JPH0626906B2 - Color reproduction method of sublimation type thermal transfer color printer - Google Patents

Description

TECHNICAL FIELD The present invention relates to a color reproduction method for a sublimation type thermal transfer color printer.

[Prior Art] Color image on a CRT created by a computer, C
Various color printers are used to reproduce and print a color image of an RT color monitor or an ordinary color image. As such a color printer, a thermal fusion transfer type color printer or an ink jet type color printer has been widely used from the past.
All of these are so-called halftone printing methods in which a color is expressed by a combination of fine dots of predetermined primary color inks such as yellow, magenta, cyan, and black. However, in such a halftone printing method, there is a problem that it is difficult to obtain the intended color because the pseudo gradation expression is performed, and there is a problem that the image quality is rough.

Therefore, in recent years, a sublimation type thermal transfer color printer has been proposed in which sublimation positive ink is used to perform uniform color expression by subtractive color mixing on each pixel of an image receiving paper. Such a sublimation type thermal transfer color printer is, for example, as shown in FIG.
An image receiving paper 2 having a substantially transparent image receiving layer 2a formed on its surface;
A platen roller that rotates at a predetermined speed so that the image receiving layer 2a and the primary color ink layer 3a are in close contact with the ink donor film 3 on which the sublimation positive primary color ink layer 3a is formed so as to face the image receiving layer 2a. 4 and the stationary thermal head 5, and the ink in the portion of the ink donor film 3 in contact with the thermal head 5 is generated in the thermal head 5 according to the applied voltage and the energization time. Is sublimated by the heat of
The process of transferring to the image receiving layer 2a is repeated for each primary color ink layer 3a of yellow, cyan, magenta, etc., and these primary color inks are sequentially transferred to the same pixel of the image receiving layer 2a, and a desired color is transferred to this pixel. It is designed for color printing. The primary color ink layer 3a of the ink donor film is yellow magenta / cyan /
Each of the primary color inks, etc. are applied in a frame sequential manner. By performing sublimation type thermal transfer for each of the primary color inks in this manner, a state similar to that in which the primary color inks are almost uniformly mixed is produced in the image receiving layer 2a, and the subtractive color mixture is used to adjust the mixing ratio of these primary color inks. Colors are formed. In addition, according to such an ink transfer method, each pixel is not represented by a halftone dot but is represented by a uniform color by subtractive color mixture, so that there is an advantage that a smooth high-quality printer output can be obtained.

[Problems to be Solved by the Invention] However, in such a conventional sublimation-type thermal transfer color printer, although a smooth high-quality printer output can be obtained, a color reproduction method for a target color has not been established yet. CR created by computer
There is a problem that it is difficult to accurately reproduce and print a color image on T, a color image on a CRT color monitor, or an ordinary color image.

The present invention has been made in view of the above conventional problems, and in a sublimation type thermal transfer color printer, a color image on a CRT created by a computer, a color image on a CRT color monitor, or an ordinary color image is displayed. It is an object of the present invention to provide a color reproduction method for a sublimation type thermal transfer color printer capable of reproducing and printing with high image quality and accurate color.

[Means for Solving the Problems] In order to achieve the above object, the first invention of the present application is such that the ink of the ink donor film is sublimated in accordance with the heat generation amount of the thermal head and is transferred to the image receiving paper. In the color reproduction method of the sublimation-type thermal transfer color printer described above, the color of the image receiving paper is measured in advance with the wavelength λ as a parameter, and based on the reflectance R ₀ (λ) measured by the color measurement, The absorption / scattering characteristic f ₀ (λ) of the image receiving paper is calculated by the formula, and at the same time, f ₀ (λ) = [1-R ₀ (λ)] ² / 2R ₀ (λ) three predetermined types i (i = 1 , 2, 3) of the primary color inks are output to the image receiving paper at a plurality of predetermined gradations Cj to create primary color gradation samples, and the primary color gradation samples are color-measured using the wavelength λ as a parameter. Based on the reflectance Ri (Cj, λ) measured by The absorption / scattering characteristic fi (Cj, λ) is calculated, and fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) −f ₀ (λ) The absorption / scattering characteristic f ₀ (λ), fi (Cj, λ) is stored as basic data for color reproduction, while the target color tristimulus values X ₀₁ , Y ₀₁ , Z _{01 are used for} color reproduction.
And the absorption and scattering characteristics fi (C
j, λ), the following two expressions [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by By numerical calculation, the gradation combination K of the above three types of primary color inks that minimizes the color difference between the tristimulus values Xs, Ys, Zs and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is calculated. There is provided a color reproduction method for a sublimation type thermal transfer color printer, which is characterized in that the target color is calculated and reproduced based on the gradation combination K.

The second invention of the present application is that the ink of the ink donor film is
A color reproduction method of a sublimation type thermal transfer color printer, which sublimates according to the amount of heat generated by a thermal head and is transferred to an image receiving paper, wherein the color of the image receiving paper is measured in advance with a wavelength λ as a parameter. Based on the reflectance R ₀ (λ) measured by colorimetry, the absorption / scattering characteristic f ₀ (λ) of the image receiving paper is calculated by the following formula, and f ₀ (λ) = [1−R ₀ (λ) ] ² / 2R ₀ (λ) Predetermined three kinds of colored primary color inks (i = 1, 2, 3) and black primary color inks (i = 4) are respectively used at a plurality of predetermined gradations Cj. The primary color gradation sample is created by outputting the image on the image receiving paper, and the primary color gradation sample is subjected to colorimetry using the wavelength λ as a parameter, and each reflectance R measured by the colorimetry is measured.
Based on i (Cj, λ), the absorption / scattering characteristic fi (Cj, λ) of each primary color gradation sample is calculated by the following formula, and fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) -f ₀ (λ) The absorption / scattering characteristics f ₀ (λ), fi (Cj, λ) are stored as basic data for color reproduction, while at the time of color reproduction, the tristimulus values of the target color are stored. X ₀₁ , Y ₀₁ , Z ₀₁
And the absorption and scattering characteristics fi (C
Using j, λ) and f ₀ (λ), the following two expressions [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by A first gradation combination for three types of primary color ink except black so that the color difference between the tristimulus values Xs, Ys, Zs and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is minimized. K
₁ and the corresponding first color difference ΔE ₁₁ are calculated by numerical calculation, and the primary color ink having the minimum tone value in the first tone combination K ₁ is replaced with the black primary color ink, and after the replacement, 3
The following two equations are used for the types of inks, using the absorption and scattering characteristics fi (Cj, λ), f ₀ (λ) stored as basic data. [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by A second gradation combination K ₂ for the three types of primary color inks that minimizes the color difference between the tristimulus values Xt, Yt, Zt and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color; The second color difference ΔE ₂₁ corresponding to this is calculated by numerical calculation, and the target color is reproduced based on the gradation combination corresponding to the smaller color difference of the first color difference ΔE ₁₁ and the second color difference ΔE _21. Provided is a color reproduction method for a sublimation type thermal transfer color printer, which is characterized in that printing is performed.

The third invention of the present application is that the ink of the ink donor film is
A color reproduction method of a sublimation type thermal transfer color printer, which sublimates according to the amount of heat generated by a thermal head and is transferred to an image receiving paper, wherein the color of the image receiving paper is measured in advance with a wavelength λ as a parameter. Based on the reflectance R ₀ (λ) measured by colorimetry, the absorption / scattering characteristic f ₀ (λ) of the image receiving paper is calculated by the following equation, and f ₀ (λ) = [1−R ₀ (λ) ] ² / 2R ₀ (λ) Predetermined three types of colored primary color inks (i = 1, 2, 3) and black primary color inks (i = 4) at a plurality of predetermined gradations Cj, respectively. The primary color gradation sample is produced by outputting the image on the image receiving paper, and the primary color gradation sample is subjected to colorimetry using the wavelength λ as a parameter, and each reflectance Ri measured by the colorimetry is measured.
Based on (Cj, λ), the absorption / scattering characteristic fi (Cj, λ) of each primary color gradation sample is calculated by the following equation, and fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) -f ₀ (λ) The absorption / scattering characteristics f ₀ (λ), fi (Cj, λ) are stored as basic data for color reproduction, while at the time of color reproduction, the target color is set with the wavelength λ as a parameter. Is measured, and the predetermined first of the target colors is determined based on the color measurement result.
The tristimulus values X ₀₁ , Y ₀₁ , and Z ₀₁ for the calculated light source (hereinafter referred to as the first light source) are calculated, and the absorption / scattering characteristics fi (C) are stored as basic data.
Using j, λ) and f ₀ (λ), the following two expressions [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by A color difference between the tristimulus values Xs, Ys, Zs of the first light source and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is minimized.
The first gradation combination K ₁ for the three types of primary color ink excluding black and the corresponding first color difference ΔE ₁₁ are calculated by numerical calculation, and the gradation value in the first gradation combination K ₁ is the minimum. Replacing the primary color ink with the black primary color ink,
The following two equations are used for the types of inks, using the absorption and scattering characteristics fi (Cj, λ), f ₀ (λ) stored as basic data. [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by A second gradation combination for the above three types of ink such that the color difference between the tristimulus values Xt, Yt, Zt of the first light source and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is minimized. K ₂ and
The second color difference ΔE ₂₁ corresponding to this is calculated by numerical calculation, and when the first color difference ΔE ₁₁ and the second color difference ΔE ₂₁ for the first light source are not equal, the gradation combination corresponding to the color difference having the smaller value. When the first color difference ΔE ₁₁ and the second color difference ΔE ₂₁ with respect to the first light source are equal while the target color is reproduced and printed, based on the color measurement result obtained by measuring the wavelength λ as a parameter. Tristimulus values X ₀₂ , Y ₀₂ , with respect to a predetermined second calculation light source (hereinafter referred to as a second light source) of the target color
Z ₀₂ is calculated, and tristimulus values X ₀₂ , Y for the second light source are calculated.
₀₂ , Z ₀₂ , the first gradation combination K ₁ for the first light source and the first color difference ΔE ₁₁ are calculated by the same method as the first gradation combination K under the second light source. while calculating the first color difference Delta] E ₁₂ for _1, the second gradation combination K ₂ for the first light source of the second color difference Δ
The second color difference ΔE for the second gradation combination K ₂ under the second light source is calculated in the same manner as when E ₂₁ is calculated.
₂₂ is calculated, and when the first color difference ΔE ₁₂ with respect to the second light source is not equal to the second color difference ΔE ₂₂ , the target color reproduction print based on the gradation combination corresponding to the color difference having the smaller value. While the first color difference ΔE with respect to the second light source
Provided is a color reproduction method for a sublimation type thermal transfer color printer, wherein target color reproduction printing is performed based on the first gradation combination K ₁ when ₁₂ and the second color difference ΔE ₂₂ are equal. To do.

[Operation and Effect of the Invention] According to the first invention of the present application, the spectral reflectance R of the image receiving paper is set using a suitable spectrophotometer and the like with the wavelength λ as a parameter.
₀ (λ) and the spectral reflectance Ri (Cj, Cj, of the primary color printer output (primary color gradation sample) of each primary color ink for a plurality of gradations.
λ) is color-measured, and the following Equation 1, Equation 2 f ₀ (λ) = [1-R ₀ (λ)] ² / 2R ₀ (λ) ... Equation 1 fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cjλ) −f ₀ (λ)
... Equation 2 calculates the absorption / scattering characteristic f ₀ (λ) of the image receiving paper and the absorption / scattering characteristic fi (Cj, λ) of the primary color gradation sample, respectively, and these are storage devices suitable as basic data for color reproduction. Stored in.

Since the printer output of the sublimation type thermal transfer color printer is a subtractive color mixture system, the absorption / scattering characteristic f (λ) of the printer output having an arbitrary gradation combination can be calculated by the following equation 3 using the above basic data. It can be calculated by [ki: prescription gradation of each primary color ink]. That is, the absorption / scattering characteristics f (λ) are the absorption / scattering characteristics of the monochrome printer output for the gradations of the primary color inks in any gradation combination,
It can be expressed as the sum of the absorption and scattering characteristics of the image receiving paper. Then, the following equation 4 R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 ... From the absorption / scattering characteristic f (λ) by the equation 4, a printer using wavelength λ as a parameter The output reflectance R (λ) is calculated, and the tristimulus values Xs, Ys, Zs of the printer output can be calculated based on the reflectance R (λ).

On the other hand, the pixels (target color) of the original image to be color-reproduced are measured using an appropriate colorimeter (for example, a spectrophotometer), and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color are calculated. It is calculated. If the original image is a color image on a CRT screen created by a computer or a color image on a CRT color monitor, the output signal to the CRT is processed to
Tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ are calculated.

Then, generally, from the tristimulus values of the target color and the tristimulus value of the printer output, a color difference ΔE of the printer output with respect to the target color is obtained by using an appropriate color difference formula such as the CIE1976 Lab method.
Can be obtained, but here from Equation 3 and Equation 4,
For example, by using a numerical calculation method such as the Newton method, the gradation combination K that minimizes such color difference of the printer output with respect to the target color is calculated. Therefore, if the printer output is performed according to the gradation combination K, a printer output having a tristimulus value that is substantially equal to the tristimulus value of the target color can be obtained. And 2 with the same tristimulus values
Since the three colors produce the same color perception as human beings, the printer output has almost the same color as the target color, and the color reproduction of the sublimation type thermal transfer color printer can be made highly accurate.

According to the second invention of the present application, first, substantially the same effects as the effects of the first invention of the present application can be obtained. In addition to this, a first gradation combination K ₁ that minimizes the color difference of the printer output with respect to the target color by using the three types of colored primary color inks excluding the black primary color ink, and the first color difference Δ
When E ₁₁ is calculated and the colored primary color ink having the minimum gradation value in the first gradation combination K ₁ is replaced with the black primary color ink, and three kinds of ink after replacement are used. Of the second gradation combination K ₂ that minimizes the color difference of the printer output with respect to the target color, and
The color difference ΔE ₂₁ is calculated. According to the printer output according to the combination K ₁ of only the color primary ink and the combination K ₂ obtained by recalculating by replacing the color primary ink having the minimum gradation value in K ₁ with the black primary color ink. and the printer output, since in general the spectral reflectance are different, the corresponding to the first color difference Delta] E ₁₁ and K ₂ corresponding to K ₁ 2
The color difference ΔE ₂₁ may not match.

Paying attention to such a fact, the first and second color differences ΔE ₁₁ and ΔE
Of the ₂₁ , the printer output is performed according to the gradation combination corresponding to the color difference of the small value.
The color reproduction of the sublimation thermal transfer color printer can be made more accurate.

According to the third invention of the present application, first, substantially the same effect as the effect of the second invention of the present application can be obtained. In addition to this,
The first color difference ΔE with respect to the first gradation combination K _{1 in} the case of using the colored 3 primary color inks excluding the black primary color inks
₁₁ is different from the second color difference ΔE ₂₁ in the second gradation combination K ₂ when the colored primary color ink having the minimum gradation value in the first gradation combination K ₁ is replaced with the black primary color ink. Under the light source, the first color difference ΔE ₁₂ for the first gradation combination K ₁ and the second pigment ΔE ₂₂ for the gradation combination K ₂ are calculated again. If the spectral distribution of the light source is different, the tristimulus values are also different.
Even if the first color difference ΔE ₁₁ and the second color difference ΔE ₂₁ are equal under the light source, the first color difference ΔE ₁₂ and the second color difference ΔE ₂₂ are not equal under the second light source. Therefore, it is possible to determine the superiority or inferiority of the first gradation combination K ₁ and the second gradational combination K _{2 which} could not be distinguished under the first light source. Then, the first and second color differences ΔE ₁₂ under the second light source,
Since the printer output is performed in accordance with the gradation combination of the one having the smaller color difference of ΔE ₂₂ , the color reproduction of the sublimation type thermal transfer color printer can be made more accurate.

[Examples] Examples of the present invention will be specifically described below.

As shown in FIG. 1, the color reproduction printing system RS
Is a color measuring device 7 that measures the color of gradation samples and target colors.
And a sublimation type thermal transfer color printer 1 for performing color printing, a control unit 8 for performing a calculation process of various data such as color measurement data, and a printer control unit 9 for controlling the output of the color printer 1. Unit 11
And a data storage device 12 for storing various basic data.

The colorimetric device 7 is an ordinary spectrophotometer which is generally used, and therefore its detailed description is omitted. As will be described later, the CRT 1 in which the original image is created by the computer
5 is a color image, the color measurement device 7 is not used,
The digital output signal of the CRT 15 is directly input to the arithmetic unit 8 of the control unit 11. When the original image is a color image on the CRT 15 by a color monitor or video, the analog output signal of the CRT 15 is converted into a digital signal through the A / D converter 16, and then the arithmetic unit of the control unit 11 is used. 8 is input.

Since the control unit 11 is a commonly used digital computer (including a microcomputer and a personal computer), detailed description thereof will be omitted.

The color printer 1 is a sublimation type thermal transfer color printer as shown in FIG. 2, but its configuration is as described with reference to FIG.

Hereinafter, a method of creating basic data for color reproduction will be described with reference to the flowchart shown in FIG.

In step A1, the color of the image receiving paper 2 is measured with white color to which no ink has been transferred. A spectrophotometer using a tungsten lamp is used for color measurement, and the wavelength is 400 to 700.
The region of nm is divided into wavelengths of 20 nm, and the reflectance R ₀ (λ) is measured for each wavelength.

In step A2, from the reflectance R ₀ (λ), the following equation 1
1, the absorption and scattering characteristics for each wavelength region (wavelength width 20 nm)
f ₀ (λ) is calculated.

f ₀ (λ) = [1-R ₀ (λ)] ² / 2R ₀ (λ) ... Equation 11 Equation 11 is the so-called Kubelka-Munk theoretical equation K / S = (1-R) ² / 2R (K / S) is a formula expressing the function f ₀ (λ) of the wavelength λ. The absorption / scattering characteristic f ₀ (λ) of the image receiving paper calculated in this way is stored in the data storage device 12 as basic data.

In step A3, the primary color gradation samples of the primary color inks of the ink donor film 3 are output in a plurality of gradations.
Four types of primary color inks of yellow, magenta, cyan, and black are used for the ink donor film 3, and each of these primary color inks is equally divided over the entire gradation range (for example, 256) ( A primary color gradation sample of each primary color ink is created by outputting to the image receiving paper 2 for each gradation Cj obtained (for example, 26 divisions). The subscript i
Indicates the type of primary color ink, i = 1, 2, 3, 4
Represents yellow, magenta, cyan, and black, respectively.

In step A4, colorimetry of the primary color gradation samples of each primary color ink is performed. The colorimetric method is the same as that when the color of the blank image receiving paper 2 is measured in step A1, and the reflectance Ri (Cj, λ) at each wavelength (wavelength width 20 nm) is measured.
(See FIGS. 5 to 8 as examples of measurement results).

In step A5, the following expression 1 is calculated from the reflectance Ri (Cj, λ).
2, the absorption / scattering characteristic fi (Cj, λ) of the primary color gradation sample of each primary color ink is calculated for each wavelength (20 nm).

fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) −f ₀ (λ)
Equation 12 The absorption / scattering characteristic fi (Cj, λ) of each primary color gradation sample calculated in this way is stored in the data storage device 12 as basic data.

The color reproduction method for reproducing and printing the pixels (target color) of the original image by the color printer will be described below with reference to the flowchart shown in FIG.

In step S1, the target color is measured. In the color measurement here, when the original image is an ordinary color image, the color measurement of the target color is performed by the color measurement device (spectrophotometer) for each pixel,
The reflectance for each wavelength region is obtained. The color measurement method in this case is the same as the color measurement performed in step A1 of the flowchart shown in FIG. On the other hand, when the original image is a color image on the CRT 15 created by a computer, the digital output signal of the CRT 15 is directly input to the calculation unit 8 of the control unit 11 to grasp the characteristic of the target color (color measurement). It If the original image is a color image on the CRT 15 by a video or color monitor, C
The analog output signal of the RT is converted into a digital signal by the A / D converter 16 and then input to the calculation unit 8, and the characteristic of the target color is grasped (colorimetry) based on the digital signal.

In step S2, the stimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color are calculated based on the reflectance or the digital signal obtained by the above color measurement by a generally used method. Standard light D ₆₅ was used as the light source (first light source) at this time.

In step S3, a so-called color match calculation is performed in which yellow, cyan, and magenta are used to calculate a gradation combination that produces a target color reproduction printer output using only the inks of the three primary colors of color.

The absorption / scattering characteristics f (λ) of the printer output when inks of three primary colors of yellow, magenta and cyan are used are expressed by the following equation 13 f (λ) = f ₁ (k ₁ , λ) + f ₂ (k ₂ ,, λ ) ＋ f ₃ (k ₃ , λ) ＋ f ₀ (λ)…
... calculated by Equation 13. The subscripts 1, 2 and 3 indicate the respective primary color inks of yellow, magenta and cyan. Formula 13
When the printer output is performed with the gradations of the three primary color inks of yellow, magenta, and cyan as k ₁ , k ₂ , and k ₃ , respectively, the absorption / scattering characteristic f (λ) of the printer output is It is shown that it can be calculated from the absorption / scattering characteristics of the printer output and the absorption / scattering characteristics of the image receiving paper when the gradations k ₁ , k ₂ and k ₃ are individually output. That is, the absorption calculation characteristic f (λ) of the printer output is the gradation ki of each primary color ink and the basic data fi (Cj, λ), f stored in the data storage device 12 without actually performing colorimetry. It can be calculated from ₀ (λ).

Then, the absorption / scattering characteristic f (λ) of the printer output calculated by the equation 13 is the following equation 14 R (λ) = f (λ) + 1- [f ² (λ) + 2f (λ)] ^0.5 ... It can be converted into the reflectance by Expression 14. Equation 14 is the following equation 11 ′ (λ) = [1−R (λ)] ² / 2R (λ) for converting the reflectance into absorption / scattering characteristics. , R (λ).

Therefore, it is possible to calculate the reflectance R (λ) of the printer output of an arbitrary gradation combination by using Expressions 13 and 14, and from this reflection R (λ), the printer R can be calculated by a commonly used method. Output tristimulus values Xs, Ys, Zs can be calculated.

In step S4, based on the color match calculation result in step S3, between the target color and the printer output,
The first gradation combination K ₁ of the chromatic three primary color inks that minimizes the color difference by the CIE1976Lab color difference formula is determined, and the first color difference when the printer output is performed with the first pleasant combination K ₁ ΔE ₁₁ is calculated.

In step S5, in the first gradation combination K ₁ , color match calculation is performed again with two color primary color inks (excluding the color gradation primary color ink having the minimum gradation) having a large gradation value, the black ink and the three primary color inks. Done.

When the three color primary inks of yellow, magenta, and cyan are subtracted from each other by an appropriate amount, it becomes black. Therefore, theoretically, it should be possible to reproduce the color only with the color three primary color inks. Since the black color generated by color mixing and the black color of black ink have different spectral reflectances, a printer with a spectral reflectance closer to the target color is calculated by performing two types of color matching calculations, one with black ink and one without. I'm trying to get the output. The color matching calculation method is the same as the method described in step S3.

In step S6, CIE1 between the target color and the printer output is calculated based on the color match calculation in step S5.
The second gradation combination K ₂ of the three primary color inks including black that minimizes the color difference by the 976Lab color difference formula is determined, and the second gradation combination K ₂ when the printer output is performed with such a second gradation combination K ₂ . The two-color difference ΔE ₂₁ is calculated.

In step S7, the magnitudes of the first color difference ΔE ₁₁ and the second color difference ΔE ₂₁ are compared. If ΔE ₁₁ <ΔE _{21 as} a result of the comparison, the first gradation combination K ₁ with a small color difference is adopted as the final gradation combination of the printer output in step S12, and then the first gradation combination in step S15. K
Printer output is performed according to ₁ .

On the other hand, if ΔE ₁₁ > ΔE _{21 as} a result of the comparison in step S7, the second gradation combination K ₂ having a small color difference is adopted as the final printer output gradation combination in step S14, and then step S15. Then, the printer output is performed according to the second gradation combination K ₂ .

If ΔE ₁₁ = ΔE _{21 as} a result of the comparison in step S7, the superiority or inferiority of the first gradation combination K ₁ and the second gradation combination K ₂ under the first light source (standard light D ₆₅ ). Is not determined, the superiority or inferiority of the first combination K ₁ and the second gradation combination K ₂ is determined under a predetermined second light source in steps S8 to S11. As described above, when the spectral distribution of the light source is different, the tristimulus values are also different. Therefore, even if the first color difference ΔE ₁₁ and the second color difference ΔE ₂₁ are equal under the first light source, they are the same under the second light source. The first color difference ΔE ₁₂ and the second color difference ΔE ₂₂ are not equal with respect to the gradation combination. Therefore, by comparing the color difference under the predetermined second light source, it is possible to determine the superiority or inferiority of the first gradation combination K ₁ and the second gradation combination K ₂ , which could not be distinguished under the first light source.

In step S8, based on the measurement result of step S1, the tristimulus values for the second light source X _02, Y _02, Z ₀₂ is calculated. The method for calculating the tristimulus value is the same as the method for calculating the tristimulus value in step S2.

In step S9, the color difference ΔE ₁₂ with respect to the target color of the printer output in the first gradation combination K ₁ is calculated under the second light source.

In step S10, the color difference ΔE ₂₂ with respect to the target color of the printer output in the second gradation combination K ₂ is calculated under the second light source.

In step S11, the first color difference ΔE _{12 with} respect to the second light source.
And the magnitude of the second color difference ΔE ₂₂ are compared. If ΔE ₁₂ <ΔE _{22 as} a result of this comparison, in step S12, the first gradation combination K ₁ with a small color difference under the second light source is adopted as the final gradation combination of the printer output, and then step S12. In S15, printer output is performed according to the first gradation combination K ₁ .

On the other hand, as a result of the comparison in step S11, ΔE ₁₂ <ΔE ₂₂
If, the second tone combination K ₂ color difference is small in the under the second light source step S14 is employed as the gradation combination of final printer output, according followed by a second tone combinations in Step S15 K ₂ Printer output is performed.

Further, as a result of the comparison in step S11, ΔE ₁₂ = ΔE ₂₂
If so, the first gradation combination K ₁ and the second gradation combination K ₂ have the same color difference both under the first light source and under the second light source, and their superiority or inferiority cannot be determined. The fact that the color difference is the same under the light source is considered that there is substantially no inferiority between the first gradation combination K ₁ and the second gradation combination K ₂ under any light source. So, in this case, step S
In step 13, the first gradation combination K ₁ is adopted as the gradation combination of the final printer output, and then step S
At 15, printer output is performed according to the first gradation combination K ₁ . At this time, the second gradation combination K ₂ may be adopted.

In this embodiment, four types of primary color inks of yellow, magenta, cyan and black are used.
When only the three colored primary color inks of magenta and cyan are used and the black ink is not used, steps S5 to S14 of the flowchart shown in FIG. 4 are omitted and the printer output is performed according to the first gradation combination K _1. I'll do it.

<Experimental Results> Hereinafter, experimental results of actual color reproduction based on the present embodiment will be described.

In this experiment, a sublimation type thermal transfer color printer manufactured by Fuji Xerox Co., Ltd. was used as a color printer, and a spectrophotometer Color-7 manufactured by Kurashiki Spinning Co., Ltd. was used as a color measurement device.

<Results of Colorimetric Measurement of Primary Color Gradation Samples> FIGS. 5 to 8 show that all gradation widths of the respective primary color inks of yellow, magenta, cyan, and black are divided evenly into 26 gradations. The results obtained by measuring the reflectance of the primary color gradation sample created by printing with a printer for each wavelength of 20 nm in the wavelength range of 400 nm to 700 nm are shown.

Further, FIGS. 9 to 12 show the characteristics of the absorption / scattering characteristics of the yellow, magenta, cyan, and black primary color inks with respect to the gradation at the maximum absorption wavelength. 9 to 1
As is clear from FIG. 2, the gradation and the absorption / scattering characteristics do not have a linear relationship. According to the present invention, the absorption / scattering characteristics and the gradation as shown in FIGS. 9 to 12 are stored in the data storage device 12 as the basic data of the functional relationship, and the absorption / scattering characteristics are stored based on the basic data. Since the reflectance is calculated accurately, the accuracy of color match calculation can be improved.

The reason why the gradation and the absorption / scattering characteristics do not have a linear relationship is that the applied voltage to the thermal head of the color printer and the gradation have a non-linear relationship, and the thermal characteristics of the thermal head are not linear. , There is a non-linear relationship between the amount of heat applied to the ink donor film and the amount of ink that sublimes / diffuses, and the dyeing property of the ink to the image receiving layer of the image receiving paper does not have a linear relationship with the gradation. That is the case.

<Color Match Calculation Results> In order to check the effectiveness of the color reproduction method (color match calculation) according to the present invention, the printer input gradation is 0 to 255.
A color matching calculation is performed on all of these printer output samples obtained by giving a combination of integer random numbers of 200 as target colors, and color reproduction is performed by the color printer 1 based on the gradation combinations obtained as a result. The reproduced color and the target color were compared. The printer output sample is used as the target color in order to check the accuracy of color reproduction within the range of colors that can be output by this printer.

The distribution status of the color difference between the target color and the reproduced color thus obtained is shown in Table 1 and FIG. Table 1 and 1
As is clear from Fig. 3, 95% of all samples have a color difference of 8
The average color difference ΔE is 4.17, which is a sufficient accuracy for practical use.

[Brief description of drawings]

FIG. 1 is a system configuration diagram showing the configuration of a color reproduction print system used for implementing the color reproduction method according to the present invention. FIG. 2 is a schematic diagram showing an example of the configuration of a sublimation type thermal transfer color printer. FIG. 3 is a flowchart showing a method of creating / saving basic data in the color reproduction method according to the present invention. FIG. 4 is a flowchart showing a color reproduction method according to the present invention. FIGS. 5 to 8 are graphs showing the characteristics of the reflectance of the primary color gradation samples of the yellow, magenta, cyan, and black primary color inks with respect to the wavelength of light. FIG. 9 to FIG. 12 are diagrams showing the characteristics of the absorption / scattering characteristics in the maximum absorption wavelength region with respect to the gradation of the gradation samples of the respective primary color inks of yellow, magenta, cyan and black. FIG. 13 is a diagram showing a histogram of the measurement results shown in Table 1. RS: color reproduction printing system, 1 ... color printer, 2 ... image receiving paper, 2a ... image receiving layer, 3 ... ink donor film, 3a ... primary color ink layer, 4 ... platen roller, 5 ... thermal Head, 7 ... Color measuring device, 8
...... Calculation unit, 9 ...... Printer control unit, 11 ...... Control unit, 12 ...... Data storage device.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Nobuaki Hata 700-3, Sawa-machi, Kato-gun, Hyogo Prefecture (72) Inventor Yasuhisa Sakurai 3-7, Ryodo-cho, Nishinomiya-shi, Hyogo (56) References Yoshinobu Naya First edition of "Industrial Color Science" (April 25, 1980) Asakura Shoten P.P. 172-182

Claims (3)

[Claims] 1. A color reproduction method for a sublimation type thermal transfer color printer in which ink of an ink donor film is sublimated according to the amount of heat generated by a thermal head and transferred onto an image receiving paper. Color measurement of the image receiving paper is performed using λ as a parameter, and based on the reflectance R ₀ (λ) measured by the color measurement, the absorption / scattering characteristic f ₀ (λ) of the image receiving paper is calculated by the following equation, and f ₀ (λ) = [1−R ₀ (λ)] ² / 2R ₀ (λ) The predetermined three types of primary color inks (i = 1, 2, 3) are respectively supplied to a plurality of predetermined gradations Cj ( (j is a positive integer) is output to the image receiving paper to create a primary color gradation sample, and colorimetry of each primary color gradation sample is performed using the wavelength λ as a parameter, and the reflectance Ri (Cj, λ) measured by this is measured. Based on, the absorption and scattering characteristics fi (Cj, λ) of each primary color gradation sample are calculated by the following equation, and fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) −f ₀ (λ) The absorption / scattering characteristics f ₀ (λ), fi (Cj, λ) are stored as basic data for color reproduction, while at the time of color reproduction, the tristimulus of the target color is stimulated. Value X ₀₁ , Y ₀₁ , Z ₀₁
And the absorption and scattering characteristics fi (C
j [λ] is used to obtain ki [ki: prescription gradation of each primary color ink] by interpolation, and the following two equations are calculated using f ₀ (λ). R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 [ki: Calculated based on the reflectance R (λ) calculated by the prescription gradation of each primary color ink] By numerical calculation, the gradation combination K of the above three types of primary color inks that minimizes the color difference between the tristimulus values Xs, Ys, Zs and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is calculated. A color reproduction method for a sublimation type thermal transfer color printer, characterized in that the target color is calculated and reproduced based on the gradation combination K. 2. A color reproduction method of a sublimation type thermal transfer color printer in which ink of an ink donor film is sublimated according to the amount of heat generated by a thermal head and is transferred onto an image receiving paper. the performs measurement of the image receiving paper color as a parameter, based on the reflectance is measured by surveying color R ₀ (lambda), and calculates the absorption-scattering characteristic f ₀ of the image receiving paper (lambda) according to the following equation, f ₀ (λ) = [1-R ₀ (λ)] ² / 2R ₀ (λ) Colored primary color inks and black primary color inks (i = 4) of three predetermined types i (i = 1, 2, 3) Are respectively output to the image receiving paper at a plurality of predetermined gradations Cj to create primary color gradation samples, the primary color gradation samples are colorimetrically measured using the wavelength λ as a parameter, and measured by the colorimetrical measurement. Each reflectance R
Based on i (Cj, λ), the absorption / scattering characteristic fi (Cj, λ) of each primary color gradation sample is calculated by the following formula, and fi (Cj, λ) = [1-Ri (Cj, λ)] ² / 2Ri (Cj, λ) -f ₀ (λ) The absorption / scattering characteristics f ₀ (λ), fi (Cj, λ) are stored as basic data for color reproduction, while at the time of color reproduction, the tristimulus values of the target color are stored. X ₀₁ , Y ₀₁ , Z ₀₁
And the absorption and scattering characteristics fi (C
Using j, λ) and f ₀ (λ), the following two expressions [Ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] Calculated based on the reflectance R (λ) calculated by ^0.5 A first gradation combination for three types of primary color ink except black so that the color difference between the tristimulus values Xs, Ys, Zs and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is minimized. K
₁ and the corresponding first color difference ΔE ₁₁ are calculated by numerical calculation, and the primary color ink having the minimum tone value in the first tone combination K ₁ is replaced with the black primary color ink, and after the replacement, 3
The following two equations are used for the types of inks, using the absorption and scattering characteristics fi (Cj, λ), f ₀ (λ) stored as basic data. [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by A second gradation combination K ₂ for the three types of primary color inks that minimizes the color difference between the tristimulus values Xt, Yt, Zt and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color; The second color difference ΔE ₂₁ corresponding to this is calculated by numerical calculation, and the target color is reproduced based on the gradation combination corresponding to the smaller color difference of the first color difference ΔE ₁₁ and the second color difference ΔE _21. A color reproduction method for a sublimation type thermal transfer color printer, which is characterized in that printing is performed. 3. A color reproduction method of a sublimation type thermal transfer color printer in which ink of an ink donor film is sublimated according to the amount of heat generated by a thermal head and is transferred onto an image receiving paper. Is used as a parameter to measure the color of the image receiving paper, and based on the reflectance R ₀ (λ) measured by the color measurement, the absorption / scattering characteristic f ₀ (λ) of the image receiving paper is calculated by the following formula, and f ₀ (λ) = [1−R ₀ (λ)] ² / 2R ₀ (λ) There are three types of predetermined color i (i = 1, 2, 3) of colored primary color ink and black primary color ink (i = 4). Are output to the image receiving paper at a plurality of predetermined gradations Cj to create primary color gradation samples, and the primary color gradation samples are color-measured under a predetermined light source using the wavelength λ as a parameter. Based on each reflectance Ri (Cj, λ) measured by colorimetry, the absorption and dispersion of each primary color gradation sample is calculated by the following equation. Characteristics fi (Cj, λ) calculates, fi (Cj, λ) = [1-Ri (Cj, λ)] 2 / 2Ri (Cj, λ) -f 0 (λ) the absorption-scattering characteristic f ₀ (lambda ), fi (Cj, λ) is stored as basic data for color reproduction, and at the time of color reproduction, the target color is measured using the wavelength λ as a parameter, and the first predetermined color of the target color is determined based on the color measurement result.
The tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ for the calculated light source are calculated, and the absorption / scattering characteristics fi (C) are stored as basic data.
Using j, λ) and f ₀ (λ), the following two expressions [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by Three types of primary color ink excluding black so as to minimize the color difference between the tristimulus values Xs, Ys, Zs of the first calculation light source and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color. For the first gradation combination K ₁ and the corresponding first color difference ΔE ₁₁ are calculated by numerical calculation, and the primary color ink having the minimum gradation value in the first gradation combination K ₁ is a black primary color ink. 3 after replacement
The following two equations are used for the types of inks, using the absorption and scattering characteristics fi (Cj, λ), f ₀ (λ) stored as basic data. [ki: prescription gradation of each primary color ink] R (λ) = f (λ) + 1− [f ² (λ) + 2f (λ)] ^0.5 Calculated based on the reflectance R (λ) calculated by The second gradation for the above-mentioned three types of ink such that the color difference between the tristimulus values Xt, Yt, Zt of the first calculation light source and the tristimulus values X ₀₁ , Y ₀₁ , Z ₀₁ of the target color is minimized. Combination K ₂
And a second color difference ΔE ₂₁ corresponding thereto are calculated by numerical calculation, and the first color difference ΔE ₁₁ and the second color difference ΔE with respect to the first calculation light source are calculated.
_{When 21} is not equal, the target color is reproduced and printed based on the gradation combination corresponding to the smaller color difference, while the first color difference ΔE ₁₁ and the second color difference ΔE with respect to the first calculation light source.
_{If 21} and ₂₁ are equal, the tristimulus values X ₀₂ , Y ₀₂ , and Z ₀₂ under the predetermined second calculation light source of the target color are measured based on the colorimetric result obtained by measuring the color with the wavelength λ as a parameter. Based on the tristimulus values X ₀₂ , Y ₀₂ , Z ₀₂ for the second calculation light source, the first gradation combination K for the first calculation light source is calculated.
_{In the} same way as when calculating ₁ and the first color difference ΔE ₁₁ ,
The first color difference ΔE ₁₂ for the first gradation combination K ₁ under the second calculation light source is calculated, while the second gradation combination K ₂ and the second color difference ΔE ₂₁ for the first calculation light source are calculated.
In the same manner as when was calculated, the second color difference ΔE with respect to the second gradation combination K ₂ under the second calculation light source.
₂₂ is calculated, and the first color difference ΔE ₁₂ and the second color difference ΔE with respect to the second calculation light source are calculated.
_{When 22} is not equal, the target color is reproduced and printed based on the gradation combination corresponding to the color difference having the smaller value, while the first color difference ΔE ₁₂ and the second color difference ΔE ₂₂ with respect to the second light source. When the two are equal, the color reproduction method of the sublimation type thermal transfer color printer is characterized in that the target color is reproduced and printed based on the first gradation combination K ₁ .