JP3215363B2 - Color conversion table creation method and color conversion method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color processing technique for digital color image data, and more particularly to a color conversion table creating method and color conversion for reproducing the same color as an original on a color copying machine, a color printer, a color monitor, and the like. About the method.

[0002]

2. Description of the Related Art In recent years, copying machines and printers have been used on a daily basis, and recently, color copying machines for copying color documents,
2. Description of the Related Art Color printers that print color documents from computers have become widespread.

[0003] Conventionally, when printing or copying a color document, it has been pointed out that the color of the document or image output by the device is different and sufficient color reproducibility cannot be ensured.
This is because the color of the printed matter differs depending on the type of the output device because the pigment is a toner, a dye, or a pigment. Furthermore, while the RGB color data handled by the computer is colored by additive color mixture, the printer prints by subtractive color mixture, and there is a large amount of color mixture in the pigment itself due to unnecessary absorption of the pigment. is there.

Various measures have been taken to solve the problem of color reproducibility between devices for color images, and the color reproducibility of devices has been gradually improved.

For example, in a PostScript printer,
The image data input based on the color rendering dictionary (CRD) representing the characteristics of the device is corrected into image data in which a desired color is reproduced, and then printed.

In an electrophotographic color copying machine,
After the RGB color data obtained by the color scanner is color-corrected by the color converter to the color data suitable for the printing color material characteristics, the data is input to the color engine and printed. The color converter is performed by a matrix calculator,
Some do with a multi-dimensional lookup table.

Hereinafter, as a conventional example 1, a case in which color conversion is performed by a color correction unit constituted by a matrix calculator will be described with reference to a block diagram of FIG.

The input data RGB is color-corrected by a linear matrix operation comprising a coefficient multiplier 801 and an adder 802, and is converted into data CMY.

Normally, the color corresponding to the data R cannot be reproduced by a single ink, but is reproduced by mixing CMY inks. The same applies to data G and B. That is, RG
The B signal is represented by CMY by the following equations (1) and (2).
Mutually converted to ink signals.

[0010]

(Equation 1)

(Equation 2) Here, Aij is a 3 × 3 matrix. Also, Aij-
1 is an inverse matrix of the matrix Aij.

The conversion matrix Aij is obtained as follows.

First, an input color chart data set Di = (C, M, Y) i covering a wide input color gamut is created, and a color chart image including the color chart data is output from a printer.

Next, the output color patch is read by a scanner to obtain each read color patch data set Si = (R, G, B) i, and a correspondence table between the input color patch data set and the read color patch data set is obtained. Create Table 1 shows an example of a color chart data set correspondence table.

[0014]

[Table 1]

The read color patch data set Si is converted by a 3 × 3 matrix to obtain a matrix which is most approximated to the input color patch data set Di.

In this case, the matrix coefficient Aij is (1)
The value Doi = (Co, Mo, Yo) i of the converted color chart data set converted from the scanner output Si = (R, G, B) i by the formula and the value Di = (C, M, Y) of the input color chart data set ) Determined by the least squares method so that the sum of squares of the error with i is minimized. The condition of the least squares method is as follows. A matrix coefficient Aij that minimizes an error is obtained by using each matrix coefficient Aij as a variable, and the following (3)
As shown in the equation, the sum of squares of each error is calculated by a matrix coefficient Aij
Can be obtained by setting the partial differential coefficient using each value of the variable as 0 as 0.

[0017]

(Equation 3) The conversion characteristics of the color corrector shown in equation (1) are obtained using the obtained matrix coefficients Aij.

In Conventional Example 1, the linear conversion matrix is optimized by the least squares method so that the error is minimized for the entire combination of color patches for calculating the conversion parameters, but the color conversion characteristics are modeled. When deviating from the linear matrix relationship, a partial error occurs in some color regions.

Next, as a second conventional example, a case where color conversion is performed by a color correction unit using a three-dimensional lookup table (hereinafter, referred to as “3D-LUT”) will be described with reference to the block diagram of FIG.

The input RGB data is separated by the image input unit 901 into upper bits and lower bits. And
The upper bits are used to extract a plurality of pieces of grid point data used for the interpolation operation from the 3D-LUT 902, and the lower bits are used by the interpolation coefficient generation unit 904 to calculate a weight coefficient required for the interpolation operation. Interpolator 903
Is the output from the 3D-LUT 902 and the interpolation coefficient generator 9
The CPU calculates the cumulative value of the weighting coefficient from step 04, and outputs a color conversion output CMY value corresponding to the input RGB value. 3D-LUT
The detailed contents and operation of the color converter according to
-99586 and JP-A-7-99587. In the triangular prism interpolation method and the oblique triangular prism interpolation method described in the above publications, linear interpolation calculation is performed using six grid point data for the interpolation calculation.

To create 3D-LUT data, a method of directly searching and setting table data by a corresponding point search method,
There is a method of tabulating the high-order matrix conversion. Here, the high-order matrix method will be described.

First, similarly to the first conventional example, an input color patch data set Di = (C, M, Y) i is created, this color patch is output, the output color patch is read by a scanner, and the read A correspondence table between the data set Si = (R, G, B) i and the original color chart data set is created.

The output RGB set is converted by a matrix function to obtain a high-order matrix coefficient Bij which is converted to the input CMY data most approximately. An example of the second-order matrix coefficient is shown in the following equation (4).

[0024]

(Equation 4) The calculation of the higher-order matrix coefficient Bij is performed in the same manner as in the first embodiment.
The sum of squares of the error between the converted color chart data set Doi = (Co, Mo, Yo) i and the input color chart data set Di = (C, M, Y) i converted from the scanner output RGB by the equation (4) is minimum. Is determined by the least squares method. The condition of the least-squares method can be obtained from the fact that the partial differential coefficient using each value of the higher-order matrix coefficient Bij as a variable becomes 0 as in the case of the equation (3).

A three-dimensional color conversion table is created by converting the input / output relationship of the equation (4) into a three-dimensional table using the obtained coefficients Bij.

The second conventional example is a multidimensional table in which the higher-order matrix operation is improved in order to improve the drawback of linear correction by increasing the order of the matrix relation and to reduce the operation load of the higher-order matrix operation. It is. However, due to the method of minimizing the overall color error, coloring tends to remain in the gray portion, and problems remain in accurate expression in the highlight portion. Further, the advantage of the table reference method in which conversion data can be freely set for each image area cannot be fully utilized.

As a third conventional example, Japanese Patent Laid-Open Publication No.
As described in Japanese Patent Application Laid-Open No. 869, there is a method in which a conversion matrix is calculated for each color region of an image, and a color conversion matrix coefficient is switched according to the color region of the input image to perform partial color conversion.

However, when a high-order non-linear matrix is used to switch the conversion parameter for each area, color discontinuity occurs in an image area extending over the area.

As a fourth conventional example, there is a method of directly obtaining a color conversion table from color chart data. Color conversion that gives the target print color by predicting and calculating the print values for all inputs from the colorimetric values of the printed color patches by triangular prism interpolation and searching a correspondence table with the predicted colorimetric values for all inputs The method of finding the table value is 1994
The annual report of the Color Forum Annual Meeting (pp. 55-58). Japanese Patent Application Laid-Open No. 6-22124 describes a method for creating a color conversion table for outputting an arbitrary print color by an interpolation operation in a triangular pyramid surrounded by four adjacent color chips in a color space. ing.

In Conventional Example 4, even in the case of color conversion that cannot be modeled, a color conversion table value can be directly obtained. However, it is necessary to create many dataset correspondence tables. Also, it is not easy to customize the table data after creating the color conversion table.

[0031]

As described above, the prior art of the color conversion method has a certain effect on the color reproducibility, but each of them has a problem.

The present invention has been made in view of the above point, and a color conversion table for color conversion purpose is easily created for each color region, and the color conversion table is set so that colors are continuous in an image region extending over the region. It is an object of the present invention to provide a color conversion table creating method and a color conversion method for combining the two.

[0033]

In order to solve the above-mentioned problems, the present invention takes the following measures. That is, the book
The color conversion table creation method according to the present invention provides a
Input color chart data set corresponding to body region and corresponding reading
Find the first color conversion matrix from the color chart data set
Process and the first color conversion using this first color conversion matrix
A step of creating a table and the input color chart data set
Select a color chart data set in a specific color value area from
Separation process and corresponding to this selected color chart dataset
The second color conversion matrix from the read color chart data set
And the second color conversion matrix
Creating a two-color conversion table;
Table and the second color conversion table.
And a step of creating a conversion table.
Was. In addition, the color conversion table creating method of the present invention may be configured such that the input color
Sorting the vote data set for each color value area;
Read color chart data corresponding to this sorted color chart data set
Color conversion matrix for each area selected from data set
And a color conversion matrix using each color conversion matrix.
Table creation process and color conversion for each area of color value
The closer the contribution of the table to the center of the color value area,
The process of setting larger and smaller as going further, and each color conversion
Sum of the product of the table values and the contribution ratio of the color conversion table
Creating a composite color conversion table by
Configuration.

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040]

[0041]

[0042]

[0043]

[0044]

[0045]

[0046]

[0047]

[0048]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A first aspect of the present invention is a step of obtaining a first color conversion matrix from an input color patch data set adapted to the entire area of an input color range and a corresponding read color patch data set; Creating a first color conversion table using the first color conversion matrix, and selecting a color patch data set in a specific color value area from the input color patch data set; A step of obtaining a second color conversion matrix from the color chart data set and the corresponding read color chart data set; a step of using the second color conversion matrix to create a second color conversion table; A step of creating a composite color conversion table by combining the one color conversion table and the second color conversion table while changing the contribution ratio. With this configuration,
The entire color conversion table can be created by combining color conversion tables having good color conversion characteristics for each area, and the color conversion characteristics of a specific color portion can be improved. According to a second aspect of the present invention, the input color patch data set is selected for each color value area, and the read color patch data set corresponding to the selected color patch data set is selected. A step of obtaining a color conversion matrix for each area; a step of creating a color conversion table using each color conversion matrix; and a synthesis color conversion table obtained by changing the contribution ratio of the color conversion table for each area according to the color value. Is provided. With this configuration, it is possible to perform color conversion on a region in which the color conversion characteristics deviate from the modeled linear matrix relationship by using a color chart suitable for the region, and realize selective color correction of a specific color portion. A fourth aspect of the present invention is directed to a first aspect.
Alternatively, in the second aspect, a color conversion matrix is independently obtained for each of a region where the saturation is lower than the reference value, a region where the saturation is lower than the reference value, and the entire region, and each color conversion table data is created using each of the color conversion matrices. For gray parts with low saturation, increase the contribution rate of the color conversion table in the low saturation area, and for primary parts with high saturation, increase the contribution rate of the color conversion table for the high saturation area. The required configuration is adopted. With this configuration, the contribution rate can be determined based on the saturation, so that it is possible to create a color conversion table in which the monochrome reproducibility of a gray portion and the color reproducibility of a high saturation region are improved. According to a fifth aspect of the present invention, in the first or second aspect, a color conversion matrix is independently obtained for each of a region where the luminance is lower than the reference value, a region where the luminance is higher than the reference value, and an entire region. Each color conversion table data is created by using, the contribution rate of the color conversion table of the low luminance area is increased for the dark part with low luminance, and the color conversion of the high luminance area is performed for the highlight part with high luminance. A configuration is adopted in which the contribution ratio of the table is increased. With this configuration, the contribution rate can be determined based on the luminance. Therefore, it is possible to create a color conversion table with enhanced smooth image reproducibility, especially in a highlight portion. According to a sixth aspect of the present invention, in the first or second aspect, an area in which the luminance is lower and higher than the reference value, an area in which the saturation is lower and higher than the reference value, and
A configuration in which color conversion matrices are independently obtained for the entire area, color conversion table data is created using the color conversion matrices, and synthetic color conversion table data is obtained by summing the contributions of the color conversion table data. take. With this configuration, the contribution ratio of the color conversion table can be switched by a combination of the luminance and the saturation. Therefore, it is possible to create a color conversion table in which reproducibility of the highlight portion and the gray portion is compatible. According to a seventh aspect of the present invention, in the first or sixth aspect, the contribution ratio of the color conversion table of each color region to the input color space position is 100% at the center position of each region. A configuration is adopted in which the value is determined so as to gradually decrease as the displacement increases, and the sum of the contribution rates of all the color conversion tables is 100% at any input point. With this configuration, the synthesized color conversion tables are smoothly and continuously connected, and color conversion characteristics with improved color continuity of the reproduced image can be realized. Further, as a result, a color conversion table for performing individual color conversion on a plurality of color regions can be created, and a color conversion device with improved overall color reproducibility can be realized. An eighth aspect of the present invention relates to a color conversion method, wherein an output value corresponding to an input value of image data is converted into a composite color created by the color conversion table creating method according to any one of the first to seventh aspects. The configuration obtained using the conversion table is adopted. With this configuration, color conversion can be performed using the entire color conversion table created by combining color conversion tables having good color conversion characteristics for each area, and a reproduced image in which the color conversion characteristics of a specific color portion are improved. Can be obtained. Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

(Embodiment 1) FIG. 1 is a block diagram showing a configuration of a color copying machine according to Embodiment 1.

As shown in FIG. 1, the color copying machine includes an input unit 101 for inputting an instruction from a user, a color chart data creating unit 102 for creating color chart data, and reading an original to obtain image data. A scanner unit 103, a color conversion table creation unit 104 for creating a color conversion table, a color conversion operation unit 105 for color-converting the read image data based on the created color conversion table, and outputting the color-converted image data It mainly comprises a printer unit 106.

The input unit 101 inputs an instruction from a user when changing a set value or the like.
02 or as a signal to the color conversion table creation unit 104.

The color chart data creation unit 102 includes an input unit 101
, And generates color patch data Di (hereinafter, referred to as “input color patch data”) for the N color patches, transmits the color patch data Di to the color conversion table creating section 104, and outputs image data composed of color patches. Is created and output to the printer unit 105.

The scanner unit 103 reads a document, and if the read document is a color chart print image, creates color chart data (hereinafter referred to as “read color chart data”) Si for each color chart and creates a color conversion table creation unit 104. If the read original is other than a color chart print image, the original is converted into image data and output to the color conversion operation unit 105.

The color conversion table creation unit 104 includes the input unit 1
A color conversion table is created from the input color patch data and the read color patch data based on the signal from 01, and this data is output to the color conversion calculation unit 105.

The color conversion operation unit 105 includes a scanner unit 103
Color conversion table creation unit 104
Color conversion is performed using the data of the color conversion table received from the printer unit 106 and output to the printer unit 106.

The printer unit 106 includes a color chart data creation unit 1
02 or the image data received from the color conversion operation unit 105.

By performing color conversion on the read image data of the document based on the data of the color conversion table, a duplicate image reproduced correctly can be obtained.

Next, the function of the color conversion table creation unit 104 will be specifically described with reference to the functional block diagram of FIG.

The color conversion table creator 104 averages the read color patch data for each color patch by a color patch data averaging section 201.
A selection criterion setting unit 202 for setting a saturation reference value in accordance with an instruction input from a user; a data selection unit 203 for selecting input color patch data equal to or less than the reference value and read color patch data corresponding thereto from the whole; A matrix creation unit 204 that creates a color conversion matrix using the color chart data and the read color chart data, a color conversion table calculation unit 205 that stores color conversion data calculated by the color conversion matrix in a table format, It mainly includes a contribution ratio setting unit 206 that sets a contribution ratio based on an instruction input from a user, and a color conversion table combining unit 207 that combines a color conversion table based on the contribution ratio.

The matrix creating unit 204 creates a color conversion matrix (hereinafter, referred to as an “entire color conversion matrix”) for the entire color chart data, and the colors selected by the data selecting unit 203. A matrix creation unit B21 that creates a color conversion matrix for the vote data (hereinafter, referred to as a “selection color conversion matrix”).
And 2.

The color conversion table calculation unit 205 calculates color conversion data based on the entire color conversion matrix and obtains color conversion data, and the color conversion table calculation unit A 221 calculates color conversion data based on the selected color conversion matrix. A color conversion table calculation unit B222.

Next, the flow of the color conversion table creation processing according to the first embodiment will be described with reference to the flowchart of FIG.

First, N color chart data sets Da = (C, M, Y) a are prepared in the color chart data creation unit 102 almost uniformly in the multidimensional input color space of the color printer, and N color chart data sets are prepared. A color chart image having a vote in an image area is created (S301), and the created color chart image is printed from the printer unit 106 (S301).
302).

Further, the reference value Vt
Is set in the contribution ratio setting unit, and a coefficient necessary for calculating the contribution ratio K is set (S303).

Next, the printed color chart image is transferred to the scanner unit 10.
3 (S304), and after averaging for each color chart by the color chart data averaging unit 201, N read color chart data sets Sa = (R, G, B) a are acquired (S305).

Next, the matrix creation unit A211 calculates the color conversion matrix coefficient Aij by the least squares approximation method, and obtains the following color conversion equation (5) (S306).

[0067]

(Equation 5) Next, the color conversion table operation unit A221 calculates a value for each entry (combination of input data sets) from Expression (5), and creates a color conversion table Ta (S3).
07). In the present embodiment, the color conversion table Ta
Is an input three-dimensional table. To be precise, Ta (i, j, k)
Although it is expressed, it is omitted and displayed. Hereinafter, similar expressions are omitted and displayed.

Next, in the data selection section 203, a saturation value Vi representing the degree of balance of the data of each color chart data set Di = (C, M, Y) i is obtained by the following equation (6).
Then, an input color patch data set (hereinafter, referred to as “selected input color patch data”) in which the saturation value Vi is smaller than the reference value Vt set in the selection reference setting unit 202, Db = (C, M,
Y) b is selected from the input color patch data set Da, and the corresponding read color patch data set (hereinafter, referred to as “selected read color patch data”) Sb = (R, G, B) b is read color patch data set It is sorted out from Sa (S308).

[0069]

(Equation 6) Next, in the matrix creation unit B212, similarly to Aij,
Calculate a sorting color conversion matrix coefficient Bij from the sorting input color chart data set Db and the sorting reading color chart data set Sb,
The following color conversion equation (7) is obtained (S309). This sorted color chart data set is a group of color charts close to gray. Therefore, Bij is a matrix coefficient for converting a color close to gray.

[0070]

(Equation 7) Next, the color conversion table calculation unit B222 calculates a value for each entry from Expression (7), and creates a selection color conversion table Tb. (S310) Next, the contribution ratio setting unit 207 calculates the contribution ratio K of the selected color conversion table Tb with respect to the saturation V by using the following equation (8) (S311). Further, the contribution ratio of the color conversion table Ta is set to 1-K so that the sum of the contribution ratios is 1.

Then, the color conversion table synthesis unit 208 synthesizes the color change table Ta and the color conversion table Tb using the contribution rate K and the following equation (9) to create a synthesized color conversion table Tc. Then, it is stored in the color correction calculation unit 105 (S312).

[0072]

(Equation 8)

(Equation 9) Here, Vth is a value that determines the spread range of the selection color conversion table Tb. When Vth is set to be large, the spread range of the color conversion table Tb is extended to the high saturation region of the color conversion table Ta. V0 is the effective range of the input data, and is 255 when the input data is 8 bits.

The function F is a function that continuously changes from 0 to 1. For example, if the function F is a linear function as shown in the following equation (10), when V changes from 0 to Vth, K linearly decreases from 1 to 0.

[0074]

(Equation 10) Further, in the function F, by giving a power characteristic (gamma characteristic) to the increase in the saturation value V, the switching curve shape of the color conversion table can be controlled.

FIG. 4 is a characteristic diagram showing the change of the contribution ratio of the color conversion table to the saturation value V. The contribution ratio K of the selection color conversion table Tb takes an effective value in the range up to Vth, and This is an example in which the value V has a gamma characteristic to speed up the reduction of the contribution ratio K of the table Tb.

As is clear from equations (8) and (9), the contribution ratio of the color conversion table Ta is gradually increased from 0 by the saturation value V, and the saturation value V When the value exceeds the boundary point Vth, data of the color conversion table Ta is set.

The color conversion table Ta and the color conversion table Tb
FIG. 5 shows a process of creating a color conversion table Tc by combining
This will be described with reference to a schematic diagram of FIG.

For example, if Vth = 64, the input RGB
If the data value is (0, 0, 0), V = 0, which corresponds to the point a in FIG. 4, and K = 1. Therefore, as shown in FIG. 5, the composite color conversion table value of Tc is such that the value of Tb is 1
00% is reflected, and becomes (9, 10, 11).

When the input RGB data values are (0, 0,
32), V = Vth / 2, which corresponds to the point b in FIG. 4, and K = 0.25. Therefore, as shown in FIG. 5, the composite color conversion table value of Tc is such that the value of Tb is 25.
The values of% and Ta are reflected by 75% and become (7, 5, 33).

When the input RGB data values are (0, 0,
64), V = Vth, which corresponds to the point c in FIG. 4, and K = 0. Therefore, as shown in FIG. 5, the composite color conversion table value of Tc is (3, 5, 60), reflecting the value of Ta by 100%.

The user scans the original from the scanner unit (S313), and prints the color-converted image on the obtained change table Tc by the printer unit (S314).

Then, as a result, when correction is required (S3
15) In S303, the reference saturation value Vt set in the selection reference setting unit 202 and the coefficient of Vth or contribution K set in the contribution ratio setting unit 207 are changed, and the subsequent processing is repeated to change the color saturation in each color region. Correct the color conversion of.

As described above, by determining the contribution ratio based on the saturation, it is possible to enhance the monochrome reproducibility and color reproducibility of a gray portion, which are problems to be solved conventionally.

Note that a plurality of selected color conversion tables Tb (T
b1 to Tbn), and the color conversion table Tc can be created by combining the color conversion table Ta and the selected color conversion tables Tb1 to Tbn.

For example, when three selection color conversion tables are prepared, first, Vth1 and Vth
2, Vth3 and Vth4 are set, and the data selection unit 1007
Means that the saturation V is 0 ≦ V ≦ Vth2, Vth1 <V ≦ V
The selected input color patch data sets and the selected read color patch data sets of three groups, th3 and Vth2 <V ≦ Vth4, are selected. Then, the least-squares calculator 1009 calculates the color conversion matrices Bij1 to Bij3, respectively, and the color conversion table generator B1011 selects the selected color conversion tables Tb1 and Tb1.
b2 and Tb3 are obtained.

The color conversion table synthesizing unit 1012 uses the contribution ratios Ka, Kb1, Kb2, and Kb3 for the respective color conversion tables set in the contribution ratio setting unit 1013 to obtain a composite color conversion table Tc according to the following equation (11). Create.

[0087]

[Equation 11] FIG. 6 is a characteristic diagram showing a change in each contribution ratio of the four color conversion tables with respect to the saturation value V.
This is an example in which the contribution rates Kb1, Kb2, and Kb3 of b1, Tb2, and Tb3 are 100% in the saturations Vth1, Vth2, and Vth3, respectively.
Each contribution rate is multiplied by the data of the corresponding color conversion table, and the sum is set as the data of the composite color conversion table. Also in this case, the sum of the four coefficients (Ka + Kb1 + Kb2 + Kb3) is standardized so as to always be 1 in each saturation value.

As described above, by preparing a plurality of selection color conversion tables, the composite color conversion table can be finely adjusted, and the color reproducibility of the apparatus can be improved.

In the present embodiment, the color conversion table is created by selecting color chart data according to the saturation. However, other elements such as hue and luminance are used instead of the saturation. Can be combined.

In this embodiment, the color conversion table for the entire color chart data and the color conversion table for the color chart data equal to or smaller than the reference value are synthesized to create a composite color conversion table. It is also possible to use a color conversion table for color chart data equal to or higher than the reference value instead of the color conversion table for, and combine this with a color conversion table for color chart data equal to or lower than the reference value. (Embodiment 2) A case in which switching of the color conversion table is performed by using two elements of saturation and luminance will be described below. The description of the parts common to the first embodiment is omitted.

FIG. 7 is a functional block diagram showing the function of the color conversion table creating section in the present embodiment.

The selection criterion setting unit 702 has a saturation criterion setting unit 731 and a luminance criterion setting unit 732, and sets reference values Vth and Lth, respectively.

The data selection unit 703 determines the saturation Vi and the luminance Li from the color chart data set Di = (C, M, Y) i (12)
It is determined by the formula.

[0094]

(Equation 12) The data set of the color chart is classified and sorted into four types according to the magnitude relation between the values of the saturation V and the luminance L and the reference values Vth and Lth.

The matrix creation unit 704 creates a color conversion matrix by the least squares method for each selected color chart data set.

The selection color conversion table creating section 705 converts the color conversion tables Ta1, Ta2, Tb1,
Calculate Tb2.

Table 2 below shows the relationship between the color chart data set classified by the saturation V and the luminance L and the color conversion table.

[0098]

[Table 2]

The contribution ratio setting section 707 includes a contribution ratio K1 of the selected color conversion tables Ta1 and Tb1 to the saturation V and a contribution ratio K2 of the selected color conversion tables Ta1 and Ta2 to the luminance L.
Is calculated by the following equation (13). At this time, the contribution ratio of the color conversion tables Ta2 and Tb2 is 1-K1, and the contribution ratio of the color conversion tables Tb1 and Tb2 is 1-K2.

[0100]

(Equation 13) V0 and L0 are the effective ranges of the input data, respectively.
The function F is a function that continuously changes from 0 to 1. For example, if the function F is a linear function, the contribution rate K1
And K2 are represented by the following equation (14).

[0101]

[Equation 14] Note that the contribution rate changes independently depending on the values of the saturation V and the luminance L of the color chart, and the sum of the contribution rates for each table is as shown in the following equation (15).

[0102]

(Equation 15) The color conversion table synthesizing unit uses the contribution rates K1 and K2 and calculates the color change table Ta according to the following equation (16).
And a color conversion table Tb to synthesize a composite color conversion table T
c is created and stored in the color correction calculation unit 105.

[0103]

(Equation 16) With the above configuration, the contribution ratio of the color conversion table can be switched by a combination of the luminance and the saturation, so that it is possible to create a color conversion table that achieves both the reproducibility of the highlight portion and the gray portion.

A color adjustment setting unit for receiving a color adjustment instruction from a user to the color conversion table generation unit of the present invention, an adjustment color conversion table generation unit for generating an adjustment color conversion table based on the color adjustment instruction, and a composite color conversion table It is also possible to provide an adjustment color conversion table synthesizing unit for synthesizing the adjustment color conversion table in the conversion table, further synthesize the adjustment color conversion table with the synthesis color conversion table, and create the adjustment color conversion table. is there.

Thus, besides the colorimetric color matching,
Color adjustment for subjective color matching is possible. The subjective color matching is performed for the purpose of making a picture, for example, to make the skin color a little red, or to make the grass green dark green.

[0106]

As described above, according to the present invention, the color conversion can be performed for each area, and the color conversion table determined for each area can be switched while maintaining the continuity. The color conversion effect can be enhanced by switching, and the image conversion can be smoothly performed even if the color conversion table is switched.

Further, according to the present invention, the color conversion table can be adjusted by synthesizing with a table created by using an arbitrary color adjuster.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a color copying machine according to a first embodiment of the present invention.

FIG. 2 is a functional block diagram illustrating functions of a color conversion table creation unit according to the first embodiment.

FIG. 3 is a flowchart showing the flow of a color conversion table creation process according to the first embodiment;

FIG. 4 is a characteristic diagram showing a change in a contribution ratio of a color conversion table to a saturation value V according to the first embodiment.

FIG. 5 is a color conversion table Ta, Tb according to the first embodiment.
Of Tc and Tc

FIG. 6 is a characteristic diagram showing a change in each contribution ratio of four color conversion tables with respect to a saturation value V according to the first embodiment.

FIG. 7 is a functional block diagram illustrating functions of a color conversion table creating unit according to the second embodiment.

FIG. 8 is a block diagram of a conventional color conversion unit that performs color correction using a linear matrix.

FIG. 9 is a block diagram of a conventional color conversion unit that performs color correction by using a three-dimensional table and three-dimensional interpolation.

[Explanation of symbols]

 Reference Signs List 101 input unit 102 color chart data creation unit 103 scanner unit 104 color conversion table creation unit 105 color conversion calculation unit 106 printer unit 201 color chart data averaging unit 202 selection criteria setting unit 203 data selection unit 204 matrix creation unit 205 color conversion table calculation Section 206 color conversion table synthesis section 207 contribution rate setting section

Continuation of the front page (72) Inventor Hideto Motomura 3-10-1, Higashi-Mita, Tama-ku, Kawasaki-shi, Kanagawa Matsushita Giken Co., Ltd. (56) References JP-A-9-331462 (JP, A) JP-A Heisei 1-1114268 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/46-1/64 G06T 1/00 510

Claims (8)

(57) [Claims] A step of obtaining a first color conversion matrix from an input color patch data set adapted to the entire area of the input color range and a corresponding read color patch data set; A step of creating a color conversion table; a step of selecting a color patch data set in an area of a specific color value from the input color patch data set; and reading color patch data corresponding to the selected color patch data set. Obtaining a second color conversion matrix from the set, a step of using the second color conversion matrix to create a second color conversion table, the first color conversion table and the second color conversion
Creating a composite color conversion table by combining the color conversion table with a table. 2. The step of creating a composite color conversion table comprises:
The first color conversion table and the second color conversion table
Color conversion characteristics to be set in the composite color conversion table
Based on the first color conversion table contribution rate and the second color conversion table.
Table contribution ratio, and the value of the first color conversion table and
The product of the first color conversion table contribution ratio and the second color conversion table
Product of the conversion table value and the second color conversion table contribution ratio
To create the composite color conversion table.
2. The method for creating a color conversion table according to claim 1, wherein
Law. 3. The method according to claim 2, wherein the second color conversion table contribution rate is determined by
The closer to the center of the constant color value area, the larger and farther
And the first color conversion table contribution ratio is
As the second color conversion table contribution ratio increases, the value decreases.
It is necessary to control the size so that it gets larger as it gets smaller.
The method for creating a color conversion table according to claim 2. 4. The method according to claim 1, wherein said second color conversion table contribution ratio K is
The maximum value is 1 at the center of the specific color value area,
The one-color conversion table contribution rate is set to (1-K).
4. A method for creating a color conversion table according to claim 2,
Law. 5. A step of selecting an input color patch data set for each color value area, and a color conversion matrix for each area selected from the selected color patch data set and a corresponding read color patch data set. And a step of creating a color conversion table using each color conversion matrix .
The contribution rate of the color conversion table for each area of the value
Set larger as you get closer to the center of the area and smaller as you go further
And the values of each color conversion table and its color conversion table
A composite color conversion table based on the sum of the products of the
A color conversion table comprising the steps of:
File creation method. 6. The contribution ratio of each of said color conversion tables is
The maximum value is 1 at the center of the color value area, and the color value
The smaller the distance from the center of the area, the smaller
The sum of the contribution ratios of the conversion table is set to 1.
How to create a color conversion table. 7. A color value, saturation value, the less the luminance value
Of claims 2 to 6, characterized in that also one
The color conversion table creation method described in any of the above . 8. A color, wherein an output value corresponding to an input value of image data is obtained by using a composite color conversion table created by the color conversion table creation method according to any one of claims 1 to 7. Conversion method.