JP2002369022A - Color conversion table generating method, color conversion method and image processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color conversion table generating method and a color conversion method by which better color reproduction is conducted not relying on a rule of thumb and trial-and-error. SOLUTION: First CMY axes are taken radially around the origin on a plane (A). The plane can express all colors expressed in two of the CMY colors. The color space is generated by adding the K axis perpendicularly to the CMY plane (B). The colors expressed by the space are colors of the CMY plane generated above to which a black color is added resulting in including all the required colors. The correspondence relation between points in the space and points in the L*a*b* space is formed into a table so as to conduct the color conversion.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for creating a color conversion table, a color conversion method, and an image processing apparatus, and more particularly to converting color data expressed in a certain color space into color data expressed in another color space. How to create a color conversion table,
The present invention relates to a color conversion method and an image processing device.

[0002]

2. Description of the Related Art To accurately reproduce colors on a printer, a given color (for example, L ^* a ^* b independent of a device) is used.
^* ), It is necessary to accurately determine the values of CMYK (cyan, magenta, yellow, and black) that can express it.

[0003] CMYK, which has been most commonly performed in the past,
Conversion is CMY conversion + GCR (GrayComponent Replacem)
ent) (or UCR (Under Color Removal)). This is because, as shown in FIG. 20, the color data (L ^*
a ^* b ^* ) into three colors of CMY, a process of creating a K plate from the CMY data, and a process of correcting the CMY data from the resulting K plate data.

This conversion method is widely used because it can be easily converted to CMY, and a reasonable image quality can be easily obtained simply by adding black to a low brightness portion.

[0005]

However, if the color conversion is performed by the conventional method, various problems occur.

First, in the process of converting L ^* a ^* b ^* to CMY, the color reproduction range by CMY is narrower than that of CMYK (for example, a combination of three CMY colors becomes dark brown instead of black. ), There is a case where a color reproduced by CMYK cannot be expressed by CMY.

Next, the K plate is made and the CMY values are corrected. However, the characteristics of the actual ink are complicated, and how many K components are present in CMY and how much CMY is corrected when the K plate is made It is difficult to know what to do, and the actual situation is that the actual conversion depends on empirical rules (or is determined by trial and error).

Accordingly, an object of the present invention is to provide a color conversion table creating method, a color conversion method, and an image processing apparatus capable of performing better color reproduction without relying on empirical rules or trial and error.

[0009]

According to one aspect of the present invention, there is provided a color conversion table creating method comprising the steps of: providing cyan and magenta; magenta and yellow;
A first step of printing a plurality of types of colors in a color space formed by a plane showing the yellow and cyan components and a gray component; a second step of measuring the printed colors; a result of the color measurement; And a third step of creating a table in which color components of time are associated with each other.

[0010] Preferably, the third step is a fourth step of preparing a first table showing colorimetric results for the color components printed in the first step, and based on the first table,
A fifth step of creating a second table for converting a color expressed in a certain color space into a color expressed in CMYK.

Preferably, the fifth step is a sixth step of determining one point in the L ^* a ^* b ^* color space, and the determined L ^* a ^*
A seventh step of reading data close to the data indicated by one point in the b ^* color space from the colorimetric results of the first table, and L ^* a ^* b determined in the sixth step using the read data. ^*
Eighth that determines a color component corresponding to one point in the color space
And a step.

According to another aspect of the present invention, a computer-readable recording medium records a color conversion table created by the above-described color conversion table creation method.

According to another aspect of the present invention, the color conversion table creating program stores a plurality of colors in a color space formed by cyan and magenta, magenta and yellow, and a plane showing yellow and cyan components and a gray component. The computer causes a computer to execute a first step of printing, a second step of measuring the color of the printed color, and a third step of creating a table in which the result of the color measurement is associated with a color component at the time of printing. .

According to another aspect of the present invention, a color conversion table creating apparatus prints a plurality of types of colors in a color space formed by cyan and magenta, magenta and yellow, a plane showing yellow and cyan components, and a gray component. A printing unit, a colorimetric unit for measuring a printed color, and a table creating unit for creating a table in which colorimetric results are associated with color components at the time of printing.

According to still another aspect of the present invention, a color conversion method uses a color space capable of expressing a device-independent color as a first color space, a cyan component and a magenta component, a magenta component and a yellow component, and A color space expressed by the plane formed by the yellow component and the magenta component and the amount of the gray component is defined as a second color space, and one point in the first color space corresponds to one point in the second color space. The color conversion is performed by using the attached table.

According to still another aspect of the present invention, a color conversion program sets a color space capable of expressing a device-independent color as a first color space, a cyan component and a magenta component, a magenta component and a yellow component, and A color space represented by a plane formed by the yellow component and the magenta component and the amount of the gray component is defined as a second color space,
Color conversion is performed using a table in which one point in the first color space and one point in the second color space are associated.

According to still another aspect of the present invention, a computer-readable recording medium records the above-described color conversion program.

According to still another aspect of the present invention, the color conversion apparatus uses a color space capable of expressing a device-independent color as a first color space, and includes a cyan component and a magenta component, a magenta component and a yellow component, and A color space expressed by the plane formed by the yellow component and the magenta component and the amount of the gray component is defined as a second color space, and one point in the first color space corresponds to one point in the second color space. Color conversion means for performing color conversion by using the attached table is provided.

According to still another aspect of the present invention, an image processing apparatus is an image processing apparatus for creating an image for printing with black ink and color ink, and the amount of black ink used is maximized. In order to further express a black color from the state, each time the color to be expressed becomes blacker, the usage amount of the color ink is increased while the usage amount of the black ink remains unchanged.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS [First Embodiment] FIG. 1 is a block diagram showing a configuration of an image processing apparatus according to a first embodiment of the present invention.

Referring to FIG. 1, an image processing apparatus includes a CPU 601 for controlling the entire apparatus, a printer 603 for printing a color-converted color image, a display 605 for displaying a color image, and an external device. LAN or modem card 6 for exchanging data with
07, an input device 609 including a keyboard and a mouse, and a flexible disk drive 611.
, A CD-ROM drive 613, a hard disk drive 615, a RAM 617, a ROM 619, and a reading device 621 that can read a color image.

A program for realizing image data and an image processing method described later includes a flexible disk F and a CD.
-It can be installed in the image processing apparatus by communication via the ROM 613a, LAN, or modem.

This image processing apparatus performs the following operations (1) and (2). (1) CK (Chroma axis-Black axis) space and L ^* a ^*
Creation of table for associating with b ^* space (2) L ^* a ^* b ^* using table created in (1)
→ Creation of CMYK color conversion table (profile) One-to-one correspondence from L ^* a ^* b ^* color space to CMYK color space
In order to achieve better color reproduction, it has conventionally been necessary to rely on empirical rules and trial and error.

In this regard, the present inventor considered that the CMYK space should be arranged in advance into a three-dimensional space having a one-to-one correspondence with L ^* a ^* b ^* . Once there is a one-to-one correspondence, L ^* a is the inverse transformation of CMYK → L ^* a ^* b ^{*
This is because *} b ^* → CMYK conversion can be easily obtained.

The coordinate system used to arrange the CMYK space in three dimensions is such that the chroma axis extends radially around the K axis representing approximately black (and gray). In this specification, this is called a CK space.

The CK space is a space in which CMYK is arranged so as to correspond to L ^* a ^* b ^* in a one-to-one correspondence. By changing the way of organizing (how to create the CK space), the CK space of the output image is changed.
Can be freely expressed from the conversion that maximizes the use amount to the conversion that uses a lot of CMY instead of K.

FIG. 2 is a diagram showing a concept of a CK space used in the image processing apparatus according to the present embodiment.

First, as shown in FIG.
Make a plane with. That is, with the origin at the center on the plane,
Take CMY axes radially. The portion sandwiched between the C-axis and the Y-axis covers the colors formed by combining C and Y. The same applies to a portion sandwiched between the M axis and the Y axis, and a portion sandwiched between the Y axis and the C axis. With this plane, all colors expressed using two colors of CMY (so-called high-key colors) can be expressed. Also, the same color does not appear twice on this plane.

Here, a three-dimensional space is created by adding a K axis perpendicular to the CMY plane as shown in FIG. The color expressed in this space is obtained by adding black to the color of the CMY plane created in (A). The only exception is when black is maximum, the same color will not appear at different locations in this space. Moreover, this space covers the necessary colors.

In this way, a color space (CK space) that has a one-to-one correspondence with L ^* a ^* b ^* is created. L from CK space
The correspondence to ^* a ^* b ^* can be easily obtained by performing colorimetry. In addition, since the conversion from the CK space to the L ^* a ^* b ^* has a one-to-one correspondence, it can be easily inverted by various methods (the conversion from the L ^* a ^* b ^* to the CK space). Can be requested. That is, as soon as the coordinates in the CK space are determined, the CMYK values can be obtained.

When conversion from L ^* a ^* b ^* to CMYK is obtained based on the data of the color space arranged in this way, the conversion using only two colors of CMY and K (that is, K is Conversion that is the largest). That is, an image is represented by C and M, M and Y or Y and C and a K component (gray component).

As shown in FIG. 2B, if color data is managed in a space represented by a hexagonal prism, the calculation process becomes complicated. Therefore, as shown in FIG. To be stored.

FIG. 3 shows the CK recorded in the image processing apparatus.
It is a figure showing data of space. Referring to FIG. 3, the center is defined as the origin of the CMY plane, and the upward direction is defined as the direction in which the M component becomes dense. Similarly, the left direction is the direction in which the C component becomes darker. The rightward direction and the downward direction are both directions in which the Y component increases. Also, the direction in which the K component becomes dark is defined as the direction penetrating the paper surface.

By performing such data management,
The CK space can be represented by a three-dimensional array, and the calculation process can be simplified. In FIG. 3, the CMY axes are divided into eight in each axis direction. By increasing the number of divisions and recording more data, more accurate color conversion can be performed.

CMYK data and corresponding L ^* a ^* b ^* data are stored at arbitrary positions in the array as shown in FIG. 3, and for example, conversion of L ^* a ^* b ^* → CMYK is performed. Is performed, L ^* a closest to the L ^* a ^* b ^*
* b ^* value is read from the array and the CM stored at that position
YK data is obtained. Most of all L ^* a ^* b ^*
When the CMYK data corresponding to the data is stored, the memory capacity becomes enormous and it is not practical. Therefore, only the data at a predetermined interval is stored, and the data during the interval is referred to by an interpolation formula as shown in the formula (1). Thus, interpolation is performed.

[0036]

(Equation 1) In equation (1), linear cubic interpolation is performed as the interpolation method, but another interpolation method may be used.

It is not necessary to brute the entire sequence for a given L ^* a ^* b ^* (if the brute force is (8 ×
16) ³ × 3 ≒ 7 million candidates will be searched). Therefore, a search may be performed at a coarse interval, a rough contact may be made, and then a search may be performed only in the vicinity.

FIG. 4 is a flowchart showing a color conversion table creating process performed by the image processing apparatus of FIG.

Referring to FIG. 4, in step S1,
A plurality of CMYK values for which colorimetry is required (ie, FIG.
Is determined. In step S3, using the printer 603, the determined CM
Printing of a color using YK as an ink component is performed.

Next, each of the colors printed in step S5 is measured by the reading device 621. Table A in which the color measurement results are associated with CMYK values
(See FIG. 3) is created in step S7.

In step S9, a table B for obtaining the value of CMYK from L ^* a ^* b ^* based on the table A is created.

FIG. 5 shows the CMYK determination process (S
It is a flowchart which shows the content of 1).

Referring to the figure, in step S101, a point in the CK space is selected. Next, in step S103, CK
From the definition of the space, the value of CMYK corresponding to the point is calculated. In step S105, the calculated CMYK value (that is, the color to be printed) is written to the memory. Step S10 until all necessary CMYK values are determined
The processing from 1 to S105 is repeatedly executed.

FIG. 6 shows the process of creating table A in FIG. 4 (S
It is a flowchart which shows the content of 7).

Referring to the figure, in step S 201, the CMYK values of the measured color are written in the corresponding positions in table A. In step S203, the value of L ^* a ^* b ^* (colorimetric value) corresponding to the color represented by the CMYK is written. The processing of steps S201 to S203 is repeatedly executed until processing of all colors is performed.

FIG. 7 shows the process of creating table B in FIG. 4 (S
It is a flowchart which shows the content of 9).

In step S301, the information is registered in table B.
Want L^*a^*b^*Determine the value of. That is, all L^*
a^*b^*Is registered in Table B,
Since it is not preferable from the viewpoint,^*a^*b
^*Is determined. In step S303, the table
L determined by searching for Bull A^*a^*b ^*To
Find the corresponding CMYK value. At this time,
L corresponding to^*a^*b^*If not, use interpolation
Thus, the value of CMYK is determined.

In step S305, L is stored in table B.
Write the values of ^* a ^* b ^* and CMYK.

By this processing, L ^* a ^* b ^{* is} converted to CMYK
A table B for performing the conversion is created.

FIG. 8 is a flowchart showing the CMYK value determination process performed in step S303 of FIG.

Referring to the figure, the nearest L ^* a ^* b ^* value is searched from table A in step S401. In step S403, an interpolation operation is performed on nearby L ^* a ^* b ^* values. In step S405, the closest one is selected, and in step S407, CMYK values are interpolated.

FIG. 9 is a flowchart showing a color conversion process performed by the image processing apparatus of FIG.

Referring to the figure, at step S501, L ^* a ^*
The value of b ^* is input. In FIG.
Is searched in the table B created in step (1), and the corresponding position in the CK space is calculated. CK in step S505
The value of each component of CMYK is calculated based on the position in the space.

The advantages obtained by the method used in this embodiment will be described below. (1) Unlike the conventional technology, the process of temporarily converting to CMY in color conversion is omitted, and all colors are directly converted to CMYK values based on actual measurement values. This eliminates the need for know-how (such as UCR) such as CMY correction processing after K-plate creation, which was required in the conventional technology.

(2) In the present embodiment, “black”
The image output from the printer does not always correspond to 100% of the black toner (K component) in response to the input. In general,
This is because a blacker color can be expressed by superimposing another color than a color consisting of only 100% of the black toner.

(3) Since the color closest to the input color in the color conversion processing is searched from the table, more accurate color conversion can be performed.

If L ^* a ^* b ^* outside the gamut space does not correspond to any CMYK, the quality of the image after the color conversion is reduced. In the present embodiment, the color conversion, by searching the input L ^* a ^* b closest to ^* L ^* a ^* b ^* from the table, the mapping is performed automatically without distinguishing gamut and out Will be.

In the present embodiment, the K ink does not need to be achromatic. As long as the inverse conversion is performed properly, even if the K ink is not achromatic, an appropriate amount of CMY ink is added to the achromatic input to output CMYK values that are achromatic. become.

[Second Embodiment] In the above-described first embodiment, the colors output as a result of color conversion are conversions using only two of CMY and K (= conversion of K maximum). Becomes In the second embodiment, conversion with an increased amount of CMY is performed by devising the K axis.

FIG. 10 is a diagram for explaining the concept of the CK space in the present embodiment. As shown in FIG. 10A, an X-axis is used in this embodiment instead of the K-axis in FIG. 2B. The X axis is an axis obtained by mixing the respective components of CMYK, and the mixing ratio is shown in (B). That is, in the portion where the value of X is close to 0, C,
While the amounts of M and Y are equal, the value of each component is increased as X increases (the output is gray). From the position where the value of X is x1, the value of K is linearly increased without changing the respective values of CMY.

Further, as shown in (C), each value of CMY increases as the distance from the X axis increases,
The initial value is set to the value of CMY in (B). As a result, the value of CMY linearly increases from any point on the X axis as the distance from the X axis increases.

As described above, a certain point on the X-axis in this embodiment represents a certain combination of CMYK, this combination almost represents gray, and the color density is monotonic with respect to the value of X. Is set to increase. When the user moves away from the X axis, the values of CMY on the X axis gradually increase, starting from the values. Thereby, the first
For exactly the same reason as in the embodiment, all colors can be covered in the CK space. Also, the same color does not appear in the CK space.

It is important that the color density monotonically increases with respect to the value of X, but it is not so important that the color matches gray. This is because even if the color on the X axis deviates from gray, the color can be correctly reproduced as long as the inverse transformation is performed appropriately.

[Effects in Embodiment] FIG. 11 shows that the input value is changed from white (0) to black (1) in the first embodiment.
6 is a graph showing the amounts of ink components used in an output image when the color changes to.

A color obtained by adding CMY to the black ink can express a darker color than using 100% of the black ink. Therefore, when the usage amount of the color ink is reduced and the usage amount of the black ink is increased, the reproduction range of black is narrowed. Conversely, if an attempt is made to keep the black reproduction range, the amount of ink used will increase.

In this embodiment, as shown in FIG. 11, when the amount of black ink (K) used reaches a peak, the amount of CMY ink increases in order to express a darker color. . In other words, from the state in which the amount of black ink used is maximized, in order to further express a black color, each time the expressed color becomes blacker, the amount of used black ink is increased and the amount of used color ink is increased. The control will be performed as follows.

As a result, the reproduction range of black can be widened, and the amount of ink used can be minimized.

FIG. 12 shows a CM when the input value changes from white to black in the color conversion processing in the second embodiment.
5 is a graph showing an amount of Y ink and an amount of K ink.
As shown in the drawing, also in the present embodiment, when a black color is further expressed from a state where the usage amount of black ink is maximized, the usage amount of color ink increases while the usage amount of black ink remains unchanged. . Thus, also in the second embodiment, the black reproduction range can be widened, and the amount of ink used can be minimized.

FIG. 13 shows a case where the amount of color ink is increased while the amount of black ink is used in order to further express a black color from the state in which the amount of black ink is maximized. May be performed.

FIG. 14 is a graph showing the relationship between the input value and the amount of ink used in a conventional general conversion process to CMYK. As shown in the figure, in the conventional method, in a gray state where the input value is close to white, CMY
Only when the input value exceeds a certain value,
Black color will be expressed with K ink. In this example, there is a problem that the amount of used ink becomes too large.

FIG. 15 is a graph showing a state in which UCR has been applied to image processing from the state shown in FIG. In this example, when the value of CMY becomes large to some extent, black is darkened by K ink. In this example, the amount of ink used can be smaller than in the example of FIG. 14, but the color reproduction range is narrowed.

FIG. 16 shows the GCR 100 from the state of FIG.
It is a graph which shows the state which performed image processing as%.

As shown in the figure, in this example, CMY inks are not used for expressing black (gray), and black and gray are expressed only with K ink. This reduces the amount of ink used, but narrows the range of color representation.

In the above embodiment, CMY
The axes are coplanar, but need not be so.

That is, as shown in FIG.
CK space can be created even if the three axes are oriented in independent directions.

Further, in general, as the amount of black increases, the change in color when other colors are added is small.
Alternatively, a CK space as shown in FIG. 8 may be created. When the black ink has sufficient covering power and the amount of the black ink used is the largest, and the black ink can be regarded as black regardless of the amount of the other inks, the entire solid in the CK space can be formed as a rectangular parallelepiped. . If the point to be measured is divided along this rectangular parallelepiped, the K axis always takes the vertex of the divided rectangular parallelepiped, which is convenient for interpolation calculation. Also, there is an advantage that the uniformity when viewed in the L ^* a ^* b ^* space can be enhanced.

[Third Embodiment] FIG. 19 is a block diagram showing a hardware configuration of a printer according to a third embodiment of the present invention.

Referring to the figure, the printer includes a CPU 201 for controlling the entire apparatus, a print engine 203 for performing printing, an input panel 205 for receiving input from a user, and a display unit 207 for displaying.
An interface 209 for externally inputting image data, a RAM 211 for temporarily storing data,
The ROM 213 stores programs and constants.

The printer according to this embodiment also prints a color image by performing the color conversion processing according to the first or second embodiment.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of an image processing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram illustrating a specific example of a CK space.

FIG. 3 is a diagram illustrating an example of storing data in a CK space in a memory.

FIG. 4 is a flowchart illustrating a process of creating a color conversion table.

FIG. 5 is a flowchart showing the contents of a CMYK determination process (S1) of FIG. 4;

FIG. 6 is a flowchart showing the contents of a table A creation process (S7) in FIG. 4;

FIG. 7 is a flowchart showing the contents of a table B creation process (S9) in FIG. 4;

8 is a flowchart showing the contents of CMYK determination processing (S303) in FIG.

FIG. 9 is a flowchart illustrating a color conversion process according to the first embodiment.

FIG. 10 is a diagram illustrating a CK space used in the image processing apparatus according to the second embodiment.

FIG. 11 is a diagram showing an effect in the first embodiment.

FIG. 12 is a diagram showing an effect in the second embodiment.

FIG. 13 is a diagram showing a process in a modified example.

FIG. 14 is a diagram illustrating a conventional general CMYK conversion process.

FIG. 15 is a diagram showing CMYK conversion on which UCR has been performed.

FIG. 16 is a diagram showing conversion processing of GCR 100%.

FIG. 17 is a diagram showing a first modification of the CK space.

FIG. 18 is a diagram showing a second modification of the CK space.

FIG. 19 is a diagram illustrating a hardware configuration of a printer according to a third embodiment.

FIG. 20 is a diagram for explaining a conventional technique.

[Explanation of symbols]

601 CPU, 603 printer, 621 reading device.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C087 AA15 BA07 BD36 BD53 5B057 AA11 CA01 CA08 CA12 CA16 CB01 CB08 CB12 CB16 CC01 CE18 CH07 DA17 DB02 DB06 DB09 DC25 5C077 LL12 LL19 MP01 MP08 PP33 PP36 PP38 PP74 SS02 SS06 TT12 HB08 HB11 KA04 LA02 LA21 LB02 MA04 NA03 NA17 NA29 PA03

Claims (11)

[Claims] 1. A first step of printing a plurality of types of colors in a color space formed by cyan and magenta, magenta and yellow, a plane showing yellow and cyan components, and a gray component, and measuring the printed colors. A color conversion table creation method, comprising: a second step of coloring, and a third step of creating a table in which the result of the color measurement is associated with the color component at the time of printing. 2. The method according to claim 1, wherein the third step is a fourth step of creating a first table indicating a colorimetric result for the color component printed in the first step, and based on the first table. A fifth step of creating a second table for converting a color expressed in a color space into a color expressed in CMYK. 3. The fifth step is a step of determining one point in an L ^* a ^* b ^* color space; and the fifth step is close to data indicated by the one point in the determined L ^* a ^* b ^* color space. A seventh step of reading data from the colorimetric results of the first table, and using the read data, corresponding to one point in the L ^* a ^* b ^* color space determined in the sixth step. The color conversion table creation method according to claim 1 or 2, further comprising an eighth step of determining a color component. 4. A computer-readable recording medium recording a color conversion table created by the color conversion table creation method according to claim 1. 5. A first step of printing a plurality of types of colors in a color space formed by cyan and magenta, magenta and yellow, a plane showing yellow and cyan components, and a gray component, and measuring the printed colors. A color conversion table creation program for causing a computer to execute a second step of coloring, and a third step of creating a table in which the result of the color measurement is associated with the color component at the time of printing. 6. A printing unit for printing a plurality of colors in a color space made up of a plane showing the components of cyan and magenta, magenta and yellow, and yellow and cyan, and a gray component, and measuring the printed colors. A colorimetric unit, and a table creating unit that creates a table that associates the colorimetric results with the color components at the time of printing.
Color conversion table creation device. 7. A plane formed by a cyan component and a magenta component, a magenta component and a yellow component, a yellow component and a magenta component, and a gray component, wherein a first color space is a color space capable of expressing a device-independent color. Is used as a second color space, and color conversion is performed by using a table in which one point of the first color space is associated with one point of the second color space. A color conversion method, characterized in that: 8. A program for causing a computer to execute color conversion, wherein a first color space is a color space capable of expressing a device-independent color, wherein a cyan component and a magenta component, a magenta component and a yellow component, And a color space expressed by a plane formed by a yellow component and a magenta component and an amount of a gray component as a second color space, one point of the first color space and one point of the second color space A color conversion program for performing color conversion by using a table in which the color conversion is performed. 9. A computer-readable recording medium on which the color conversion program according to claim 8 is recorded. 10. A plane formed by a cyan component and a magenta component, a magenta component and a yellow component, a yellow component and a magenta component, and a gray component, wherein a color space capable of expressing a device-independent color is defined as a first color space. Is used as a second color space, and color conversion is performed by using a table in which one point of the first color space is associated with one point of the second color space. A color conversion device comprising color conversion means. 11. An image processing apparatus for creating an image for printing with black ink and color ink, wherein an expression is used to further express a black color from a state where the amount of black ink used is maximized. An image processing apparatus characterized in that the use amount of color ink is increased while the use amount of black ink remains unchanged each time a desired color becomes blacker.