JPH09321996A - Color reproduction method - Google Patents

Abstract

(57) [Abstract] [PROBLEMS] To easily and accurately reproduce an arbitrary color without requiring many preparation steps. SOLUTION: A CMYK signal value 70 and an arbitrary chromaticity 80
The color material transfer amount 74, which is a physical quantity, is treated as an intermediate amount, and the single color characteristic 72 representing the relationship of the color material transfer amount 74 with respect to the signal value 70 and the transfer amount of each color material of a plurality of inks. 74 (ink amount) and the mixed color characteristic 76 representing the relationship between the chromaticity 80, and the obtained single color characteristic 72.
And a color mixture characteristic 76, and a signal value / chromaticity characteristic obtained by synthesizing them is obtained as a color conversion table 78. In this way, the single color characteristic and the color mixing characteristic are separately obtained, and the relationship between the signal value and the chromaticity can be determined by the color conversion table 78 according to the obtained characteristic, and the color reproduction is realized with high accuracy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color reproduction method, and more particularly to a color reproduction method for reproducing a predetermined color when performing multicolor printing or multicolor display.

[0002]

2. Description of the Related Art As is well known, the colors of an object surface and an original image are tristimulus values (X, Y, Z) of the CIE standard XYZ color system.
It can be represented by the chromaticity represented by and can be specified as standard on the chromaticity diagram. It is also known that the tristimulus values X, Y, and Z can be obtained if the spectral distribution of reflected or transmitted light from an object or the like can be measured.

In recent years, for example, in the field of design work, for design evaluation, there is a demand for a color reproduction technique capable of faithfully reproducing a color desired by a designer. That is,
When performing design work using a computer,
Accurately display the colors obtained by the designer's desired chromaticity, measurement, etc., and the images containing those colors on a CRT display (hereinafter referred to as CRT) or by using a hard copy device. It is necessary to reproduce colors.

With the recent development of information communication networks, it has become possible to send and receive information representing images and colors between remote places. In that case, both CRTs and hard copy devices are the same. It is necessary to output the information (representing the color and the image) as the same color.

FIG. 1 shows a CR by an additive color mixing process.
A general method for displaying an arbitrary color on T has been shown. In this method, the chromaticity 10 represented by an arbitrary tristimulus value (X, Y, Z) is converted by a determinant using the chromaticity of each phosphor of CRT red green blue (hereinafter referred to as RGB). It is converted into RGB emission intensity 14 by 12, and then converted into signal value 18 which is a device value of CRT. In the conversion processing 16 from the emission intensity 14 to the signal value 18, a conversion method using a model formula showing the relationship between the emission intensity and the signal value (for example, applied voltage) (RSBerns, RJMotta and MEGo) is used.
rzynski, CRT Colorimetry.Part1: Theory and Practi
ce, COLOR research and application Vol.18 (No.5), pp.
299-314, 1993) or a conversion method using a lookup table (hereinafter referred to as LUT) (DLPost a
nd CSCalhoun, An evaluation of methods for produci
ng specific colors on CRTs, Proceedings of the Huma
n Factors Society 31st Annual Meeting, pp.1276-128
0,1987, see). By inputting this signal value 18 to a CRT display system (a system combining a CRT and a D / A converter, hereinafter referred to as a CRT system), chromaticity represented by an arbitrary tristimulus value (X, Y, Z) Can be displayed.

In order to reproduce a color having an arbitrary chromaticity on a CRT, it is necessary to grasp all the emission intensity of the phosphor corresponding to each signal value as the relationship between the signal value and the emission intensity of the phosphor. . However, it is not realistic to measure the emission intensity of the phosphor for all signal values, because the number of measurement points is huge. Therefore, the characteristics of the CRT are modeled in advance, the parameters of the model formula are obtained from a small number of measurement points, and the emission intensity of the phosphor with respect to the signal value other than the measurement points is
It is often obtained from the calculated value of the model formula.

When the method using the model formula is applied to the conversion of the emission intensity into the signal value, the chromaticity of each of the RGB phosphors of the CRT is set so that the RGB phosphors are made to emit maximum light in advance. Measure with a colorimeter. In addition, a model formula for the conversion process from the emission intensity to the signal value can be generally represented by the following formula (1) for each single color.

[0008]

[Equation 1]

The gamma characteristic value γ in the above equation (1) is RG
The emission intensity at a plurality of signal values is measured in advance for each monochromatic color of B, and it is obtained in advance from the measured values. In this way, the emission intensity of the phosphor for the signal value other than the measurement point can be obtained by using the model formula in which the characteristics of the CRT are modeled.

On the other hand, the relationship between the light emission intensity and the signal value is calculated by the LUT.
In the case of, the emission intensity at a plurality of signal values is measured in advance for each single color, and the measured values are linearly interpolated to obtain the emission intensity for an arbitrary signal value. As described above, instead of using the model formula, there is a method of obtaining the emission intensity of the phosphor for the signal value other than the measurement point by linear interpolation of the measured data. In this case, it is not necessary to consider the accuracy of the model formula, and the relationship between the signal value and the emission intensity of the phosphor can be expressed even in an actual CRT system that does not necessarily exhibit ideal behavior.

However, there are CRT systems that do not exhibit the ideal behavior for additive color mixing. For example, R
When each of the GB colors is displayed in a single color with a predetermined signal value,
The emission intensity of each color may be different from the case of mixed color display in which each color of GB is simultaneously displayed with a predetermined signal value, although the same signal value is displayed. In this case, it is not possible to reproduce the color with high accuracy using the emission intensity / signal value characteristics obtained by measuring the color displayed in a single color. That is,
The tristimulus value obtained by combining (adding) each of the tristimulus values obtained when the RGB colors are displayed in a single color does not match the tristimulus value obtained when the RGB colors are displayed in a mixed color. The phenomenon of inconsistency occurs (inconsistency of additive color mixture). For example, when the signal value is 127, as shown in the following inequality, the tristimulus value obtained by adding the tristimulus values measured by displaying a single color for each of the RGB colors causes the RGB signal colors to be mixed and displayed with the same signal value. The measured tristimulus values may not match.

(Xa, Ya, Za) ≠ (X ₁ , Y ₁ , Z
₁ ) + (X ₂ , Y ₂ , Z ₂ ) + (X ₃ , Y ₃ , Z ₃ ) where (Xa, Ya, Za): (Ra, Ga, Ba) = (127,127,12)
7) Tristimulus value (X ₁ , Y ₁ , Z ₁ ): (Ra, G ₀ , B ₀ ) ＝ (127, 0, 0) Tristimulus value (X ₂ , Y ₂ , Z 1). ₂ ): Tristimulus value when (R ₀ , Ga, B ₀ ) = (0,127, 0) (X ₃ , Y ₃ , Z ₃ ): (R ₀ , G ₀ , Ba) = (0, 0, 127) Tristimulus value at

Further, when a hard copy having an arbitrary chromaticity is produced by a hard copy apparatus using a subtractive color mixing process, it is difficult to obtain data corresponding to the light emission intensity. To the color prediction equation and the three-dimensional LUT (hereinafter,
3D-LUT) and the like, and an arbitrary chromaticity 10 is, for example, cyan, magenta, yellow,
And a black (hereinafter referred to as CMYK) signal value 22. Note that in subtractive color mixing, a color corresponding to K color can be generated from each combination of CMY, so that the signal value can be configured only by CMY excluding K color as a signal value.

As described above, in order to realize highly accurate color reproduction in the color reproducing apparatus by the subtractive color mixing process, CMY is used.
It is important to understand the relationship between the K signal value and chromaticity. As a method therefor, there are an analytical method using Neugebauer equations that can be applied only when colors are reproduced in printing with halftone dots, a statistical method such as the least square method, and a method using an LUT. Further, in the subtractive color mixing process, a method is known in which the color reproduction of a single color and the color reproduction of a single color are considered, and the color reproduction is performed by separating the processing for each single color and the processing for the color mixing (Japanese Patent Publication No. 7-123284).
Reference). However, with this technology, processing for each single color,
Although processing for color mixing is separated, sufficient consideration is not given to the relationship between single color and color mixing, and sufficient color reproduction accuracy cannot be obtained. Further, since it is difficult to correct the single color characteristics of the color material by the processing for each single color, it is difficult to correct the color difference between the color material manufacturing lots, for example.

As the method using the LUT, there is a technique for reproducing a color by using a single color LUT for the analysis optical density (Japanese Patent Publication No.
No. 28426) is known. In this technique, since the color is reproduced only from the single color LUT at the time of output, sufficient color reproduction accuracy cannot be obtained. Further, since the monochromatic LUT is for the analysis optical density, it requires a large number of man-hours for data unit management, measurement man-hours, and the like.

A technique for color reproduction using a 3D-LUT (Japanese Patent Laid-Open No. 53-123201, Japanese Patent Laid-Open No. 56-14).
No. 237) is also known. With this technology, 3
Although the color is reproduced using the D-LUT, it is difficult to correct the color difference between the color material manufacturing lots, for example, because the characteristics that differ for each single color are not taken into consideration. Therefore, 3D-
There is known a method of using spline interpolation in order to improve color reproduction accuracy by using an LUT (Japanese Patent Laid-Open No. 7-
50760 gazette). In this technique, the number of data needs to be an integer cubed, and for example, the number of data 125
The number of data next to the number (5 to the 3rd power) is 216 (6 to the 3rd power)
And required a huge amount of data.

As described above, in the hard copy apparatus, it is necessary to consider the detailed heat generation temperature and dye transfer amount characteristics in order to improve the color reproduction accuracy, but a large storage capacity is required to implement the 3D-LUT. Are required, which increases the processing speed and increases the cost of the device. Further, in order to directly and in detail obtain the relationship between the signal value and the chromaticity,
A large amount of measurement data was required. Furthermore, in the color reproduction, various corrections, for example, in the case of correcting the color difference between the color material manufacturing lots, the measurement and the calculation are performed again to perform the 3D-LUT.
Need to be created, and the processing time increases as the man-hour increases. Further, when adjusting the color tone (color adjustment) such as white balance adjustment, a process such as distorting the correspondence of a part or the whole of the 3D-LUT is required, and the process is complicated.

[0018]

As described above, in the conventional color reproduction method, the reproduction accuracy depends on the number of measurement points, and in order to improve the accuracy, it is essential to increase the number of measurement points. However, a lot of measurement man-hours will be required. CR
Since the characteristics of T and hard copy devices change with time, it is necessary to frequently measure and reproduce the color by reflecting the characteristics of the device at that time. However, the great preparation man-hours for this measurement are highly accurate. This is a major obstacle in maintaining color reproduction. Further, in an office or the like where a large number of CRTs and hard copy devices are operating, it becomes difficult to maintain the color reproduction accuracy of all devices when the number of preparation steps for each device increases.

Further, when color reproduction is performed by a hard copy device, it is difficult to express the characteristics of the ink that is the source of color generation by a model formula, and nonlinearity is present, unlike when color reproduction is performed by a CRT. strong. Therefore, a large number of measurements must be performed in order to obtain sufficient accuracy with the method using linear interpolation.

In consideration of the above facts, an object of the present invention is to obtain a color reproduction method capable of easily and highly accurately reproducing an arbitrary color without requiring many preparation steps.

[0021]

In order to achieve the above-mentioned object, the invention according to claim 1 is provided with a plurality of basic colors, and a color information value represented by a first color system as a predetermined color, A device value represented by a second color system different from the first color system is used to determine the formation amount of each basic color when color reproduction is performed on the color reproduction medium by mixing the plurality of basic colors. In the color reproduction device that reproduces the predetermined color on the color reproduction medium by converting and outputting the color corresponding to the device value, the formation amount of each basic color when color reproduction is performed by mixing a plurality of the basic colors. When,
The monochromatic characteristics for each of the basic colors representing the relationship with the device value for determining the formation quantity are obtained, and based on the obtained monochromatic characteristics, the predetermined formation quantity of each of the plurality of basic colors and the predetermined formation quantity The color mixing characteristics representing the relationship with the chromaticity of the color reproduced by the color formation are obtained, and the color information value of each arbitrary color of the first color system is calculated based on the obtained single color characteristics and the color mixing characteristics. Convert to a value.

The invention according to claim 2 is the color reproducing method according to claim 1, wherein an arbitrary color can be formed by synthesizing a plurality of basic colors for which subtractive color mixture is established. In the color reproduction device for mixed colors, the monochromatic characteristic and the mixed color characteristic are obtained.

According to a third aspect of the present invention, in the color reproducing method according to the first or second aspect, the color mixture characteristic is a predetermined formation amount of each of the plurality of basic colors and a color based on the predetermined formation amount. It is characterized in that the formation amount of each basic color corresponding to an arbitrary chromaticity is estimated by performing spline interpolation based on a plurality of relationships with the chromaticity of the color reproduced by the formation of.

An invention according to claim 4 is the color reproducing method according to any one of claims 1 to 3, wherein the basic color when the monochromatic characteristic and the mixed color characteristic are obtained is When a color material different from the color material to be formed is used, or when the color material has substantially the same color, only the single color characteristic is obtained.

The invention according to claim 5 is the color reproducing method according to claim 4, wherein, when monochromatic characteristics are obtained using the different color materials, the monochromatic characteristics of the different color materials are different from each other. And the maximum formation amount in the single color characteristics of different color materials obtained from the relationship between the formation amount and the device value for determining the formation amount. When it is less than, the maximum formation amount of the different color material is set as the maximum formation amount for the monochromatic characteristic of the other color material, and the device value corresponding to the formation amount exceeding the maximum formation amount of the different color material is different from the device value. It is characterized in that the maximum formation amount in the monochromatic characteristic of the coloring material is made to correspond to obtain the monochromatic characteristic for each of the basic colors.

The invention according to claim 6 is the color reproducing method according to any one of claims 1 to 5, wherein when the tint of the predetermined color to be reproduced is adjusted, It is characterized in that the single color characteristic corresponding to the tint to be adjusted is adjusted.

The invention according to claim 7 is the color reproducing method according to any one of claims 1 to 6, wherein the formation amount is a color formed according to the formation amount or It is characterized in that it is the color difference between the color formed by the device value that determines the formation amount and the color of the color reproduction medium.

An eighth aspect of the present invention is the color reproduction method according to the seventh aspect, wherein the single color characteristics are, for each of the basic colors, a color of the color reproduction medium and a color based on a maximum formation amount. It is characterized in that a chart of a plurality of colors in which the color difference between them is substantially equal is created, and the chart is used to obtain the chart.

According to the color reproduction method of the first aspect, the relationship between the formation amount of each basic color and the device value for determining the formation amount when the color reproduction is performed by mixing a plurality of basic colors used in the color reproduction apparatus. The monochromatic characteristic for each basic color is calculated. The basic color here is a color used for color mixing when performing color reproduction, for example, a color depending on each color material of cyan, magenta, and yellow in a hard copy device that performs color reproduction by subtractive color mixing, and also additive color mixing. It is a color depending on the phosphor for emitting each color of red light, green light, and blue light in a CRT that performs color reproduction by. This color reproduction device is provided with a means for forming a plurality of basic colors, that is, a plurality of single colors depending on the color material, phosphor, etc., and reproduces a predetermined color on a color reproduction medium such as paper or CRT. The color reproduction medium mentioned here is a paper or C for forming a plurality of single colors depending on a color material, a phosphor, and the like.
A material medium such as RT.

For example, the predetermined color is represented by a color information value (for example, tristimulus value XYZ) according to the first color system of the generally standard XYZ color system, and a plurality of colors corresponding to the color information value are used. It is recognized that each of the basic colors is mixed, that is, each of the plurality of basic colors is formed on the color reproduction medium by the amount of the color material of the color material, the amount of light emission of the phosphor, and the like. Therefore, in the color reproduction apparatus, the color information value based on the first color system is used to form each basic color when color reproduction is performed on the color reproduction medium by mixing a plurality of basic colors, that is, the color material amount of the color material. And the first is the amount of light emission
Device values represented by a second color system different from that of
In other words, the YMCK value of the color system for which subtractive color mixing is established or the RGB value of the color system for which additive color mixing is established is converted, and a predetermined color is reproduced on the color reproduction medium by outputting a color according to the device value. . Since the relationship between the formation amount of each of the plurality of color materials and the device value for determining the formation amount can be independently determined for each basic color, each basic color that represents the relationship between the formation amount and the device value is represented. It is possible to obtain the monochromatic characteristics for each color.

On the basis of each of these single color characteristics, a color mixture characteristic representing a relationship between a predetermined amount of each color material formed and a chromaticity of a color reproduced by forming a color with each predetermined amount is obtained. That is, the chromaticity of the color in the color reproduction medium formed by mixing each of the plurality of color materials, that is, the color material amount of the color material, the light emission amount of the phosphor, etc. Corresponds to quantity. Since each of these formation amounts can be independently determined for each basic color using the monochromatic characteristics, as the color mixture characteristics, a predetermined formation amount of each basic color when mixing a plurality of basic colors and each predetermined color The relationship with the chromaticity of the color reproduced by the color formation depending on the formation amount can be obtained.

Based on these single color characteristics and mixed color characteristics, the color information value of each color of the first color system is converted into a device value. The color information value of each color of the first color system of the predetermined color is converted into the formation amount by the color mixture characteristic, and the converted formation amount is converted into the device value by the single color characteristic. By doing so, the predetermined color can be reproduced on the color reproduction medium.

In order to realize highly accurate color reproduction in the color reproducing apparatus by the subtractive color mixing process, it is important to understand the relationship between CMYK signal values and chromaticity. Therefore, as described in claim 2, in the subtractive color reproduction apparatus capable of forming an arbitrary color by synthesizing a plurality of basic colors for which a subtractive color mixture is established, the single color characteristic and the color mixture characteristic Usually, the relationship between the signal value and the chromaticity, which do not have a linear relationship, is separated into the monochromatic characteristic of each basic color only for forming a color and the mixed color characteristic when each basic color is mixed. Can be grasped.

In order to realize highly accurate color reproduction, it is necessary to understand the relationship between the color information value and the chromaticity. This relationship is generally obtained by measuring at least the chromaticity of the reproduced color. However, obtaining all relationships by measurement requires a huge number of steps. Therefore, claim 3
As described above, the spline interpolation is performed based on the plurality of relationships between the predetermined formation amount of each of the plurality of basic colors and the chromaticity of the color reproduced by the formation of the color by the predetermined formation amount. By doing so, the formation amount of each single color corresponding to an arbitrary chromaticity is estimated. As a result, at least one of the color mixture characteristics can be obtained with high accuracy by a limited number of measurements.

It should be noted that the monochromatic characteristic may be obtained for each basic color by performing spline interpolation from a plurality of relationships between the basic color formation amount and the device value so as to obtain the relationship between the arbitrary formation amount and the device value. Good. By doing so, at least one of the single color characteristic and the color mixture characteristic can be obtained with high accuracy by a limited number of measurements.

Here, in the color reproducing apparatus, it is sometimes necessary to replace or change the color material which is a means for forming the basic color. When this color material is replaced or changed, the monochromatic characteristics and the color mixture characteristics may change, and thus it may be necessary to re-obtain it. In that case, as described in claim 4, when a color material different from the color material for forming the basic color when the single color characteristics and the color mixture characteristics are obtained is used, when the color materials having substantially the same color are used, Since the color materials have the same color, there is little or no change in the color mixing characteristics. Only the single color characteristics are obtained and the color mixing characteristics are made uniform, so that highly accurate color reproduction can be realized.

Further, when the color material is replaced or changed as described above, after the color material is replaced or changed, the formation amount for the same device value is the same as the previous formation amount for the same device value. May vary from quantity. For example,
If the maximum formation amount due to the monochromatic characteristics of the replaced or changed color material is smaller than the previous formation amount, the device value corresponding to the previous maximum formation amount will correspond to the smaller maximum formation amount after replacement or change. The change in the amount of formation of the changed color material is out of balance with respect to the color material other than the exchanged or changed color material. That is, the balance is lost when the device value does not correspond to the formation amount after the color material is replaced or changed. Therefore, as described in claim 5, when the monochromatic characteristic is obtained by using the different color material, the monochromatic characteristic of the different color material is a device for determining the formation amount of the different color material and the formation amount. Calculated from the relationship with the value. When the maximum formation amount in the monochromatic characteristics of the obtained different color materials is less than the maximum formation amount in the monochromatic characteristics of other color materials other than the different color materials, the monochromatic characteristics of the other color materials are different from each other as the maximum formation amount. Sets the maximum amount of color material formed. At the same time, the maximum formation amount of the different color materials in the single color characteristic is made to correspond to the device value corresponding to the formation amount exceeding the maximum formation amount of the different color materials. As a result, the device value corresponds to the formation amount after the color material is replaced or changed. By doing this,
A device value that does not correspond to the formed amount after the color material is replaced or changed does not occur.

When a predetermined color is reproduced by the color reproduction device,
For example, the tint may be adjusted so as to increase reddishness or decrease bluishness. In the present invention, the tint can be changed only by the single color characteristic. Therefore, as described in claim 6, when adjusting the tint of the predetermined color to be reproduced, the single-color characteristic corresponding to the tint to be adjusted is adjusted among the plurality of single-color characteristics to make the mixed-color characteristics the same. By doing so, it is possible to easily adjust the tint according to the readjustment or the user's intention without breaking the relationship between the color information value and the chromaticity.

As the forming amount, as described in claim 7, a color formed according to the forming amount or a color formed by a device value that determines the forming amount, and a white color of the color reproduction medium. And the color difference from gray can be used.
In this case, as described in claim 8, as a single color characteristic, a chart of a plurality of colors for which the color difference between the color of the color reproduction medium and the color with the maximum formation amount is substantially uniform for each of the basic colors. It is preferable to create a (color patch) and use the created chart.

[0040]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

[Principle] First, the principle of color reproduction for an arbitrary color will be described.

FIG. 3 shows the process of color reproduction from the display of the CRT by the signal value representing the color to the perception of the color (chromaticity).

The colors represented on the computer are a signal value for controlling the light intensity of R color (hereinafter, R signal value), a signal value for controlling the light intensity of G color (hereinafter, G signal value) and B color. It is often represented by a signal value (hereinafter, B signal value) for controlling the light intensity of the. The digital signal value 30 composed of these R signal value, G signal value and B signal value is converted into an analog video signal 34 by a conversion process 32 which is a process of a D / A converter. This video signal 34 is input to the CRT, and C
The intensity of the electron beam 38 is converted by a circuit process 36 which is a process in an electric circuit (not shown) in the RT. C
At RT, the phosphor is irradiated with an electron beam having an intensity of 38,
The phosphor emits light in accordance with the intensity of the electron beam irradiated by the light emitting process 40. Therefore, in the CRT, each of the RGB color phosphors emits light with each emission intensity 42. As is well known, the light emitted from each of these phosphors emits light at the same time.
4) and is perceived as a color (chromaticity) 46. Here, it is known that these phosphors have a constant tint regardless of the emission intensity. Therefore, it can be expressed that the light emission depending on the intensity of the electron beam of the phosphor changes only the scalar amount in the direction of a constant vector in the color space.

As shown in FIG. 4, the above-described color reproduction process includes a conversion process 48 until the signal value 30 is converted into the emission intensity 42 of the phosphor as the intensity information value, and each phosphor emits light at the same time. It can be roughly divided into a perceptual process 44 in which light is emitted at an intensity 42 to be mixed and perceived as a color (chromaticity) 46.

In principle, the conversion process 48 exists independently for RGB. Therefore, the conversion process 4
8 is capable of predicting the emission intensity of the phosphor from the signal value and predicting the signal value from the emission intensity of the phosphor by grasping the relationship between the signal value and the emission intensity of the phosphor for each color. It will be possible.

On the other hand, the perceptual process 44 calculates from the emission intensity of the phosphors by a calculation using a matrix of 3 × 3 by utilizing the fact that the tint of each phosphor described above is constant and using the additive color mixing theory. It is possible to predict the perceived chromaticity and predict the emission intensity of the phosphor from the chromaticity. Therefore, the chromaticity can be predicted from the signal value and the signal value can be predicted from the chromaticity.

However, there are CRT systems that do not show the ideal behavior for additive color mixing. For example, as described in the section of the above-mentioned conventional technique, in the case of displaying each of the RGB colors in a single color with a predetermined signal value, and in the case of performing a mixed color display in which each of the RGB colors is simultaneously displayed with a predetermined signal value,
Despite the same signal value, the emission intensity of each color may be different. In this case, it is not possible to reproduce the color with high accuracy using the emission intensity / signal value characteristics obtained by measuring the color displayed in a single color. That is, each of the tristimulus values obtained when each of the RGB colors is displayed in a single color is combined (added).
The tristimulus values described above and the tristimulus values obtained when the RGB colors are mixed-displayed do not match, resulting in a phenomenon of mismatch between the single-color display and the mixed-color display (mismatching of additive color mixture). For example,
Assuming that the signal value is 127, as shown in the above inequality, the tristimulus value obtained by adding the tristimulus values measured by displaying a single color for each of the RGB colors is measured by displaying the RGB signal colors in the same signal value. It may not match the tristimulus value.

Accurate color reproduction in such a CRT system has the same problem as in the case of a color reproduction apparatus using subtractive color mixture as described below.

FIG. 5 shows the process of color reproduction in a color printer as a hard copy device. Here, a thermal sublimation type color printer using CMYK dyes as a printing color material will be described as an example. In addition, in this color printer, cyan (C), magenta (M), and yellow (Y, Y, when the single color is used in the following description, will be referred to as Ye in order to avoid Kondo with the tristimulus value Y) as the printing color material. The case where the black (K) dye is used will be described.

From the computer to the color printer, C
The signal of each MYK color material is output. These signal values 31
Is a process of converting into an analog voltage by the D / A converter,
The print head conversion process 33, which is a process of causing the print head to generate heat by the voltage, is converted into a heat generation temperature 35. The heat generation temperature 35 generated by the printing head is converted into a color material transfer amount 39 by a conversion process 37 which is a process in which a sublimation type ink film is heated in a thermal sublimation type color printer to sublimate a color material (dye) and transfer it to paper. To be done. The amount of the color material transferred corresponding to the heat generation intensity (temperature) of the print head is determined by the temperature / color material (dye) transfer amount characteristic of the sublimation type ink film. Since the transferred color material (dye) is semi-transparent, the color obtained by overlapping each color material (dye) is subtractive color mixing, and as is well known, by the visual sense (or measuring device) (subtractive color mixing process ), And is perceived as a color (chromaticity) 46. In this subtractive color mixture, a linear relationship is not established between the color material (or dye) transfer amount of each color and the perceived color, and the relationship is complicated. Further, in actuality, for example, in an apparatus that prints in the order of CMYK, the phenomenon in which the color material (dye) of C is reversely transferred to the ink film of M by printing M, an analytical modeling is performed. Is impossible to do. Note that the subtractive color mixture using halftone dots, which is an area printing method such as offset printing, can be analytically modeled to some extent, but here, a general subtractive color mixture is targeted.

In order to realize highly accurate color reproduction with such an apparatus, it is necessary to determine the CMYK signal value after predicting the chromaticity of the printing result. As shown in FIG.
The relationship between the YK signal value and the chromaticity (CMYK signal value-chromaticity characteristic 49) must be understood. For that purpose, a statistical method or a method of interpolating in a three-dimensional space is used.

By grasping this relationship, it is possible to predict the CMYK signal value for reproducing the chromaticity from an arbitrary chromaticity value. Therefore, it suffices to have a process for estimating the relationship between the CMYK signal value capable of reproducing this arbitrary chromaticity and its chromaticity. That is, as shown in FIG.
A CMYK output signal value 31 is converted by a conversion process 47 that predicts a CMYK output signal value that reproduces the desired chromaticity value 46A. This gives the desired chromaticity value of 46A.
Is predicted as a CMYK output signal value that reproduces the chromaticity. By giving the output signal value to the color printer, an image having a predetermined chromaticity can be obtained. That is, the converted CMYK output signal value 31 reaches the subtractive color mixing process 41 as described above, and is perceived as a color (chromaticity) 46.

[Color Reproducing Device] Next, a detailed description will be given of an embodiment in which the present invention is applied to color reproduction in a sublimation type color printer as a hard copy device that establishes subtractive color mixture. In the present embodiment, a sublimation printer will be described as an example of an 8-bit printing apparatus having cyan, magenta, yellow, and black as basic colors. Note that, although a sublimation printer is described as an example in the present embodiment, the present invention is not limited to this, and can be applied to an inkjet or bubble jet printer and a thermal transfer printer. is there.

As shown in FIG. 8, the color reproduction apparatus of the present embodiment includes a color printer 60 and a microcomputer 5.
2. The keyboard 53 and the color measuring device 54 are used as input devices for inputting data such as execution instructions and data input for processing programs, which will be described later. Microcomputer 52
A keyboard 53, a color measuring device 54 and a color printer 60 are connected to the. This microcomputer 5
2 includes a CPU 52A, a ROM 52B, a RAM 52C, a memory 52D for storing a table and a processing routine described later, and an input / output device (I / O) 52E,
These are the buses 52 that enable the exchange of data and commands.
F is connected. A keyboard 53, a color printer 60 and a color measuring device 54 are also connected to the input / output device 52E. Color printer 60
Forms a color corresponding to the signal input from the microcomputer 52 on the medium and outputs the print 62. The color measuring device 54 has a built-in driving device 56A for carrying or scanning the print 62 on which a color is formed, and a probe 56B functioning as a colorimetric sensor in synchronization with the carrying or scanning of the driving device. Computer 52
The color formed on the print 62 is automatically measured by the input of the control signal from and the color is output to the microcomputer 52. It should be noted that the present invention is not limited to automatically measuring the printed color (chromaticity) as the color measuring device 54, and manually measured data can be used. In this case, the data obtained by manually measuring the color may be input from the keyboard or the color measuring device 54.

[Operation of Embodiment] Next, the operation of the present embodiment will be described.

An image with an arbitrary chromaticity is formed by mixing CMYK color materials in respective predetermined color material transfer amounts (including formation by lamination). The color material transfer amount of each color material corresponds to a signal value and can be independently determined for each color material. The color obtained as a result of color mixing is considered to correspond to the color material transfer amount of each color material. Therefore,
The present inventor separates these two relationships,
We have obtained the knowledge that color reproduction can be performed with high accuracy even with a small number of measurement points.

That is, when each ink color is printed as a single color, the relationship between the transfer amount of the color material and the signal value (characteristic of ink level / printing ink amount, hereinafter referred to as single color characteristic),
The relationship between the signal value and the chromaticity can be determined from the chromaticity characteristics (hereinafter referred to as the color mixing characteristics) for each ink amount resulting from mixing a plurality of inks, thus separating the single color characteristics and the color mixing characteristics. By doing so, we have found that color reproduction can be accurately realized.

Therefore, in the present embodiment, as shown in FIG. 9, the conversion between the CMYK signal value 70 and the arbitrary chromaticity 80 is performed, and the color material transfer amount 74, which is a physical amount, is converted.
Is treated as an intermediate amount, and the color material transfer amount 7 for the signal value 70
4 and the color mixture characteristic 76 representing the relationship between each color material transfer amount 74 (ink amount) and chromaticity 80 of a plurality of inks are obtained, and the obtained monochromatic characteristic 72 and color mixture characteristic 76 are obtained. The signal value / chromaticity characteristics obtained by combining the above are obtained as the color conversion table 78. Thus, the single color characteristic and the color mixture characteristic are separately obtained, and the color conversion table 78 according to the obtained characteristic can determine the relationship between the signal value and the chromaticity.
Realizes color reproduction with high accuracy.

This color conversion table (3D-LUT) is
It is a set of information representing the relationship between ink colors and ink levels that give arbitrary chromaticity Lab values. Obtaining this 3D-LUT is to obtain an ink color / ink level that gives arbitrary chromaticity. However, since there are a finite number of combinations of ink colors and ink levels (the number of ink colors is a finite number, and the ink levels are discrete values with upper and lower limits), it is practically possible to select any chromaticity. The process is to select the closest chromaticity from the "finite number of chromaticities". Therefore, a 3D-LUT can be obtained by obtaining the relationship between finite arbitrary ink color / ink level and chromaticity.

The simplest and most accurate method for obtaining this 3D-LUT is to create and measure samples for all combinations of ink colors and ink levels, and use the results to obtain a finite number of chromaticities and ink colors. The relationship with the ink level is obtained, but this method requires a huge amount of sample and a huge processing load.

Therefore, in the present embodiment, from the measurement results of a small number of samples, an arbitrary ink color / ink level,
The relationship with the chromaticity is estimated, and the relationship between the finite number of chromaticities and the ink color / ink level is obtained from the estimation result. The detailed method will be described below.

[Definition of Single Color Characteristic and Color Mixing Characteristic] FIG. 10 shows the process until the ink level is converted into a color. The red (R) ink level Lr, which is the data 400, is converted into a printing ink amount by the ink level / printing ink amount characteristic 402. Specifically, the ink level / printing ink amount characteristic is determined from the process of ink level → heat amount of printing head → printed ink amount. Similarly, orange O (406, 408, 410) and other colors are also converted, and the printing ink amount of each color is determined. After that, the final color is determined by the color mixture characteristic 412 which is a characteristic when the inks of the respective colors are superposed, and the chromaticity 41
4 is obtained.

The relationship between the ink level and the printing ink amount is affected by the state of color mixing (color mixing state) as described above. That is, the amount of printing ink is different between the case of printing on a surface on which some color has already been printed and the case of printing on a surface on which nothing is printed, even at the same ink level. In addition, by printing an arbitrary color and then printing another color, the ink may be reduced to the previously printed color (reverse transfer to the subsequently printed ink sheet).

In the present embodiment, the characteristics of the ink level and the printing ink amount when each ink color is printed in a single color are called the single color characteristics, and the relationship between the printing ink amount and the color mixture resulting chromaticity based on the single color characteristics. Is called a color mixing characteristic. As described above,
A phenomenon caused by an actual change in the amount of printing ink is also treated as a color mixing characteristic. This separation has the advantages of simplifying the complicated color mixture characteristics, improving the interpolation accuracy, and easily responding to changes in the ink ribbon characteristics such as differences between manufacturing lots.

As a monochromatic characteristic, a chemical analysis is required to actually obtain the sublimation ink amount in a sublimation printer, which is not realistic. Therefore, in the present embodiment,
The color difference from the white background of the paper is used instead of the ink amount. In addition, the color difference obtained with the maximum ink level is 1.0
Standardize as follows. Therefore, the monochromatic characteristic in the present embodiment represents the relationship between the color difference from the standardized white background where each ink level is obtained and the ink level.

The process of reproducing an arbitrary color and outputting an image will be described below together with the derivation of the single color characteristic 72, the color mixing characteristic 76 and the color conversion table 78.

When the color reproducing apparatus of this embodiment is turned on, the processing routine of FIG. 11 is executed. First, Y
A color conversion table 78 relating to MCK is generated as described later and is also stored in the memory of the microcomputer 52 (step 100), and a correspondence between a signal value and chromaticity is obtained to output a desired color for each pixel, and printing is performed. The color calculation process is performed (step 102), and is repeatedly performed until the process of step 102 is completed for all pixels (step 104). When this routine ends, the color printer 60 outputs the print 62 on which the image of the desired color is formed.

Next, the outline of the table generation (processing of step 100 in FIG. 11) and color calculation processing (processing of step 102 in FIG. 11) in this embodiment will be described. The color conversion table generated in the present embodiment represents the correspondence of each signal value for obtaining each color material amount of the four colors YMCK used in the color printer 60 with respect to an arbitrary color (chromaticity).

In FIG. 12, 4 corresponding to step 100 is executed.
A color conversion table (3
A flow of processing for creating a D-LUT) is shown.

First, in step 130, the printer 60
Each of the single color charts (details will be described later) for each color material single color created in advance by (1) is measured by the measuring device 54 which is a colorimeter that automatically measures the chromaticity of each color, and in the next step 132, The measured value is stored in the memory in the measuring device 54 as single color measurement data. Next Step 13
In 4, the stored single-color measurement data is used to obtain the single-color characteristic representing the relationship between the signal value and the color material transfer amount, and the obtained single-color characteristic is stored. The calculation of this single color characteristic is CMYK.
Is independently performed for each color (step 136). Specifically, it is preferable to use a monotone increasing spline function described later, but the present invention is not limited to this.

After the monochromatic characteristics are obtained (step 1
Affirmative determination in 36), in step 138, each of the pre-created color mixing charts (details described later) are measured by the measuring device 54 that is a colorimeter, and in the next step 140, the measured values are stored as color mixing measurement data. To be done. In the next step 142, the stored monochromatic characteristics and the mixed color measurement data are read, and in the next step 144, the monochromatic characteristics and the mixed color measurement data are used to determine the mixed color characteristics (the combination of the CMYK material transfer amounts for arbitrary chromaticity). The relationship is shown.) Is required. In the calculation of this color mixture characteristic, the process of converting the signal value of each color material of the color mixture chart into the color material transfer amount (color difference from white) using the single color characteristic (details will be described later), and the color material transfer amount and measurement data The process of estimating the combination of the color material transfer amount with respect to the unmeasured chromaticity from (chromaticity). In the process of estimating the latter combination, it is preferable to derive the color material transfer amount instead of the output signal value in the method described in Japanese Patent Application Laid-Open No. 7-50760 already filed by the present applicant. The combination of the color material transfer amount with respect to the unmeasured chromaticity may be estimated by linearly interpolating a plurality of color material transfer amounts and their chromaticities without limitation.

In the next step 146, the single color characteristic and the mixed color characteristic are read out, and in the next step 148, the above-mentioned single color characteristic and the mixed color characteristic are combined to form a 3D color conversion table.
-LUT (indicating a combination of output signals of CMYK colors for an arbitrary chromaticity) is obtained. More specifically, the color material transfer amount obtained for each chromaticity is converted into a signal value using the single color characteristic, thereby obtaining a combination of signal values of CMYK colors for each of a plurality of chromaticities.

FIG. 13 shows the flow of processing for printing an image corresponding to step 102 in FIG. First, in step 150, C for optimally displaying an RGB image is displayed.
The CRT-LUT in which the RT characteristics are stored in advance is read, and in the next step 152, the image to be printed represented by the RGB values is read. Next Step 154
Then, the RGB value of the RGB image is converted into the XYZ image by the XYZ value using the read CRT-LUT. This conversion uses a monotone increasing spline function and a determinant described later. Note that the method is not limited to using the monotone increasing spline function and determinant, and a method using another function and determinant may be used. If the image to be output is the XYZ image represented by the XYZ values, the process of step 154 is unnecessary. Next step 15
In 6, the 3D-LUT described below is read, and the XYZ values of the XYZ image are converted into CMYK signal values using the 3D-LUT read in the next step 158, and the CMYK image is obtained. In the next step 160, the CMYK signal values of the CMYK image are output and printing is performed. It should be noted that, in general, an image is subjected to a unique process such as an image enlargement process of a color printer to print.

[Third-Order Spline Interpolation Method for Monotonically Increasing y = f (x)] Next, spline interpolation for obtaining an arbitrary relationship between the signal value and the color material transfer amount will be described.
Here, spline interpolation regarding a monotonically increasing function (y = f (x)) by two variables (x, y) having a functional relationship will be described as an example.

First, for two variables (x, y) having a functional relationship, n values (x [j], y [j]; j = 0, 1, ...
, N−1) and monotonically increases between the values of these two variables (x, y) (x [j] <= x [j + 1], y
[J] <= y [j + 1]).

The interpolation by the spline function for these two variables (x, y) can be expressed by the following equation (2).

[0077]

[Equation 2]

In the above equation (2), N [i, 4, x]
Is determined by the element u [i] obtained from the value x [j] as described later, and p [i] is the value y.
Element c [i] obtained from [j] as described later
And N [i, 4, x]. This variable p [i] can be obtained as follows.

Let c [i] be an element obtained from the value y [j] as described later and C be its matrix. Further, when the matrix of N [i, 4, x [j]] for each value x [j] and each i is N and the matrix of the element p [i] is P, the following equation (3) is given. Have a relationship.

C = N · P (3) Since these matrices C and N can be determined from the value y [i],
The matrix P is determined by the following equation (4).

P = N ⁻¹ · C (4) From this matrix P, the element p [i] can be obtained.
Therefore, N [i, 4, x] for each i, and the element p
The value y can be obtained from [i] using the above equation (2).

The parameter N [i, of this spline function is
4, x] and the parameter p [i] are further described with reference to FIG. First, step 22 in FIG.
The value x [j], y [j] is read at 0, and the next step 2
At 22, the element u [i] of the matrix of (2n + 4) rows is calculated from the value x [j] as shown in [Definition 1] below.

[Definition 1] u [0] = x [0] u [1] = x [0] u [2] = x [0] u [3] = x [0] u [4] = x [ 1] u [5] = x [1] u [(j−1) · 2 + 4] = x [j] u [(j−1) · 2 + 4 + 1] = x [j] where 2 ≦ j ≦ (n− 2) u [(n-2) · 2 + 4] = x [n-1] u [(n-2) · 2 + 4 + 1] = x [n-1] u [(n-2) · 2 + 4 + 2] = x [n −1] u [(n−2) · 2 + 4 + 3] = x [n−1]

In the next step 224, the element c [i] of the matrix of (2n-1) rows is calculated from the measured value y [j] as shown in [Definition 2] below.

[Definition 2] c [0] = y [0] c [1] = left end condition (g value of value x [0], arbitrary value setting) c [2] = y [1] c [3 ] = G value of value x [1] c [j · 2] = y [j] where 2 ≦ j ≦ (n−2) c [j · 2 + 1] = g value of value x [j] where 2 ≤ j ≤ (n-2) c [(n-1) · 2] = y [n-1] c [(n-1) · 2 + 1] = right end condition (g value of value x [n-1]) However, the g value is obtained from the following equation (5). g = Dy [i] / Dxy [i] (5)

These Dy [i] and Dxy [i] are points (x [i-1], y before and after the point (x [i], y [i]).
The distance in the y direction and the straight line distance between [i-1]) and (x [i + 1], y [i + 1]) are shown. In the spline interpolation, the g value is the point (x
[I], y [i]) shows the inclination of the straight line. If the g value is determined using the above equation (5), the slope at the point (x '[i], y' [i]) of the interpolation result matches the slope of the straight line connecting the points before and after that point.

Next, in step 226, each element of the matrix N of 2n rows and 2n columns is calculated as shown in Table 1 below.

[0088]

[Table 1]

Each element N [i, 4, x] of the above matrix N,
N ′ [i, 4, x] is obtained from the following equation (6).

[0090]

(Equation 3)

However, when k = 1, x ≠ u [2n + 4-
1] and (u [i] <u [i + 1] and u [i] ≦ x
If <u [i + 1]), set a value of 1.0; otherwise, set a value of 0.0. Further, when k = 1, x = u [2
n + 4-1] and (u [i] <u [i + 1] and u
If [i] <x ≦ u [i + 1]), a value of 1.0 is set, and otherwise, a value of 0.0 is set.

On the other hand, N '[i, k, x] is obtained from the following equation (7).

[0093]

(Equation 4)

The process of obtaining each element of these matrices is a recursive process (Zenka formula). To obtain N [i, 4, x], N [i, 1, x], N [i, 2, x], N
It is necessary to find [i, 3, x]. At this time, x is a measured signal value, i is 0 to 2n-1, and u [i] used in this processing is obtained by the above method.

In the next step 228, the matrix P is calculated from the inverse matrix N ^{−1 of the} matrix N and the matrix C based on the variable c [i]. That is, the matrix P is calculated from the matrix calculation formula according to the formula (6). The variable p [i] can be obtained from this matrix P.

Then, in step 230, the calculated element u [i] and element p [i] are stored in the memory.

Next, the calculation of the color material transfer amount for an arbitrary signal value will be described with reference to FIG. First, in step 240 of FIG. 15, an arbitrary signal value x, and in the next step 242, the element u stored in step 230 of FIG.
Read [i] and set i to 0 in the next step 244.
From 2n−1 to the element N as explained above.
Find [i, 4, x]. That is, i = 0 to 2n−
The matrix N of 1 and 2n rows and 1 column is obtained. Next step 246
Then, the stored element p [i] is read, and in the next step 248, the color material transfer amount y is calculated using the above equation (4) representing the spline function.

In this way, the relative color material transfer amounts for all signal values are obtained. Ie 0 to 255
The color material transfer amount can be obtained for all the signal values of (1) by a spline function (see the equation (4)) using the elements N [i, 4, x] and p [i] that are parameters.

[Lab in Consideration of Observation Light Source Color] Next, the concept of Lab conversion in consideration of observation light source color will be described. In the present embodiment, when the color is reproduced by the color printer, the Lab value considering the observation light source color is used instead of directly operating the XYZ values.

The tristimulus values (X, Y, Z) of the image are mainly
As a result of illuminating an object with an arbitrary light source, a color due to reflection on the object is shown. In the following explanation,
The tristimulus values (X, Y, Z) are abbreviated as XYZ values. Therefore, in order to obtain a reproduced image from an image, the color that should be reproduced by a print (hard copy) that is the output of a device such as a color printer is not intended to reproduce the color of the actual object, but the color due to reflection. , The color resulting from illuminating the object with any light source.

On the other hand, prints are always viewed under any light source. That is, the print is perceived in color under the viewing light source. Therefore, the goal of substantial color reproduction is that "the color perceived in the environment (under the light source) as a result of illuminating the object with a certain light source is reproduced on the print under the observation light source of the print". . Therefore, in order to accurately realize color reproduction, environmental adaptation by the light source should be considered. Therefore, in the color reproduction according to the present embodiment, the light source color is represented by the chromaticity that matches in the Lab space with the white reference. That is, the Lab including the observation light source is calculated from the XYZ values of the image as follows.
Convert to a value.

The XYZ values of the image can be expressed by the following equation (8). Although a geometrical light amount is actually required, detailed description thereof is omitted here to avoid complication.

[0103]

(Equation 5)

Further, the XYZ values are expressed by the following equation (9),
It can be converted into a Lab value by the expression (10).

[0105]

(Equation 6)

On the other hand, chromaticity of print color (XYZ value)
Is calculated by the following equation (11).

[0107]

(Equation 7)

However, S (λ): Spectral reflectance of the light source in the field for observing the print R (λ): Spectral reflectance of the print This XYZ value is L according to the following equations (12) and (13).
Can be converted to ab value.

[0109]

(Equation 8)

The goal of color reproduction is to realize the spectral reflectance R (λ) in which the Lab values are the same as shown in the following equation (14).

L ^* o = L ^* a ^* o = a ^* (14) b ^* o = b ^* Here, since the above equations (10) and (13) are equivalent, the following ( The target for color reproduction can be replaced as shown in equation (15).

[0112]

[Equation 9]

Here, the spectral reflectance So (λ) of the light source in an actual field differs depending on the orientation of the surface, for example, and is generally difficult to calculate. Therefore, in the present embodiment, the spectral emissivity So of the light source in equation (9) is
(Λ) is simply assumed to be the C light source, and the light source for observing the print is also assumed to be the same C light source. Therefore, the above equation (9) can be expressed by the following equation (16).

[0114]

(Equation 10)

As described above, in the present embodiment, since the color conversion is performed by the 3D-LUT in the Lab space, the tristimulus values (Xo, Yo, Zo) of the image are expressed by the above equations (16) and (10). It is converted into a Lab value by an expression. This (16)
The process of converting an XYZ value, which is a tristimulus value, using an equation into a Lab value is referred to as a light source correction for convenience in the following description.

The detailed processing of this light source correction is necessary at the time of printing. First, in the present embodiment, the light source correction coefficients KSX, KSY, KSZ are obtained by the following equation (17) using the spectral reflectance S (λ) of the observation light source.

[0117]

[Equation 11]

The light source correction at the time of printing can be processed by multiplying the XYZ value of each pixel of the image by the light source correction coefficients KSX, KSY, KSZ as shown in the following equation (18).

Xo '= KSX.Xo Yo' = KSY.Yo (18) Zo '= KSZ.Zo

[Color Conversion to Ink Level] The color converted to the Lab value as described above needs to be converted to the ink level of the ink actually used for printing. The concept of color conversion to the ink level will be described. In the following description, 8 colors (R, O,
The case of using the inks of Ye, G, B, P, M, and K) will be described.

The image data of the XYZ values is (16) above.
After the light source is corrected by the formula, L is calculated by the formula (10).
converted to ab value. The Lab value is converted into a printing ink amount (ink level) that reproduces the Lab value by the 3D-LUT. That is, an image in which each pixel is represented by three kinds of values of XYZ is used for each color (R, O, Ye,
G, B, P, M, K) ink level meters are converted into images represented by eight values.

As shown in FIG. 17, the 3D-LUT is L
It is a data group in which the ab color space is divided into a three-dimensional grid shape having equal intervals in height and width, and ink colors and ink levels are described so as to reproduce the Lab chromaticity of each grid point. In the present embodiment, the chromaticity of each grid point D is reproduced with three color inks, and 100 * 100 * 100 grid points D are used.
3D describing the three ink colors and ink levels for
-Use LUT.

As shown in FIG. 18, an arbitrary Lab value, that is, chromaticity (L ^* , a ^* , b ^* ) has eight lattice points D0.
~ D7 or located inside a cube surrounded by eight grid points D0 to D7. For all eight grid points D0 to D7, the ink color and ink level for reproducing the chromaticity are referred to, and the La of the target chromaticity point Dd and each grid point
The ink color and the ink level that give the chromaticity of the chromaticity point Dd are determined by the interpolation of the ink level by weighting according to the distance in the b space. That is, when the chromaticity point Dd and the eight grid points D0 to D7 have the relationship shown in FIG. 18, the ink color and ink level at each grid point can be expressed as shown in the following equation (19).

(C1n, L1n, C2n, L2n, C3n, L3n) (19) where n: 0,1,2,3,4,5,6,7 (number of each grid point) C1n: First color ink color L1n: First color ink level C2n: Second color ink color L2n: Second color ink level C3n: Third color ink color L3n: Third color ink level

In this embodiment, in order to interpolate the chromaticity point Dd, the equation (19) is replaced with an ink level vector of each ink as shown in the following equation (20) for generalization. .

(Lrn, Lon, Lyn, Lgn, Lbn, Lpn, Lmn, Lkn) (20) where n: 0,1,2,3,4,5,6,7 (for each grid point No.) Lrn: R ink level Lon: O ink level Lyn: Ye ink level Lgn: G ink level Lbn: B ink level Lpn: P ink level Lmn: M ink level Lkn: K ink level

The first color used in the equation (19) above,
The ink level is stored for either the second color or the third color, and the ink level 0 is stored for the other ink colors.

In the interpolation, three kinds of weights corresponding to the Lab axes are used as shown in the following equation (21).

WL = (L-L0) / (L1-L0) Wa = (a-a0) / (a1-a0) (21) Wb = (b-b0) / (b1-b0)

The ink level of each color is obtained from the following equation (22). Lc = (1-WL). (1-Wa). (1-Wb) .Lc0 + (1-WL). (Wa). (1-Wb) .Lc1 + (1-WL). (1-Wa ) * (Wb) * Lc2 + (1-WL) * (Wa) * (Wb) * Lc3 + (WL) * (1-Wa) * (1-Wb) * Lc4 + (WL) * (Wa) * (1-Wb) * Lc5 + (WL) * (1-Wa) * (Wb) * Lc6 + (WL) * (Wa) * (Wb) * Lc7 ... (22) However, c: R, O , Ye, G, B, P, M, K colors

X corrected by the light source by the above equation (16)
The image data of YZ value is La according to the above equation (10).
Converted to b value. However, the XYZ values are all 0 or more. Eight grid points can be obtained from these Lab values.

Next, regarding each of the single color characteristic and the mixed color characteristic,
Will be explained. [Concept of Deriving Monochromatic Characteristic] First, the process of obtaining the monochromatic characteristic
Details will be described with reference to FIG. The process of FIG. 19 is the same as that of FIG.
This corresponds to the processing of steps 130 to 136 in step 2. FIG.
In step 310 of step 1, a predetermined number of
Link level (in the present embodiment, the density near 0 is set to 37
By outputting the (point) signal to the color printer,
For each ink level, the color chart (support
Sample) is created. That is, each from the color printer
A color chart is output for each single color. In this case,
Bell li is the minimum ink level (actual
In the embodiment, the ink amount from 0) to the maximum value is covered.
Is set in advance. In the next step 312,
The output color chart is measured and the measured color values are stored. sand
That is, by colorimetry, for each single color and for each ink level
To the corresponding chromaticity data L^*[li] a^*[li] b ^*[li] got
And stored as chromaticity data. In this embodiment,
As measurement conditions <Specular exclude / small
(S) Aperture> is set and manufactured by Murakami Color Research Laboratory Co., Ltd.
Using a spectral reflectance measuring device (CMS-35SP), each unit
Each patch on the color chart was measured.

At the next step 314, the chromaticity data Lw, a of the minimum ink level (0) is calculated from the obtained chromaticity data.
By subtracting w and bw, the color difference is obtained, and in the next step 316, this color difference is stored as color difference data DE [li] from the white background of the paper of the output color chart for each single color. That is, the calculation of the color difference data from this white is considered to be white (that is, the Lab value for ink level 0) as a reference,
It can be obtained from the following equation (23).

ΔEab = {(L-Lw) ² + (a-aw) ² + (b-bw) ² } ^1/2 (23) where ΔEab: color difference (DE) L, a, b: Lab value for each ink level Lw, aw, bw: Lab for white ink level
Value Here, when the ink level is densely set to 0, 1, 2, 3 and a color chart is created and colorimetric is performed, the color difference data does not monotonically increase with respect to the ink level. Despite increasing levels, color differences may decrease. This phenomenon is due to the instability of the color printer and the colorimeter, and also becomes a hindrance to the subsequent monotonically increasing spline interpolation. It is preferable to correct the color difference data.

Therefore, in the next step 318, it is judged whether or not the color difference data needs to be corrected based on the tendency of the ink level and the color difference before and after, and if the correction is necessary, the measurement error in the next step 320 is performed. In addition to correcting the reversal portion due to the above, the corrected data is stored as color difference data DE ′ [li] in the next step 322. That is, whether or not the color difference data for each ink level has a reversal portion, that is, despite that the ink level is i1 <i2,
It is determined whether or not there is a portion where DE (il)> DE (i2). If yes, correct it as follows. First, the color difference is reset so that the characteristics near the reversal portion are smooth. For example, the amount of change in the gradient of the curve representing the characteristic of the color difference data with respect to the ink level is set to be small. In this case, almost all of them can be corrected by giving an average value of the color difference values before and after it or an average value of the dead weight instead of the color difference value that is by far the largest or the smallest.

On the other hand, if it is determined in step 318 that the correction is unnecessary, that is, if the color difference data increases monotonically with respect to the ink level, the color difference data DE [li] is used as it is after the correction. The processing proceeds to step 324 as [li].

At step 324, the color difference data DE '[l
i] is the maximum ink level, color difference data DE [25
By dividing by 5], the color difference data obtained at the maximum ink level is standardized to be “1”, and in the next step 326, the standardized color difference data is standardized data D (= DE ′ [ li] / DE [255]).

In the next step 328, the color difference with respect to the ink level other than the ink level for which the color chart was created by the above-described monotonically increasing spline interpolation (see FIGS. 14 and 13) is obtained, and in the next step 330 it is obtained by interpolation. Color difference data D [L] for an arbitrary ink level L is stored. By performing this processing for each color (step 332), the color difference from white with respect to the arbitrary ink level is obtained for each color, and the correspondence relationship between the obtained ink level and the color difference data is stored as a single color characteristic table.

The monochromatic characteristic table generated as described above is a spline interpolation limited to monotonically increasing monochromatic characteristic data (having a color difference value only for the ink level at which the measurement is performed) for each color. And the color difference for all ink levels is determined. FIG. 21 shows an example of monochromatic characteristics. 21 (1) shows the relationship of color difference with respect to all ink levels, and FIG. 21 (2) shows the relationship of color difference with respect to ink levels up to the ink level 10.

[Creation of Single Color Chart] The above single color chart (sample) created in step 310 of FIG.
Is created by printing with a predetermined number of ink levels for each color of R, O, Ye, G, B, P, M, and K. In the present embodiment, when creating a single color chart for each color, 38 ink levels (0, 1, 2, 3, 4, 5, 6, 7,
8,9,10,15,20,25,30,40,50,60,70,80,90,100,110,120,1
30, 140,150,160,170,180,190,200,210,220,230,240,25
0,255) is used.

Further, the sublimation type color printer has a characteristic that the printing density changes depending on the printing screen area in the printing head direction (main scanning direction). Therefore, in the present embodiment,
The single color charts are arranged in a line in a direction (sub-scanning direction) orthogonal to the main scanning direction, and are formed so that only one chart corresponding to one ink level exists in the main scanning direction. In a device having a function of correcting the above phenomenon as a sublimation type color printer, the above limitation is not necessary for forming a single color chart.

[Derivation of Color Mixing Characteristic] Next, details of the process for obtaining the color mixing characteristic will be described with reference to FIG. The process of FIG. 20 corresponds to the process of steps 138 to 148 of FIG. First, in step 360 of FIG. 20, a color mixing chart is created (details will be described later). In this step 360,
Using the single color characteristics of each color described above, several ink levels at which the color difference is substantially equal (in this embodiment, five ink levels including the maximum and minimum values 0 and 255) are obtained, and a plurality of ink levels are calculated. Create a color chart for each ink level for the ink color combinations of. In this embodiment,
(R, O, K), (O, Ye, K), (Ye, G,
K), (G, B, K), (B, P, K), (P, M,
K) and (R, M, K) are set to a combination of a plurality of ink colors, and 5 × 5 × 5 = 125 for each ink color combination.
Create a color mixing chart of 875 colors in total.

As described above, each combination is composed of two colors having adjacent hues and K color. As a result, the color space is roughly divided for each hue, and each color is reproduced with two chromatic colors and K color.

At the next step 362, the color mixing charts thus created are measured. In this embodiment, <Specular exclude / Small (s) aperture> is set as the measurement condition, and a spectral reflectance measurement device (CMS-35SP) manufactured by Murakami Color Research Laboratory Co., Ltd. Each patch was measured.

In the next step 364, the ink level is converted into an ink amount, and in the next step 366, the chromaticity for each ink amount combination is obtained. For example, paying attention to one combination of arbitrary ink colors, the color name of the first color is x1, the color name of the second color is x2, the third color name is x3, and a color chart is created. Level 1x1
i, lx2i, lx3i (in the present embodiment, i = 1,
2, 3, 4, 5 and l × 1 = 0, l × 5 = 255). These ink levels are based on the previously obtained monochromatic characteristics of each color, and the printing ink amounts ax1i, ax2i, ax3.
converted to i.

In detail, each of the mixed color characteristic measurement data (spectral reflectance) is classified for each ink color combination,
It is converted into a Lab value using the above equation (10) and stored as color mixture data. It should be noted that the data of the C light source is used as the data of the light source during this conversion. Then, the printing ink amount corresponding to the monochromatic ink level is obtained from the ink level of the color mixture chart and the monochromatic characteristic table, and a plurality of correspondences between the value and the Lab value are summarized and stored for each ink color combination. In the present embodiment, 0
To an integer value of 255 (discrete printing ink amount). The conversion to the discrete printing ink amount facilitates an instruction from an existing application or the like.

In the next step 368, the three-dimensional spline interpolation (from the applicant of the present application) is performed by expanding the above-described spline interpolation into three dimensions from the discrete printing ink amount (ax1i, ax2i, ax3i) and the corresponding chromaticity data. (See Japanese Patent Application Laid-Open No. 7-50760) by application (extrapolation of high brightness and low brightness), and chromaticity for all discrete printing ink amount combinations of 0 to 255 is obtained, and optional in the next step 370. The chromaticity is calculated for the combination of the ink amounts.

The above processing is carried out for each of the above seven ink color combinations (step 372), and finally a database showing the relationship of chromaticity with respect to all combinations of ink colors and printing ink amounts is created.

At the next step 374, one of the grid points of the 3D-LUT is set, and at the next step 376, the chromaticity closest to the chromaticity of the set grid point is searched from the database, and the chromaticity of the search result is searched. The ink color / printing ink amount with respect to the chromaticity is obtained as the ink color / printing ink amount at the set grid point. In the next step 378, the ink color / printing ink amount is converted into an ink level by referring to the single color characteristics obtained above, and an ink color / ink level combination giving the chromaticity of the grid point is obtained. By performing the above processing for all grid points of the 3D-LUT (step 380), the 3D-LU
The ink color / ink level combination that gives the chromaticity of each grid point of T is obtained, and the color mixing characteristics are obtained. This color mixing characteristic is stored as a final color conversion table. Therefore, the color conversion table associates the chromaticity (ABC value) with the ink level, and is a total of the single color characteristics and the color mixing characteristics.

[Creation of Mixed Color Characteristic Measurement Chart] The mixed color chart prepared in step 360 of FIG. 20 is prepared by first setting ink levels for the mixed color chart and printing at each ink level. That is,
Based on the above-mentioned monochromatic characteristics, as shown below, five ink levels (including ink levels 0 and 255) are set so that the color difference between monochromatic colors is substantially uniform. In this embodiment, the ink level is (R: 0, 29, 59, 113, 25
5), (O: 0,34, 73,121,255), (Ye: 0,34, 73,12)
1,555), (G: 0,37, 80,135,255), (B: 0,74,113,
167,255), (P: 0,46, 95,154,255), (M: 0,28, 5
7,111,255), (K: 0,45, 93,152,255).

As described above, the color mixture chart is 7
Combinations of ink colors, that is, (R, O,
K), (O, Y, K), (Y, G, K), (G, B,
K), (B, P, K), (P, M, K), (R, M,
K) is created by combining the above ink levels. Therefore, the number of color patches to be created is 5 x 5 x
5 × 7 = 875 colors.

It should be noted that a color patch having a predetermined value (for example, 127) of each monochromatic color / ink level is formed on one sheet of the color mixing chart formed in this embodiment. The color patch having the predetermined value can be used for the stability check.
As will be described later, from this color patch, it is possible to check the print density variation, and it is possible to improve the reliability of the measured value in the color measuring device.

In the above embodiment, in order to obtain the chromaticity, the printed single color chart and the mixed color chart were measured by the measuring device connected to the computer. However, the measurement was performed by an independent and separate color measuring device. You may use the measured value.

Further, in the above embodiment, in order to determine the relationship between the ink level (signal value) and the chromaticity, one color conversion table, 3D-LUT, is obtained, and the obtained color conversion table is used. The case where the XYZ image is converted into an image composed of ink level values has been described. However, the present invention is not limited to this, and as shown in FIG. 9, each of the single color characteristics 72 and the mixed color characteristics 76 is stored in a table. As the (LUT), monochromatic characteristics and mixed color characteristics are independently configured, and XY
The XYZ values of the Z image may be converted into the transfer color material amount using the color mixture characteristic, and then the transfer color material amount may be converted into the signal value using the single color characteristic.

Further, in the above-mentioned embodiment, the case where the white paper is used as the color reproduction medium is explained, but the present invention is not limited to this, and a transparent or semitransparent medium or an arbitrary color is used. Paper or a medium may be used.

In the present embodiment, the single color characteristic and the color mixture characteristic are obtained separately. That is, after the monochromatic characteristics are obtained, the 3D-LUT is generated together with the mixed color characteristics. In this way, by separately obtaining the single-color characteristics and the color-mixing characteristics, for example, when using color materials of different manufacturing lots (color material replacement of substantially the same shade, etc.) and changes over time of the color printer, Adjustment for correction becomes easy. That is, when the color materials of different manufacturing lots are used or when the change with time of the printer is corrected, the single color characteristics have substantially the same tint, and the fluctuation of the measurement value due to the color mixing chart is small. Therefore, it is possible to return to a state in which color reproduction can be sufficiently performed by adjusting the measurement value based on the single color chart.
For this reason, only a single-color chart is created and measured to obtain a new single-color characteristic. By obtaining the 3D-LUT by combining the obtained new single color characteristic with the existing color mixture characteristic, it is possible to perform the color correction in an optimum state with a small number of measurements and a calculation amount.

In addition, when the color materials of different manufacturing lots are used (for example, the color materials having substantially the same tint are replaced) or when the color printer is corrected over time, the color material transfer amount of each color material is adjusted. Is preferably corrected. For example, in FIG.
Shows the characteristics of the color material transfer amount when the color material of a different manufacturing lot is changed and the previous color material transfer amount. FIG.
In (1), the dotted line shows the previous characteristics and the solid line shows the changed characteristics of the Cy coloring material. In addition, FIG. 22 (2)
Shows the characteristics of the M coloring material with a solid line, and the dotted line shows the previous characteristics of the Cy coloring material. As can be seen from the figure, for the Cy color material, the previous transfer characteristic (dotted line) has the maximum transfer amount T1 and the changed transfer characteristic (solid line) has the maximum transfer amount T2 (T1> T2). The color material of M has the maximum transfer amount T3 (T3>T1> T2).

Here, the monochromatic characteristic obtained before the replacement is obtained by the characteristic shown by the dotted line in FIG. That is,
For the C (cyan) color material, the dynamic range is obtained up to the maximum transfer amount T1. Therefore, when only the single color characteristics are changed, the color material transfer amount of the Cy color material corresponding to the ink level (signal value) S1 for which the maximum transfer amount T3 of the M color material should be instructed exceeds the maximum transfer amount T2. Therefore, the transfer amount of Cy cannot be substantially indicated. Therefore, when the maximum transfer amount of the C color material is lower than that before the change, such as when using color materials of different manufacturing lots, another color material (for example, MYK 3
A single color LUT is set so that the maximum transfer amount of the color, M in the example of FIG. 22, matches the maximum transfer amount of the C color material (straight line TT shown in FIG. 22 (2)). That is, if the maximum transfer amount of the changed or adjusted color material is lower than before, the transfer amount of another color material that exceeds the maximum transfer amount of the changed or adjusted color material is changed or adjusted. The single color characteristic is set to match the maximum transfer amount of. As described above, when the maximum transfer amount of the C color material is lower than that before the change, the single color LUT is set so that the maximum transfer amounts of the other color materials match the maximum transfer amount of the C color material. As a result, it is possible to prevent deterioration of the color balance of the low lightness portion.

When the color tone (color) of the color to be reproduced is adjusted, the single color characteristic of each color material may be changed and the 3D-LUT calculation process may be performed together with the existing color mixture characteristic data. . For example, when it is desired to emphasize the yellowness of the image, the color material transfer amount corresponding to each signal value for the C color and M color monochromatic characteristics should be set smaller than it actually is (for example,
(Multiply uniformly by 0.9) and change the color material transfer amount corresponding to each signal value for the single color characteristic of Ye color to be larger than the actual amount (for example, uniformly multiply by 1.1).
Just change it.

In the above embodiment, the case where the present invention is applied to the color printer in which the subtractive color mixture is established is described, but it is also effective in the CRT system in which the additive color mixture is not established.

[Evaluation of Color Reproduction Accuracy] Next, the color reproduction accuracy when an arbitrary color is reproduced using the color conversion table created as described above was evaluated. FIG.
Shows the processing flow for evaluation of color reproduction accuracy. In addition,
Two types of evaluations were performed, one containing an achromatic color and the other consisting of only an achromatic color. These will be described in order.

First, a case will be described in which the color reproduction accuracy is evaluated using an arbitrary 50 color patch from an existing color patch. FIG.
In step 500, a color chart as a reference for evaluation of color reproduction accuracy is set. In the present embodiment, this arbitrary 50
Colors were selected from the DIC color chart (including achromatic colors) so that hue, saturation, and lightness are not biased. In Table 2 below, these color chart names are shown together with the chromaticity evaluation results (color difference, etc.) described later. In the next step 502, a plurality of set color chips are measured by a colorimeter (Murakami Color CMS-35S
P) is measured (color measurement), and in the next step 504, tristimulus values (XYZ values) under the C light source (that is, under the light source for which the color conversion table is created) are obtained. In this step 504, the Lab value is calculated and stored. Next, after the obtained XYZ values are subjected to the data processing at the time of printing (including the light source correction for observation under the C light source) in step 506, the next step 5
It is output at 08. This allows the color printer 60
A print 62 on which color patches are printed is output (printed out).

Specifically, after the tristimulus values are obtained, the Lab value under the C light source is calculated, and the image data is created so that the color patch is formed in the above shape (series arrangement). Transferred to the color printer 60, a print 62 is created.

The color patch formed on the printed out print 62 is printed with the C light source in the next step 512 after the print color of the color patch is measured by the colorimeter in the same step 510 as in the step 510. La at
The b value is determined.

Next, in step 514, step 50
4 and the Lab value of the color patch obtained in step 512 and the Lab value of the color patch formed by the printing of the color chart are read and subtracted to obtain the color difference.

Table 2 below shows DICs of arbitrary 50 colors.
#, The Lab chromaticity (target color) for each of these DIC # s, the Lab chromaticity of the printing result, and the color difference from the target color are shown. In addition, Table 3 shows the average value, standard deviation, and maximum value of the color differences in Table 2. The relationships between these target colors and printing colors are shown in FIGS. 24, 25 and 26. FIG. 24 shows the distribution of target colors in the chromaticity diagram with the vertical axis a ^* and the horizontal axis b ^*, and in FIG. 25, the vertical axis is L ^* and the horizontal axis is DI.
The distribution of target colors in the coordinate system designated as C # is shown. It is understood that there is no bias in the distribution on the chromaticity diagram. FIG.
Indicates the color difference ΔEab for each color of DIC #.

From this, it can be understood that, for any color, each printed color is reproduced as a target color. The target color that gives the largest color difference (# 14)
Are considered to be outside the color reproduction range.

[0168]

[Table 2]

[0169]

[Table 3]

Next, the case where the achromatic color reproduction accuracy is evaluated will be described. First, the chromaticity of the achromatic color to be evaluated can be obtained on a microcomputer. Therefore, the Lab value can be obtained in advance. As a result, FIG.
In step 500 of (1), the lightness of an achromatic color is set as a reference for evaluation of color reproduction accuracy. In Table 4 below, these achromatic colors are indicated by the number # and are shown together with the chromaticity evaluation results (color difference, etc.). Since the chromaticity of the achromatic color can be obtained in advance, in the next step 502, the chromaticity of the set achromatic color is read, and in the next step 504, under the C light source (that is, under the light source that created the color conversion table). ), The tristimulus values (XYZ values) are obtained. Next, the calculated XY
The Z value is subjected to the above-described data processing at the time of printing (including light source correction for observation under the C light source) in step 506, and then output in the next step 508. As a result, the color printer 60 outputs (prints out) the print 62 on which the color patch is printed.

For the color patches formed on the printed out print 62, the printing color of the color patch is measured by a colorimeter in the same manner as the above processing (steps 510, 512, 514), and the color patch is measured under the C light source. The Lab value is obtained, and the Lab value of the achromatic color and the Lab value of the color patch formed by the achromatic print are read and subtracted to obtain the color difference.

The evaluation of the reproduction accuracy of the achromatic color was conducted in two types, that is, the examination for the entire lightness area and the examination for the high lightness area. This is because it is important for observing an image that color reproduction is performed in a high lightness / low saturation region, and it is necessary to particularly examine the high lightness region.

Examination for all brightness areas Table 4, Table 5, Table 6 and FIG. 27, FIG. 28, FIG. 29, FIG.
0 is the result of examination for the entire brightness region.

Table 4 shows the target color La of the achromatic color / total brightness region.
b chromaticity, Lab chromaticity of print result, and color difference from target color
Indicated. Since we are targeting achromatic colors here, the target color
Of a ^* Value, b^* The value is 0. Also, the number in the table #
Items with () are colors outside the color reproduction range (brightness)
It is. Table 5 shows the average value of color difference in all lightness range,
Table 6 shows the flatness of the color difference only for the colors within the color reproduction range.
The average value was shown.

In FIG. 27, the horizontal axis represents the target color L ^* (that is, the input value to the color printer), and the vertical axis represents the printing color L ^*.
(That is, the output value from the color printer). As understood from this figure, the straight line has a slope of 1 which is a substantially ideal characteristic, but deviates from the ideal straight line in the low brightness region and the high brightness region. It is considered that these lightness regions are outside the color reproduction range.

In FIG. 28, the horizontal axis shows the target color L ^* , and the vertical axis shows the difference between the target color L ^* and the printing color L ^* .
Further, in FIG. 29, the horizontal axis shows the target color L ^* and the vertical axis shows the a ^* and b ^* values of the printing color. A ^{* for} achromatic color
And the b ^* value is 0, the distance from the horizontal line whose vertical axis value is 0 in this figure indicates the color difference of the printing color as it is. In FIG. 30, the horizontal axis represents L ^* of the target color, and the vertical axis represents the color difference between the target color and the printing color. As can be seen from the figure, it shows a substantially flat characteristic except for the low lightness region and the high lightness region, and it is understood that each of the printed colors is reproduced as the target color for any color. It

[0177]

[Table 4]

[0178]

[Table 5]

[0179]

[Table 6]

Examination on High Brightness Area Table 7, Table 8, Table 9 and FIGS. 31, 32, 33, 3
No. 4 is the result of examination for the high brightness region.

Table 7 shows the target color Lab chromaticity in the achromatic color / high brightness region, the Lab chromaticity of the printing result, and the color difference from the target color.
Of course, the a ^* and b ^* values of the target color are 0. Also,
In the table, numbers with # in parentheses are colors (brightness) outside the color reproduction range. Table 8 shows the average value of color differences in all the high lightness regions. Further, Table 9 shows the average value of color differences and the like only for the colors within the color reproduction range.

In FIG. 31, the horizontal axis represents the target color L ^* (that is, the input value to the color printer), and the vertical axis represents the printing color L ^*.
(That is, the output value from the color printer). The ideal characteristic is that it is a straight line with a slope of 1, but in this result it can be seen that it deviates significantly from the ideal straight line in the high brightness range. This is because these lightness areas are outside the color reproduction range.

In FIG. 32, the horizontal axis shows the target L ^* , and the vertical axis shows the difference between the target color L ^* and the printing color L ^* . In FIG. 33, the horizontal axis represents the target color L ^* and the vertical axis represents the printing color a.
^{* And} b ^* values are taken. Since the a ^* and b ^* values are 0 for an achromatic color like the above, the distance from the vertical axis 0 in this figure indicates the color difference of the printing color as it is. FIG.
In FIG. 4, the horizontal axis represents L ^* of the target color and the vertical axis represents the color difference between the target color and the printing color. As can be seen from the figure, the color difference fluctuations are reduced to fairly high brightness, and in general,
Target colors are reproduced for arbitrary colors.

[0184]

[Table 7]

[0185]

[Table 8]

[0186]

[Table 9]

As described above, in the present embodiment,
Even with a small number of measurements and a small amount of data required to be stored, color reproduction can be performed in consideration of the detailed characteristics of the color printer, and highly accurate color reproduction can be realized. Further, when the present method is applied to the color reproduction method described in Japanese Patent Application Laid-Open No. 7-50760 already filed by the present applicant, the relationship between the signal value of each color material single color and the color material transfer amount is obtained. Since there is no restriction on the number of data and the number of measurement data and the signal value for measurement can be set appropriately for each color material,
It is possible to accurately grasp the non-linearity of the relationship between the signal value for each color material single color and the color material transfer amount without enlarging the number of data.

Further, in the present embodiment, the color conversion table created for realizing the color reproduction with high accuracy, that is, the relationship between the signal value and the chromaticity can be determined, and the color mixture characteristic and the single color characteristic can be determined. Since it is calculated separately, even if the monochromatic characteristics change due to variations in the manufacturing lot of color material bodies or deterioration of the heating efficiency of the printing head, it is sufficient to change or update only the monochromatic characteristics, and it is necessary to change the color mixing characteristics. There is no.
Derivation of the color mixing characteristics requires a large amount of measurement data and calculation processing, and by eliminating this processing, it is possible to greatly reduce the amount of calculation when changing or updating.

Further, in the above color printer, when the maximum transfer amount of the changed or adjusted color material is lower than before, such as when using color materials of different manufacturing lots, the maximum amount of the changed or adjusted color material is reduced. The single color characteristic is set by matching the transfer amount of the other color material that exceeds the transfer amount with the maximum transfer amount of the changed or adjusted color material. In this way, to match the minimum value of the standardized maximum transfer amount of each color material,
By limiting the maximum transfer amount of each color material to the paper, it is possible to maintain good color balance in the low lightness portion.

Further, in the above color printer, since the color mixture characteristic and the single color characteristic are separately obtained, when it is necessary to adjust the color tone (tint) of the color to be reproduced,
By changing the monochromatic characteristics of each color material and changing only the monochromatic characteristics to change the transfer amount of each color material, the color balance and the like can be easily adjusted.

Here, in general, chemical analysis or the like is required to obtain the transfer color material amount. Although it is conceivable to use optical density as an alternative means, it does not always match the perceived color depth, and in particular CM that is a general coloring material.
When using a color material other than YK, it is difficult to obtain an optical density that matches the perceived color density. Also,
Since it is essential to obtain the chromaticity of the output chart when accurate color reproduction is performed with a color printer, the use of optical density makes it possible to use multiple color systems (optical density and chromaticity value) in the same system. ) Is present and the handling of data becomes complicated, which is not preferable. Further, in order to obtain the optical density and chromaticity, it is necessary to prepare an expensive spectroscopic measurement type measuring instrument, or to prepare each of the optical density measuring instrument and the color measuring instrument to complicate the apparatus configuration. When preparing an optical density measuring device and a color measuring device, it is necessary to separately measure with each measuring device. In this embodiment, since the color difference is used, it is not necessary to measure the density and the like, and the data processing can be easily performed with a simple configuration. In addition, by using the color difference, it is possible to obtain data having a small degree of redundancy with respect to perception, and it is possible to realize high color reproduction accuracy with a small number of measurements.

[0192]

As described above, according to the present invention, a single color characteristic representing the relationship between the formation amount of each of a plurality of color materials and the device value and the color formation by each predetermined formation amount of a plurality of color materials are reproduced. The color information value of each arbitrary color is converted to the device value based on the obtained monochromatic characteristic and the mixed color characteristic, so that the mixed color characteristic and the monochromatic characteristic are separated. Therefore, even if the monochromatic characteristics change due to variations in manufacturing lots of color material bodies or deterioration of heat generation efficiency of the print head, it is sufficient to update only the monochromatic characteristics, and it is not necessary to change the color mixing characteristics.

Regarding the non-linear relationship between the device value and the chromaticity of the reproduced color, the device value is changed to the material formation amount by the monochromatic characteristic representing the relationship between the device value and the color material formation amount. By converting and obtaining the relationship between the formation amount of the color material and the chromaticity of the reproduced color as a color mixing characteristic, the relationship between the strongly nonlinear device value and the chromaticity of the reproduced color is directly calculated. It is possible to obtain the relationship between the device value and the chromaticity of the reproduced color more accurately with a smaller number of data than in the case of obtaining.

Furthermore, when the maximum amount of formation of the color material on the color reproduction medium changes due to replacement of the color material or the like, each color is made to substantially match the minimum value of the standardized maximum amount of formation. By limiting the maximum amount of material to be formed on the color reproduction medium, it is possible to maintain good color balance in the low lightness portion.

Furthermore, when adjusting the tint of the predetermined color to be reproduced, it is only necessary to adjust the monochromatic characteristic corresponding to the tint to be adjusted among the plurality of monochromatic characteristics, so that the color balance and the like can be easily adjusted. be able to.

Further, as the formation amount, the color difference between the color formed according to the formation amount or the color formed by the device value that determines the formation amount and the white or gray of the color reproduction medium can be used. Each characteristic can be easily obtained without requiring complicated measurement such as chemical analysis for obtaining the formation amount. By using this color difference, it is possible to obtain data with a small degree of redundancy with respect to perception, and it is possible to realize high color reproduction accuracy with a small number of measurements.

[Brief description of drawings]

FIG. 1 is a block diagram showing a flow of general processing when an arbitrary color is displayed on a CRT.

FIG. 2 is a block diagram showing a processing flow when a hard copy having an arbitrary chromaticity is created by the hard copy device.

FIG. 3 is a conceptual diagram showing a process of color reproduction from display of a CRT by signal values representing colors to perception of color (chromaticity).

FIG. 4 is an explanatory diagram for explaining that the process of FIG. 3 can be roughly divided into a conversion process and a perceptual process.

FIG. 5 is a conceptual diagram showing a color reproduction process in a color hard copy device.

FIG. 6 is an image diagram showing a conceptual configuration for predicting chromaticity of a printing result and determining CMYK values.

FIG. 7 is a conceptual diagram showing details of the process of color reproduction by predicting the chromaticity of the printing result in the color hard copy device.

FIG. 8 is a diagram showing a schematic configuration of a color reproduction device according to the present embodiment.

FIG. 9 is an image diagram showing a conceptual configuration of a color conversion table.

FIG. 10 is an image diagram showing a process until an ink level is converted into chromaticity.

FIG. 11 is a flowchart showing a flow of a calculation processing routine executed by the color reproduction device of the present embodiment.

FIG. 12 is a flowchart showing the flow of processing for generating a color conversion table.

FIG. 13 is a flowchart showing a flow of processing for printing an image.

FIG. 14 is a flowchart showing a flow of preprocessing of spline interpolation.

FIG. 15 is a flowchart showing a flow of a calculation process for obtaining a color material transfer amount for an arbitrary signal value.

FIG. 16 is an explanatory diagram for explaining a g value used in spline interpolation.

FIG. 17 is a color conversion table (3D) in Lab space.
It is an image figure which shows -LUT).

FIG. 18 is an image diagram for explaining how to obtain an ink color / ink level from an arbitrary Lab value in the color conversion table (3D-LUT) on the Lab space in FIG. 17;

FIG. 19 is a flowchart showing a flow of processing for deriving a single color characteristic.

FIG. 20 is a flowchart showing a flow of processing for deriving a color mixing characteristic.

FIG. 21 is a diagram showing monochromatic characteristics represented by an ink level and a color difference from white.

FIG. 22 is a diagram showing a relationship between a signal value (ink level) between cyan and magenta color materials and a color material transfer amount in color material exchange and the like.

FIG. 23 is a flowchart showing the flow of processing for evaluating color reproduction accuracy.

FIG. 24 a of an arbitrary target color used for evaluation of color reproduction accuracy
It is a diagram showing a distribution on a ^* -b ^* chromaticity diagram.

FIG. 25: L of an arbitrary target color used for evaluation of color reproduction accuracy
It is a diagram showing a distribution of ^* .

FIG. 26 is a diagram showing a distribution of color differences of arbitrary target colors used for evaluation of color reproduction accuracy.

27 is a diagram showing a target achromatic L ^* and the printing colors in the L ^* relationship for all brightness region used for the evaluation of the color reproduction accuracy.

FIG. 28 is a difference ΔL between the target achromatic color L ^* used in the evaluation of color reproduction accuracy, the target color L ^*, and the print color L ^*.
It is a diagram which shows the relationship of ^* .

[Figure 29] and the target achromatic total brightness region used for the evaluation of color reproduction accuracy L ^*, a graph showing the a ^* and b ^* relationship.

FIG. 30 is a diagram showing a relationship between L ^* of a target achromatic color in the entire lightness range used for evaluation of color reproduction accuracy and color difference ΔEab.

FIG. 31 is a diagram showing a relationship between L ^* of a target achromatic color in a high lightness range and L ^* of a printing color used for evaluation of color reproduction accuracy.

FIG. 32 is a difference ΔL between the target achromatic color L ^* used in the evaluation of color reproduction accuracy and the target color L ^* and the printing color L ^*.
It is a diagram which shows the relationship of ^* .

FIG. 33 is a diagram showing the relationship between L ^* and a ^* and b ^* of the target achromatic color in the high lightness range used for evaluation of color reproduction accuracy.

FIG. 34 is a diagram showing a relationship between a target achromatic color L ^{* in} a high lightness range used for evaluation of color reproduction accuracy and a color difference ΔEab.

[Explanation of symbols]

 52 Microcomputer 54 Measuring device

Claims (8)

[Claims] 1. A plurality of basic colors are provided, and the first predetermined color is used.
Different from the first color system in order to determine the formation amount of each basic color when the color information value represented by the color system is reproduced on the color reproduction medium by the color mixture of the plurality of basic colors. In a color reproduction device that reproduces the predetermined color on a color reproduction medium by converting to a device value represented by a second color system and outputting a color according to the device value, Obtaining the monochromatic characteristics for each of the basic colors, which represents the relationship between the formation amount of each basic color when reproducing colors with mixed colors and the device value for determining the formation amount, and based on the obtained monochromatic characteristics, Of the basic color and the chromaticity of the color reproduced by the formation of the color based on the predetermined formation amount, the color mixture characteristic is obtained, and based on the obtained single color characteristic and the color mixture characteristic, the first Convert the color information value of each color of the color system of to the device value, The current method. 2. A subtractive color reproduction apparatus capable of forming an arbitrary color by synthesizing a plurality of basic colors for which subtractive color mixing is established, wherein the monochromatic characteristic and the mixed color characteristic are obtained. The color reproduction method according to claim 1. 3. The color mixture characteristic is spline-interpolated based on a plurality of relationships between a predetermined formation amount of each of the plurality of basic colors and a chromaticity of a color reproduced by the formation of a color by the predetermined formation amount. The color reproduction method according to claim 1, wherein the formation amount of each basic color corresponding to an arbitrary chromaticity is estimated by the above. 4. When using a color material different from the color material for forming the basic color when the single color characteristics and the color mixture characteristics are calculated, or when the color materials having substantially the same color are used, only the single color characteristics are calculated. The color reproduction method according to any one of claims 1 to 3, wherein: 5. When obtaining monochromatic characteristics using the different coloring materials, the monochromatic characteristics of the different coloring materials are obtained from the relationship between the formation amount of the different coloring materials and a device value for determining the formation amount, When the maximum formation amount in the monochromatic characteristics of the obtained different color materials is less than the maximum formation amount in the monochromatic characteristics of other color materials other than the different color materials, the monochromatic characteristics of the other color materials are different from each other as the maximum formation amount. In addition to setting the maximum formation amount of the color material, the device amount corresponding to the formation amount exceeding the maximum formation amount of the different color material is made to correspond to the maximum formation amount in the monochromatic characteristic of the different color material, and the single color for each of the basic colors The color reproduction method according to claim 4, wherein the characteristic is obtained. 6. The method according to claim 1, wherein, when adjusting the tint of the predetermined color to be reproduced, a monochromatic characteristic corresponding to the tint to be adjusted among the plurality of monochromatic characteristics is adjusted. 5. The color reproduction method according to any one of 5 above. 7. The formation amount is a color difference between a color formed according to the formation amount or a color formed by a device value that determines the formation amount and a color of the color reproduction medium. The color reproduction method according to claim 1, wherein 8. The single-color characteristic is created by creating a chart of a plurality of colors in which the color difference between the color of the color reproduction medium and the color with the maximum formation amount is substantially uniform for each of the basic colors. 8. The color reproduction method according to claim 7, wherein the color reproduction is performed using a chart.