JP3427615B2 - Color reproduction method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color 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.

Further, with the recent development of the information communication network, it has become possible to exchange information representing images and colors between remote places. In that case, the same (color and The information (representing the image) must be displayed in 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 3]

However, Y: emission brightness Yo: emission brightness when the signal value is 0 Yc: Light emission brightness at the maximum signal value D: arbitrary signal value γ: CRT gamma characteristic value

The gamma characteristic value γ of 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 can be obtained for the signal values other than the measurement points 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 determined 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.

Further, when a hard copy having a desired 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. By a conversion process 20 such as a color prediction formula or a three-dimensional LUT that expresses the relationship between the signal value and the chromaticity, the arbitrary chromaticity 10 is, for example, cyan, magenta, yellow, and black (hereinafter, CMY).
K. ) Is converted to a 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.

[0013]

When a color of arbitrary chromaticity is reproduced on a CRT, if the CRT system can be accurately expressed by a model formula using gamma characteristic values, (1)
The γ value in the equation can be obtained from the signal value 0, the maximum signal value, and any one signal value other than these two signal values.

However, the emission intensity / signal value characteristic of the CRT system cannot be accurately expressed by the model formula using the gamma characteristic value. The cause may be that the conversion characteristics of the D / A converter or the video signal value / applied voltage conversion characteristics of the CRT are not linear.

That is, an actual CRT often does not behave as theoretically. For example, in the case where each of the RGB colors is displayed in a single color with a predetermined signal value, and in the case of a mixed color display in which each of the RGB colors is displayed simultaneously with a predetermined signal value, the emission intensity of each color is the same even though the signal values are the same. 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, the tristimulus values obtained by combining (adding) the tristimulus values obtained when the RGB colors are displayed in a single color do not match the tristimulus values obtained when the RGB colors are displayed in a mixed color. The phenomenon of display inconsistency occurs (inconsistency of additive color mixture). For example, when the signal value is 127, as shown in the following equation (2),
The tristimulus value obtained by adding the tristimulus values measured by single-color display for each RGB color may not be the same as the tristimulus value measured by color mixing display of each RGB color with the same signal value.

(Xa, Ya, Za) ≠ (X ₁ , Y ₁ , Z ₁ ) + (X ₂ , Y ₂ , Z ₂ ) + (X ₃ , Y ₃ , Z ₃ ) ... (2) where , (Xa, Ya, Za): (Ra, Ga, Ba) = (127, 127, 127) tristimulus values (X ₁ , Y ₁ , Z ₁ ): (Ra, G ₀ , B ₀ ) = (127, 0, 0) tristimulus values when the _{(X 2, Y 2, Z} 2) :( R 0, Ga, B 0) = (0,127, tristimulus values when the _{0) (X 3, Y 3} , Z ₃ ): Tristimulus value when (R ₀ , G ₀ , Ba) = (0, 0, 127)

Since the emission intensity / signal value characteristic is affected not only by the CRT characteristic but also by the D / A converter characteristic, it cannot be expressed only by a model formula using the gamma characteristic value. Therefore, in the case of color reproduction with a CRT, since there is a discrepancy between the modeled characteristics and the actual characteristics in the color reproduction method using the conventional model formula, there is a limit to the accuracy and there is a difference between the modeled characteristics. In a region (luminance region) where the deviation of the actual characteristics is large, the color reproduction accuracy may be extremely deteriorated.

Furthermore, when the colors of a plurality of CRTs are matched, the CRT system itself is adjusted so that the whites of the CRTs match, and then the characteristics of each CRT system are measured and corrected. As a simple and general method for adjusting, the characteristics of the D / A converter are often adjusted. When the characteristics of the D / A converter are adjusted in this manner, the emission intensity / signal value characteristics greatly deviate from the above model formula.

Therefore, when using the model formula,
The emission intensity of many signal values is measured, and the γ value is determined by a statistical method such as the least square method. By this,
Although a slight improvement in accuracy is recognized in expressing the emission intensity / signal value characteristics, the accuracy is limited because the model formula itself deviates from the actual phenomenon.

On the other hand, in the method using the linear interpolation and the LUT for the conversion processing, the accuracy depends on the number of measurement points at which the correspondence between the emission intensity and the signal value is obtained. Therefore, in order to improve the accuracy, it is indispensable to increase the number of measurement points, which requires a large number of measurement steps. Since the characteristics of CRTs and hard copy devices are subject to changes over time, it is necessary to perform frequent measurements and to reproduce colors by reflecting the characteristics of the devices at that time, but the large number of preparation steps for this measurement is 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 which is the source of color generation by a model formula, and nonlinearity is caused, 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.

[0023]

In order to achieve the above object, the color reproducing method of the present invention according to claim 1 uses a color information value represented by a first color system as a predetermined color in a first table. A color reproducing apparatus that reproduces the predetermined color by converting into a device value represented by a second color system different from the color system and outputting a color corresponding to the device value A plurality of predetermined device values are input for each of the basic colors constituting the, the plurality of output colors are colorimetrically measured, and the intensity information of the colors to be output in the color reproduction device based on the colorimetric values is input. each calculated value, obtained spline function represented by the following formula based multiple on correspondence between the device value x and the intensity information value y
Define the parameters N [i, 4, x] and p [i] ,

[0024]

[Equation 4]

Using the spline function, the correspondence between the device value and the strength information value including the plurality of correspondences and other than the plurality of correspondences is adjacent when the device values or the strength information values are arranged in order of magnitude. Any device value between one corresponding device value with a smaller device value of the corresponding correspondence and the other corresponding device value with a larger device value,
The device value and the strength information value so as to correspond to any strength information value between one corresponding strength information value having a smaller strength information value and the other corresponding strength information value having a larger strength information value. Between the basic color forming the second color system, the color information value represented by the first color system as an arbitrary predetermined color using the obtained conversion property. To the device value.

In the color reproducing method of the present invention, the color information value represented by the first color system as the predetermined color is represented by the second color system different from the first color system. To a color reproduction device using additive color mixture that reproduces the predetermined color by converting the device color into a device value and outputting a color corresponding to the device value, and a predetermined value for each basic color that constitutes the second color system. The device values of the monochromatic color are input, and the output colors are measured, and a plurality of mixed device values based on the predetermined device values of the basic colors forming the second color system are input and output. Based on the colorimetric value of the monochromatic device value and the colorimetric value of the mixed color device value, the color reproduction device should output corresponding to each of the mixed color device values. each calculated color intensity information value, the device value x before and determined Parameter N of the spline function expressed by the following equation based on a plurality of corresponding intensity information value y
Determine [i, 4, x] and p [i] ,

[0027]

[Equation 5]

Using the spline function, the correspondence between the device value and the strength information value including the plurality of correspondences and other than the plurality of correspondences is next to that when the device values or the strength information values are arranged in the order of magnitude. Any device value between one corresponding device value with a smaller device value of the corresponding correspondence and the other corresponding device value with a larger device value,
The device value and the strength information value so as to correspond to any strength information value between one corresponding strength information value having a smaller strength information value and the other corresponding strength information value having a larger strength information value. Between the basic color forming the second color system, the color information value represented by the first color system as an arbitrary predetermined color using the obtained conversion property. To the device value.

The invention described in claim 3 is the invention according to claim 1 or 2.
In the color reproduction method described in [3], the correspondence between the device values and the intensity information values obtained in advance is characterized in that the obtained intensity information values have substantially equal intervals.

In the invention of claim 1, the color information value represented by the first color system is converted into a device value represented by a second color system different from the first color system, and the device is converted. By outputting the color corresponding to the value, the color reproduction device reproduces and outputs the predetermined color. The color reproduction device includes a display device such as a CRT and a printing device such as a color printer. As the first color system, there is a color system represented by well-known tristimulus values XYZ,
As a second color system different from the first color system, there are RGB color systems used in display devices and YMCK color systems used for printing. Further, the device value includes a digital signal value for displaying an image on the display device and a digital signal value for outputting a print from the printing device. A plurality of device values determined in advance for each of the basic colors forming the second color system are input to the color reproduction apparatus, and the output colors are measured. Based on the colorimetric values, the intensity information values of the colors to be output in the color reproduction device are obtained. This intensity information value contains a CRT
There is a light emission intensity and a brightness in a display device such as, and in a printing device such as a color printer, there is a color difference for determining a color of an output result, a Lab value, and a value of a predetermined color system.

The obtained device value x and strength information value y
Parameters of spline function based on multiple correspondences with
N [i, 4, x] and p [i] are determined, and the conversion characteristic between the device value and the intensity information value including the plurality of correspondences constitutes the second color system by using the spline function. Calculate for each basic color. Correspondence between device values and strength information values other than multiple correspondences is that the device value is larger from the device value of one of the neighboring correspondences when the device values or strength information values are arranged in order of magnitude. Any device value up to the other corresponding device value, and any intensity between one corresponding intensity information value with a small intensity information value to the other corresponding intensity information value with a large intensity information value A conversion characteristic between the device value and the intensity information value is obtained so as to correspond to the information value. As a result, the conversion characteristic between the device value and the intensity information value has a monotonically increasing relationship. Therefore, by interpolating the correspondence between the device value and the intensity information value from the relationship of the adjacent correspondences, the correspondence between the adjacent correspondences can be obtained. Since this conversion characteristic has a monotonically increasing relationship as described above, the conversion characteristic can be obtained using the spline function by determining the parameters of the spline function from the correspondence between the device value and the intensity information value.

Therefore, if the obtained conversion characteristic is used, the color information value of each color of the first color system which does not have the correspondence obtained in advance can be converted into the device value. In this way, since the color information value of any color can be converted into the device value without using the model formula, the accuracy due to the deviation between the model formula and the actual one does not deteriorate. In addition, since linear interpolation is not used to find the correspondence between adjacent correspondences, it is possible to achieve high accuracy from a small number of measurement data. Further, since the conversion characteristic between the color information value and the device value is obtained by including a plurality of correspondences obtained in advance, the plurality of correspondences obtained in advance are always provided, and the accuracy of the required accuracy can be easily managed. Furthermore, when the strength information values or the device values are arranged in the order of magnitude, the relationship between the strength information values and the device values between adjacent correspondences is an intermediate value between the strength information values and the device values that are adjacent to each other. A conversion characteristic between the intensity information value and the device value is obtained. Therefore, the amount of change (eg, differential value) in each correspondence is either positive or negative,
A stable result can be obtained without causing a vibration phenomenon that occurs in a known interpolation method, for example, spline interpolation.

According to the second aspect of the present invention, the color information value represented by the first color system as the predetermined color is changed to the second color information value different from that of the first color system.
By converting to a device value represented by the color system and outputting a color corresponding to the device value, a predetermined color is reproduced and output by a color reproducing device using additive color mixing. A display device such as a CRT is known as a color reproduction device using the additive color mixture. A monochromatic device value of a predetermined value is input to each of the basic colors forming the second color system to the color reproduction device, and each output color is measured. At the same time, a plurality of mixed color device values based on predetermined device values of the respective basic colors constituting the second color system are input, and the plurality of output colors are measured. Accordingly, it is possible to obtain a colorimetric value based on a monochromatic device value and a colorimetric value based on a mixed color device value. In addition, it is known that in additive color mixing, chromaticity and the like can be predicted from intensity information values such as emission intensity using a 3 × 3 matrix. That is, if the intensity information values are integrated into a 3 × 3 matrix having the tristimulus values at the highest intensity for each color, the chromaticity, which is the measured value, is obtained. Therefore, if a 3 × 3 inverse matrix is used, it is possible to obtain the emission intensity, which is the intensity information value, by integrating the measured values. Therefore, the intensity information value for each single color of the color to be output in the color reproduction apparatus, for example, the emission intensity can be obtained from the colorimetric value of the mixed color device value using the colorimetric value of the monochromatic device value.

Therefore, based on the colorimetric value of the monochromatic device value and the colorimetric value of the mixed color device value, the intensity information value of the color to be output in the color reproducing apparatus corresponding to each of the mixed color device values, For example, each emission intensity is obtained.
As a result, the correspondence between each monochromatic device value and the intensity information value in which the characteristics of color mixture are taken into consideration is obtained.

The parameter N of the spline function is calculated based on a plurality of correspondences between the obtained device value x and intensity information value y.
[I, 4, x] and p [i] are determined, and the spline function is used to include the plurality of correspondences as described above, and the correspondence between the device value and the strength information value other than the plurality of correspondences is
When the device values or strength information values are arranged in the order of magnitude, one of the device values from one corresponding device value with a smaller device value to the other corresponding device value with a larger device value among the adjacent correspondences , Of the device value and the strength information value so as to correspond to any strength information value between one corresponding strength information value having a smaller strength information value and the other corresponding strength information value having a larger strength information value. The conversion characteristic between the two is calculated for each basic color that constitutes the second color system. As a result, the conversion characteristic between the intensity information value and the device value has a monotonically increasing relationship. Therefore, by interpolating the correspondence between the strength information value and the device value from the relationship of the adjacent correspondences, the correspondence between the adjacent correspondences can be obtained. Since the conversion characteristic has a monotonically increasing relationship as described above, it is possible to determine the parameter of the spline function from the intensity information value and the device value and to obtain it by using the spline function.

Therefore, when the characteristics of the device value and the intensity information value are obtained from the measurement values when the color information is output, the required number of measurements is reduced, and especially when the color information values near the achromatic color are used. Can realize good color reproduction even in a display system in which intensity information values such as emission intensity change due to color mixing.

In the color reproduction method, the correspondence between the device values and the intensity information values obtained in advance should be such that the obtained intensity information values have substantially equal intervals. You can As a result, the correspondence between the device value and the intensity information value can be found from the measured values that are almost even for the system that perceives color, and the redundancy of the measured values can be avoided, and the accuracy due to the sparse interval of the measured values. It is possible to prevent the deterioration.

[0038]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an example of 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 classified 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 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.

FIG. 5 shows the color reproduction process in the color hard copy apparatus. Note that, here, a thermal sublimation type hard copy device using CMYK dyes as the printing color material will be described as an example.

CMYK from computer to printer
The signal of each color material is output. These signal values 31 are D /
The temperature is converted into a heat generation temperature 35 by a process of converting into an analog voltage by the A converter and a process of converting the print head by the voltage, which is a process 33 of converting the print head. In the thermal sublimation type hard copy apparatus, the heat generation temperature 35 by the printing head is set to a color material transfer amount 39 by a conversion process 37 which is a process in which a sublimation type ink film is heated to sublimate a color material (dye) and transferred to paper. To be converted. 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. Transferred color material (dye)
Is semi-transparent, the color obtained by superimposing each color material (dye) is a subtractive color mixture, and as is well known, by the visual sense (or measuring device) (subtractive color mixture process), the color (chromaticity) 46 Is perceived as. 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.
In addition, in actuality, for example, in an apparatus that prints in the order of CMYK, the phenomenon that 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 predict the chromaticity of the printing result and then determine the CMYK signal value. As shown in FIG.
It is necessary to understand the relationship between the YK signal value and the chromaticity. 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 that realizes the chromaticity from an arbitrary chromaticity value.

[First Embodiment] Next, a first embodiment of the present invention will be described. The present embodiment is an example of a case where color reproduction is performed using measurement data when a single color is displayed on a CRT.

As shown in FIG. 7, the color reproducing apparatus according to the present embodiment has a CRT system 50 and a microcomputer 5.
2 and a color measuring device 54 having a probe 56. A color measuring device 54 is connected to the microcomputer 52, and the microcomputer 52 is a C
It is connected to the RT system 50. The microcomputer 52 includes a CPU 52A, a ROM 52B, and a RAM 52.
C, a memory 52D for storing a table and a processing routine which will be described later, and an input / output device (I / O) 52E, which are connected to a bus 52F capable of exchanging data and commands. A keyboard 53 is connected to the input / output device 52E as an input device for executing a processing program to be described later and for inputting data.
The CRT system 50 and the color measuring device 54 are also connected (see FIG. 8). The probe 56 included in the color measuring device 54 functions as a sensor that measures the color (chromaticity) displayed on the display screen 50A of the CRT system 50. The CRT system 50 also includes a D / A conversion device (not shown).

Next, the operation of this embodiment will be described.

When the color reproducing apparatus of the present embodiment is turned on, the arithmetic processing routine of FIG. 9 is executed. In step 100 of FIG. 9, R representing the correspondence between the emission intensity and the signal value
A table for each color of GB is generated and stored in the memory of the microcomputer 52, and the process proceeds to step 102.
In step 102, in order to display a desired color for each pixel,
Color calculation processing to find the correspondence between the signal value and chromaticity is executed,
The process is repeated until the process of step 102 is completed for all pixels (step 104). When this routine is finished, an image of a desired color is displayed on the screen 50A of the CRT system 50.

Next, the details of step 100 will be described.
In step 100, the processing of FIG. 10 is executed, color patches that are colored with predetermined signal values are displayed for each of the RGB colors, and the displayed colors are measured by a measuring machine. This is a process of creating a table for each color from the relationship with the values and storing each created table in the memory of the microcomputer.

First, in step 110 of FIG. 10, R color,
One color is set from the G color and the B color. In addition, R color,
Since the processing for each of the G color and the B color is the same, the following description will be given for the case where the R color is set.

In step 112, a plurality of signal values are set in order to measure a plurality of colors as will be described later. It is desirable that the plurality of signal values be a predetermined number of values at which the brightness of the displayed color patch is substantially evenly spaced. For example, in an 8-bit CRT system in which gamma is set to 1.8, 0, 8, 24, 48, 80, 116, 156, 20
It is a value of 9 levels of 4,255. The plurality of signal values include the maximum value (255 in this case) and the minimum value (0 in this case). In addition, the above 8-bit C
An example of the RT system is Ap as a microcomputer.
ple Power Mac 7500/100, BUG XA-Pro video board installed, BARCO Reference Calibrator
There is a system configured by connecting. The signal value is not limited to each of the above values, and can be set appropriately.

Next, in step 114, the color patch of each signal value is displayed, and in the next step 116, the color of each color patch is measured. By measuring this color, the tristimulus value (X _ml , Y _ml , Z _ml ) of the color of each color patch (m = r,
g, b: l = 0, 8, 24, ..., 255) is obtained. Tristimulus values (X _ml , Y _ml , Z obtained in the present embodiment
_ml ) is the minimum signal value (signal value 0 in this embodiment).
_Tristimulus value (X _m0 , Y _m0 , Z _m0 ) of the color patch displayed by
And the tristimulus values (X _m255 , Y _m255 , Z) of the color patch displayed with the maximum signal value (255 levels in this embodiment).
_m255 ) is included. The tristimulus values (X _m0 , Y _m0 , Z _m0 ) of the color patch displayed with the minimum signal value are tristimulus values at the 0 level at the time of minimum light emission in the present embodiment, and are the same for each RGB color. _Therefore , in the following description, tristimulus values (X _m0 , Y _m0 , Z _m0 ) at the time of minimum light emission will be described.
Is used as a tristimulus value (X ₀ , Y ₀ , Z ₀ ). The color patch is displayed on the entire screen or only the color patch is displayed in a predetermined size in the center of the screen. In addition, although it is desirable to perform the measurement in all darkness (for example, in a dark room), since bias correction is performed in this embodiment as described later, the measurement can be performed in a bright room regardless of the surrounding environment. Further, in order to improve the accuracy of measurement, it is desirable to measure the same color a plurality of times and use the average value or the like as the measured value.

In the measurement of color, as a measuring device, for example, a TV color analyzer CA manufactured by Minolta Co., Ltd.
Each value of x, y, and Y can be obtained by using -100.

In the next step 118, the tristimulus values (X _m255 , _Ym255 , Z _m255 ) at the maximum light emission measured above are stored, and in the next step 120, the tristimulus values (X ₀ , Y ₀ at the minimum light emission). , Z ₀ ) is stored as a bias value.

Next, in step 122, the emission intensity is calculated. That is, the obtained measured value (tristimulus value)
Among the above, as shown in the following formula (3), after subtracting the measurement value (bias value) at the signal value 0 for the Y value corresponding to the brightness (luminance), the measurement value at the signal value 255 (maximum light emission) The relative luminance is obtained by normalization by dividing the relative luminance by tristimulus value) and the relative luminance is defined as the emission intensity y _ml .

[0059]

[Equation 6]

In step 124, the parameters of the spline function for spline interpolation are obtained as follows. As will be described in detail later, as shown in Table 1 below, the emission intensity y _ml and its signal value x _ml are set as a set, and the value x
[J] and y [j] are set, and the parameters N [i, 4, x] and the parameter p [i] of the spline function are obtained.
At that time, the end condition may be, for example, a condition that the left side is 0.0 and the right side is the same as the slope determined by the relative luminance of each of the signal value 204 and the signal value 255, and is determined from the measured values other than this. It may be a value.

[0061]

[Table 1]

In the next step 126, the relative light emission intensities for all the signal values are calculated using the obtained parameters of the spline function. Ie 0 to 25
Emission intensity (relative brightness) for all 5 signal values
Is determined by a spline function (equation (4) below) using the parameters N [i, 4, x] and p [i].

At the next step 128, as shown in Table 2 below, a table showing the correspondence between each signal value and the emission intensity is generated and stored in the memory. That is, it is stored as a table in which each signal value and its relative light emission intensity are paired. In addition, the measured value (tristimulus value) at the bias-corrected signal value 255 is stored. These tristimulus values are
It is used as a color conversion matrix which is an element of a matrix calculation formula (formula (11) shown below) whose details will be described later.

[0064]

[Table 2]

However, l = 1, 2, ..., 255 m = r, g, b In step 130, it is determined whether or not the above processing is completed for all colors. That is, the above processing is performed for G color and B color, and a table is prepared for each color. [Third-Order Spline Interpolation Method for Monotonically Increasing y = f (x)] Here, there is a functional relationship between the parameters of the spline function obtained in step 124 and the correspondence between all the signal values obtained in step 126 and the emission intensity. A monotonically increasing function of two variables (x, y) (y = f
The spline interpolation regarding (x) 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 (4).

[0068]

[Equation 7]

However, n: number of values to be original data for interpolation i: 0, 1, ..., 2n-1 In the above equation (4), N [i, 4, x] is a value x.
An element u [i] obtained from [j] as described later.
P [i] is determined by the following equation, and p [i] is an element c [i] and N obtained from the value y [j] as described later.
It is determined by [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, if the matrix of N [i, 4, x] for each value x [j] and each i is N and the matrix of the element p [i] is P, the following (5)
It has the relationship shown in the formula.

C = N · P (5) Since these matrices C and N can be determined from the value y [i],
The matrix P is determined by the following equation (6).

P = N ⁻¹ · C (6) 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 (4).

This spline function parameter N [i,
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] However, 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 values y [j] as shown in [Definition 2] below.

[0076]   [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]                           However, 2 ≦ j ≦ (n−2) c [j · 2 + 1] = g value of value x [j]                           However, 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], arbitrary value setting) However, the g value is obtained from the following equation (7). g = Dy [i] / Dxy [i] (7)

These Dy [i] and Dxy [i] are the 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 a point (x
[I], y [i]) shows the inclination of the straight line. If the g value is determined using the above equation (7), 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 the point.

Next, in step 226, each element of the matrix N of 2n rows and 2n columns is calculated as shown in Table 3 below.

[0079]

[Table 3]

Each element N [i, 4, x] of the above matrix N,
N ′ [i, 4, x] is obtained from the following equation (8).

[0081]

[Equation 8]

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
A value of 1.0 is set when [i] ≦ x <u [i + 1]), and a value of 0.0 is set otherwise.

On the other hand, N '[i, k, x] is obtained from the following equation (9).

[0084]

[Equation 9]

The process for obtaining each element of these matrices is a recursive process (Zoom equation). 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 emission intensity for an arbitrary signal value corresponding to step 126 will be described with reference to FIG.

First, in step 240 of FIG. 13, an arbitrary signal value x, and in step 242, step 230 of FIG.
Read the element u [i] stored in step 24,
In step 4, i is set to 0 to 2n-1, and the element N [i, 4, x] is obtained as described above. That is, a matrix N of 2n rows and 1 column of i = 0 to 2n-1 is obtained. In the next step 246, the stored element p [i] is read, and in the next step 248, the emission intensity y is calculated using the above equation (4) representing the spline function.

In this way, the relative emission intensity for all signal values is obtained. That is, the emission intensity of all the signal values from 0 to 255 can be obtained by the spline function (equation (4)) using the parameters N [i, 4, x] and p [i]. .

Next, a case of displaying an arbitrary color on the CRT using the table generated as described above will be described with reference to FIG. In order to simplify the description, here, a CRT is configured by arranging a large number of vertical and horizontal pixels,
The case where an arbitrary color is displayed on one pixel will be described as an example. When an arbitrary color is displayed on all the display screens, the following process may be performed on all pixels forming the screen.

In step 132 of FIG. 11, the bias value and the tristimulus value at the time of maximum light emission that have been stored in advance are read, and in the next step 134, the following light intensity calculation formula is set.

[0093]

[Equation 10]

Next, in step 136, any color to be displayed is read. This arbitrary color is represented by tristimulus values. The tristimulus value of this arbitrary color is bias-corrected in the next step 138, and the matrix calculation formula (1
The emission intensity of each color that displays an arbitrary color in 0) is obtained.

In the next step 142, the table of each color is read, and the signal value x _{ml of} each color corresponding to the emission intensity is obtained in the next step 144 using each table and displayed in the next step 146. The bias value is
It is the measured value at the signal value 0 stored in the memory. At this time, as a processing method for determining a signal value that is an integer by using a relative brightness that is a real number and a table, for example, the relative brightness is obtained by dividing the target relative brightness by two-branch search method,
Among these two methods, there is a method of obtaining a signal value closer to the target relative luminance. By displaying the signal value thus obtained on the display, it is possible to display an arbitrary color.

The present inventor conducted various experiments as follows regarding the relationship between the digital signal value as the signal value in the CRT and the emission intensity.

[Experiments with Equidistant Measurement Points] In FIGS. 18, 19, and 20, 65 points at equal intervals for each RGB single color are set as measurement points (signal values), and digital signal values at each measurement point are measured. Then, the emission intensity of each monochromatic color was obtained, and the experimental results were shown from which the relationship between the digital signal value and the emission intensity was obtained from the data using the above method.

FIG. 18 (1) shows the relationship between the digital signal value for R color and the light emission intensity. For the same signal value, the light emission intensity obtained as described above and the light emission intensity by measurement are shown. Have the same value. That is, in the present embodiment, the desired emission intensity always passes the measurement point of emission intensity by measurement. Therefore, as shown in the enlarged view of the digital signal values from 0 to 28 in FIG. 18B, at each of the measured signal values, the emission intensity of the measurement and the emission intensity of the calculation are the same. .

Similarly, FIG. 19 (1) shows the relationship between the digital signal value for G color and the emission intensity.
(2) shows an enlarged view of digital signal values from 0 to 28. Further, FIG. 20 (1) shows the relationship between the digital signal value and the emission intensity for the B color, and FIG. 20 (2) shows an enlarged view of the digital signal values from 0 to 28.

[Experiment by Equidistant Luminance] In FIG. 21, FIG. 22 and FIG. 23, the digital signal values of 9 points such that the luminance is substantially evenly spaced for each RGB single color are measured, and the emission intensity thereof is obtained. , And the experimental results in which the relationship between the digital signal value and the emission intensity was obtained from the data are shown.

The measured digital signal values are 0, 8,
24 points, 48 points, 80 points, 116 points, 156 points, 204 points, and 255 points. The emission intensity was calculated from the measured values at these 9 points.
In Table 4 below, the emission intensity obtained by calculation and the emission intensity obtained by actual measurement are described. As can be understood from Table 4, the emission intensity obtained by the present embodiment and the emission intensity actually measured are substantially the same, and according to the present embodiment, the digital signal value with high accuracy can be obtained even from the measurement of only 9 points. It is possible to find the relationship with the emission intensity.

[0102]

[Table 4]

[Second Embodiment] Next, a second embodiment will be described. In this embodiment, C
This is an example of color reproduction using measurement data when a plurality of colors are simultaneously displayed (mixed color display) on the RT. Since the present embodiment has the same configuration as the above-described embodiment, the same parts are designated by the same reference numerals, and detailed description thereof will be omitted.

Proceeding to step 150 in FIG. 14, each signal value 1 is set. In the present embodiment, each signal value 1 is set to a value at which the brightness of the displayed color patch becomes brightness values at substantially equal intervals. That is, in the 8-bit CRT system in which the gamma is set to 1.8 as in the above embodiment, 0, 8, 24, 48, 80, 116, 156, 204,
Set the 9th level value of 255. The R, G, and B color signal values are set to be equal.

At the next step 152, the color patches with the same signal values of the set three colors are displayed. That is,
Color patches of substantially black, a plurality of grays having different intensities, and whites having the same R, G, and B color signal values 1 are displayed. Each of the displayed color patches is measured in step 154 to obtain tristimulus values ( _Xwl , _Ywl , _Zwl ).

In the next step 156, the tristimulus values (X _w0 , Y _w0 , Z _w0 ) which are measured values when the signal value is 0 are stored as bias values. In the next step 158, for each measured color patch, the tristimulus values (X ′ _wl , Y ′ _wl , Z ′) which are the colors after bias correction with the bias value subtracted, as shown in the following equation (11). _wl ) is calculated.

X ′ _wl = X _wl −X _w0 Y ′ _wl = Y _wl −Y _w0 Z ′ _wl = Z _wl −Z _w0 (11)

Next, in step 160, the color used in the following monochromatic processing is set, and in the next step 162, a predetermined signal value l (l = 25 in the present embodiment) is set for each color.
5) is set. It is desirable that the predetermined signal value gives the maximum brightness of each single color, but the present invention is not limited to this.

At the next step 164, the set signal value is set and the set color (any one of red, green and blue) is set.
Color patches are displayed (monochromatic light is emitted), the color patches displayed in the next step 166 are measured, and tristimulus values (X
_m255 , Y _m255 , Z _m255 ) (m: any one of RGB colors is set). With respect to these measured color patches, in the next step 168, the tristimulus values (X ' _m255 , _Y'm255 , _Z'm255 ) which are the colors after the bias correction are performed in the same manner as in step 158 (see the above equation (12)). Is calculated and stored in the next step 170 as the tristimulus value at the time of maximum light emission after bias correction.

When the above process is completed for all colors (step 172), the process proceeds to step 174, and the determinant for each color is generated as follows. That is, both the data obtained for single-color emission and the data obtained for mixed-color emission are converted into tristimulus values, and the tristimulus values obtained for each monochromatic emission are subtracted from the tristimulus values at signal value 0 to obtain tristimulus values. The matrix is as follows. This matrix corresponds to the color conversion matrix of the above formula (11).

[0111]

[Equation 11]

In the next step 176, the light emission intensity calculation formula is set. That is, the emission intensity E _rl , E _gl , E _bl of each basic color in the mixed color display color is obtained by calculating the product of the tristimulus values obtained for the mixed color display color and the inverse matrix of the above matrix. You can That is, the following expression (12) similar to the above expression (10) is set as the light emission intensity calculation expression.

[0113]

[Equation 12]

Next, in step 178, the above (1
2) using the formula of the emission intensity calculation equation, in determined bias corrected tristimulus values using the emission intensity E _rl during the mixing step 158, E _gl, E _bl is calculated. By performing the same process for each mixed color display color, the emission intensity of each basic color can be obtained for the signal value for which the mixed color display is performed. For example, in the case of using the above-mentioned measurement data of the single color display, the number of measurements of 8 × 3 + 1 = 25 (measurement of each single color other than signal value 0 and measurement of signal value 0) is required, while the present embodiment Then, it is possible to process with the number of measurements of 9 + 3 = 12.

Next, in step 180, the relative light emission intensity is calculated. That is, the obtained luminescence intensity is converted into the relative luminescence intensity by dividing by the luminescence intensity of the signal value 255 (value which becomes the maximum luminescence intensity) as shown in the following equation (13).

Y _il = E _il / E _i255 (13)

In step 182, parameters for spline interpolation are calculated. That is, the values x [j] and y [j] are set with the relative emission intensity obtained in step 180 and its signal value as one set, and the parameter N [i] of the spline function is set in the same manner as in the above embodiment. ，
4, x] and p [i] are obtained.

The end condition in this case may be, for example, a condition that the left side is 0.0001 and the right side is the same as the slope determined from the relative brightness of the signal values 204 and 255. It may be a value obtained from the measured value of.

In the next step 184, the relative light emission intensity is calculated for all the signal values, and the next step 18
At 6, a table is created and stored. That is, for all signal values from 0 to 255, the relative light emission intensity (relative brightness) is set to the parameters N [i, 4, x], p.
A table in which each signal value and its relative luminance are paired is generated and stored by the spline function using [i] and stored.

The above processing is performed for all colors (step 188), and a table is generated and stored for each color of red, green and blue.

The present inventor conducted various experiments with respect to the color reproduction accuracy in CRT as follows.

[Color Reproduction Accuracy in CRT (Study on Number of Measurements)] The signal values of 100 colors uniformly generated by random numbers and RGB colors are (R, G, B) = (255, 255, 255). ),
(127, 127, 127), (15, 15, 15), (2
55, 0, 0), (0, 255, 0), (0, 0, 255),
(127, 0, 0), (0, 127, 0), (0, 0, 12
7), (15, 0, 0), (0, 15, 0), (0, 0, 1
The 12 colors determined in 5) were repeated 5 times, and the color reproduction accuracy according to the present embodiment was verified for a total of 160 colors.

65 digital signal values (0, 4, 8, 12, ..., 252, 252, at even intervals for each RGB single color)
255), the emission intensity thereof is obtained, the relationship between the digital signal value and the emission intensity is obtained from the data as in the above embodiment, and the color (chromaticity) is estimated from the digital signal value. Is compared with the color difference between the measured chromaticity value and the average value of the color difference (CIE ΔE ^* ab) 0.4103, standard deviation 0.2347, and maximum value 1.2.
The result is 738. As can be understood from this result, good accuracy could be obtained.

Further, for each of the RGB single colors, digital signal values (0, 32, 64, 96, 12) at nine points at equal intervals are set.
8, ..., 224, 255), and the average value of the color difference (CIE ΔE ^* ab) was 0.6228, the standard deviation was 0.4940, and the maximum value was 2.5479.

Furthermore, the digital signal values (0,
8, 24, 48, 80, 116, 156, 204, 25
5) is measured and the color difference (CIE ΔE ^* ab)
The average value was 0.4587, the standard deviation was 0.2315, and the maximum value was 1.1933.

As described above, although relatively good results are obtained, it is possible to make the measurement points uniform with respect to the brightness by
Even with only the measurement points, it is possible to obtain the same result as in the case of measuring 65 points.

[Study on Accuracy] First, regarding the digital signal values 15, 127, and 255,
Simultaneous emission of RGB (for example, signal values [255, 255,
255]) and a single color emission of RGB (for example, signal values [255, 0, 0], [0, 255, 0],
[0, 0, 255]), the color reproducibility based on the color mixing measurement values was verified by obtaining the color difference from the color obtained by summing the tristimulus values of each color. In the measurement for the CRT manufactured by A company, the signal value is 255, the color difference is 0.6714, and the signal value is 127.
The color difference is 0.2572 and the signal value is 15 and the color difference is 0.8090.
5 has a color difference of 0.9625, and a signal value of 127 has a color difference of 1.335.
5, a signal value of 15 and a color difference of 2.3200 were obtained.
It is understood that the CRT manufactured by Company A has a relatively small color difference and relatively good results are obtained, while the CRT manufactured by Company B has a relatively large color difference.

Regarding this CRT manufactured by Company A, digital signal values of nine points of each monochrome (luminance equal intervals, total 8 * 3 + 1 (black) = 2
The relationship between the digital signal value and the emission intensity is obtained based on the measurement values of (5 points), and the color difference (C
As a result, the average value of IE ΔE ^* ab) was 0.4587, the standard deviation was 0.2315, and the maximum value was 1.1933.
In addition, the relationship between the digital signal value and the emission intensity is obtained based on the measured value of the digital signal value of 9 points of mixed colors (9 * 1 + 3 (each single color) = 12), and the color difference (C
The results were that the average value of IE ΔE ^* ab) was 0.4452, the standard deviation was 0.2065, and the maximum value was 1.1432.
From these comparisons, it was possible to obtain good accuracy even when the color mixture was measured.

Further, the same applies to the CRT manufactured by Company B, and the relationship between the digital signal value and the emission intensity is obtained based on the measured values of the digital signal values of 9 points for each monochromatic color, and the measurement is performed after color reproduction. , Average color difference 1.0326, standard deviation 0.697
9, the maximum value of 3.5935 was obtained. Further, the relationship between the digital signal value and the light emission intensity is obtained based on the measured values of the digital signal values of 9 points of color mixture, and the color difference is measured to obtain an average value of 1.0772 and a standard deviation of 0.639.
7, the maximum value of 2.4389 was obtained. In particular, regarding the maximum color difference, the color difference is smaller in the case of the mixed color measurement, which is preferable. It is considered that the CRT manufactured by Company B has a property that the color is different between the case of a single color and the case of a mixed color, and therefore, the color reproduction accuracy is generally improved by using the mixed color measurement data.

[Third Embodiment] Next, a third embodiment will be described. The present embodiment is an example of color reproduction by a hard copy device. In addition,
In the present embodiment, a sublimation type printer will be described as an example of an 8-bit printing apparatus that uses cyan, magenta, yellow, and black as basic colors. In addition, since the present embodiment has the same configuration as the above-described embodiment, the same reference numerals are given to the same portions, and detailed description thereof will be omitted. 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. 15, the color reproducing apparatus of the present embodiment includes a color printer 60 and a color measuring apparatus 54 having a microcomputer 52 and a probe 56 as in the above-described embodiment. . The color printer 60 forms a color corresponding to a signal input from the microcomputer 52 on a medium and prints it 62.
Is output.

Next, the operation of this embodiment will be described.

When the power of the color reproducing apparatus of the present embodiment is turned on, the arithmetic processing routine of FIG. 9 is executed in the same manner as in the above embodiment. First, a table for each color of YMCK is generated and stored in the memory of the microcomputer 52 (step 100), and a color calculation process for obtaining a correspondence between a signal value and chromaticity is executed in order to output a desired color for each pixel. The process is repeated (step 102), and is repeatedly executed until the process of step 102 is completed for all pixels (step 104). When this routine is completed, the print 62 on which the image of the desired color is formed is formed from the color printer 60.
Will be output.

Details of table generation according to this embodiment will be described below with reference to FIG. First, in step 200, each signal value for print output is set. It is desirable that each of the signal values to be set be values such that the color differences of the displayed color patches are approximately equal intervals.
It is desirable that the areas that exhibit complicated behavior be dense. For example, a sublimation printer uses a signal value in which the signal values of the color patches to be output are dense because the behavior is complicated when the signal value is 10 or less. In this embodiment, as each signal value, 0,1,2,3,4,5,6,7,8,9,10,15,20,25,30,40,5
0,60,70,80,90,100,110,120,130,140,150,160,170,180,
The values of 190, 200, 210, 220, 230, 240, 250, 255 are set for each color (for example, each of the basic colors of cyan, magenta, yellow, and black which are CMYK colors). The signal value is not limited to the above value, and may be set appropriately.

At the next step 202, the color patch for which the signal value is set is output (printed), and at the next step 204.
At, each output color patch is measured. For example, first, for cyan, a color patch is output with each of the above signal values, the color is measured by a measuring machine, and the measured value is stored in a memory. In this embodiment, as a color measurement,
Murakami Color Research Laboratory CMS-35SP colorimeter is used to obtain the spectral reflectance to measure the color, and the tristimulus value is obtained from the spectral reflectance. In order to improve the accuracy of measurement, it is desirable to output and measure a plurality of samples as color patches for the same color and use the average value or the like as the measured value.

When the measurement of the color patch is completed, step 2
At 06, the obtained measured value is converted into a Lab value. That is, L ^* a ^* b ^* is obtained via the tristimulus values XYZ.

At the next step 208, the color difference from white is obtained, and the relative color difference normalized by the maximum color difference is calculated. That is, the color difference El between the L ^* a ^* b ^* of the white background of paper (signal value 0) and the color patch of each signal value is obtained. Then the signal value 2
The color difference El at each signal value is divided by the color difference E ₂₅₅ at 55 to obtain a relative color difference el.

In the next step 210, parameters for spline interpolation are calculated. That is, the relative color difference and its signal value are set as one set, and the values x [j] and y [j] are set.
Is set, and the parameters N [i, 4, x], p [i] of the spline function are obtained by calculation on a separate sheet. At that time, the end condition may be 0 on the left side and 0 on the right side, or may be a value obtained from the measured value.

In the next step 212, the relative color difference is calculated for all the signal values, and in the next step 214 a table is generated and stored. Ie 0 to 25
The relative color difference of all the signal values of 5 is obtained by the spline function using the above parameters N [i, 4, x], p [i], and each signal value and its relative color difference are paired. Is generated and stored.

As described above, in the color reproducing apparatus according to the above embodiment, a small number of measurement points are monotonically increased (or
By interpolating with a spline function limited to (decrease), it is possible to express a relationship between a highly accurate signal value and a color difference from white, that is, an ink amount.

Further, the above spline interpolation is calculated in advance and stored in a memory as a table (lookup table), and when actually displaying an image or the like, by referring to this table, calculation speed can be increased. Can be planned. In the case of a CRT, the relative brightness standardized by the brightness in the maximum light emission state of the phosphor is used as the emission intensity, and in the case of a hard copy device, it is specified by the color difference from the white background of the paper at the maximum ink amount. By using the converted relative color difference,
It is possible to easily express the relationship between the digital signal value and the emission intensity of the phosphor without requiring a complicated procedure such as chemical analysis.

Further, the emission intensity of each basic color is obtained from the measurement data of the colors displayed in the mixed colors, and the relationship between the signal value and the emission intensity of the phosphor is obtained from the emission intensity, whereby each basic color is obtained from one measurement data. Since the emission intensity data of is required, the number of measurements can be reduced, and especially when using the measurement values of colors in the vicinity of an achromatic color, the same signal value for monochromatic light emission and for mixed color light emission is used. Good color reproduction can be realized even in a display system having different emission intensities.

That is, in the color reproducing apparatus according to the above embodiment, the signal value-coloring intensity characteristic of each basic color passes through the data points obtained by the measurement, and the differential values at the measurement points are all positive or 0. Or all negative or 0
Is represented by a spline function. Therefore, since the method does not use the model formula, the accuracy does not deteriorate due to the difference between the model formula and the actual characteristic. Further, since it is not linear interpolation, it is possible to realize high accuracy from a small number of measurement data. Further, since the data points obtained by the measurement are always passed, accuracy control is easy.
Furthermore, since the differential value at all data points is either positive or negative, there is no vibration phenomenon which is a problem in general spline interpolation, and stable results can be obtained.

Further, the digital signal value-coloring intensity characteristic of each basic color of the color reproducing device can be stored in advance in the storage device as a look-up table recording the coloring intensity for each digital signal value. In this way, since it is stored in advance as a look-up table, it is possible to convert the color development intensity into a signal value (or vice versa) at high speed. For example, when accurate color reproduction is performed for an image, it is necessary to convert the color intensity from all pixels to signal values. However, when a large amount of conversion is performed in this way, a lookup table is used. The effect of speeding up is great.

Furthermore, it is possible to use a plurality of measurement points such that the color differences between the colors displayed (or printed) by two adjacent digital signal values are substantially equal. in this way,
By avoiding the redundancy of measurement values, by obtaining the signal value vs. color development intensity characteristics from the measurement values that are approximately equal to color vision, and
It is possible to prevent deterioration of accuracy due to sparse measurement points.

Furthermore, a measured value for one digital signal value of each basic color of a single color and a plurality of digital signal values of each basic color are combined and displayed simultaneously (color mixture display).
The emission intensity corresponding to the digital signal value of each basic color displayed in the mixed color can be obtained from the measured value in this case, and the digital signal value-coloring intensity characteristic of each basic color can be obtained from the emission intensity data. In this way, by determining the signal value vs. color intensity characteristic from the measured values when mixed colors are displayed, the required number of measurements occurs, and especially when the measured values of colors near achromatic colors are used, mixed colors Thus, good color reproduction can be realized even in a display system in which the emission intensity changes.

[0147]

As described above, according to the invention described in claim 1, the device value corresponding to one of the adjacent device values or the intensity information values having the smaller device value when arranged in order of magnitude. From any corresponding device value from the corresponding corresponding device value with a large device value to the other corresponding strength information value with a smaller strength information value to the corresponding corresponding strength information value with a larger strength information value. Since the conversion characteristic between the intensity information value and the device value is obtained so as to correspond to any of the intensity information values of, the color information value of an arbitrary color is set to the device value without using the model formula. It can be converted, the accuracy does not deteriorate due to the difference between the model formula and the actual one, and since linear interpolation is not used to find the correspondence between adjacent correspondences, high accuracy can be realized from a small number of measurement data To do It is, there is an effect that.

According to the second aspect of the invention, the intensity information value of the color to be output in the color reproducing apparatus, for example, the emission intensity is obtained from the colorimetric value of the mixed color device value using the colorimetric value of the monochromatic device value. Therefore, due to the conversion characteristics between the device value and the intensity information value obtained from multiple correspondences of the obtained device value and the intensity information value, the device value and the intensity information value can be If the characteristics can be obtained, the required number of measurements is reduced, and especially when color information values in the vicinity of an achromatic color are used, even a system in which the intensity information value such as emission intensity changes due to color mixing is good. The effect is that color reproduction can be realized.

[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 diagram showing a schematic configuration of a color reproduction device according to the first embodiment.

FIG. 8 is a diagram showing a conceptual configuration of a microcomputer.

FIG. 9 is a flowchart showing a flow of an arithmetic processing routine executed by the color reproduction apparatus according to the first embodiment.

FIG. 10 is a flowchart showing a flow of processing of table generation / storage according to the first embodiment.

FIG. 11 is a flowchart showing a flow of processing for displaying an arbitrary color on a CRT.

FIG. 12 is a flowchart showing the flow of preprocessing for spline interpolation.

FIG. 13 is a flowchart showing a flow of a calculation process of light emission intensity with respect to an arbitrary signal value.

FIG. 14 is a flowchart showing a flow of processing of table generation / storage according to the second embodiment.

FIG. 15 is a diagram showing a schematic configuration of a color reproduction device according to a third embodiment.

FIG. 16 is a flowchart showing a flow of processing of table generation / storage according to the third embodiment.

FIG. 17 is an explanatory diagram illustrating a g value used in spline interpolation.

FIG. 18 is a diagram showing an experimental result showing a relationship of light emission intensity with respect to signal values of R color at equal intervals.

FIG. 19 is a diagram showing an experimental result showing a relationship of light emission intensity with respect to signal values of G color at equal intervals.

FIG. 20 is a diagram showing an experimental result showing a relationship of light emission intensity with respect to signal values of B color at equal intervals.

FIG. 21 is a diagram showing an experimental result in which a relationship between a signal value and a light emission intensity such that luminance has substantially equal intervals for R color is obtained.

FIG. 22 is a diagram showing an experimental result in which a relationship between a signal value and a light emission intensity such that luminance is substantially evenly spaced for G color is obtained.

FIG. 23 is a diagram showing an experimental result in which a relationship between a signal value and a light emission intensity such that luminance is substantially evenly spaced for color B is obtained.

[Explanation of symbols]

50 CRT 52 Microcomputer 54 Measuring device

─────────────────────────────────────────────────── ─── Continued Front Page (51) Int.Cl. ⁷ Identification Code FI G09G 5/00 G09G 5/00 550C 510 5/10 B 550 H04N 1/40 D 5/10 B41J 3/00 B H04N 1/46 H04N 1/46 Z (56) Reference JP-A-4-180354 (JP, A) JP-A-6-326861 (JP, A) JP-A-7-115556 (JP, A) JP-A-7-23247 ( JP, A) JP 6-291996 (JP, A) JP 5-227423 (JP, A) JP 4-180355 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H04N 1/40-1/409 H04N 1/46 H04N 1/60

Claims (3)

(57) [Claims] 1. A color information value represented by a first color system as a predetermined color is converted into a device value represented by a second color system different from the first color system to obtain the device value. A plurality of device values determined in advance for each of the basic colors forming the second color system are input to a color reproduction device that reproduces the predetermined color by outputting a corresponding color, and the plurality of output values are output. Measure each color,
The intensity information value of the color to be output in the color reproduction device is obtained based on the colorimetric value, and is represented by the following formula based on a plurality of correspondences between the obtained device value x and the intensity information value y. para spline function that
Defining the meters N [i, 4, x] and p [i], Using the spline function, including the plurality of correspondences,
In addition, the correspondence between the device values other than the plurality of correspondences and the strength information values is the device value or the device value from one of the corresponding correspondences in which the device values are smaller among the neighboring correspondences when the strength information values are arranged in order of magnitude. Whichever is larger up to the other corresponding device value, and any one between the smaller intensity information value corresponding to one corresponding intensity information value and the larger intensity information value corresponding to the other corresponding intensity information value Corresponding to the intensity information value of, the conversion characteristic between the device value and the intensity information value is obtained for each basic color forming the second color system, and the obtained conversion characteristic is used. A color reproduction method in which a color information value represented by the first color system as an arbitrary predetermined color is converted into a device value. 2. A color information value represented by a first color system as a predetermined color is converted into a device value represented by a second color system different from the first color system to obtain the device value. A device value of a single color, which is a predetermined value, is input for each basic color that constitutes the second color system, and is output to a color reproduction device using additive color mixing that reproduces the predetermined color by outputting a corresponding color. Each of the basic colors forming the second color system, and inputting a plurality of device values of mixed colors according to predetermined device values, and measuring the output plurality of colors. The intensity information value of the color to be output in the color reproduction device is obtained corresponding to each device value of the color mixture based on the colorimetric value of the device value of based on the plurality of correspondence between the intensity information value y and the device value x Para spline function represented by the following formula Te
Defining the meters N [i, 4, x] and p [i], Using the spline function, including the plurality of correspondences,
Further, the correspondence between the device value and the strength information value other than the plurality of correspondences is the device value or the device value from the corresponding one of the adjacent correspondences when the strength information values are arranged in order of magnitude. Whichever is larger up to the other corresponding device value, and any one between the smaller intensity information value corresponding to one corresponding intensity information value and the larger intensity information value corresponding to the other corresponding intensity information value Corresponding to the intensity information value of, the conversion characteristic between the device value and the intensity information value is obtained for each basic color forming the second color system, and the obtained conversion characteristic is used. A color reproduction method in which a color information value represented by the first color system as an arbitrary predetermined color is converted into the device value. 3. The color reproduction method according to claim 1, wherein the plurality of device values obtained in advance and the intensity information values correspond to each other such that the obtained intensity information values have substantially equal intervals. .