JP2000050090A - Estimating method for measured color value on color batch, generating method for device profile using the same and picture processor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To estimate a highly precise measured color value through the use of a few batches by obtaining the inversion conversion relation of a sample value against the measured color value from the conversion relation of a sample value and the measured color value of the color batch based on the sample value and setting the sample value decided from the inversion conversion relation against the prescribed measured color value to be the input of a nonlinear model system. SOLUTION: A non-linear model parameter deciding means 28 decides non-linear model parameter for estimating a measured color value from the measured color value of an output batch 14. A measured color value estimating means 29 estimates the measured color value by using the obtained parameter. An LUT (CMY → XYZ) generation means 65 stores the result of the measured color value estimating means 29 in LUT. A non-linear masking parameter deciding means 66 decides the parameter of nonlinear masking, which is the inversion conversion of the obtained linear interpolation value of LUT, by using it. A device output estimating means 67 estimates a printer output value by using obtained parameter.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for estimating a measured value relating to a color patch, a method for creating a device profile using the method, and an image processing apparatus, and more particularly to a method for color matching between various input / output devices. It relates to estimation of colorimetric values.

[0002]

2. Description of the Related Art Color matching is performed between a plurality of color input / output devices such as input devices such as scanners and digital cameras and output devices such as monitors and printers by using profiles which are data representing color conversion characteristics. ing.

For example, creation of an output profile for a printer is performed by the following method. First, a predetermined number of color patches of those colors are output by a printer based on RGB values (or CMYK values) which are color signals of a color space dependent on the printer, and the color patches are measured by measuring the color patches. XYZ values (or Lab values) which are color signals in a color space not to be obtained,
The relationship between the R, G, B values and the X, Y, Z values is determined. Next, by utilizing the relationship between the RGB values and the XYZ values obtained in this way, a masking coefficient is determined by an iterative method or the like, or the mapping from the RGB values to the XYZ values is determined. The relationship from the XYZ value (or Lab value), which is the relationship of the inverse conversion, to the RGB value (or CMYK value) can be obtained as color correction data.

In the above-described profile creation processing, when the relationship from the RGB values (or CMYK values) to the XYZ values (or Lab values) is obtained, the accuracy increases as the number of samples such as patches increases. It is not realistic to print out all the colors in the RGB color space as samples. Therefore, RGB value (or CMYK value)
To get the relationship from to the XYZ value (or Lab value)
Conventionally, the following method has been used.

A method of measuring an XYZ value by a Neugebauer equation using a basic color such as RGB or the like as a stimulus value.

[0006] The color patches having the same distance in the color space are measured to determine the relationship between the RGB values and the XYZ values,
A method of estimating colorimetric values by linear interpolation for intermediate colors between these color patches to obtain a similar relationship.

[0007] Similar to the above method, but a method of performing curve interpolation on the relationship obtained by colorimetrically measuring patches to further improve accuracy.

[0008]

The above method is based on C (Cya)
n), M (Magenta), Y (Yellow), R (Red), G (Gree
n), B (Blue), K (Black) and the color W (W
XYZ values and CMY as stimulus values for 8 points
This is a method of estimating an XYZ value with respect to an arbitrary CMY value by a Neugebauer equation using each area ratio of a basic color such as. This method is equivalent to three-dimensional interpolation using eight basic colors as vertices. However, since the actual color conversion characteristics are more complicated, there is a problem that accuracy is generally poor.

The methods (1) and (2) both use patches at regular intervals. As the values of the color patches, FIG.
As shown in FIG.
The coordinate values of grid points at equal intervals in the GB space are selected (in the example of FIG. 5, 5 × 5 × 5). In this case, generally, if the number of grid points is increased, the accuracy of estimating the colorimetric value is improved, but the number of times of the colorimetric measurement is also increased, so that the time required for the measurement is also increased. Although the distribution of color patches is uniform in a device-dependent coordinate system such as RGB or CMYK, the color-measured XYZ
When values are mapped to a uniform color space such as Lab values, the distribution usually has a bias. Therefore, even if the number of grid points is increased, a portion where the effect of improving the accuracy is obtained and a portion where the effect is not obtained are correspondingly obtained. And the efficiency of the estimation process may be reduced.

In the method, when estimating a colorimetric value of a point between patches, an XYZ value (or Lab value) obtained by the colorimetric measurement is referred to a look-up table (hereinafter simply referred to as "L").
UT ”) at the corresponding grid point, and the RGB value or CMYK value in the middle of the patch is subjected to linear interpolation such as eight-point interpolation or four-point interpolation using eight or four neighboring points. This is a method of estimating XYZ values. Such linear interpolation generally lacks smoothness in the interpolation result,
Since the error from the actual characteristics is relatively large, the estimation result by this method is used for the AtoBOTag of the ICC profile.
When the print result is stored on a monitor, there is a problem that a large amount of noise is included when a print result is previewed on a monitor. Further, when an input value such as an RGB value indicates the same coordinates as a grid point, the output value becomes a colorimetric value itself, and there is a problem that a colorimetric error at the time of colorimetric measurement is directly reflected in the output.

[0011] In contrast to the above method, the method is a method of performing curve interpolation using three or more points in the vicinity of an RGB value or a CMYK value using an LUT in the same manner as in the method (for example, 63-254888), and there is a high possibility that a better result can be obtained than linear interpolation. However, since attention is paid only to points in the vicinity of the input value, there is a problem that the colorimetric error at the time of colorimetric measurement is relatively large for each of these nearby points and cannot be alleviated.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and an object of the present invention is to enable more accurate estimation of a colorimetric value using a small number of patches. An object of the present invention is to provide a method for estimating a colorimetric value, a method for creating a device profile using the method, and an image processing apparatus.

[0013]

According to the present invention, there is provided:
From the conversion relationship between a sample value which is a value of a color space dependent on the printing device and a colorimetric value of a color patch printed by the printing device based on the sample value, a colorimetric value with respect to another sample value in the printing device Preparing a non-linear model expression representing the input / output characteristics of a printing apparatus that inputs a value of the color space and outputs a colorimetric value corresponding to the value, and prepares a sample value and the sample value. Calculating the conversion relationship with the colorimetric value of the color patch based on the value, obtaining the inverse conversion relationship of the sample value with respect to the colorimetric value from the conversion relationship, and determining the sample value determined from the inverse conversion relationship with respect to a predetermined colorimetric value As the input of the nonlinear model formula, a colorimetric value is obtained as the output, and the color difference is smaller than a predetermined value according to the color difference between the obtained colorimetric value and the predetermined colorimetric value. When By adjusting the coefficient of so that the non-linear model expression to determine the non-linear model expression to estimate the colorimetric values by non-linear model expression and the determined, characterized in that comprising the step.

Further, from the conversion relationship between a sample value which is a value of a color space depending on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value, the device / device of the printing apparatus is determined. A method of creating a profile, comprising preparing a non-linear model expression representing input / output characteristics of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value, and inputting the colorimetric value. Preparing a color correction formula that outputs the value of the color space that is input to the nonlinear model formula, obtains the conversion relationship between a sample value and a colorimetric value of a color patch based on the sample value, and performs the conversion. From the relationship, an inverse conversion relationship of the sample value with respect to the colorimetric value is obtained, and a sample value determined from the inverse conversion relationship with respect to a predetermined colorimetric value is used as an input of the nonlinear model formula, thereby obtaining the output. The colorimetric value is obtained, and according to the color difference between the obtained colorimetric value and the predetermined colorimetric value, the coefficient of the nonlinear model formula is adjusted so that the color difference becomes smaller than a predetermined value. The nonlinear model formula is determined, a predetermined colorimetric value is input to the correction formula, and the value of the color space obtained by the input is input to the nonlinear model formula to determine a colorimetric value. According to the color difference between the obtained colorimetric value and the predetermined colorimetric value,
Adjusting a coefficient of the color correction formula so that the color difference becomes smaller than a predetermined value to determine the color correction formula.

Further, from the conversion relationship between a sample value which is a value of a color space depending on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value, another sample in the printing apparatus is used. An image processing apparatus for estimating a colorimetric value for a value, wherein a non-linear model formula representing input / output characteristics of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value is provided. Calculating the conversion relationship between the sample value and the colorimetric value of the color patch based on the sample value; obtaining the inverse conversion relationship of the sample value with respect to the colorimetric value from the conversion relationship; By using a sample value determined from the inverse conversion relationship as an input of the nonlinear model formula, a colorimetric value is obtained as the output, and a color difference between the obtained colorimetric value and the predetermined colorimetric value is calculated. Adjusting the coefficients of the nonlinear model formula so that the color difference is smaller than a predetermined value, determining the nonlinear model formula, and estimating a colorimetric value by the determined nonlinear model formula. It is characterized by doing.

Further, from the conversion relationship between a sample value which is a value of a color space depending on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value, the device / device of the printing apparatus is determined. An image processing apparatus for creating a profile, comprising: preparing a non-linear model formula representing an input / output characteristic of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value; Prepare a color correction formula that outputs the value of the color space that is input to the nonlinear model formula as an input, and obtains the conversion relationship between a sample value and a colorimetric value of a color patch based on the sample value. From the conversion relationship, obtain the inverse conversion relationship of the sample value to the colorimetric value, by using a sample value determined from the inverse conversion relationship for a predetermined colorimetric value as the input of the nonlinear model formula, A colorimetric value is obtained as the output, and according to a color difference between the obtained colorimetric value and the predetermined colorimetric value, a coefficient of the nonlinear model formula is adjusted so that the color difference becomes smaller than a predetermined value. The nonlinear model formula is determined, a predetermined colorimetric value is input to the correction formula, and the value of the color space obtained by the input is input to the nonlinear model formula to determine a colorimetric value. According to a color difference between the obtained colorimetric value and the predetermined colorimetric value, a process of adjusting the coefficient of the color correction expression so that the color difference is smaller than a predetermined value and determining the color correction expression is performed. It is characterized by doing.

According to the above arrangement, a predetermined number of patches are printed by the printing device, and a nonlinear model expression representing the input / output characteristics of the printing device is determined based on the colorimetric values obtained from the patches. Since the other colorimetric values can be estimated by the nonlinear model formula, the colorimetric values are estimated with relatively high accuracy even if the number of the predetermined number of patches to be actually output is not large. In addition, the color correction data can be created using this.

[0018]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) FIG. 1 is a conceptual diagram of an image processing system according to an embodiment of the present invention, and FIG.
FIG. 2 is a block diagram showing a configuration for estimating a colorimetric value in this system.

In FIG. 1, a color patch image 11 to be printed by a printer 13 as an output device is shown.
Is generated when an operator inputs sample values in the host computer 12, and the data is output to the printer 13. A color patch 14 is printed out by the printer 13, and the color patch 14 is measured by a colorimeter (not shown) to obtain colorimetric data.

The system shown in FIG. 1 connects a scanner or digital camera as an input device, a monitor as a output device, and a copying machine in addition to the above-described devices. It goes without saying that normal printing is performed in addition to print output.

The configuration shown in FIG. 2 includes a host computer 12, a printer 13, and a colorimeter. More specifically, it is configured by CPU processing in the host computer 12 and memories such as ROM and RAM, input means such as a keyboard, CPU processing in the printer 13, a memory, and a print mechanism such as a print head. .

In FIG. 2, reference numeral 21 denotes a sample value input unit for inputting sample values in the color space of the printer 13 for generating a color patch, and 22 denotes a plurality of sample values input by the sample value input unit 21 respectively. The color patch image generating means 24 for generating the corresponding patch image data 11 is a color patch reading means provided with a memory and for reading the generated color patch image data 11. It is comprised in.

Reference numeral 25 denotes a color patch image printing unit that prints out the color patches 14 based on the color patch image data 11 output from the color patch image reading unit. The printed color patches 14 are measured by the color patch color measuring means 27.

Reference numeral 28 denotes a non-linear model / parameter determining means for determining parameters of a non-linear printer model from a sample value in a color space of a printer as an output device and its colorimetric values, as described later. Non-linear model
Colorimetric value estimating means for estimating a colorimetric value for an arbitrary sample value from the non-linear model and the parameters obtained by the parameter determining means 28, and these means are constituted by the host computer 12.

More specifically, the processing in the above configuration will be described. When sample values in a printer color space such as RGB or CMYK are selected, these sample values are stored in a uniform color space such as a Lab color space. When mapped, a plurality of sample values are selected so as to be substantially equal in this space, and input by the sample value input means 21. Specifically, individual sample values may be set by an operator's operation of a keyboard or the like, or may be set by selecting from predetermined sample values. When it is difficult to select a uniform sample in the uniform color space, sample values may be equally spaced in the output device. Next, the color patch image generation unit 22
Are output to the printer 13 to be temporarily fetched into the memory by the color patch reading means 24. And the printer 13
Color patch image printing means 25 constituted by
Thus, the color patch image 26 is printed out.

The output color patch image 26 is measured by a color patch colorimeter 27 such as a colorimeter, and a colorimetric value in a device-independent color space such as XYZ or Lab is obtained for each patch. Thus, the sample values such as RGB and CMYK in the color patch are associated with the colorimetric values such as XYZ and Lab, and the parameters of the non-linear model are determined by the non-linear model / parameter determining means 28 based on this.

The non-linear model used in the non-linear model / parameter determining means 28 differs depending on the type of the color space of the output device and the like. A photographic printer will be described as an example. Of course, the present invention is not limited to the printer system. For example, the system uses thermal energy to generate bubbles in the ink, and ejects each of the YMCK inks by the pressure of the bubbles. You may.

The non-linear model of the printer of this embodiment is
For example, the following 3 × 20 coefficient matrix that receives CMY values as inputs and outputs XYZ values, and C, M, Y
Can be modeled by a non-linear matrix consisting of the product of the matrix with a 1 × 20 matrix containing up to third-order terms.

[0030]

(Equation 1)

The Neugebauer equation is, for example, the following equation for estimating the value of XYZ with respect to the CMY value from each area ratio of CMY.

[0032]

(Equation 2)

Here, (Xc, Yc, Zc), (Xm,
Ym, Zm), (Xy, Yy, Zy), (Xr, Yr,
Zr), (Xg, Yg, Zg), (Xb, Yb, Z
b), (Xk, Yk, Zk), (Xw, Yw, Zw) indicate XYZ values for eight basic color points.

When this equation is expressed by a functional expression, the following is obtained.

[0035]

X = f (CMY, CM, MY, YC, C, M, Y) (3) Y = g (CMY, CM, MY, YC, C, M, Y) (4) Z = h (CMY, CM, MY, YC, C, M, Y) (5) When Expressions (3), (4), and (5) are compared with Expression (1), it is expressed by Expression (1). Nonug model of printer is Neug
It can be seen that it includes the ebauer equation. That is, C
Assuming that the XYZ value for the MY value can be actually estimated by the Neugebauer equation, the XYZ value for any CMY value is estimated by determining the model of the 3 × 20 matrix in the non-linear matrix of equation (1) and determining the model. You can do it.

As described above, when the model of the nonlinear matrix is determined by the nonlinear model / parameter determining means 28 and the model is determined, the arbitrary C
By inputting the MY value, an XYZ value corresponding to the MY value can be obtained.

The coefficient (parameter) determination processing by the above-described nonlinear model / parameter determination means 28 will be described in detail with reference to FIGS.

FIG. 3 is a diagram conceptually showing this determination processing. In FIG. 3, reference numeral 31 denotes the sample value input means 21.
This is a table corresponding to the inverse conversion of the relationship 30 between the sample values input by (see FIG. 2) and the patches based on the sample values and the colorimetric values actually obtained by the colorimetric means 27. Dependent color CMY
This is a table that stores the relationship to. Reference numeral 32 designates an output device-dependent color CMY as an input and a device-independent color XaYAZ
This is the non-linear printer model shown in the above equation (1) that outputs a. 33 is an actual colorimetric value (target value) (X
tYtZt) by a conversion 34 and a Lab value obtained by conversion with a colorimetric value (estimated value) estimated by a non-linear model.
The color difference ΔEab between the XaYaZa and the Lab value obtained by the conversion 35 is obtained, and the parameter (coefficient) a _ij (i = 1... 3, j) of the nonlinear model is determined based on the magnitude of the color difference.
= 1... 20).

FIG. 4 is a flowchart showing the procedure of the parameter determination process.

In this process, first, in step S401, the nonlinear model 32 is initialized.

In the initialization, for example, the following values are assigned as initial values of coefficients in the nonlinear printer model according to the above equation (1).

[0042]

(A11, a21, a31) = (Xc, Yc, Zc) (a12, a22, a32) = (Xm, Ym, Zm) (a13, a23, a33) = (Xy, Yy, Zy) ( a121, a221, a321) = (Xw, Yw, Zw) where (Xc, Yc, Zc), (Xm, Ym, Z
m), (Xy, Yy, Zy) and (Xw, Yw, Zw) are XYZ values for Cyan, Magenta, Yellow, and White, respectively, and coefficients not shown are all zero.

Next, in step S402, the relation table 30 from the CMY values obtained by the color measurement to the XYZ values is read. In step S403, the inverse conversion of the obtained relation table 30 is obtained, and the XtYtZt value is converted to the CMY value. The relation table 31 is created. The method of obtaining this inverse transformation is simply a method of C, so that the correspondence between CMY and XYZ is not broken.
MY and XYZ may be interchanged. Thereby, XYZ
Since a sample value in the CMY color space can be obtained based on the value, the XYZ value can be used as a target value. Next, step S404
Then, a plurality of target values X obtained as described above
tYtZt is input in a predetermined order. As a result, it is determined whether or not the parameters are appropriate for each target, as described below, and finally a parameter appropriately representing the printer model can be obtained.

That is, first, in step S405, the CMY value corresponding to the target value (XtYtZt) is obtained from the XtYtZt → CMY relation table 31 obtained in step S403, and in step S406, the CMY value thus obtained is 31 to obtain an estimated value (XaYaZa). That is, step S401
The estimated values (XaYaZa) are obtained by substituting the respective values of the CMY into the equation (1) initialized by (1). In step S407, the XYZ values (estimated values) obtained as described above are converted to La by the conversion 35 in order to evaluate the color difference.
Convert to coordinates in space b. On the other hand, in step S408, the value of XtYtZt input as the target value is converted into coordinates in the Lab space by the conversion 34 in order to evaluate the color difference.

In step S409, the Lab value obtained from the target value (XtYtZt) and the estimated value (X
The color difference ΔEab from the Lab value obtained from aYaZa) is obtained, and it is determined in step S413 whether the color difference has been calculated for all target values. If the color difference has not been calculated for all target values, step S4
In step 14, the input order of the target values is shifted, and
It returns to the process of 04. On the other hand, if it is determined that color differences have been obtained for all target values, step S410
Then, these color differences are evaluated, and the accuracy of the obtained printer model is determined.

That is, in step S410, for example, it is determined whether the average of the obtained color differences for all target values is smaller than a predetermined threshold value. If the average of the color differences is smaller than the predetermined threshold, it is determined that a high-precision printer model has been obtained, and the process is terminated. On the other hand, if the average of the color differences is larger than the predetermined threshold, the above-described optimization processing is repeated.

It should be noted that the upper limit of the number of times the above-described optimization processing is repeated may be determined. If the average of the color difference does not fall below the predetermined threshold even after the number of times of the repetition reaches the upper limit, an error is notified to the user. Furthermore, the average of the final color differences is reported, and the user is requested to make a judgment.

When the optimization process is repeated, the printer model is changed based on the change in the average of the previous color difference and the average of the current color difference. For example, when the average of the color differences has become larger than the previous time, the change amount of the printer model is reduced. As described above, the amount of change in the printer model is adjusted so that the optimization process converges.

In the above description, CMY is an example of an output device color space, which is RGB or CMYK.
Of course, it may be. Similarly, XYZ is
An example of a device-independent color space, which is Lab or L
uv or the like, and the color difference is ΔEab
Of course, the present invention is not limited to this.

As described above, when the CMY values for obtaining the target values as the colorimetric values are obtained and the same CMY values are also input to the non-linear printer model, the output is the same (close) to the actual system. (Target value). If the values are the same (close), the nonlinear model can be considered to be almost the same as the actual system. If the values are different, the parameters of the nonlinear model are corrected and the same is repeated again. That is, a target value is input to a system in which a known inverse conversion system (inverse colorimetric conversion 31) and an unknown forward conversion system (nonlinear model 32) are combined, and whether the output matches the target value ( Neighborhood). Here, in order to evaluate how close the estimated value (output) is to the target value, the present embodiment uses the color difference.
The evaluation based on the color difference can guarantee that the visual approximation error of the estimation result is small. If the degree of fine adjustment of the parameter is changed according to the difference in the color difference, the parameter can be quickly converged.

When an equally spaced sample value in the printer color space is selected as an input by the sample value input means 21, the distribution of the XYZ values with respect to the sample value is generally not uniform in the Lab color space but biased. become. As a result, when optimization is performed using such XYZ values as target values, the estimation accuracy for sample values corresponding to regions that are densely distributed in the Lab space is high, but the distribution is sparsely distributed in the Lab space. The accuracy of sample estimation corresponding to the region becomes low. As a method for solving this problem, it is conceivable to increase the number of sample values corresponding to a region that is sparsely distributed in the Lab space, or add a point near a CMY value with low conversion accuracy as a sample value. .

Further, besides the method of increasing the number of samples, when determining the degree of fine adjustment of the parameter, L
A method may be considered in which the weight (contribution rate) of the evaluation result of the target values having a sparse distribution in the ab space is made heavier than the target values having a dense distribution.

By adjusting the sample distribution and the weighting for each target value, the overall accuracy can be improved.

(Embodiment 2) In this embodiment, when the nonlinear model described in the first embodiment is determined, and the estimation result based on the model is used, this is stored in the LUT and the colorimetric result is stored. At high speed.

The more complicated the nonlinear model described above, the longer the calculation time for estimation by the model becomes. For this reason, in the present embodiment, the estimation result of the colorimetric value can be speeded up by storing the estimation result of the nonlinear model in the LUT. This LUT is generated by storing the result calculated based on the obtained nonlinear model at the lattice point of the LUT.

Such an LUT can be used, for example, when previewing an image created on a host computer on a monitor before printing out.

Here, the input of the LUT is RGB or CMY.
Is a three-dimensional LUT, and CMYK is a four-dimensional LUT
It depends on the number of components of the output device such as UT.

As shown in FIG. 5A, in the method of storing colorimetric values in the LUT and performing linear interpolation without using the method of the present invention, the number of grids when the colorimetric values are stored Even if the number of grids is increased, the accuracy does not change because it only compensates for the grid increased by linear interpolation. For example, when the output device color space is sampled by 9 × 9 × 9 sample values, and the colorimetric values are directly stored in a 9 × 9 × 9 LUT to obtain an arbitrary colorimetric value, the output device color space The result of the linear interpolation for the 33 × 33 × 33 sample values above is again converted to a 33 × 33 × 33 LUT
, And the accuracy is the same as when a 9 × 9 × 9 LUT is used, even if linear interpolation is performed using a 33 × 33 × 33 LUT.

On the other hand, in the model approximation using the non-linear model parameters to which the present invention is applied, since the accuracy is determined not by the number of grids but by the parameters, the accuracy of the model is directly reflected on the grid values, and is shown in FIG. As described above, if an LUT having a large number of grids is used, a more accurate interpolation result can be obtained.

(Embodiment 3) The present embodiment relates to an apparatus for creating a device profile by using a result of estimation of a measured value by a nonlinear model.

CMY → XYZ obtained as described above
By using the non-linear printer model and the parameters, the parameters of the non-linear masking which is an unknown inverse transformation system (XYZ → CMY) can be determined, and a printer profile can be created.

FIG. 6 is a block diagram showing a configuration for creating a profile. In FIG. 6, the same elements as those shown in FIG. 2 are denoted by the same reference numerals.

In FIG. 6, reference numeral 27 denotes a color patch colorimetric means for reading a colorimetric value for the output patch 14;
Reference numeral 8 denotes a non-linear model parameter determining unit for determining a non-linear model parameter for estimating a colorimetric value from the read colorimetric values, and 29 denotes a non-linear model parameter determining unit 28. This is a colorimetric value estimating means for estimating a colorimetric value using parameters, and these are the same as the elements described in the first embodiment.

Reference numeral 65 denotes an LUT for the result of the colorimetric value estimating means 29.
LUT (CMY → XYZ) creating means for storing in
Reference numeral 66 denotes a non-linear masking parameter determining unit for determining a non-linear masking parameter, which is an inverse transform thereof, using the linear interpolation value of the LUT obtained by the LUT (CMY → XYZ) generating unit 65. This will be described in detail with reference to FIGS.

Reference numeral 67 denotes a device output value estimating unit for estimating a printer output value using the parameters obtained by the non-linear masking parameter determining unit.
A color space compression means for performing color space compression in accordance with the color reproduction range obtained from the colorimetric values of the output patch 14;
Reference numeral 9 denotes XY which samples the XYZ space at equal intervals with respect to the color space compression performed by the color space compression creating means 68.
The Z value is input, and the output is used as the device output value estimation means 67
XYZ including color space compression by inputting
LUT for creating LUT for CMY conversion (XYZ → CM
Y) It is a creation means.

610 is an LUT (CMY → XY)
Z) LUT and LUT (XYZ) for converting device-dependent colors obtained by creation means 65 into device-independent colors
→ CMY) This is a profile output unit for writing out the conversion LUT from the device-independent color to the device-dependent color obtained by the creation unit 69 as an output device profile 611.

In the ICC profile which is standard in the technical field of the present invention, AtoBxTag for converting from a device-dependent color to a device-independent color, and AtoBxTag for converting from a device-independent color to a device-dependent color. The LUT is stored for each BtoAxTag. The results of the estimation using the non-linear model and the non-linear masking are AtoB as LUTs, respectively.
By storing in xTag and BtoAxTAg, accurate proofing and the like can be performed.

The determination of the parameters by the above-described nonlinear masking parameter determining means 66 will be described below with reference to FIGS.

In FIG. 7, reference numeral 71 denotes a target value included in the color reproduction range of the printer as an output device, and reference numeral 72 denotes a non-linear masking model for obtaining a relationship from an output device-independent color to a device-dependent color. Yes,
XY obtained by converting the target value by conversion 75
An estimated value (CaMaYa) is output based on the Z value.

Reference numeral 73 denotes an LUT for estimating the colorimetric value obtained by the LUT (CMY → XYZ) creating means 65;
74 is L from the target value 71 and the non-linear masking 72
This is a process of obtaining a color difference of a colorimetric value (estimated value) estimated via the UT 73 and changing a parameter of non-linear masking according to a magnitude of the color difference.

FIG. 8 is a flowchart showing a procedure of a parameter determining process for nonlinear masking.

First, in step S801, initialization is performed on the parameters of the non-linear masking.

For example, assuming a 3 × 20 matrix shown in the following equation (6) as non-linear masking,

[0074]

(Equation 5)

For initialization, for example, the following values are assigned as initial values of coefficients.

[0076]

(B11, b21, b31) = (0, 0.5, 0.5) (b12, b22, b32) = (0.5, 0, 0.5) (b13, b23, b33) = (0.5, 0.5, 0) ( b120, b220, b320) = (1, 1, 1) Here, all coefficients not shown are assumed to be zero.

Next, in step S802, the first embodiment
As described above, the parameters of the non-linear model of the printer are determined based on the contents of the table 30. On the other hand, in step S804, the target value within the color reproduction range of an output device printer _{(L t a t b t)} 71, sets the input in a predetermined order. Thus, for each of the target value _{(L t a t b t)} , as follows, parameters of non-linear masking is that whether or not appropriate or not.

That is, in step S804, the conversion 75
(See FIG. 7), the target value (L _t a _t b _t)
Is converted to an XYZ value, and in step S805, the non-linear masking of the expression (6) initialized as described above is converted to the XYZ value.
An operation of inputting a value and outputting an estimated value CaMaYa is performed. Next, in step S806, the LUT creation unit 65
Using the LUT 73 created by
(MaYa) is converted to an estimated colorimetric value (XaYaZa), which is converted 76 in step S807 (see FIG. 7).
To the value of Lab.

In step S808, step S803
In calculating settings and input target value L _t a _t b _t, the color difference between Lab obtained as described above. And
Similar to steps S410 to S414 in FIG. 4 according to the first embodiment, the parameter adjustment of the non-linear masking 72 is performed for all target values until the color difference becomes smaller than a predetermined threshold.

As described above, by using the nonlinear printer model described in the first embodiment, it is possible to determine the parameters of the nonlinear masking for correcting the color of the input data. It is possible to perform a masking process suitable for the printer model.

It should be noted that the masking set in this way can be used as a table as an LUT.
As described in the second embodiment, this is the same as the case of the printer model.

<Other Embodiments> The present invention, as described above,
The present invention may be applied to a system including a plurality of devices (for example, a host computer, an interface device, a reader, a printer, and the like) or may be applied to an apparatus including one device (for example, a copying machine and a facsimile machine).

The software for realizing the functions of the above-described embodiment is installed in a device or a computer in the system connected to the various devices so as to operate the various devices so as to realize the functions of the above-described embodiment. The present invention also includes a program code supplied and executed by operating the various devices according to a stored program in a computer (CPU or MPU) of the system or apparatus.

In this case, the software program code itself implements the functions of the above-described embodiment, and the program code itself and means for supplying the program code to a computer, for example, the program code The stored storage medium constitutes the present invention.

As a storage medium for storing such a program code, for example, a floppy disk, hard disk, optical disk, magneto-optical disk, CD-ROM, magnetic tape, nonvolatile memory card, ROM and the like can be used.

When the computer executes the supplied program code, not only the functions of the above-described embodiment are realized, but also the OS (operating system) running on the computer or another program code. Needless to say, the program code is included in the embodiment of the present invention even when the functions of the above-described embodiment are realized in cooperation with application software or the like.

Further, the supplied program code is stored in a memory provided on a function expansion board of a computer or a function expansion unit connected to the computer, and then stored in the function expansion board or the function storage unit based on the instruction of the program code. It is needless to say that the present invention includes a case where a provided CPU or the like performs part or all of the actual processing, and the processing realizes the functions of the above-described embodiments.

[0088]

As described above, according to the present invention,
A printing apparatus prints a predetermined number of patches, and a model formula representing input / output characteristics of the printing apparatus is determined based on colorimetric values obtained from the patches,
Since other colorimetric values can be estimated by this model formula, even if the number of the predetermined number of patches to be actually output is not large, the colorimetric values can be estimated with relatively high accuracy, In addition, color correction data can be created using this.

As a result, it is not always necessary to use color patches at regular intervals, and any color patches can be used.

Further, highly accurate colorimetric values can be estimated with a small number of color patches.

Further, it is possible to reduce the fluctuation of the colorimeter due to disturbance and the colorimetric error due to the non-uniform operation.

Further, since a rough approximation is obtained, a smooth estimation result is obtained, and noise at the time of preview can be reduced.

Further, by storing the estimation result of the colorimetric value based on the model and the parameters in the LUT, it is possible to increase the speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a print system according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration for determining a nonlinear model parameter according to the first embodiment of the present invention.

FIG. 3 is a diagram showing the concept of the above-described nonlinear model / parameter determination processing.

FIG. 4 is a flowchart showing a procedure of the above-described nonlinear model / parameter determination processing.

FIG. 5 is a diagram illustrating an effect according to the second embodiment of the present invention.

FIG. 6 is a block diagram showing a configuration for determining a parameter for nonlinear masking according to a second embodiment of the present invention.

FIG. 7 is a diagram showing the concept of a parameter determination process of the above-mentioned nonlinear masking.

FIG. 8 is a flowchart illustrating a procedure of a parameter determining process of the non-linear masking.

FIG. 9 is a diagram for explaining a conventional example of colorimetric value estimation using a color patch.

[Explanation of symbols]

Reference Signs List 12 Host computer 13 Printer 30 Table showing relationship of colorimetric value to sample value 31 Table showing relationship of CMY value to target value 32 Printer model 71 Target value 72 Masking process 73 Printer model LUT

Claims (10)

[Claims] 1. A colorimetric method for a color patch, wherein a colorimetric value for an arbitrary color patch is estimated by approximating a colorimetric value for a plurality of color patches by a model of a printing apparatus and parameters of the model. How to estimate the value. 2. A conversion method according to claim 1, wherein a sample value which is a value of a color space dependent on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value are converted to another sample in the printing apparatus. A method for estimating a colorimetric value for a value, comprising: preparing a non-linear model expression representing input / output characteristics of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value; Calculating the conversion relationship between the color value and the colorimetric value of the color patch based on the sample value; calculating the inverse conversion relationship of the sample value with respect to the colorimetric value from the conversion relationship; By using a sample value determined from the relationship as an input of the nonlinear model formula, a colorimetric value is determined as the output, and the color difference is determined according to a color difference between the determined colorimetric value and the predetermined colorimetric value. Adjusting the coefficient of the nonlinear model formula so as to be smaller than a predetermined value to determine the nonlinear model formula, and estimating a colorimetric value by the determined nonlinear model formula. Method of estimating colorimetric values for color patches to be applied. 3. A device profile creation method, wherein colorimetric values for an arbitrary color patch are estimated by approximating colorimetric values for a plurality of color patches with a model of a printing apparatus and parameters of the model. . 4. A conversion method between a sample value, which is a value in a color space dependent on the printing apparatus, and a colorimetric value of a color patch printed by the printing apparatus based on the sample value. A method of creating a profile, comprising preparing a non-linear model expression representing input / output characteristics of a printing apparatus that inputs a value of the color space and outputs a colorimetric value corresponding to the value, and inputs a colorimetric value. Preparing a color correction formula that outputs the value of the color space input to the nonlinear model formula, and obtains the conversion relationship between a sample value and a colorimetric value of a color patch based on the sample value; From the relationship, the inverse conversion relationship of the sample value with respect to the colorimetric value is obtained, and the sample value determined from the inverse conversion relationship with respect to the predetermined colorimetric value is used as the input of the non-linear model equation, thereby obtaining the output and The colorimetric value is obtained by adjusting the coefficient of the nonlinear model formula according to the color difference between the obtained colorimetric value and the predetermined colorimetric value so that the color difference becomes smaller than a predetermined value. A non-linear model formula is determined, a predetermined colorimetric value is input to the color correction formula, and a value of the color space obtained by the input is input to the non-linear model formula to obtain a colorimetric value. Determining the color correction formula by adjusting the coefficient of the color correction formula so that the color difference is smaller than a predetermined value, according to the color difference between the obtained colorimetric value and the predetermined colorimetric value. A method for creating a device profile. 5. An image processing apparatus comprising a non-linear model formula determined by the colorimetric value estimating method according to claim 2 as a look-up table. 6. An image processing apparatus comprising a non-linear model expression and / or a color correction expression determined by the device profile creation method according to claim 4 as a look-up table. 7. Another sample in the printing apparatus is obtained from a conversion relationship between a sample value which is a value of a color space depending on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value. An image processing apparatus for estimating a colorimetric value for a value, wherein a non-linear model formula representing input / output characteristics of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value is provided. Calculating the conversion relationship between the sample value and the colorimetric value of the color patch based on the sample value; obtaining an inverse conversion relationship of the sample value with respect to the colorimetric value from the conversion relationship; By using a sample value determined from the inverse transformation relationship as an input of the nonlinear model formula, a colorimetric value is obtained as the output, and according to a color difference between the obtained colorimetric value and the predetermined colorimetric value. Adjusting the coefficient of the nonlinear model formula so that the color difference is smaller than a predetermined value, determining the nonlinear model formula, and estimating a colorimetric value based on the determined nonlinear model formula. An image processing apparatus characterized by the above-mentioned. 8. A conversion method between a sample value, which is a value of a color space dependent on the printing apparatus, and a colorimetric value of a color patch printed by the printing apparatus based on the sample value. An image processing apparatus for creating a profile, comprising: preparing a non-linear model expression representing an input / output characteristic of a printing apparatus for inputting a value of the color space and outputting a colorimetric value corresponding to the value; A color correction formula is prepared that receives the color space value input to the non-linear model formula as an input, and obtains the conversion relationship between a sample value and a colorimetric value of a color patch based on the sample value. From the conversion relationship, an inverse conversion relationship of the sample value to the colorimetric value is obtained, and a sample value determined from the inverse conversion relationship for a predetermined colorimetric value is used as an input of the nonlinear model formula. A colorimetric value is obtained as an output, and according to a color difference between the obtained colorimetric value and the predetermined colorimetric value, a coefficient of the nonlinear model formula is adjusted so that the color difference becomes smaller than a predetermined value. Determining the non-linear model formula, inputting a predetermined colorimetric value into the color correction formula, inputting the value of the color space obtained by the input into the non-linear model formula to obtain a colorimetric value, According to a color difference between the obtained colorimetric value and the predetermined colorimetric value, a process of adjusting the coefficient of the color correction expression so that the color difference is smaller than a predetermined value and determining the color correction expression is performed. An image processing apparatus comprising: 9. A conversion method according to claim 1, wherein a sample value which is a value of a color space depending on the printing apparatus and a colorimetric value of a color patch printed by the printing apparatus based on the sample value are converted to another sample in the printing apparatus. A storage medium storing a program for estimating a colorimetric value with respect to a value in a manner readable by an information processing device, the program comprising: inputting a value of the color space and outputting a colorimetric value corresponding to the value. A non-linear model expression representing the input / output characteristics of the printing apparatus to be prepared is obtained, and the conversion relationship between the sample values and the colorimetric values of the color patches based on the sample values is determined. The inverse conversion relationship of the value is obtained, and a sample value determined from the inverse conversion relationship with respect to a predetermined colorimetric value is input to the nonlinear model formula, whereby the output is obtained. Calculating a colorimetric value, and adjusting a coefficient of the non-linear model equation so that the color difference is smaller than a predetermined value according to a color difference between the obtained colorimetric value and the predetermined colorimetric value. A storage medium having a step of determining the nonlinear model formula. 10. A conversion method between a sample value, which is a value of a color space dependent on a printing apparatus, and a colorimetric value of a color patch printed by the printing apparatus based on the sample value. A storage medium storing a program for processing for creating a profile in a manner readable by an information processing apparatus, the program comprising: a printing apparatus that inputs a value of the color space and outputs a colorimetric value corresponding to the value; A non-linear model expression representing input / output characteristics is prepared, and a color correction expression is prepared which receives a colorimetric value as input and outputs the value of the color space input to the non-linear model expression as a sample value and the sample value. The conversion relationship between the colorimetric values of the color patches based on the colorimetric values is determined. From the conversion relationship, the inverse conversion relationship of the sample values with respect to the colorimetric values is determined. By taking a sample value determined from the conversion relationship as an input of the nonlinear model formula, a colorimetric value is obtained as the output, and according to a color difference between the obtained colorimetric value and the predetermined colorimetric value, The nonlinear model formula is determined by adjusting the coefficient of the nonlinear model formula so that the color difference is smaller than a predetermined value. A predetermined colorimetric value is input to the correction formula, and the color space obtained by the input is determined. Is input to the nonlinear model formula to determine a colorimetric value, and according to a color difference between the determined colorimetric value and the predetermined colorimetric value, the color difference is smaller than a predetermined value. A storage medium having a step of adjusting a coefficient of a color correction equation to determine the color correction equation.