JPH05176166A - Color reproducing method - Google Patents

Abstract

(57) [Summary] [Structure] Color display means 1 for measuring the tristimulus values of the display colors, means 2 for measuring the spectral reflectance characteristics of the printing colors of the printer, and from these color measurement results the display Y for determining the color reproduction model formula and the color reproduction model formula of the printer and reproducing the display color of the display for the input data from the host computer by the printer,
The calculation unit 4 calculates the M and C ink amounts. [Effect] The Y, M, and C ink amounts for reproducing a color faithful to the display color of the color display can be calculated by a color reproduction model.

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 for a printer, and more particularly to a color reproduction method for reproducing a color faithful to a display color on a color display.

[0002]

2. Description of the Related Art A generally known general color reproduction method is to convert RGB data from a computer into density data so that a difference between input density data and printed density data is minimized. There is a method in which the masking coefficient is put into the masking equation which has been determined and the equation is calculated to generate color correction data so that the density value of the input density data is obtained. For example,
As disclosed in Japanese Patent Application Laid-Open No. 58-178355 or Japanese Patent Application Laid-Open No. 60-220660, for converting an RGB image for displaying on a display into a CMY image when a hard copy is made by a printer. Is 1 as in equation (1)
The following masking equation is used.

[0003]

[Equation 1]

Here, R, G, B, C, M, and Y are variables indicating the density values of the respective primary colors, and a11 to a33.
Is called a primary masking coefficient and is a parameter that influences the conversion. These nine parameters are determined from the ratio of the maximum density values of the three primary colors. For example, some pixels are selected as sampling pixels, and the same sampling pixel has an error between the RGB system density value and the CMY system density value. These nine parameters are set by performing a calculation using the least squares method so as to minimize.
Color adjustment is performed by adjusting nine parameters or by adjusting the gamma correction curve for each of Y, M, and C.

The above is an example of color reproduction using the first-order masking equation. However, RGB second-order terms RR, GG, BB, R
A method for improving color reproducibility by establishing a quadratic masking equation including G, GB, and BR is also known.

[0006]

However, the color reproduction characteristic of the display and the color reproduction characteristic of the printer are greatly different, and the correspondence relationship between the display color of the display and the print color of the printer for the same RGB data is a non-linear mapping relationship. is there. Therefore, in the color reproduction method using the masking equation,
The non-linear mapping relationship cannot be corrected sufficiently and the average color difference is large. Further, although the color adjustment for matching colors may be performed by the gamma correction curve, it is impossible to adjust so as to match the colors as a whole.

An object of the present invention is to establish color reproduction models of a display and a printer, respectively, and match the print color of the display with the print color of the printer with high accuracy by calculation.

[0008]

[Means for Solving the Problems] A structure for achieving the above object comprises means for measuring tristimulus values of display colors of a color display, and means for measuring spectral reflectance characteristics of printing colors of a printer. , For determining the color reproduction model formula of the display and the color reproduction model formula of the printer from these color measurement results and for reproducing the display color of the display for the input data from the host computer by the printer,
And a calculation unit that calculates the amounts of M and C inks.

[0009]

[Function] A display color reproduction model formula is established by the calculation unit from the color measurement result of the means for measuring the tristimulus values of the color display, and the color measurement result of the means for measuring the spectral reflectance characteristics of the printing color of the printer. Create a color reproduction model formula for the printer. The chromaticity value of the display color for the input data from the host computer is calculated, and this is used as the target color.
The Y, M, and C ink amounts of the printer are calculated by a color reproduction model so that the printed result will be the target color displayed on the color display.

The chromaticity value of the color display is such that the maximum values of only R data, the maximum values of only G data, the maximum values of only B data, and the maximum values of all of R, G, B data are displayed on the color display. Chromaticity value (tristimulus value X
RGB-X to obtain tristimulus values XYZ of display colors for R, G, B data from these values.
Contrary to the YZ conversion formula, R, G, B from arbitrary tristimulus values XYZ
The XYZ-RGB conversion formula for obtaining is calculated, the gradation color for any gradation data of R, G, B is displayed on the color display, the tristimulus values XYZ thereof are measured, and XYZ-RGB conversion is performed from these. Calculate R, G, B by the formula,
The γ characteristic value of the display is obtained from these output values for the input gradation data, and the arbitrary input data RGB
Γ conversion is performed using the γ characteristic value, and the tristimulus value XYZ of the display color is obtained by the RGB-XYZ conversion formula.

The color reproduction model of the printer is such that the gradation palette is printed in Y, M, and C single colors, and the absorption and scattering coefficient ratio with respect to the gradation and the wavelength is obtained from the spectral reflectance obtained by measuring the colors. The absorption / scattering coefficient ratio of an arbitrary color mixture is created by adding the absorption / scattering coefficient ratio of each of the Y, M, and C ink amounts by a relative coefficient and the absorption / scattering coefficient ratio of a white background. The relative coefficient, which is a coefficient, measures the spectral reflectances of multiple color mixing palettes to find their absorption / scattering coefficient ratios, and minimizes the difference between these and the absorption / scattering coefficient ratios calculated from the reproduction color prediction formula. Obtain the relative coefficient by the least squares method, determine the reproduction color prediction formula, and use this to obtain the absorption / scattering coefficient ratio of the arbitrary color mixture palette, and from this absorption / scattering coefficient ratio, determine the spectral reflectance of the color mixture palette. The chromaticity value of the reproduced color To.

As described above, the relative coefficient, which is an unknown number, is used to obtain the tristimulus value of the color from the spectral reflectances of a plurality of color mixture palettes, and from this, the Munsell value (hue H, brightness V, vividness) which is the amount of human perception. C) is obtained, and these are set as target colors, and the unknown relative coefficient may be determined by using the Newton method so that the color difference between the Munsell value obtained from the reproduction color prediction formula and the Munsell value of the target color is minimized. ..

The Y, M, and C ink amounts for printing the target color are obtained by performing a convergence calculation such as the Newton method from the appropriate initial values of the Y, M, and C ink amounts using the color reproduction model. Desired.

Note that the basic characteristic data is stored instead of measuring the color each time the type of display or the type of ink or paper of the color printer changes, and the basic characteristic data is stored according to the display, ink or paper used. Select to create a color reproduction model for a display or color printer,
The Y, M, and C ink amounts for printing the target color may be calculated using this.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the color reproduction system includes a chromaticity measuring device 1 that measures a display color of a color display, a printing device 7 that prints a color palette including a gradation palette and a plurality of color mixture palettes, and a printing device. Spectral reflectance measuring device 2 for measuring the spectral reflectance of each of the color palettes, and calculation for processing the data measured by the chromaticity measuring device 1 and the spectral reflectance measuring device 2 and the input data from the host computer. A control unit 3 substantially composed of a section 4, a memory 5 for storing the processing result, and a printing apparatus control section 6 for controlling the output of the printing apparatus 7, and a panel switch 8 for inputting a command value to the control unit 3 and the like. It consists of and.

The chromaticity value measuring device 1 measures tristimulus values of colors. Is color measurement data input online by connecting the control unit 3 and the chromaticity value measuring device 1 with a cable? Alternatively, the input is performed from the panel switch 8 offline. The spectral reflectance measuring device 2 is a commonly used ordinary spectrophotometer, and color measurement data is input online by connecting the control unit 3 and the spectral reflectance measuring device 2 with a cable. Input from the panel switch 8 with. The printing device 7 is a sublimation type thermal transfer color printer, a melting thermal transfer color printer, an optical color printer, a color inkjet printer, or the like, and includes Y, M, C three colors or Y, M, C,
A printing device for performing color printing with four colors of Bk. The control unit 3 is a commonly used digital computer and is configured as a printer built-in controller or an external controller.

FIG. 2 shows the calculation executed by the calculation unit 4 for each block. The color display color reproduction model generation unit 9 generates a color reproduction model of the color display from the color measurement data from the chromaticity measuring device 1. RG
The B-HVC conversion unit 10 uses the color reproduction model from the color display color reproduction model generation unit 9 to convert the input data RGB into the chromaticity values (for example, hue H, lightness V, and saturation C) of the display color. Munsell value that represents color with one value)
Convert to. On the other hand, the color printer color reproduction model generation unit 11 generates a color reproduction model of the color printer from the color measurement data from the spectral reflectance measuring device 2. HVC-YM
The C conversion unit 12 includes a color printer color reproduction model generation unit 1
The color reproduction model from 1 is used to generate YMC data for printing the HVC data that is the target color. These YMC data are output to the printer control unit 6.

FIG. 3 is a flow chart for explaining a method for creating a color reproduction model of a color display. At step z1, only the R data maximum value, the G data maximum value, and the B data maximum value are displayed on the color display.
The colors of the maximum values of all R, G, B data are displayed, and their chromaticity values (called tristimulus values XYZ) are measured. At step z2, an XYZ-RGB conversion formula for obtaining R, G, B from arbitrary tristimulus values XYZ is reversely obtained from the RGB-XYZ conversion formula for obtaining the tristimulus values XYZ of the display color for these R, G, B data. Ask. The method of obtaining these conversion formulas is from p128 to p130 of "Basics of Color Engineering".
It is described in. In step z3, the gradation color for any gradation data of R, G, B is displayed on the color display, and the tristimulus values XYZ thereof are measured. At step z4, R, G, and
B is obtained, and the γ characteristic value of the display is obtained from this output value for the input gradation data.

In the method of converting the input data RGB into the Munsell value, the input data RGB is first gamma-converted by the gamma characteristic value, and the tristimulus value XYZ of the display color is obtained by the RGB-XYZ conversion formula. There is an MTM method as a method for converting from the tristimulus values XYZ, for example, "Journal of Television Society".
(Vol. 43, No. 10) in the article "Color data (R, G, B) → (H, V, C) mathematical conversion method" by Makoto Miyahara. This is done in the following steps.

Non-linear conversion (formula (2)) is performed from X, Y and Z to obtain H1, H2 and H3.

[0021]

[Equation 2]

Using H1 and H2, S1 and S are obtained from the equation (3).
Get 2.

[0023]

[Equation 3]

Using H3 and S1 and S2, H, V and C data are obtained from the equation (4).

[0025]

[Equation 4]

FIG. 4 is a flow chart for explaining a method of creating a color reproduction prediction formula of a color printer (a formula for estimating a chromaticity value of a print result from a combination of Y, M and C gradation data). In step a1, a color palette is printed by the printing device 7 (a target color printing device, for example, a sublimation thermal transfer color printer). This color palette is a combination of the Y, M, and C gradation data shown in Table 1 and is printed in the order of Y, M, and C. Each data is integer data from 0 to 255. This

[0027]

[Table 1]

The basic structure of the color palette of is Y, M,
A gradation palette in which the amount of ink is C single color and is divided into a plurality of stages from 0 to 100%, and a plurality of Y, M, C, R, G and B color mixture palettes in which Y, M and C inks are mixed. Is.

In step a2, the spectral reflectance measuring device 2 measures the spectral reflectances of the white background and the Y, M, and C monochromatic gradation palettes and a plurality of mixed color palettes. The measurement is in the visible light range (38
0nm-780nm or 400nm-700nm)
Is performed in 20 nm steps. Note that the steps are not limited to this step, and other steps such as 5 nm, 10 nm, and 30 nm may be used. The printing device 7 shown in FIGS. 5, 6 and 7.
7 shows spectral reflectance characteristics of Y, M, and C gradation palettes printed by a sublimation-type thermal transfer color printer as an example. At step a3, the absorption and scattering coefficient ratios KSw (λ) and KS of the white background of the paper and the gradation palette are calculated from the spectral reflectances.
y (Ly, λ), KSm (Lm, λ), KSc (Lc,
λ) is calculated using the equations (5) and (6).

[0030]

[Equation 5]

[0031]

[Equation 6]

Here, R (Li, λ) is the reflectance at gradation Li and wavelength λ.

At step a4, the absorption / scattering coefficient ratio for the gradation data of 0 to 255 for each wavelength is obtained and stored in the memory. FIG. 8, FIG. 9, and FIG. 10 are plots for each of Y, M, and C using the wavelength of the absorption / scattering coefficient ratio for gradation data as a parameter. The absorption / scattering coefficient ratio for the measured gradation data other than the gradation palette is obtained by interpolating the measurement result. In step a5, in order to calculate the absorption / scattering coefficient ratio of the color-mixed palette, the reproduction color prediction formula ((Y, M, C) multiplied by the relative coefficient and the absorption / scattering coefficient ratio of the white background are added ( 7) is set.

[0034]

[Equation 7]

Here, kym, kyc, kmy, km
c, kcy, and kcm are relative coefficients, and g (Ly), g
(Lm) and g (Lc) are functions that change depending on the gradation data. This function is a straight line as shown in FIG.
It is a simple function expressed by a downward convex, S-shaped, N-shaped curve,
For example, any one of printing methods such as a sublimation type thermal transfer type, a fusion type thermal transfer type, and an electrophotographic type is selected. In addition,
The function may be changed for each of Y, M, and C. Further, instead of the expression (7), simplified reproduction color prediction expressions (8) and (9) as shown below may be used.

[0036]

[Equation 8]

[0037]

[Equation 9]

Here, the relative coefficients are ky, km and kc, and g (Ly), g (Lm) and g (Lc) are the functions shown in FIG. In this embodiment, the function g () multiplied by the relative coefficient
As an upper convex curve shown in FIG. This curve is obtained experimentally in order to improve the accuracy of the predicted value, and it is necessary to confirm it before obtaining the relative coefficient. Actually, several curves as shown in FIG. 11 are prepared as g (), and the relative coefficient is optimized by the method shown below to minimize the reproduction color prediction error g ().
Select. In step a6, using the result of measuring the color of the color mixture palette, the six relative coefficients are stored in the memory by using the least square method or the Newton method, and the reproduction color prediction formula is determined.

When the ink film and the paper used in the color printer do not change and only the gamma characteristic (density characteristic with respect to gradation data from 0 to 255) changes, the spectral reflectance is not measured again and the spectral reflectance is not measured. The gradation data may be associated with the gamma characteristic when the reflectance is measured and the gamma characteristic after the change so as to have the same density value, and the conversion may be performed so that the ink amount becomes the same.

A procedure for obtaining the six relative coefficients (unknown numbers) in the equation (7) will be described with reference to the flowchart shown in FIG. The spectral reflectance characteristics of a plurality of color mixing palettes are measured (step b1), and the absorption / scattering coefficient ratio is obtained from equations (2) and (3) (step b2). The relative coefficient of the equation (7) is calculated by the least square method so that the difference between the absorption / scattering coefficient ratio and the absorption / scattering coefficient ratio calculated by the equation (7) is minimized (step b).
3). Then, the obtained relative coefficient is stored in the memory (step b4).

Instead of the least square method described above, the Newton method may be used to obtain the relative coefficient so that the color difference is minimized. As for the color difference, there are a Lab color difference formula and a Luv color difference formula defined on Lab and Luv space which are uniform color spaces defined by CIE in 1976, but here, a modified Munsell space (HVC space) defined after that Using the color difference formula above. This color difference formula is called Godlove color difference and is introduced on page 263 of "Color Engineering Handbook". Godl
The color difference between ove is color A (Ha, Va, Ca), color B (Hb,
Vb, Cb) is expressed by the following equation.

[0042]

[Equation 10]

Now, the Newton method for obtaining the relative coefficient will be described with reference to the flowchart of FIG.
In step c1, a target color difference for optimizing the relative coefficient is set. In step c2, Y, M, C, R, G, B
Multiple color mixture palettes (here, YB shown in Table 1)
Spectral reflectance characteristics of k, MBk, CBk, RBk, GBk, and BBk (9 color mixture palettes each) are measured. At step c3, tristimulus values XYZ are obtained from these spectral reflectances. At step c4, V, S1 and S2 on the modified Munsell space are obtained from the tristimulus values XYZ by the MTM method and stored in the memory. Since the Newton method needs to be calculated in the orthogonal coordinate system, VS1S is used instead of HVC.
Let 2 be the target color.

Next, the relative coefficient of the reproduced color prediction formula is obtained.
First, in step c5, the initial values of the relative coefficients kym0, k
Set yc0, kmy0, kmc0, kcy0, kcm0. At step c6, the absorption / scattering coefficient ratio obtained from the initial value and the gradation data is substituted into the equation (7) to obtain the absorption / scattering coefficient ratio. In step c7, the spectral reflectance is calculated from the absorption / scattering coefficient ratio by the following equation,

[0045]

[Equation 11]

At step c8, tristimulus values XYZ are obtained from the spectral reflectance according to the following equation.

[0047]

[Equation 12]

Here, H represents the spectral radiant flux of the reference white light source, and x, y, z represent color matching functions. Step c9
Then, using the MTM method, the three stimulus values XYZ to V, S1, S
Ask for 2. At step c10, the Munsell values V, S1, S2 obtained by the above steps and the target values V, S1,
The color difference from S2 is calculated by equation (10). Step c
At 11, the total sum or average value Ey, Em, Ec, Er, Eg, Eb of the color differences is obtained for each of the Y, M, C, R, G and B systems. In step c12, it is checked whether or not the color difference is less than or equal to the target value color difference. If it is less than the target value, step c
16. If not, go to the next step. The expressions from steps c2 to c11 are put together into functions Jy, Jm,
Jc, Jr, Jg, Jb,

[0049]

[Equation 13]

Can be written as In step c13, the slopes of the functions Jy, Jm, Jc, Jr, Jg, Jb at the initial values are calculated.

[0051]

[Equation 14]

Similarly, qJmi, qJci, qJri, q
Jgi, qJbi (i = kym, kyc, kmy, km
c, kcy, kcm). In step c14,
Solving the following simultaneous equations, the change in relative coefficient dky
m, dkyc, dkmy, dkmc, dkcy, dkc
Find m.

[0053]

[Equation 15]

At step c15, a new relative coefficient is set by the following equation.

[0055]

[Equation 16]

Steps c2 to c15 are repeated, and when the sum of the color differences is below the target value, the convergence calculation is stopped,
Determine the relative coefficient.

FIG. 1 shows the procedure for predicting the color reproduction of arbitrary input data.
This is shown in the flowchart of FIG. In step d1, the absorption / scattering coefficient ratio is calculated for each of the input Y, M, and C gradation data, and in step d2, the absorption / scattering coefficient ratio for the white background and the Y, M, and C gradation data is expressed by equation (7). To obtain the absorption / scattering coefficient ratio for the image data. Step d3
Then, the spectral reflectance of the reproduced color with respect to the input data is obtained by the equation (11). From this spectral reflectance in step d4, 3
The stimulus values XYZ are calculated from the equation (12). This is the chromaticity value of the reproduced color.

When four colors of Y, M, C, and Bk are used, the minimum value of Y, M, and C gradation data is obtained as shown in Japanese Patent Laid-Open No. 2-187375, and the minimum value or the minimum value is 1 or less. The value obtained by multiplying by the coefficient is used as Bk data, and the reproduction color prediction calculation is performed using the value obtained by subtracting this Bk data from the Y, M, and C gradation data and Bk data. The formula for performing the reproduction color prediction is the following formula in which the term relating to the Bk ink is added to the formula (7).

[0059]

[Equation 17]

Fbk is an absorption / scattering coefficient ratio with respect to Bk gradation data, and is obtained by measuring the color of the Bk gradation palette.
The function g () is an upwardly convex curve shown in FIG. There are 12 relative coefficients, which can also be obtained by measuring the colors of a plurality of color mixing palettes as in the case of the three colors.

The above-described color reproduction method can be applied to the Y, M, and even when the spectral reflectance characteristics of the paper or ink used in the printer change.
An optimum color reproduction model can be obtained by printing the C gradation palette and measuring the color. It is also possible to incorporate the spectral reflectance measuring device 2 in the printer and operate it when the spectral reflectance characteristic of the printer changes to adaptively change the color reproduction model. The spectral reflectance measuring device 2 may be outside the printer and may measure the spectral reflectance of the color palette offline.

Now, with respect to the method of estimating the Y, M, C ink amounts for printing the target color by using the formula for obtaining the chromaticity value of the printed color palette from the Y, M, C ink amounts, FIG. This will be described with reference to the flowchart of.

At step y1, initial values Ly0, Lm0,
Determine Lc0 appropriately.

At step y2, Ly0, Lm0, Lc0
KSy (Ly0, λ), KSm (Lm
0, λ) and KSc (Lc0, λ) are represented by K in FIGS. 7, 8 and 9.
It is obtained from the S curve, and these are put in the equation (7) to obtain KSmix (λ) of the color mixture in the initial value.

At step y3, the reflectance for each wavelength is calculated from this KSmix (λ) by the equation (11).

At step y4, from this reflectance, the expression (1
X, Y, Z are obtained by 2).

At step y5, MT from this X, Y, Z
Although H, V, and C are obtained by the M method, since the H, V, and C are cylindrical coordinate systems, it is difficult to use the Newton method. So H,
C is corrected to S1 and S2 of the orthogonal coordinate system.

At step y6, the steps from y2 to y5 are collectively defined as functions F, G and H.

[0069]

[Equation 18]

At step y7, F, G, and
Find the slope of H.

[0071]

[Formula 19]

Similarly, qfm, qfc, qgy, qgm,
Find qgc, qhy, qhm, qhc.

At step y8, target Ht, Vt, Ct
Vt, S1t, S2t is obtained from V, S obtained above
The error between 1 and S2 is calculated.

[0074]

[Equation 20]

At step y9, it is judged whether or not the above error is minimum. If not the minimum, proceed to step y10,
The following simultaneous equations are solved to obtain dLy, dLm, dLc.

[0076]

[Equation 21]

At step y11, an initial value is added to this to obtain Ly, Lm1 and Lc1.

[0078]

[Equation 22]

Steps y2 to y11 are repeated using these Ly1, Lm1, and Lc1 as new initial values.

When the error of the equation (20) becomes sufficiently small, the iterative calculation is terminated, and the obtained Ly, Lm and Lc are the gradations to be obtained. In addition, Ly, L in the repeated calculation
m and Lc are between 0 and 255.

The result of the experiment for predicting the reproduced color according to this embodiment will be described. The printers used in the experiment were a sublimation type thermal transfer color printer and a fusion type thermal transfer color printer. In the sublimation thermal transfer color printer, the gradation expression method is the density gradation method, and the upward convex curve shown in FIG. 11 is used as the function g (). In the fusion type thermal transfer color printer, an 8 × 8 halftone dot density pattern method was used for gradation expression, and an upward convex curve was used as the function g (). The relative coefficient in the reproduction color prediction formula of this method is a sublimation type and is -0.4, -0.5, 0.3, -0.2, 0.4, 0.4.
4 and the melting type, -0.2, -0.3, 0.1, -0.
It is 2, 0.3 and 0.3. Using this reproduction color prediction formula,
As a result of predicting the reproduced color for 512 mixed color palettes created by combining gradation data obtained by dividing Y, M, and C into eight equal parts, and evaluating the color difference of Godlove from the measured value,
The average color difference is 1.2 for the sublimation type and 1.4 for the fusion type, which is predicted with high accuracy. In other printing methods as well, highly accurate prediction can be expected by optimizing the relative coefficient.

According to the present embodiment, the color reproduction model of the display can be constructed from the chromaticity values of the primary colors R, G and B, the chromaticity value of white and the gamma characteristic. Further, the color reproduction model of the color printer can be constructed from the spectral reflectances of the Y, M, and C ink monochromatic gradation palettes and the spectral reflectances of several mixed color palettes and the spectral reflectance of the white background of the paper. Then, the target color is calculated and Y, M, and
The C ink amount can be estimated.

As another color reproduction method, chromaticity values and spectral reflectance data are prepared in advance for each type of display, type of Y, M, C ink, and type of paper and stored in memory.
Then, the chromaticity value and spectral reflectance data corresponding to the display, ink, and paper to be used are selected by a command from the panel switch or host computer, and a color reproduction model is constructed. Then, the target color is obtained by calculation, and Y, M, and C that are the target colors are obtained by calculation from the color reproduction model of the color printer.
Estimate the amount of ink.

According to the present embodiment, it is not necessary to carry out the measurement work every time the display or the like is changed, and the optimum color reproduction model can be easily constructed and high-precision color reproduction can be realized.

[0085]

According to the present invention, there is an effect that highly accurate color reproduction can be performed by using a color reproduction model.

[Brief description of drawings]

FIG. 1 is a block diagram of a color printer system used for implementing a color reproduction method according to the present invention.

FIG. 2 is a block diagram of calculation contents of a calculation unit.

FIG. 3 is a flowchart for creating a color reproduction model formula of a color display.

FIG. 4 is a flowchart for explaining a method for creating a reproduction color prediction formula for a printer.

FIG. 5: Y, M, in a sublimation thermal transfer color printer
FIG. 6 is a spectral reflectance characteristic diagram of a grayscale palette of C single color.

FIG. 6 shows Y, M, and Y in a sublimation type thermal transfer color printer.
FIG. 6 is a spectral reflectance characteristic diagram of a grayscale palette of C single color.

FIG. 7: Y, M, in a sublimation type thermal transfer color printer
FIG. 6 is a spectral reflectance characteristic diagram of a grayscale palette of C single color.

FIG. 8 is an explanatory diagram showing the wavelength of the characteristic of absorption / scattering coefficient ratio for Y, M, and C gradation data as a parameter.

FIG. 9 is an explanatory diagram showing the wavelength of the characteristic of absorption / scattering coefficient ratio for Y, M, and C gradation data as a parameter.

FIG. 10 is an explanatory diagram showing wavelengths of characteristics of absorption / scattering coefficient ratio for Y, M, and C gradation data as parameters.

FIG. 11 is an explanatory diagram showing a form of a function that multiplies a relative coefficient.

FIG. 12 is a flowchart illustrating a method of optimizing a relative coefficient of a reproduction color prediction formula by a least square method.

FIG. 13 is a flowchart illustrating a method of optimizing the relative coefficient of the reproduction color prediction formula by the Newton method.

FIG. 14 is an explanatory diagram of a procedure of predicting a reproduced color from Y, M, and C gradation data.

FIG. 15 is an explanatory diagram of a procedure for estimating Y, M, and C ink amounts for printing a target color.

[Explanation of symbols]

1 ... Chromaticity measuring device, 2 ... Spectral reflectance measuring device, 3 ... Control unit, 4 ... Calculation part, 5 ... Memory, 6 ... Printing device control part, 7 ... Printing device, 8 ... Panel switch.

Claims (1)

[Claims] 1. A method for reproducing the color of a color image displayed on a color display with a color printer,
A memory for storing chromaticity values and γ characteristic values when the color data R (red), G (green), B (blue), W (white) are displayed on the color display, for each type of the color display used. Stored in and select a set of characteristic values according to the color display used,
Using them, a color reproduction model of the color display is created and the chromaticity value of the screen is calculated for arbitrary color data. On the other hand, in a color printer, Y (yellow) and M (magenta) for standard density characteristics are calculated. , C (cyan) ink gradation palette absorption / scattering coefficient ratios are stored in memory for each ink type, and white paper absorption / scattering coefficient ratios are stored in memory for each paper type, and are used in a color printer. A color reproduction model is created by selecting from them according to the ink and the paper, and the Y, M, and C ink amounts for printing the color displayed on the color display are calculated by the Newton method convergence calculation and printed. A color reproduction method characterized by the above.