JP2011101255A - Correction unit for color measurement unit mounted in printing apparatus equipped with the color measurement unit, and correction lut for color measurement unit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct a color measurement unit which serves as the base for color correction values. <P>SOLUTION: When an LUT for correction is generated, wherein a correction value equivalent to a difference between a color measurement value in a spectroreflectometer of a color measurement unit which serves as a reference and a color measurement value, in a spectroreflectometer of a color measurement unit which serves as a correction object as the data, the LUT for correction includes a wavelength, a reflectance and a change rate to the change of the wavelength of the reflectance as elements of the argument. Also, a color measurement unit is provided to compute a color material amount set corresponding to the combination of the wavelength, the reflectance and the change rate and obtain the correction value on the basis of the color measurement result of a patch printed by the color material amount set. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a correction device for a colorimeter and a correction LUT for the colorimeter in a printing apparatus including the colorimeter.

In the process of improving the printing accuracy (color reproducibility) in the printing apparatus, the accuracy of the colorimeter is important.
In general, a colorimeter is used as one that can obtain accuracy that satisfies a certain standard. However, according to “Diagnosing and Correcting Systematic Errors in Spectral-Based Digital Imaging” in the “13th Color Imaging Conference Final Program and Proceedings” held from November 7th to 11th, 2005, the variation of each colorimeter As one factor, a wavelength scale error is disclosed as an error caused by a mechanical element.

  It is disclosed that there are a linear error and a non-linear error corresponding to the wavelength, and the error component is a change in spectral reflectance with respect to a change in wavelength.

“Diagnosing and Correcting Systematic Errors in Spectral-Based Digital Imaging” at “13th Color Imaging Conference Final Program and Proceedings”

With regard to variations among colorimeters, an analysis has been performed on the existence of an error whose element is a change in spectral reflectance with respect to a change in wavelength, but a method for eliminating the error component has not yet been disclosed.
An object of the present invention is to make it possible to perform color correction that takes into account variation individual differences between colorimeters.

  In order to achieve the above object, the present invention provides a correction for referring to a correction value corresponding to a difference between a colorimetric value of a standard colorimeter and a colorimetric value of a colorimeter to be corrected. The correction LUT includes a LUT and corrects the colorimeter in the printing apparatus. The correction LUT includes, as its argument elements, a wavelength, a reflectance, and a change rate of the reflectance with respect to the wavelength change. A color material amount set corresponding to a combination of wavelength, reflectance, and change rate is obtained by calculation, and the correction value is obtained based on the color measurement result of a patch printed with the same color material amount set.

  That is, in order to correct the colorimeter in the printing apparatus, a correction having a correction value corresponding to the difference between the colorimetric value of the reference colorimeter and the colorimetric value of the colorimeter to be corrected. The LUT is used. This correction LUT includes, as its argument elements, the wavelength, the reflectance, and the rate of change of the reflectance with respect to the change in wavelength. For this reason, a color material amount set corresponding to a combination of the same wavelength, reflectance, and change rate is obtained in advance, and the correction value is obtained based on the color measurement result of the patch printed with the same color material amount set.

  In addition, in order to obtain the color material amount set, a reference spectral reflectance acquisition unit that selects a predetermined plurality of color patches and obtains a colorimetric result obtained by measuring the color of the printed patch using a reference colorimeter. And a color material amount set calculating means for setting the spectral reflectance obtained by changing the rate of change using the colorimetric result and obtaining a color material amount set for reproducing the spectral reflectance by calculation. It may be.

  That is, the reference spectral reflectance acquisition unit selects a predetermined plurality of color patches, obtains a color measurement result obtained by measuring the color of the patch printed with the reference colorimeter, and sets the color material amount set calculation unit. However, using this colorimetric result, the spectral reflectance obtained by changing the rate of change is set, and a color material amount set that reproduces the spectral reflectance is calculated.

  Further, the correction LUT measures the color of the patch with a patch printing unit that prints a patch with the printing apparatus using the color material amount set obtained by calculation, and a reference colorimeter, and a spectral reflectance. The colorimetric spectral reflectance acquisition means for obtaining the colorimetric values, the target colorimeter spectral reflectance obtaining means for measuring the color of the patch by the colorimeter to be corrected and obtaining the spectral reflectance, and the reference for each patch. A difference-by-patch acquisition unit that obtains the difference in spectral reflectance between the colorimeter to be corrected and the colorimeter to be corrected, and a colorimetric result in which the wavelength and the reflectance are the same for the colorimetric results of all patches. Using the reflectance change rate corresponding difference acquisition means for specifying the correspondence between the change rate and the difference, the wavelength, the reflectance, and the change rate corresponding to the identification result as argument elements Correction LUT generation means for generating the correction LUT; Thus, it may also be generated.

  That is, a predetermined patch is printed by a printing apparatus, and the color of the patch is measured by a reference colorimeter and a correction target colorimeter. Next, based on the colorimetric values obtained by measuring the patches, the difference in spectral reflectance between the reference colorimeter and the correction target colorimeter is obtained for each patch. In addition, for the color measurement results of all patches, a correspondence relationship between the change rate and the difference is specified by using a color measurement result having the same wavelength and reflectance. Then, the correction LUT is generated with the wavelength, the reflectance, and the change rate corresponding to the identification result as argument elements.

Next, when the correction LUT is generated, the weighting of the color measurement result in the dark area may be reflected with a small weight.
That is, as another aspect, the weighting of the color measurement result in the dark area can be reflected by reducing it so that it is not affected by the color measurement result with low accuracy.

Further, when the correction LUT is generated, the weight of the peak band of the visual characteristic may be increased and reflected.
In other words, in pursuit of accuracy, an error far from the human sense may adversely affect an area sensitive to the human sense. Therefore, the biased method reflecting the human visual characteristics is more likely to be satisfied as a result.

Furthermore, when the correction LUT is generated, the characteristics of the light source of the colorimeter may be acquired from the model name of the printing apparatus, and the weight corresponding to the characteristics may be reflected.
Like human visual characteristics, colorimeters have characteristics, one of which is the characteristics of light sources. For this reason, since the calibration of the printing press is performed by reflecting the characteristics of the light source, it is advantageous to reflect the characteristics of the light source. For this reason, the characteristics of the light source of the colorimeter can be acquired from the model name of the printing apparatus, and the weighting corresponding to the characteristics is reflected, so that the calibration can be performed accurately.
As another aspect of the present invention, a correction LUT that refers to a correction value corresponding to a difference between a colorimetric value in a standard colorimeter and a colorimetric value in a colorimeter to be corrected. It is good. In this case, the parameters include the wavelength, reflectivity, and the rate of change of the reflectivity with respect to the change in wavelength, and further calculate the color material amount set corresponding to the combination of the same wavelength, reflectivity, and rate of change. The correction value is obtained based on the color measurement result of the patch printed with the same color material amount set.
In addition, the printing apparatus itself provided with a colorimeter may be used as an embodiment to which the present invention can be applied. That is, the present invention can be applied when correcting the color reproducibility by reflecting the color measurement result from the colorimeter. Further, in the sense of correcting the color of the printing apparatus, it can be applied as a printing control apparatus or a color correction apparatus. Thus, the scope of application of the present invention is not limited to the description of the scope of claims.

The present invention is not necessarily limited to a substantial apparatus, and it can be easily understood that the present invention also functions as a method. For this reason, there is no difference in being effective not only as a substantial apparatus but also as a method.
By the way, the idea of the present invention is not limited to this and includes various aspects, such as the case where the apparatus of the present invention may exist alone or may be used in a state of being incorporated in a certain device. Therefore, it can be changed as appropriate, such as software or hardware.

In the case of software as an embodiment of the idea of the invention, it naturally exists on a recording medium on which such software is recorded, and it must be used.
Of course, the recording medium may be a magnetic recording medium, a magneto-optical recording medium, or any recording medium that will be developed in the future. In addition, the duplication stages such as the primary duplication product and the secondary duplication product are equivalent without any question. In addition, even when the communication method is used as a supply method, the present invention is not changed.

Further, even when a part is software and a part is realized by hardware, the idea of the invention is not completely different, and a part is stored on a recording medium and is appropriately changed as necessary. It may be in the form of being read.
When the present invention is realized by software, a configuration using hardware or an operating system may be used, or may be realized separately from these. For example, even if it is a variety of arithmetic processing, if it can be processed by calling a predetermined function in the operating system, it can also be input from hardware without calling such a function. is there. It can be understood that the present invention can be implemented only by this program in the process in which the program is recorded on the medium and distributed even though it is actually realized under the intervention of the operating system.

  When the present invention is implemented by software, the present invention is not only realized as a medium storing a program, but the present invention is naturally realized as a program itself, and the program itself is also included in the present invention.

1 is a block diagram of a printing control apparatus including a colorimeter correction apparatus to which the present invention is applied. FIG. 2 is a block diagram illustrating a software configuration of the print control apparatus. It is a flowchart of the process which specifies the patch for LUT production | generation for correction | amendment. It is a flowchart of a correction LUT generation process. It is a graph which shows a wavelength, a reflectance, and the difference (inclination) of a reflectance. It is a figure which shows the correspondence of a colorimetry result and a difference for every patch. It is a figure which shows the condition which changes the inclination in a colorimetry result. It is a figure explaining the calculation for calculating a color value based on a spectral reflectance. It is a schematic diagram showing a flow of processing for optimizing the ink amount set. It is a schematic diagram which shows a mode that an ink amount set is optimized. It is a figure which shows the condition which connects the inclination and difference in a certain wavelength and reflectance smoothly. It is a figure which shows the relationship between a wavelength and a reflectance. It is a table which shows the correspondence of the model of a printer, and the characteristic of a light source.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings in the following order.
1. Configuration of the colorimeter correction device:
2. Correction LUT generation processing:
3. Variations:

1. Configuration of Colorimeter Correction Device FIG. 1 shows a hardware configuration of a print control apparatus including a colorimeter correction device according to an embodiment of the present invention. In FIG. 1, the print control apparatus is mainly composed of a computer 10, and the computer 10 includes a CPU 11, a RAM 12, a ROM 13, a hard disk drive (HDD) 14, a general-purpose interface (GIF) 15, a video interface (VIF) 16, and an input interface. (IIF) 17 and a bus 18. The bus 18 implements data communication between the elements 11 to 17 constituting the computer 10, and communication is controlled by a chip set (not shown). The HDD 14 stores program data 14a for executing various programs including an operating system (OS), and the CPU 11 executes calculations according to the program data 14a while expanding the program data 14a in the RAM 12. . The GIF 15 provides an interface conforming to the USB standard, for example, and connects the external printer 20 and the spectral reflectometer 30 to the computer 10. The VIF 16 connects the computer 10 to an external display 40 and provides an interface for displaying an image on the display 40. The IIF 17 connects the computer 10 to an external keyboard 50a and a mouse 50b, and provides an interface for the computer 10 to acquire input signals from the keyboard 50a and the mouse 50b.

The external printer (printing apparatus) 20 and the spectral reflectometer 30 may be separate or integrated. In recent years, in order to obtain high-precision print reproducibility, there are some in which both are integrated. Such a single unit may be used, or separate units may be used.
The spectral reflectometer 30 corresponds to a reference colorimeter and a correction target colorimeter. The spectral reflectometer 30 serving as a reference colorimeter can actually perform color measurement each time, or can obtain and replace the already measured color results.

  FIG. 2 shows a software configuration of a program executed by the computer 10 together with a schematic data flow. In the figure, the computer 10 mainly executes an OS P1, a sample printing application (APL) P2, a printer driver (PDV) P3, a spectral reflectometer driver (MDV) P4, and a display driver (DDV) P5. The OS P1 provides an image equipment interface (GDI) P1a and a spooler P1b as one of APIs that can be used by each program. PDV P3 and DDV P5 are called. The GDI P1a provides a general-purpose mechanism for the computer 10 to control image output in an image output device such as the printer 20 or the display 40, while the PDV P3 or DDV P5 is a process specific to the model of the printer 20 or the display 40. Etc. The spooler P1b is interposed between the APL P2, the PDV P3, and the printer 20, and executes job control and the like. APL P2 is an application program for printing a sample chart SC including a patch, generates print data PD in RGB bitmap format, and outputs the print data PD to GDI P1a. In generating the print data PD, the target colorimetric data MD is acquired from the MDV P4. The MDV P4 controls the spectral reflectometer 30 in response to a request from the APL P2, and outputs the spectral reflectance data RD obtained by the control to the APL P2.

  The print data PD generated by the APL P2 is output to the PDV P3 via the GDI P1a and the spooler P1b, and the PDV P3 executes processing for generating print control data CD that can be output to the printer 20 based on the print data PD. . The print control data CD generated by the PDV P3 is output to the printer 20 via the spooler P1b provided by the OS P1, and the printer 20 performs an operation based on the print control data CD to print a sample chart SC including patches. Print on paper.

2. Correction LUT Generation Processing FIGS. 3 and 4 are flowcharts executed by the print control apparatus. FIG. 3 shows a flowchart of processing for identifying a patch to be measured, and FIG. 4 shows a flowchart for generating a colorimetric correction LUT by measuring the color of the patch.
In the present invention, a color material amount set corresponding to a combination of wavelength, reflectance, and change rate is obtained by calculation, and a correction value of the correction LUT is obtained based on the color measurement result of a patch printed with the same color material amount set. The color material amount set is obtained by the flowchart shown in FIG. 3, and the correction value is obtained by the flowchart shown in FIG.

First, a process for specifying a patch to be measured will be described.
In step 11, “select a color as a grid point”. Although calibration can be performed for a large number of colors, the present embodiment is premised on being used in a system that prints a predetermined number of predetermined colors with high reproducibility. Therefore, if this specific number of colors are targeted, the effect of improving color reproducibility is great. In step 12 in which all or some of the specific many colors are extracted as sampling colors, the selected sampling color patch is printed by the printer 20. In order to achieve high color reproducibility, each patch is printed based on data corresponding to the ink color.
In step 13, the sampling color patch is measured by the spectral reflectometer 30 of the colorimeter serving as a reference. However, since the color measurement result of the reference colorimeter is constant, if there is already measured spectral reflectance data, it may be obtained. The measured spectral reflectance of the sampling color is expressed as a target spectral reflectance Rt (λ) composed of discrete wavelengths and reflectances at the same wavelength, and the spectral reflectance storing the target spectral reflectance Rt (λ). Data RT is acquired.
Steps 11 to 13 correspond to a reference spectral reflectance acquisition unit, and a color measurement result obtained by selecting a plurality of predetermined color patches and measuring a color obtained by printing the patch with a reference colorimeter. It has gained.
FIG. 5 is a graph showing the correspondence between wavelength and spectral reflectance for each patch. As shown in the figure, the target spectral reflectance Rt (λ) can be plotted with a colorimetric result with the horizontal axis representing wavelength and the vertical axis representing reflectance. The rate of change of the reflectance value obtained based on the reflectance at each wavelength is referred to as “tilt” and is shown in the figure. According to this, the difference in reflectance between adjacent wavelengths is defined as “slope”. In this embodiment, based on the fact that such “gradient (change rate)” affects the color measurement result, it is used for calibration of the colorimeter.
FIG. 6 shows a graph for plotting the colorimetric result of the reference spectral reflectometer 30 and the colorimetric result of the spectral reflectometer 30 to be corrected and using the difference as the correction amount. ing. Since this difference fluctuates according to the inclination, in addition to the wavelength on the horizontal axis and the reflectance on the vertical axis, the axis of the inclination value in the depth direction is shown. Further, in this figure, the result of color measurement is plotted for each patch, and the color measurement result A in the spectral reflectance meter 30 serving as a reference for patch # 1 and patch # 2 and the spectral reflectance to be corrected. The color measurement result B in the total 30 is plotted, and the manner of obtaining the difference in reflectance at each wavelength is shown.
A sufficient colorimetric result corresponding to the slope component is not always obtained from the selected sampling color patch. For this reason, it is necessary to create a patch that artificially changes the inclination. As the number of patches with different inclinations increases, the color measurement work increases significantly. In this embodiment, five inclinations are set.
FIG. 7 schematically shows the inclination to be set. When the horizontal direction is 0 degree, the inclination is −90 degrees at the minimum and +90 degrees at the maximum. This range is divided into five equal parts, and five angles (−72 degrees, −36 degrees, 0 degrees, +36 degrees, +72 degrees) are set in the center of one area, and 1 to 5 are represented by j. I will decide.
In step 14, the reflectance curve at the reference wavelength is redrawn to the above-mentioned angle with respect to the reference target spectral reflectance Rt (λ), and the target spectral reflectance Rtj (λ) is changed. (J = 1 to 5) is set.
In step 15, in order to reproduce the target spectral reflectance Rtj (λ) (j = 1 to 5) with different inclinations (five), the corresponding ink color material amount set for the patch is specified. Note that such target spectral reflectance Rtj (λ) (j = 1 to 5) is also stored as spectral reflectance data RD.
As shown in FIG. 2, the LUG P3a includes an ink amount set calculation module (ICM) P3a1, a spectral reflectance prediction module (RPM) P3a2, an evaluation value calculation module (ECM) P3a3, and an LUT output module (LOM) P3a4. Has been.
When target spectral reflectance data RD is specified, a process of calculating an ink amount set that can reproduce the same spectral reflectance R (λ) as the target spectral reflectance Rt (λ) indicated by the spectral reflectance data RD I do. At that time, the above-described RPM P3a2 and ECM P3a3 are used.

FIG. 8 shows the nature of the target spectral reflectance Rt (λ). As a result of measuring the target spectral reflectance Rt (λ) for the target TG that is a sampling color patch, it is assumed that spectral reflectance data RD indicating the distribution of the target spectral reflectance Rt (λ) is obtained as illustrated. Note that the target TG means an object surface that is a target for spectral reproduction, and corresponds to, for example, an artificial object surface formed by another printing apparatus or a coating apparatus, a natural object surface, or the like. On the other hand, the D65 light source has a non-uniform distribution of spectral energy P (λ) in the visible wavelength region as shown in the figure, and the spectral energy of reflected light of each wavelength when the target TG is irradiated with the D65 light source is This is a value obtained by multiplying the target spectral reflectance Rt (λ) and the spectral energy P (λ) for each wavelength. Further, the spectral energy spectrum of the reflected light is convolved with the color matching functions x (λ), y (λ), z (λ) corresponding to the human spectral sensitivity characteristics, and normalized by the coefficient k. Thus, tristimulus values X, Y, and Z are obtained. The above is expressed by the following equation (1).

  By converting the tristimulus values X, Y, and Z by a predetermined conversion formula, an L * a * b * value indicating a color when the target TG is irradiated with the D65 light source can be obtained. Thereby, for example, if it is desired to obtain the RGB value for display, the RGB value for display can be obtained from the L * a * b * value by using the RGB profile.

FIG. 9 schematically shows a flow of processing for calculating an ink amount set that can reproduce a spectral reflectance R (λ) similar to the target spectral reflectance Rt (λ) indicated by the spectral reflectance data RD. .
In response to the input of the ink amount set φ from the ICM P3a1, the RPM P3a2 predicts the spectral reflectance R (λ) when the printer 20 ejects ink onto a predetermined print sheet based on the ink amount set φ. The spectral reflectance R (λ) is output to the ECM P3a3 as the predicted spectral reflectance Rs (λ).

The ECM P3a3 calculates the difference D (λ) between the target spectral reflectance Rt (λ) and the predicted spectral reflectance Rs (λ) indicated by the spectral reflectance data RD for each wavelength λ, and assigns a weight to each wavelength λ. The obtained weight function w (λ) is multiplied by the difference D (λ). The square root of the mean square of this value is calculated as the evaluation value E (φ). The above calculation can be expressed by the following equation (2).

  In the above equation (2), N means the finite number of sections of wavelength λ. In the above equation (2), the smaller the evaluation value E (φ), the smaller the difference between the target spectral reflectance Rt (λ) and the predicted spectral reflectance Rs (λ) at each wavelength λ. That is, the smaller the evaluation value E (φ) is, from the spectral reflectance R (λ) reproduced on the recording medium when the printer 20 prints with the input ink amount set φ, and the corresponding target TG. It can be said that the obtained target spectral reflectance Rt (λ) is approximate. Further, according to the above equation (1), although the absolute color value indicated by the target TG corresponding to the recording medium when the printer 20 prints with the ink amount set φ according to the fluctuation of the light source both fluctuates. If the spectral reflectance R (λ) is approximated, it can be said that the same color is perceived relatively regardless of the variation of the light source. Therefore, according to the ink amount set φ in which the evaluation value (φ) becomes small, it can be said that a print result perceived in the same color as the target TG can be obtained in any light source.

前記の（３）式においては、等色関数ｘ（λ），ｙ（λ），ｚ（λ）を加算することにより、重み関数ｗ（λ）が定義されている。なお、前記の（３）式の右辺全体に所定の係数を乗算して、重み関数ｗ（λ）の値の範囲を正規化してもよい。前記の（１）式によれば、等色関数ｘ（λ），ｙ（λ），ｚ（λ）が大きい波長域ほど、色彩値（Ｌ*ａ*ｂ*値）に大きく影響するということができる。従って、等色関数ｘ（λ），ｙ（λ），ｚ（λ）を加算した重み関数ｗ（λ）を使用すれば、色への影響が大きい波長域を重視した二乗誤差が評価可能な評価値Ｅ（φ）を得ることができる。例えば、人間の目に知覚されない近紫外波長域においてはｗ（λ）が０となり、当該波長域における差分Ｄ（λ）は評価値Ｅ（φ）の増大に寄与しないこととなる。 In the present embodiment, the following equation (3) is used as the weighting function w (λ).

In the above equation (3), the weighting function w (λ) is defined by adding the color matching functions x (λ), y (λ), and z (λ). The range of the value of the weighting function w (λ) may be normalized by multiplying the entire right side of the equation (3) by a predetermined coefficient. According to the above equation (1), the wavelength range where the color matching functions x (λ), y (λ), and z (λ) are larger greatly affects the color value (L * a * b * value). Can do. Therefore, if a weighting function w (λ) obtained by adding the color matching functions x (λ), y (λ), and z (λ) is used, a square error that emphasizes a wavelength region that has a large influence on the color can be evaluated. An evaluation value E (φ) can be obtained. For example, w (λ) is 0 in the near ultraviolet wavelength region that is not perceived by human eyes, and the difference D (λ) in the wavelength region does not contribute to the increase in the evaluation value E (φ).

  In other words, even if the difference between the target spectral reflectance Rt (λ) and the predicted spectral reflectance Rs (λ) is not necessarily small in the entire visible wavelength range, the target spectral reflectance in the wavelength range that is particularly strongly perceived by the human eye. If Rt (λ) and the predicted spectral reflectance Rs (λ) are similar, a small evaluation value E (φ) can be obtained, and the spectral reflectance R (λ) corresponding to the perception of the human eye can be obtained. The evaluation value E (φ) can be used as an index of closeness. The calculated evaluation value E (φ) is returned to ICM P3a1. That is, the ICMP 3a1 outputs an arbitrary ink amount set φ to the RPM P3a2 and the ECM P3a3, whereby the evaluation value E (φ) is finally returned to the ICM P3a1. The ICM P3a1 repeatedly executes to obtain the evaluation value E (φ) corresponding to an arbitrary ink amount set φ, so that the evaluation value E (φ) as the objective function is minimized. Calculate the optimal solution. As a method for calculating the optimum solution, for example, a nonlinear optimization method such as a gradient method can be used.

FIG. 10 schematically shows how the ink amount set φ is optimized. In the figure, as the ink amount set φ is optimized, the predicted spectral reflectance Rs (λ) when printing is performed with the ink amount set φ approaches the target spectral reflectance Rt (λ). Further, by using the weighting function w (λ), the target spectral reflectance of the predicted spectral reflectance Rs (λ) is increased in the wavelength region where the color matching functions x (λ), y (λ), and z (λ) are larger. The constraint on Rt (λ) is strong, and the difference between the predicted spectral reflectance Rs (λ) and the target spectral reflectance Rt (λ) is small. In this way, the predicted spectral reflectance Rs (λ) is preferentially applied to the target spectral reflection of the target TG in the wavelength range where the color matching functions x (λ), y (λ), and z (λ) are large and have a great influence on vision. Since the rate Rt (λ) can be constrained, it is possible to calculate the ink amount set φ such that the appearance is close when an arbitrary light source is irradiated. As described above, it is possible to calculate the ink amount set φ that can be reproduced by the printer 20 with an appearance similar to the target TG in any light source. Note that the optimization termination condition may be the number of repetitions of the ink amount set φ update or the threshold value of the evaluation value E (φ).
It should be noted that such weighting processing also corresponds to increasing the weight of the peak band of the visual characteristics when reflecting the correction LUT.

In this way, an ink amount set capable of reproducing the same spectral reflectance R (λ) as the target spectral reflectance Rtj (λ) is calculated. The calculated ink amount set is stored in correspondence with the spectral reflectance data RD storing the target spectral reflectance Rtj (λ).
Steps 14 and 15 correspond to the color material amount set calculation means, set the spectral reflectance by changing the change rate using the colorimetric result of the reference colorimeter, and calculate the spectral reflectance. The color material amount set to be reproduced is calculated.
Next, a correction LUT is generated using the ink amount set prepared in this way.
The generation of the correction LUT is performed according to the flowchart shown in FIG.
In step 21, the patch is printed by the printer 20 using the ink amount set prepared as described above. In order to achieve high color reproducibility, each patch is printed based on data corresponding to the ink color. Note that step 21 corresponds to patch printing means, and a patch is printed by the printing apparatus with the color material amount set obtained by the calculation.

In step 22, the patch of the sampling color is measured by the spectral reflectometer 30 of the reference colorimeter. However, since the color measurement result of the reference colorimeter is constant, if there is already measured spectral reflectance data, it may be obtained. Note that step 22 corresponds to a reference colorimeter spectral reflectance acquisition means, and a patch is measured with a reference colorimeter to obtain a spectral reflectance.
In step 23, the sampling color is measured by the spectral reflectometer 30 of the colorimeter to be corrected. The result of color measurement at the spectral reflectometer 30 to be calibrated is obtained. Step 23 corresponds to the target colorimeter spectral reflectance acquisition means, and the patch is colorimetrically measured with the colorimeter to be corrected to obtain the spectral reflectance.

  In step 24, the difference in spectral reflectance at each wavelength is plotted as a correction amount for each patch.

In step 25, the plotted correction amounts are smoothly connected to generate a continuous correction amount. Since the colorimetric result of the spectral reflectometer 30 outputs the reflectance for each discrete wavelength value, the calculated difference is also discrete, and the correction amount is smooth and continuous using interpolation calculation. It shall be As a method of the interpolation calculation, a proportional and linear linear interpolation calculation, a curvilinear interpolation calculation using a high-dimensional function, and the like are known, and any method may be used.
Steps 24 and 25 correspond to patch-by-patch difference acquisition means, and the difference in spectral reflectance between the reference colorimeter and the correction target colorimeter is obtained for each patch.

  In step 26, for all patches, the difference and the change rate of the spectral reflectance are associated with each wavelength and each reflectance, and plotted as a correction amount. In the color measurement result of each patch, only one value of reflectance at a certain wavelength can be obtained. However, if the patches are different, the spectral reflectance curve changes, and there may be a plurality of curves having different slopes while passing through points having the same wavelength and the same reflectance. This is also an indication that the spectral reflectometer 30 outputs different colorimetric results using “slope” as an argument element. In this step, first, for each wavelength and each reflectance, a correction amount that associates the difference with the change rate of the spectral reflectance is obtained. This correction amount is also discrete.

  Next, in step 27, the difference between the correction amounts is smoothly connected using a multidimensional function to generate a continuous correction amount. As a result, for a certain wavelength and spectral reflectance, an optimal correction amount is obtained using the difference (inclination) in reflectance as an argument. In FIG. 11, a continuous correction amount is estimated by smoothly connecting the differences with respect to the respective slopes using a known interpolation calculation method such as a multi-order function. Steps 26 and 27 correspond to the reflectance change rate corresponding difference acquisition means, and the change rate and the difference are obtained by using the colorimetric results having the same wavelength and reflectance for the colorimetric results of all patches. The correspondence with is specified.

Since the correction amount is obtained for each grating as described above, in Step 28, as a specific result, a three-dimensional correction table (LUT) using the wavelength, the reflectance, and the change rate (slope) of the reflectance as argument elements is obtained. Generate. Step 28 corresponds to correction LUT generation means, and generates a correction LUT using the wavelength, the reflectance, and the change rate corresponding to the specific result as argument elements.
When a correction LUT that refers to a correction value corresponding to a difference between a colorimetric value in a reference colorimeter and a colorimetric value in a colorimeter to be corrected is used, the colorimeter in the printing apparatus is used. Thus, the color of the printed matter of the printing apparatus can be measured to obtain a deviation from the reference value. Then, after correcting this shift, the correction device can be realized by reflecting the color measurement result and feeding back to the print data for the printing device. There are various specific implementation methods, and correction parameters may be stored in the printer driver and reflected at the time of printing.

3. In the above embodiment, a three-dimensional correction table is generated, but a higher-dimensional correction table can be generated. That is, in addition to the reflectance change rate (slope), the change rate (slope) change rate (slope) may be used as a new argument element. In this modification, the correction LUT includes, as its argument elements, the wavelength, the spectral reflectance, the rate of change of the spectral reflectance with respect to the wavelength change, and the rate of change of the rate of change.
Next, in the above embodiment, it is assumed that all colorimetric values obtained by colorimetry are used. However, as a practical problem, there is an originally low accuracy area as a colorimetric value. For example, the colorimetric value has a low reflectance. The low reflectance means that dark reflected light is measured, and the accuracy of the colorimetric value is low. Therefore, even if a strict correction calculation is performed in such a low accuracy region, it does not contribute to accuracy improvement.

For this reason, the calculation of the correction amount may not be performed when a colorimetric result of a threshold value such as “0.2 or less” is obtained for the reflectance. In other words, since accuracy cannot be expected, correction is not performed.
In this sense, in the present modification, when the correction LUT is generated, the weighting of the color measurement result in the dark area is reflected in a smaller manner.
FIG. 12 shows an approximate relationship between the wavelength and the reflectance, but the sensitivity tends to be low in such a short wavelength region, and the colorimetric value in the case of 450 nm or less has low accuracy. Accordingly, the correction amount may not be calculated and correction may not be performed even in such a region.
Such weighting can be reflected by a method using a weighting function w (λ) as shown in FIG.
Furthermore, it is possible to reflect the characteristics of the light source. As shown in FIG. 8, the spectral characteristic emitted from the light source affects the color measurement result. In this embodiment, a D65 light source is used. However, if the light source is different, the spectral characteristics shown in FIG. The spectral reflectometer 30 often has a plurality of light sources depending on the colorimetric environment, but the type integrated with the printer 20 often specifies a light source.
FIG. 13 shows the correspondence relationship between the model of the printer 20 and the light source characteristics used in the spectral reflectometer 30 provided in the printer 20. That is, by making it possible to obtain the light source characteristic from the model name of the printer 20 and using the weighting function w (λ) reflecting the light source characteristic, calibration focusing on each light source can be realized. For example, it is possible to reduce the weighting in a wavelength band that is not emphasized by each light source, and increase the weighting in an important wavelength band.
In this sense, in this modification, when the correction LUT is generated, the characteristics of the light source of the colorimeter are acquired from the model name of the printing apparatus, and the weight corresponding to the characteristics is reflected.

In addition, as the category of the invention, it can be easily understood that the gist of the device invention has the same effect in the inventions of other categories. Therefore, it can be said that the present invention discloses other categories of inventions that are not described in the scope of claims within the scope of the above embodiments, such as method inventions, program recording medium inventions, and program inventions.
In addition, the present invention is not limited to the above-described embodiments and modifications, and the configurations disclosed in the above-described embodiments and modifications are mutually replaced or the combination is changed, the known technology, and the above-described configurations. Configurations in which the respective configurations disclosed in the embodiment and the modified examples are mutually replaced or combinations are changed are also included.

  DESCRIPTION OF SYMBOLS 10 ... Computer, 11 ... CPU, 12 ... RAM, 13 ... ROM, 14 ... HDD, 15 ... GIF, 16 ... VIF, 17 ... IIF, 18 ... Bus, 20 ... Printer, 30 ... Spectral reflectometer, 40 ... Display 50a ... Keyboard, 50b ... Mouse, P1 ... OS, P1a ... GDI, P1b ... Spooler, P2 ... APL, P2a ... UIM, P2b ... MCM, P2c ... PDG, P3 ... PDV, P3a1 ... ICM, P3a2 ... RPM, P3a3 ... ECM, P3a4 ... LOM, P4 ... MDV, P5 ... DDV.

Claims (7)

A correction LUT that refers to a correction value corresponding to a difference between a colorimetric value in a reference colorimeter and a colorimetric value in a colorimeter to be corrected is provided. A correction device for correcting,
The correction LUT includes, as its argument elements, the wavelength, the reflectance, and the rate of change of the reflectance with respect to the wavelength change,
A colorimeter that calculates a color material amount set corresponding to a combination of the same wavelength, reflectance, and change rate by calculation, and obtains the correction value based on a color measurement result of a patch printed with the same color material amount set. Correction apparatus for the colorimeter in a printing apparatus comprising: A reference spectral reflectance acquisition unit that selects a plurality of predetermined color patches and obtains a colorimetric result obtained by measuring the color of the printed patch using a reference colorimeter;
A color material amount set calculating means for setting a spectral reflectance with the change rate changed using the colorimetric result and obtaining a color material amount set for reproducing the spectral reflectance by calculation is provided. A correction device for the colorimeter in a printing apparatus including the colorimeter. Patch printing means for printing a patch in the printing apparatus with the color material amount set obtained by calculation;
Color measurement of the patch with a reference colorimeter, and a reference colorimeter spectral reflectance acquisition means for obtaining spectral reflectance,
A target colorimeter spectral reflectance acquisition means for measuring a color of the patch with a colorimeter to be corrected and obtaining a spectral reflectance;
For each patch, a patch-by-patch difference acquisition unit for obtaining a difference in spectral reflectance between the reference colorimeter and the correction target colorimeter;
For the color measurement results of all patches, a reflectance change rate corresponding difference acquisition means for specifying a correspondence relationship between the change rate and the difference using a color measurement result in which the wavelength and the reflectance coincide with each other;
3. The correction LUT generation means for generating the correction LUT using the wavelength, the reflectance, and the change rate corresponding to the specified result as argument elements. A correction device for the colorimeter in a printing apparatus provided with the described colorimeter.   The colorimeter according to any one of claims 1 to 3, wherein when the correction LUT is generated, the weighting of the colorimetric result in a dark luminance area is reflected in a small manner. Correction device for the colorimeter in a printing apparatus.   The printing with a colorimeter according to any one of claims 1 to 3, wherein when the correction LUT is generated, the weighting of the peak band of the visual characteristic is increased and reflected. Correction device for the colorimeter in the apparatus.   The said correction | amendment LUT WHEREIN: The characteristic of the light source of the said colorimeter is acquired from the model name of the said printing apparatus, and the weighting corresponding to the characteristic is reflected. A correction apparatus for the colorimeter in a printing apparatus comprising the colorimeter according to any one of claims 5 to 6. A colorimetric correction LUT that refers to a correction value corresponding to a difference between a colorimetric value at a reference colorimeter and a colorimetric value at a correction target colorimeter,
The correction LUT includes, as its argument elements, the wavelength, the reflectance, and the rate of change of the reflectance with respect to the wavelength change,
A color material amount set corresponding to a combination of the same wavelength, reflectance, and change rate is obtained by calculation, and the correction value is obtained based on a color measurement result of a patch printed with the same color material amount set. A correction LUT for the colorimeter in a printing apparatus including the colorimeter.

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