etc.) included in the image data is indicated by Y, which indicates the amount of combination when YMCK colors are mixed at the time of color reproduction.
Color conversion for converting into an MCK value (data for each basic color) is performed. At this time, the K value of the area determined to be the monochrome image in the process S2 is converted to a value larger than the K value of the area determined to be the color image. That is, the K color ink usage amount when outputting a monochrome image is set to be larger than the K ink usage amount when outputting a color image. If the K ink used is completely achromatic, it is possible to convert the L * a * b * values of the area of the black and white image into only K values (intermediate gradations are DK, LK, L
It is expressed by half-toning using LK).

Even when the output image is determined to be a color image, the K value is set to be smaller than the minimum value of the YMC values in the area where each color of YMCK of the output image is a main color. It may be set large. That is, when converting the main color data of the image data into YMCK values and determining the color, the ink usage amount of the K color should be larger than the minimum ink usage amount of the YMC ink usage amounts. Have decided the color. Specifically, if the brightness of the output image is lower than, for example, around L * = 50, conversion may be performed so that the K value becomes larger than the minimum value among the YMC values. As a method of increasing the K value in this way, for example, Japanese Patent No. 2952489 (maximizing the K amount) or Japanese Patent Laid-Open No. 6-242523 (smoothing is performed,
Make the change of each color material smooth)) and the like may be applied. When the YMCK value is obtained by converting the L * a * b * value, the process proceeds to step S4.

In step S4, halftoning is performed based on the input YMCK value. Examples of the halftoning method include multi-valued error diffusion, dither method, and blue noise mask method. In the present embodiment, the halftoning method will be described by exemplifying a case where an error diffusion method is used as shown in FIG. 3, but a specific method of the error diffusion method is disclosed in Japanese Patent Laid-Open No. 9-139842. Publication (Y
MC performs error diffusion independently) and Japanese Patent Laid-Open No. 2000-2
For example, those described in Japanese Patent Publication No. 95478 (YMCK independently performs error diffusion) may be applied.

In step S401, each value of YMCK is subjected to gradation conversion, and the process proceeds to step S402. That is, process S
In 401, in order to prevent data loss due to halftoning, conversion is performed in advance to increase the number of gradations of each color of YMCK from, for example, 8 bits to 12 to 14 bits. In step S402, each value of YMCK subjected to gradation conversion is divided into upper data and lower data. The upper data represents, for example, a color corresponding to the above level of ink,
The lower data represents the color of the intermediate gradation between the levels generated by the error diffusion method as described later. And
The upper data is moved to the processing S404, and the lower data is moved to the processing S403.

In the process S403, the error diffusion method is applied to the lower data of YMCK to reproduce the color of the intermediate gradation, and the process S403 is performed.
Move to 404. At this time, as described in Japanese Patent Application Laid-Open No. 7-264423, it is preferable to perform error diffusion separately for the lower data of YMC and the lower data of K, but the lower data of YMCK are separately provided. It may be configured to perform error diffusion.

In step S404, the upper data of YMCK and the lower data of YMCK reproduced by error diffusion are
Each ink (Y, DM, LM, DC, LC, DK, LK,
LLK) output data is determined, and the process proceeds to step S405.

In the process S405, Japanese Patent Laid-Open No. 2000-295 is used.
As described in Japanese Patent No. 478, supercell generation for correcting output data of each ink is performed, and the process proceeds to step S5.

In step S5, an ejection signal indicating the ejection amount and ejection position of each recording head 3, a movement signal indicating the movement amount of the carriage 4 and the conveyance amount of the recording medium, etc. are created from the output data of each ink. Then, the process proceeds to step S6.
In step S6, the ejection signal, the movement signal, and the like are output to the respective units (carriage 4, conveying means 2, recording head 3) to operate the respective units, and printing is performed on the recording medium.

As described above, according to the ink jet printer 1 of the present embodiment, the level number indicating the total number of the dark color ink and the light color ink is YM for each color of YMCK.
It is determined based on the difference in lightness between the dark color ink and the lightness of white for each color of CK, and Y increases as the lightness difference increases.
Since the number of levels for each MCK color is set to monotonically increase, the dark ink having a larger lightness difference has a larger number of levels than the light ink, and the ink level corresponding to the lightness of the color to be output. Can be selected. Therefore, it is possible to easily correspond to the brightness of the output color and reduce the graininess of the output image.

If the lightness of the output image is lower than the predetermined lightness, the control unit 30 controls the L of the output image.
When converting * a * b * values to YMCK values, the K value becomes YM
Since it is set to be larger than the minimum value of the C values, the recording head 3 is configured so that the ejection amount of the K ink in the recording head is larger than the minimum ejection amount of the YMC ink ejection amounts. Is determined. Therefore, when outputting an image, K
Since the colors are reproduced by combining the above inks, it is possible to stabilize the gray balance against a device variation and a light source variation. If only YMC ink is combined and an image with low lightness is output, YMC will be used to reduce the lightness.
However, since the ink of K having low lightness is combined with the above configuration, the image of the target lightness can be expressed while suppressing the usage amount of the YMCK ink as a whole.

Further, when the control unit 30 divides the output image into a monochrome image region and a color image region from the image data and converts the L * a * b * values of the output image into YMCK values. Since the K value of the monochrome image area is set to a value larger than the K value of the color image area, the K ink ejection amount when outputting the monochrome image area is the same as that of the color image area. It is set to be larger than the ejection amount of K ink when performing. Therefore, for a black-and-white image, it is possible to further stabilize the gray balance against variations in equipment and variations in light source.

Of course, the present invention is not limited to the above-mentioned embodiment, but can be appropriately modified. For example, in the present embodiment, the control unit 30 of the inkjet printer 1 creates the output data of each ink, but the data output device (for example, a personal computer) that outputs the image data to the inkjet printer, It may be configured to generate output data of ink. In addition, in the present embodiment, an inkjet printer that uses only YMCK ink is illustrated, but an inkjet printer that uses a special color ink such as RGB in addition to the YMCK ink is also applicable. The special color ink is an ink made by especially mixing colors that may be different or cannot be expressed by the YMCK ink.

In this embodiment, the case has been described in which the lightness / darkness level for each basic color is determined by the type of ink having different lightness for each basic color. May be determined by at least one of the formation position, the number, and the size of the dots for each basic color that are output from the recording head within the unit area (predetermined region). In general, when the formation position, number, and size of dots output from the recording head within a unit area are different, the lightness of each basic color per unit area is different. Examples of a method of changing the formation position or the number of dots output within this unit area include, for example, a method of changing the output position of ink of a unit area, a method of changing the number of times of dot output, or both of them. The combination of In order to make the output positions different, for example, applying the above-described super cell generation or the like may be applied. In such a case, it is preferable to use a dark color ink as the basic ink. Further, in the case where the number of times of outputting dots is different, it is preferable to use a light color ink having a higher lightness than the dark color ink as the basic ink. Also,
To make the size of the dots different, for example, there is a method of making different the driving states of the piezo elements that output ink, which are provided in the recording head. With this configuration,
Even if the type of ink is not increased for each basic color, it is possible to output a color having a lightness corresponding to each level, and it is possible to reduce the cost. The brightness level may be determined by combining at least two of the dot output position, number, size, and ink type. In such a case, it is possible to set the brightness level more finely.

[0053]

According to the first aspect of the present invention, the basic color having a larger difference in brightness from white has a larger number of levels than the bright basic color, and the brightness of the output color even if the color is dark. It can have a brightness level close to. For this reason,
It is easy to correspond to the brightness of the color to be output, and it is possible to reduce the graininess of the output image when the color is reproduced by using many dark colors. Then, even when the color of K is frequently used to reproduce the color, it is possible to correspond to the brightness to be output, and it is possible to reduce the graininess of the output image. According to the second aspect of the present invention, for example, when the lightness level is determined by at least one of the formation position, the number, and the size of the dots for each basic color, the ink for each basic color is used. It is possible to output a color having a lightness corresponding to each level without increasing the number of types, and it is possible to reduce the cost. Also,
When the lightness level is determined by the type of ink with different lightness provided for each basic color, the darker the ink, the larger the lightness difference from white, the greater the number of levels, and the darker the color It is possible to select the ink having the lightness level close to the lightness of the color to be output. For this reason, it is possible to easily correspond to the brightness of the color to be output, and it is possible to reduce the graininess of the output image when the color is reproduced by frequently using dark color, for example, black ink.

According to the third aspect of the invention, when the image is output, the K inks are combined in the main colors, and at least the lowest usage amount among the basic colors except K is used. However, the K ink will be used with a larger usage amount. The K ink is spectrally stable, and by combining this K ink, it is possible to stabilize the gray balance against device fluctuations and light source fluctuations. Further, at this time, not only the black ink but also the gray ink having high brightness is used as the K ink, so that the generation of graininess is prevented. Further, when an image of a color with low lightness is output mainly by combining inks of respective basic colors except K, each ink of YMC is used to reduce the lightness, and the amount of YMC ink used increases. However, with the above configuration, in order to reduce the brightness, K
Since the ink of No. 3 is used and the usage amounts of the three colors of YMC are reduced accordingly, it is possible to represent the image of the target lightness while suppressing the usage amount of the entire ink of YMCK.

According to the invention described in claim 4, the resolution is 3
If it is 60 dpi or more and the number of K levels is 3 or more, an output image with less graininess can be reliably obtained. According to the invention of claim 5, for a monochrome image,
Therefore, the gray balance can be stabilized against variations in equipment and light sources.

[Brief description of drawings]

FIG. 1 is a main control block diagram showing a main part of an inkjet printer according to an embodiment of the present invention.

FIG. 2 is a flowchart showing a control procedure up to ink ejection performed by the inkjet printer of FIG.

FIG. 3 is a flowchart showing a control procedure of halftoning shown in FIG.

FIG. 4 is a spatial frequency-response diagram showing the frequency response of the human eye.

[Explanation of symbols]

1 Inkjet printer (color image output device) 30 Control unit (control means)

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) H04N 1/60 H04N 1/40 D 5C079 F term (reference) 2C056 EA04 EA11 EC76 ED07 ED10 EE03 EE09 2C087 AA16 AC07 BA03 BA08 BA12 BD24 BD36 2C262 AA02 AA24 AB13 BA12 BA16 BB16 BC01 BC09 5B057 CA01 CA08 CA16 CB01 CB08 CB16 CE17 CE18 5C077 MP08 NN05 NN06 NN07 PP32 PP33 PP36 PP38 PQ08 SS02 TT05 5C079 HB01 H12 03B12 HB03 HB05 H12

Claims (6)

[Claims] 1. A basic color including at least Y (yellow), M (magenta), C (cyan) and K (black) is provided with at least one lightness level number, and the basic colors of each level are combined. A color image output device for performing color reproduction, wherein for each of the basic colors, the number of levels is determined based on the difference in brightness between the lowest level brightness and the white brightness of each of the basic colors, Moreover, the number of levels for each of the basic colors is determined to increase monotonically as the difference in lightness for each of the basic colors increases, and the number of levels of the color of K is equal to the level of K. The color image is set to have the largest number of levels of each of the excluded basic colors or more and more than the number of levels of one of the basic colors except at least the K. Out Apparatus. 2. The color image output apparatus according to claim 1, wherein each of the basic colors is provided with at least a basic ink that is a basic, and a recording head that outputs the basic ink to a recording medium is provided. The lightness level is provided for at least the formation position, the number, and the size of the dots for each of the basic colors output from the recording head within a predetermined area of the recording medium, and for each of the basic colors. A color image output device characterized by being determined by any one of ink types having different lightness. 3. The color image output device according to claim 2, further comprising control means for determining color by converting color data included in the image data into data for each basic color, wherein the control means is the When converting the main color data of the image data into data for each basic color to determine the color, the ink usage amount of the K color is set to the minimum amount of the ink usage amount of each basic color excluding the K color. A color image output device characterized in that a color is determined so as to be larger than an ink usage amount. 4. The color image output device according to claim 3, wherein the resolution is 360 dpi or more and the number of levels of K is 3 or more. 5. The color image output device according to claim 2, further comprising control means for converting color data included in the image data into data for each basic color to determine a color, and the control means is an image. Based on the data, the output image is divided into a black-and-white image and a color image, and the K color ink use amount when outputting the black and white image is calculated from the K color ink use amount when outputting the color image. A color image output device characterized by increasing the number of colors. 6. A basic dark color ink is provided for each basic color containing at least Y (yellow), M (magenta), C (cyan) and K (black), and one of the basic colors is provided. One or more colors are provided with a kind of light color ink having a lightness higher than that of the dark color ink, or two or more kinds of light color ink having a lightness higher than that of the dark color ink and different in lightness from each other, and these inks are combined. A method of selecting ink used in a color image output device for performing color reproduction by means of the method, wherein the number of levels indicating the number of types of ink obtained by combining the basic color and the dark color ink and the light color ink is It is determined on the basis of the lightness difference between the lightness of the dark ink and the lightness of white for each basic color, and as the lightness difference in each of the basic colors increases, the number of levels of each of the basic colors becomes simple. Ink selection, which is determined so as to increase the tone, and inks having different lightness from each other by the same number of types as the number of levels set for each of the basic colors are selected for each of the basic colors. Method.