JP4905425B2 - Color conversion table creation method, color conversion table, color conversion table creation program, and color conversion table creation device - Google Patents

Description

  The present invention relates to a color conversion table creation method, a color conversion table, a color conversion table creation program, and a color conversion table creation apparatus.

  Conventionally, when RGB data created by a personal computer or the like is color-converted into CMYK data for a color printer, for example, a color conversion table (LUT: Look-Up-Table) is used. In the color conversion table, color conversion values (CMYK values in the above example) are not registered for all RGB values, but a plurality of grid points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into a plurality of RGB directions. In general, the color conversion value is registered only in. When color conversion is performed using such a color conversion table, the color conversion values of points other than the grid points are obtained by interpolation calculation based on the color conversion values registered at the grid points. For such interpolation calculation, volume interpolation calculation is generally used, and cubic (rectangular) interpolation and triangular pyramid interpolation are known as volume interpolation.

In Patent Document 1, among cubic regions having lattice points as vertices, those that do not include an achromatic color axis (gray axis) are subjected to interpolation calculation by cubic interpolation, and those that include an achromatic color axis are included. In addition, a configuration is disclosed in which interpolation calculation is performed by further dividing into a plurality of tetrahedrons.
JP 2004-179819 A

  By the way, when using a color conversion table for converting from RGB to CMY, CMYK, etc., if interpolation calculation is performed with triangular pyramid interpolation with the achromatic color axis as one side, the gray gradation print result will be smooth, When the interpolation calculation is performed by the cubic interpolation, there is a problem that a striped pattern is generated in the gray gradation printing result (as shown in FIG. 7).

Here, the cause of such a problem will be described. First, in order to facilitate understanding, a two-dimensional description is given.
In FIG. 8, among the lattice points G1 to G4, the lattice points G1 and G4 are lattice points on the achromatic axis. Here, when the color conversion value of the point P1 on the achromatic color axis is obtained by triangular pyramid interpolation, the interpolation calculation is performed based only on the color conversion values of the achromatic color grid points G1 and G4. On the other hand, in the case of cubic interpolation, not only the color conversion values of the achromatic grid points G1 and G4 but also the color conversion values of the chromatic grid points G2 and G3 are used for the interpolation calculation. Depending on the balance of the color conversion values, the color conversion value of the point P1 becomes a slightly dark value or a light value, and as a result, a striped pattern as shown in FIG. 7 occurs.

Next, the same content will be described in three dimensions.
In FIG. 9, among the lattice points A to H, lattice points A and G are lattice points on the achromatic axis.
Here, when the color conversion value of the point on the achromatic color axis is obtained by triangular pyramid interpolation, the interpolation calculation is performed based only on the color conversion value of the lattice points A and G of the achromatic color. On the other hand, in the case of cubic interpolation, interpolation calculation is performed using 8 points of grid points A to H. As described above, the use of color conversion values of grid points other than the grid points A and G on the achromatic color axis is a cause of rattling (striped pattern).

  As described above, if the interpolation calculation is performed by triangular pyramid interpolation, the gray gradation printing result becomes smooth, but the triangular pyramid interpolation has a problem that the program is more complicated and time-consuming than cubic interpolation. is there. In this regard, in the configuration described in Patent Document 1 described above, the cubic region including the achromatic color axis is divided into a plurality of tetrahedrons to perform interpolation calculation, and cubic interpolation solves the above problem. I can't.

  The present invention has been made in view of these problems. A color conversion table creation method, a color conversion table, and a color conversion table creation that can reproduce gray well even when interpolation calculation is performed by cubic interpolation. It is an object to provide a program and a color conversion table creation device.

A method for creating a color conversion table of the first configuration made to achieve the above object is to register a color conversion value at each of the lattice points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into a plurality of RGB directions. This is a method for creating a color conversion table. In this creation method, the average value of the color conversion values of three grid points adjacent to each other in the RGB directions with respect to a grid point on the achromatic color axis in a cubic region including the achromatic color axis is the three grids. The color conversion values of these three lattice points are adjusted so as to approach the color conversion value at the intersection of the plane passing through the point and the achromatic color axis.

  According to such a creation method, it is possible to create a color conversion table that can reproduce gray well even when interpolation calculation is performed by cubic interpolation. That is, when the color conversion value of the conversion target point other than the lattice point is obtained by cube interpolation, the interpolation calculation is performed using eight lattice points corresponding to the vertices of the cubic region including the conversion target point. Here, when the conversion target point exists on the achromatic color axis, as shown in FIG. 9, among the remaining six lattice points excluding the two lattice points A and G on the achromatic color axis, The weight coefficients of the color conversion values of B, D, and E are equal, and similarly, the weight coefficients of the color conversion values of the grid points C, F, and H are also equal. Therefore, if the average value of the color conversion values of the grid points B, D, and E and the average value of the color conversion values of the grid points C, F, and H respectively express gray appropriately, the conversion is performed. The color conversion value of the target point is also an appropriate gray value.

  Therefore, in the method of creating the color conversion table of the present invention, three grid points adjacent in the respective RGB directions with respect to the grid points on the achromatic color axis (in FIG. 9, three grid points B, D, E, and the average value of the color conversion values of the three lattice points C, F, H) adjacent to the lattice point G are the intersections α, β of the plane passing through the three lattice points and the achromatic color axis. The color conversion values of these three grid points so that the color conversion values approach each other (in other words, the sum of the color conversion values of the three grid points approaches three times the color conversion value of the intersection point). Adjust. Here, in terms of reproducing gray well, it is most preferable that the average value of the three grid points matches the color conversion value of the intersection. If a color conversion table created by such a creation method is used, gray can be reproduced well even when interpolation calculation is performed by cubic interpolation.

  When the RGB space is divided into, for example, 8 in each RGB direction, the grid points are arranged in 9 steps of 0, 32, 64, 96, 128, 160, 192, 224, and 255 when the RGB value is represented by 8 bits. Is done. In this case, the value difference between the lattice points is 0 to 224, but the value difference between the lattice points is 31 to 224 to 255, and cannot be strictly equal. For this reason, some of the cubic regions here are not strictly cubes, but in order to make the invention easier to understand, these are also expressed as cubic regions (this For this reason, it may be expressed as “cuboid region” instead of “cubic region”).

  By the way, in the color conversion table creation method of the present invention, the color conversion values of the three grid points are adjusted in order to reproduce gray well. However, this adjustment may adversely affect reproducibility other than gray. It is done.

Therefore, for example, in the color conversion table creation method of the second configuration , the adjustment amount of the color conversion value is suppressed for the lattice points used for the interpolation calculation of a specific color region among the three lattice points. According to such a creation method, it is possible to make it difficult for a specific color region to have an adverse effect on reproducibility. Here, “suppressing the adjustment amount” includes not only reducing the adjustment amount but also setting the adjustment amount to 0 (not adjusting).

Here, examples of the specific color area include a color area representing a skin color as in the third configuration . In this way, it is possible to make it difficult for adverse effects to occur in the reproducibility (color tone, etc.) of the skin color.

Specifically, for example, as in the fourth configuration , when the cubic region is obtained by dividing the RGB color space into eight in each RGB direction, the grid points used for the interpolation calculation of the color region representing the skin color Is a grid point that constitutes a grid point sequence that exists at a position shifted by one in the R direction from the achromatic color axis, among grid point sequences parallel to the achromatic color axis. Therefore, for the lattice points constituting this lattice point sequence, by suppressing the adjustment amount of the color conversion value, it is possible to prevent adverse effects on the skin color reproducibility.

Next, the color conversion table of the fifth configuration is such that color conversion values are registered at each of the lattice points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into a plurality of RGB directions. In this color conversion table, the average value of the color conversion values of three grid points adjacent to each other in the RGB direction with respect to the grid point on the achromatic color axis in the cubic region including the achromatic color axis is It is adjusted to be equal to the color conversion value at the intersection of the plane passing through the three grid points and the achromatic color axis.

According to such a color conversion table, gray can be reproduced well even when interpolation calculation is performed by cubic interpolation.
Next, the color conversion table creation program of the sixth configuration creates a color conversion table in which color conversion values are registered at each of the lattice points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into a plurality of RGB directions. It is for making a computer perform the step for performing. The color conversion table creation program calculates the average value of the color conversion values of three grid points adjacent in the RGB directions with respect to the grid points on the achromatic color axis in the cubic region including the achromatic color axis. Then, the computer is caused to execute a step of adjusting the color conversion values of the three grid points so as to approach the color conversion value of the intersection of the plane passing through the three grid points and the achromatic color axis.

According to such a color conversion table creation program, the color conversion table creation method of the first configuration can be realized, and thereby the above-described effects can be obtained.
Next, the color conversion table creation device of the seventh configuration creates a color conversion table in which color conversion values are registered at the respective lattice points corresponding to the vertices of each cubic region obtained by dividing the RGB color space into a plurality of RGB directions. Is to do. In this color conversion table creation device, the average value of the color conversion values of three lattice points adjacent to each other in the RGB directions with respect to the lattice points on the achromatic color axis in the cubic region including the achromatic color axis is obtained. And an adjusting means for adjusting the color conversion values of the three lattice points so as to approach the color conversion value of the intersection of the plane passing through the three lattice points and the achromatic color axis.

According to such a color conversion table creation device, the color conversion table creation method of the first configuration can be realized, and thereby the above-described effects can be obtained.

Embodiments to which the present invention is applied will be described below with reference to the drawings.
[1. overall structure]
FIG. 1 is a block diagram illustrating a schematic configuration of a personal computer 10 as a color conversion table creation apparatus according to an embodiment.

As shown in the figure, the personal computer 10 includes a control unit 11, an operation unit 15, a display unit 16, a USB interface 17, a communication unit 18, and a storage unit 19.
The control unit 11 is configured mainly with the CPU 12, the ROM 13, the RAM 14, and the like, and comprehensively controls each unit constituting the personal computer 10.

The operation unit 15 is for inputting a command by an external operation from a user, and for example, a keyboard or a pointing device (such as a mouse) is used.
The display unit 16 is for displaying various types of information as an image that can be visually recognized by the user. For example, a liquid crystal display is used.

The USB interface 17 performs data transmission / reception processing via a USB cable.
The communication unit 18 performs data transmission / reception processing via a network. In the present embodiment, the personal computer 10 can communicate with the color printer 40 via a network (LAN: Local Area Network in this embodiment).

  The storage unit 19 is for storing various information, and for example, a hard disk device is used. The storage unit 19 is installed with an operating system (OS) 21 and a color conversion table creation program 22 for causing the control unit 11 to execute a table adjustment process (FIG. 3) described later.

[2. Overview of table adjustment process]
The personal computer 10 according to the present embodiment uses eight (8) RGB color spaces in each RGB direction as a color conversion table for converting RGB color space color values into CMYK color space color values depending on the color printer 40. A color conversion table is created in which color conversion values (CMYK values) are registered for each of the lattice points corresponding to the vertices of each cubic area divided into bits (every 32 in the case of bits (0 to 255)). Specifically, the color conversion table (base color conversion table) created by a conventional method is created by performing table adjustment processing described later. The method for creating the base color conversion table is not particularly limited.

  That is, as described above, when the color conversion table created by the conventional method is subjected to interpolation calculation by cubic interpolation, the interpolation calculation is performed using grid points other than the grid points on the achromatic color axis. In some cases, a stripe pattern was generated in the gradation printing result (FIG. 7).

Therefore, in the present embodiment, this problem is solved by adjusting the color conversion values registered at the grid points of the color conversion table as a base.
Here, it demonstrates in detail using FIG. When obtaining the color conversion value of the conversion target point on the achromatic color axis by cubic interpolation, among the remaining six grid points excluding the two grid points A and G on the achromatic color axis, Weight coefficients of color conversion values of three lattice points B, D, and E adjacent in each RGB direction (in other words, a line connecting each of the eight lattice points that are the vertices of the cubic region and the conversion target point is a diagonal line. Among the eight rectangular parallelepiped regions, the volume of the rectangular parallelepiped region having the vertexes of the lattice points facing each of the lattice points B, D, and E on the diagonal of the cube region are equal to each other. The weight coefficients of the color conversion values of the three lattice points C, F, and H adjacent in the RGB directions are also equal.

  Therefore, the sum of the color conversion values of the grid points B, D, and E is three times the color conversion value of the intersection α of the plane BDE and the line segment AG (a point at a position 1: 2 on the line segment AG). In other words, the color conversion values of the grid points B, D, and E are adjusted so that the average value of the color conversion values of the grid points B, D, and E becomes the color conversion value of the intersection α. Similarly, the sum of the color conversion values of the lattice points C, F, and H is the color conversion value of the intersection β (the point at a position 2: 1 from A on the line segment AG) between the plane CFH and the line segment AG. The color conversion values of the grid points C, F, and H are adjusted so as to be tripled. If the color conversion table adjusted in this way is used, gray can be reproduced well even when interpolation calculation is performed by cubic interpolation.

However, adjusting the color conversion table to balance the achromatic color axis may adversely affect the pale orange color that is close to the Japanese skin color.
The graph shown in FIG. 2B is a vertex of each cubic area obtained by dividing the color value of each pixel constituting the image (image obtained by photographing the skin) of FIG. Is plotted in a color conversion table having grid points as viewed from the white (255, 255, 255) side in the achromatic color axis (gray axis) direction. The white circle represents an achromatic color axis, the surrounding black circle represents an axis shifted by one from the achromatic color axis, and the surrounding circle represents an axis displaced by two from the achromatic color axis.

  It can be seen that the grid points on which the above-described adjustment is performed are grid points (black circles) on an axis shifted by one from the achromatic color axis, and a part of the grid points is used for interpolation calculation of the skin color region. That is, the skin color region is considered to be affected by the adjustment described above.

  Specifically, the grid points that affect the skin color region are grids that form a grid point array (a grid point array parallel to the achromatic color axis) that exists at a position shifted by one in the R direction from the achromatic color axis. It is point Ga. Therefore, in the present embodiment, the adjustment amount of the color conversion value of the lattice point Ga (the amount of change from the base color conversion table) is suppressed, and the amount that cannot be adjusted at the lattice point Ga is the other two. This is compensated by allocating to the adjustment amounts of the color conversion values of the grid points Gb and Gc (grid points existing at positions shifted by one in the G and B directions from the achromatic color axis).

[3. Specific contents of the table adjustment process]
Next, table adjustment processing executed by the control unit 11 in accordance with the color conversion table creation program 22 will be described with reference to the flowchart of FIG. This table adjustment process is started when the user performs an operation for adjusting the base color conversion table via the operation unit 15.

  When starting the table adjustment process, the control unit 11 first determines in S101 whether or not all adjustment points have been processed. Here, the adjustment point corresponds to a point including an achromatic color axis in a cubic region obtained by dividing the RGB color space into eight parts in each RGB direction. Specifically, as shown two-dimensionally in FIG. 4, there are eight adjustment points (cubic regions including the achromatic color axis indicated by dotted lines), and adjustments related to points α and β are performed for each adjustment point. Become. That is, in S101, it is determined whether all eight adjustment points have been processed. Note that the processing here is the processing of S102 to S107 described later.

If it is determined in S101 that all adjustment points have not been processed (there are unprocessed adjustment points), the process proceeds to point α-related processing (S102 to S104).
That is, first, in S102, based on the values of the grid points A and G (color conversion values), the value of the point α (color conversion value) on the achromatic color axis is obtained by linear interpolation. Here, the value of the point α is obtained from the following equation (1).

Value of point α = (value of point A × 2 + value of point G) / 3 (1)
Subsequently, in S103, the values (color conversion values) of the target grid points B, D, and E for the point α are acquired.

  Subsequently, in S104, a grid point value adjustment process is performed for adjusting the values of the target grid points B, D, and E so that the sum of the values of the target grid points B, D, and E approaches three times the value of the point α. To do. The specific contents of the grid point value adjustment processing will be described later (FIG. 5).

Subsequently, the process proceeds to point β-related processing (S105 to S107).
That is, first in S105, based on the values of the grid points A and G, the value of the point β on the achromatic axis is obtained by linear interpolation. Here, the value of the point β is obtained from the following equation (2).

Point β value = (Point A value + Point G value × 2) / 3 Formula (2)
Subsequently, in S106, the values of the target grid points C, F, and H for the point β are acquired.
Subsequently, in S107, a grid point value adjustment process for adjusting the values of the target grid points C, F, and H so that the sum of the values of the target grid points C, F, and H approaches three times the value of the point β (see FIG. 5) is executed. Thereafter, the process returns to S101.

Note that the point α-related processing (S102 to S104) and the point β-related processing (S105 to S107) are performed for each of the four colors C, M, Y, and K.
Then, by performing the processes of S102 to S107 for the eight adjustment points, if it is determined in S101 that all the adjustment points have been processed, this table adjustment process is terminated.

  Next, the grid point value adjustment process executed in S104 and S107 of the table adjustment process will be described with reference to the flowchart of FIG. In this process, both “value of point α” and “value of point β” are expressed as “value of achromatic color axis”, and “target grid points B, D, E” and “target grid points C, Both “F, H” are simply expressed as “target grid points”.

When starting the grid point value adjustment process, the control unit 11 first determines in S201 whether the sum of the values (color conversion values) of the three target grid points is zero.
If it is determined in S201 that the sum of the values of the three target grid points is 0, the process proceeds to S202, and the value of the achromatic axis is substituted for the target grid point. Thereafter, the lattice point value adjustment process is terminated.

  On the other hand, if it is determined in S201 that the sum of the values of the three target grid points is not 0, the process proceeds to S203, and an adjustment coefficient is calculated. Here, the adjustment coefficient is a value obtained from the following equation (3). Note that the process of S201 prevents the calculation of setting the denominator of Equation (3) to 0.

Adjustment coefficient = Achromatic color axis value × 3 / Sum of target grid point value Equation (3)
Subsequently, in S204, it is determined whether or not all three target grid points have been processed. In addition, the process here is a process of S205-S210 mentioned later.

  If it is determined in S204 that all three target grid points have not been processed (there are unprocessed target grid points), the process proceeds to S205, in which one of the unadjusted target grid points is set. Is selected as a processing target, and the value of the target grid point is adjusted according to the following equation (4). That is, the value of the target grid point is multiplied by the adjustment coefficient.

Target grid point value = Target grid point value × Adjustment coefficient Equation (4)
Subsequently, in S206, it is determined whether or not the processing target grid point is a skin color adjustment target grid point. Specifically, as described above, the lattice point shifted by +1 from the achromatic color axis in the R direction becomes the lattice point to be adjusted for skin color.

  If it is determined in S206 that the target grid point to be processed is not a skin color adjustment target grid point, the process proceeds to S207 to determine whether the value of the target grid point is greater than 255. In this embodiment, since the RGB value is represented by 8 bits, the range that the numerical value can take is 0 to 255. That is, it is determined whether or not the value of the target grid point has exceeded the maximum value of 255 as a result of the adjustment in S205.

  If it is determined in S207 that the value of the target grid point is larger than 255, the process proceeds to S208, and the amount exceeding 255 is stored as an excess amount (amount that cannot be adjusted) (excess amount = target). Value after adjustment of grid points -255). Thereafter, the process proceeds to S210.

On the other hand, if it is determined in S207 that the value of the target grid point is not greater than 255 (below 255 or less), the process proceeds to S210 as it is.
If it is determined in S206 that the processing target grid point is a skin color adjustment target grid point, the process proceeds to S209, and after adjusting the adjustment amount, the process proceeds to S210.

  Specifically, the excess amount and the target grid point value are obtained according to the following equations (5) and (6). Here, the skin color adjustment coefficient is a value set in the range of 0 to 1, and is set to 0.5 in the present embodiment. As can be seen from the equations (5) and (6), when the skin color adjustment coefficient is set to 0, the skin color adjustment target grid points are not adjusted at all, and skin color reproducibility is given the highest priority. . On the other hand, when the skin color adjustment coefficient is set to 1, 100% adjustment is performed in the same manner as the grid points other than the skin color adjustment target, and gray reproducibility is given the highest priority.

Excess amount = (value after adjustment of target grid point−value before adjustment) × (1.0−skin color adjustment coefficient) (5)
Target grid point value = value before adjustment of target grid point + (value after adjustment of target grid point−value before adjustment) × skin color adjustment coefficient Equation (6)
In S210, the distribution amount to other target lattice points is calculated based on the excess amount obtained in S208 or S209, and then the process returns to S204. In the present embodiment, the excess amount is equally distributed to the remaining two target grid points. At this stage, only the distribution amount is calculated, and the actual distribution is performed in the process (S211) described later.

  If it is determined in S204 that all the three target grid points have been processed by performing the processes in S205 to S210 as described above, the process proceeds to S211 and is calculated in S210. Allocation amounts are allocated to other target grid points. Thereafter, the lattice point value adjustment process is terminated. The allocation amount is assigned as much as possible within the range of possible values (0 to 255) as the color conversion value. That is, 0 is set when it is less than 0, and 255 is set when it is greater than 255.

[4. effect]
As described above, the personal computer 10 of the present embodiment is adjacent to the grid points on the achromatic color axis in the RGB directions in the cubic region of the RGB → CMYK color conversion table including the achromatic color axis. The color conversion values of the three lattice points are adjusted so that the average value of the color conversion values of the three lattice points approaches the color conversion value of the intersection of the plane passing through the three lattice points and the achromatic color axis. According to such a color conversion table creation method, it is possible to create a color conversion table that can reproduce gray well even when interpolation calculation is performed by cubic interpolation.

  In addition, among the three grid points, the adjustment amount of the color conversion value is suppressed for the grid points used for the interpolation calculation of the color region representing the skin color (S206: YES, S209), so the skin color is also good. Can be reproduced.

[5. Correspondence with Claims]
In the personal computer 10 of the present embodiment, the control unit 11 that executes the table adjustment process corresponds to the adjustment unit.

[6. Other forms]
As mentioned above, although embodiment of this invention was described, it cannot be overemphasized that this invention can take a various form, without being limited to the said embodiment.

  For example, the above embodiment has been described on the premise that a color conversion table in which CMYK values are registered at each of the lattice points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into eight in each RGB direction has been described. The number of divisions is not limited to this. In particular, if the RGB color space is divided into 16 or more in each of the RGB directions, as shown in FIG. 6, the axis is shifted by one from the achromatic color axis on which the adjustment for reproducing gray is performed satisfactorily. Grid points (black circles) are not used for the interpolation calculation of the skin color area, and the skin color area is not affected by the adjustment. For this reason, in this case, it is possible to eliminate the lattice points for skin color adjustment (the processing in S206 and S209 is unnecessary). However, for example, in the case of 16 divisions, the number of grid points is 17 × 17 × 17, and the required memory capacity and processing load are significantly increased compared to the case of 8 divisions (9 × 9 × 9). Therefore, the effect of suppressing the adjustment amount of the lattice point of the skin color adjustment target while being divided into 8 as in the above embodiment is high.

  In the above embodiment, the adjustment amount of the grid points that affect the color area representing the skin color is suppressed. However, the present invention is not limited to this, and the same processing is performed for the color area other than the skin color. Is also possible. However, it is preferable to suppress at least the influence on the skin color since the influence on the skin color is particularly noticeable in a photographed image of a person.

  Furthermore, in the above embodiment, the description has been made on the assumption that a color conversion table of RGB → CMYK is created. However, the present invention is not limited to this, and the same applies to the case of creating a color conversion table for conversion to other than CMYK. It can be implemented.

  On the other hand, in the above-described embodiment, the configuration in which the table adjustment process is performed on the personal computer 10 side is illustrated, but the present invention is not limited to this. For example, the table adjustment process may be performed on the color printer 40 side. For example, the color printer 40 stores a base color conversion table in advance, and can perform table adjustment processing on the color conversion table as necessary.

It is a block diagram showing schematic structure of the personal computer of embodiment. It is explanatory drawing for demonstrating the problem which has a bad effect on the color of a skin color. It is a flowchart of a table adjustment process. It is explanatory drawing of an adjustment point. It is a flowchart of a lattice point value adjustment process. It is a graph at the time of dividing RGB color space into 16 in each RGB direction. It is explanatory drawing of the printing result of a gray gradation. It is explanatory drawing for demonstrating the cause which a striped pattern arises in a gray gradation in two dimensions. It is explanatory drawing for demonstrating the cause which a striped pattern arises in a gray gradation in three dimensions.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Personal computer, 11 ... Control part, 12 ... CPU, 13 ... ROM, 14 ... RAM, 15 ... Operation part, 16 ... Display part, 17 ... USB interface, 18 ... Communication part, 19 ... Memory | storage part, 21 ... OS 22 ... Color conversion table creation program, 40 ... Color printer

Claims (7)

A method for creating a color conversion table in which color conversion values are registered at each of the lattice points corresponding to the vertices of each cubic region obtained by dividing the RGB color space into a plurality of RGB directions,
A plane in which the average value of the color conversion values of three lattice points adjacent to each other in the RGB direction with respect to the lattice point on the achromatic color axis in the cubic region including the achromatic color axis passes through the three lattice points. A method of creating a color conversion table, characterized in that the color conversion values of the three grid points are adjusted so as to be equal to the color conversion value of the intersection of the achromatic color axis. The color conversion table creation method according to claim 1, wherein an adjustment amount of a color conversion value is suppressed for a lattice point used for interpolation calculation of a specific color region among the three lattice points. The color conversion table creation method according to claim 2, wherein the specific color area is a color area representing a skin color. The cubic region is obtained by dividing the RGB color space into eight in each direction of RGB,
The grid points used for the interpolation calculation of the color region representing the skin color constitute a grid point sequence existing at a position shifted by one in the R direction from the achromatic color axis among the grid point sequences parallel to the achromatic color axis. The color conversion table creation method according to claim 3, wherein the color conversion table is a grid point. A color conversion table in which color conversion values are registered in each of the lattice points corresponding to the vertices of each cubic region obtained by dividing the RGB color space into a plurality of RGB directions,
A plane in which the average value of the color conversion values of three lattice points adjacent to each other in the RGB direction with respect to the lattice point on the achromatic color axis in the cubic region including the achromatic color axis passes through the three lattice points. A color conversion table characterized by being adjusted to be equal to the color conversion value at the intersection of the achromatic color axis. Creation of a color conversion table for causing a computer to execute a step for creating a color conversion table in which color conversion values are registered at the respective lattice points corresponding to the vertices of each cubic area obtained by dividing the RGB color space into a plurality of RGB directions. A program,
A plane in which the average value of the color conversion values of three lattice points adjacent to each other in the RGB direction with respect to the lattice point on the achromatic color axis in the cubic region including the achromatic color axis passes through the three lattice points. A color conversion table creation program that causes a computer to execute a step of adjusting the color conversion values of the three grid points so as to be equal to the color conversion value of the intersection of the color axis and the achromatic color axis. A color conversion table creation device for creating a color conversion table in which color conversion values are registered at each of the lattice points corresponding to the vertices of each cubic region obtained by dividing the RGB color space into a plurality of RGB directions,
A plane in which the average value of the color conversion values of three lattice points adjacent to each other in the RGB direction with respect to the lattice point on the achromatic color axis in the cubic region including the achromatic color axis passes through the three lattice points. A color conversion table creating apparatus comprising adjusting means for adjusting the color conversion values of the three grid points so that the color conversion values at the intersections of the color axis and the achromatic color axis are equal .