JP2008168444A - Color matching method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make it possible to match the color of ink, which realizes not even by an expert aim color in printing easily and, at the same time, under predetermined printing conditions. <P>SOLUTION: In the color matching method, in which all or some part of the process color inks such as cyan, magenta and yellow are blended with medium, based on the difference between the colorimetric value of the aim color and the colorimetric value of the spread material by test in and on the color difference between these two colorimetric values, the correction quantities of the respective process color inks and of the medium are calculated from the formulation of the test ink. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method and apparatus for toning a desired color ink.

  In order to reproduce a desired desired color in a printed matter, it is necessary to create ink that matches the printing conditions. Although this is called toning, the toning of this ink is performed by blending all or part of the process color inks of cyan (C), magenta (M), and yellow (Y) and medium (Me). . Medium is a colorless cocoon-shaped resin for adjusting the density of ink to be toned. Medium is also sometimes referred to as a binder.

Conventionally, it has been usual for a skilled person to perform toning of a desired color based on experience, but in recent years it has been possible to perform toning without relying on the skilled person. In order to achieve this, a computer color matching (CCM) apparatus for calculating a blend of process color ink and medium for toning a desired color ink has also been developed.
JP 2005-94353 A JP 2005-189182 A JP-A-11-235810

  However, since the conventional CCM apparatus is very expensive, it cannot be introduced anywhere, and even if the process color ink and the medium are blended according to the calculation result, the desired color is actually difficult. There is also a problem that cannot be reproduced.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a toning method and apparatus capable of toning an ink that can easily reproduce a color close to the target color without being skilled, and that can be configured at low cost. It is what.

  In order to achieve the above object, the toning method according to the present invention is a method for toning by combining all or a part of cyan, magenta and yellow process color inks with medium and measuring the target color. Based on the difference between the color value and the colorimetric value of the developed color of the test ink, and the color difference between these two colorimetric values, the correction amount for each process color ink and medium from the test ink formulation is calculated. It is characterized by seeking.

  Further, the toning device according to the present invention is based on the difference between the colorimetric value of the target color, the colorimetric value of the developed color of the test ink, and the color difference between these two colorimetric values. Control means for determining the correction amount of each process color ink and medium from the blend of the ink is provided.

  In the toning method according to the present invention, the correction amount of each process color ink and medium from the test ink, the difference between the colorimetric value of the target color and the colorimetric value of the developed product of the test ink, and both Since it is calculated based on the color difference, the accuracy of the correction amount can be improved, so that the number of corrections of the blend can be reduced, the efficiency of the toning process can be improved, and the target color can be improved. Therefore, it is possible to reduce the cost of the ink used for producing the ink for achieving the above.

  In the toning apparatus according to the present invention, the composition of each process color ink and medium that achieves the target color when printed under predetermined printing conditions is not obtained from the beginning, but is created by an appropriate method. Since the process color ink and medium correction amount for achieving the target color from the test ink is calculated, the calculation is only a simple calculation and can be easily performed with high accuracy. For this purpose, a special computer system is not required, and a personal computer system that is widely used can be used.

  Hereinafter, embodiments of the invention will be described with reference to the drawings. FIG. 1 is a flowchart showing an embodiment of a toning method according to the present invention.

  By the way, the toning process is roughly as follows. First, a target color to be reproduced by printing is presented. Next, all or part of the CMY process color ink and medium are appropriately blended to realize the target color when printed under predetermined printing conditions. Prepare an ink that will be (this is referred to herein as the test ink). Then, based on the difference between the colorimetric value of the target color and the colorimetric value of the developed color created using the test ink, the blend of the process color ink and medium of the test ink was modified, and the blend was modified. Using the ink as a new test ink, the process of measuring the target color and the developed product of the object to be measured, and correcting the blend of process color ink and medium based on the difference between the colorimetric values of the two, Repeat until the colorimetric value difference is within the allowable range.

  It will be clear that this is the process. This is because even if an expert decides the blend of process color ink and medium when making a test ink, or even with a CCM device, it is an ink that can surely reproduce the target color with that blend. This is because it is necessary to confirm whether or not there is.

  Accordingly, in the above-described toning process, if the correction value of the blend is high in the stage of obtaining the correction value of the blend, the number of repetitions of the correction of the blend can be reduced, and the whole As a result, the efficiency of the toning process can be improved. The present invention pays attention to that and intends to make the correction value of the blend more accurate.

In FIG. 1, when a target color is presented, the target color is measured (step S1). Since the target color is usually presented in the form of a color sample such as a printed material, the color may be measured with a colorimeter. If the target color is presented as a numerical value such as L ^* a ^* b ^* or XYZ, the numerical value may be used as it is.

Although what color system value is adopted as the colorimetric value is arbitrary, it is preferable to use a widely used standard color system value. As the color system, there are CIEXYZ color system and CIELAB (CIE1976L ^* a ^* b ^* ) color system defined by the International Commission on Illumination (CIE), but here L ^* a ^* b ^* color system. A system shall be used.

  Next, a test ink is prepared (step S2). This test ink is an ink that will be able to reproduce the target color when printed under predetermined printing conditions. This test ink may be prepared by a conventional method. That is, a skilled person may determine the blend of CMY process color ink and medium, or may calculate the blend with a conventional CCM apparatus and create the blend according to the calculation result. Further, if there is an ink having a color close to the target color among the inks prepared so far, it may be used as a test ink. Furthermore, if the print requested this time is so-called repeat printing and the previously created ink for the target color remains, whether or not the ink can still be used in this printing despite the secular change. In order to confirm this, the ink may be used as a test ink.

  Next, a developed color of the test ink prepared in step S2 is created and colorimetry is performed (step S3). At this time, it is only necessary to measure the color of the 100% portion of the displayed color.

Next, differences ΔL ^* and Δa ^* between the tristimulus values of the colorimetric values of the target color acquired in step S1 and the tristimulus values of the colorimetric values of the test ink developed in step S3 ^. , Δb ^* and a color difference ΔE between the two colorimetric values (step S4).

Here, the tristimulus values of the colorimetric values of the target color are L _T ^* , a _T ^* , b _T ^*, and the tristimulus values of the color measurement values of the test ink color product are L _S ^* , a _S ^* , As b _S ^*
ΔL ^* = L _T ^* −L _S ^* (1)
Δa ^* = a _T ^* −a _S ^* (2)
Δb ^* = b _T ^* −b _S ^* (3)
It shall be expressed as As is well known, the color difference ΔE is a distance between two points in the color space of the color system, and in this case,
ΔE = ((L _T ^* −L _S ^* ) ² + (a _T ^* −a _S ^* ) ² + (b _T ^* −b _S ^* ) ² ) ^1/2 (4)
It is represented by

As apparent from the equation (4), the color difference ΔE is not independent of the colorimetric values L ^* , a ^* , b ^*, but here, how close the color of the created ink is to the target color, Alternatively, the color difference ΔE is used as an index for measuring how far away.

Next, the tristimulus value differences ΔL ^* , Δa ^* , Δb ^* of these colorimetric values and the color difference ΔE between the two colorimetric values are all within a predetermined allowable range. Whether or not (step S5) and if all are within the allowable range (YES in step S5), the toning is completed. That is, the test ink at this time is used at the time of actual printing. Since the blending of each process color ink and medium in this ink is already known, the color matching of the ink at this time can be easily performed.

However, if all of ΔL ^* , Δa ^* , Δb ^* , and ΔE are not within the allowable range (NO in step S5) as determined in step S5, the process proceeds to step S6 and prepared in step S2. Correction amounts [Delta] C, [Delta] M, [Delta] Y, [Delta] Me for the blends of the process color inks and the medium from the test ink are obtained (step S6).

  ΔC, ΔM, ΔY, ΔMe can be obtained as follows. In the following, no unit is given to the amounts of CMY process color inks and media, but they may be weight or capacity.

  Now, let's consider modifying the C color ink composition of a certain ink by ΔC. Note that the sign of ΔC may be positive or negative. For example, when the sign of ΔC is positive, the amount of C color ink is insufficient in the test ink, and if the direction of increasing the blending of the C color ink is assumed, if the sign of ΔC is negative, the test ink Then, since there was too much amount of C color ink, it becomes the direction which reduces the mixing | blending of C color ink. When ΔC = 0, it means that the composition of the C color ink is not changed.

Now, when the composition of the C color ink is changed, the colorimetric value of the developed color of the ink after the change is changed. Focusing on L ^* value, when the L ^* value when changing small amount of blending of the C color ink is changed by ∂L ^* / ∂C, changing the formulation △ C only, L ^* variation value (∂L ^* / ∂C) · ΔC. The colorimetric value of the color developed product of the ink changes in the same way when the composition of the M color ink and the Y color ink is changed, and the colorimetric value changes in the same way when the composition of the medium is changed. .

Therefore, the correction amount of each process ink of CMY and the correction amount of medium are respectively set to ΔC, ΔM, ΔY, and ΔMe, and the mixing amount of each ink of C color, M color, and Y color is very small. the amount of change in L ^* value in the case of changing ^{each, ∂L * / ∂C, ∂L *} / ∂M, and a ∂L ^* / ∂Y, when is small change in the amount of blending of Mejiumu Assuming that the amount of change in the L ^* value is ∂L ^* / ∂Me, the L ^* value of the colorimetric values of the ink color developed after the correction of the composition is calculated from the L ^* value of the ink before the correction ( ∂L ^* / ∂C) · △ become ^{C + (∂L * / ∂M)} · △ M + (∂L * / ∂Y) · △ Y + (∂L * / ∂Me) · △ Me only change that. The same applies to the other colorimetric values a ^* and b ^* and the color difference ΔE.

From this, the tristimulus value differences ΔL ^* , Δa ^* , Δb ^* , and color difference ΔE of the colorimetric values acquired in step S4 are the process color inks from the test ink prepared in step S2. It can be seen that it can be expressed by the following simultaneous partial differential equation (5) using the correction amounts ΔC, ΔM, ΔY, ΔMe of the blending of medium and medium.

  Then, from the equation (5), the correction amounts ΔC, ΔM, ΔY, ΔMe of the blend can be obtained by the following equation (6).

  When the correction amounts ΔC, ΔM, ΔY, and ΔMe of each process color ink and medium are obtained in this way, the composition of each process color ink and medium of the test ink prepared earlier is corrected according to the correction amount. Then, a new ink is created, and this is used as a new test ink. The process returns to step S2, and the processes after step S3 are repeated until the judgment in step S5 becomes YES.

  In the series of steps described above, it is important that the viscosity of each process color ink used and the viscosity of the medium be the same and that they be kept the same. This is because color and gradation reproducibility change if the viscosity is different.

Also, △ L ^* of formula ^{(6), △ a *,} △ b *, so the 16 coefficients in the matrix of the △ E can be determined in advance, may be used that value. For example, the value of the coefficient ∂L ^* / ∂C is measured while sequentially changing the C color ink in several steps by an appropriate amount, and the blended amount of the C color ink and the colorimetric L ^* value at those times. It can be obtained based on the relationship. The same applies to other coefficients and coefficients relating to process colors of other colors. The same applies to the coefficient relating to the medium. For example, the color of the medium added to the ink of an appropriate color is measured while sequentially changing the appropriate amount in several steps, and the amount of the medium mixed in each time is measured. It can be determined based on the relationship with the color value.

  As described above, according to this toning method, the correction amount of each process color ink and medium from the test ink is determined by the colorimetric value of the target color and the colorimetric value of the developed product of the test ink. Since it is determined based on the difference and the color difference between the two, the accuracy of the correction amount can be improved, so that the number of corrections of the blending can be reduced, and the efficiency of the toning process can be improved. In addition, the cost of the ink used for creating the ink for achieving the target color can be reduced.

  Next, an embodiment of the toning device according to the present invention will be described. FIG. 2 is a diagram showing an embodiment of the toning device, in which 1 is control means, 2 is input means, 3 is display means, 4 is a database (hereinafter referred to as DB), 5a, 5b, 5c is an interface (hereinafter referred to as I / F).

  The control unit 1 is a control unit including a CPU, a ROM, a RAM, and the like, and executes processing to be described later. The input means 2 is composed of a keyboard, a mouse and the like. The display means 3 is composed of an appropriate display device such as a liquid crystal display device. The I / Fs 5a, 5b, and 5c are for connecting a measuring device (not shown in FIG. 2) such as a colorimeter, a viscometer, and a weight meter to the control unit 1.

  Various data are registered in the DB 4. First, in DB4, the inks created so far are registered, which includes information for identifying the ink such as the name and ID number of the ink, and the composition of each process color ink and medium in the ink. , And its colorimetric value, more specifically, the colorimetric value of the developed color of the ink, etc. are registered.

Also, in DB4, for each of the process color ink and medium used for toning, the amount of change in each colorimetric value and the amount of change in color difference when the blending is changed in a small amount correspond to various viscosity values. Each of them is registered. Therefore, As for the C color inks, for a single viscosity ^{value, ∂L * / ∂C, ∂a *} / ∂C, ∂b * / ∂C, 4 one coefficient value of ∂E / ∂C Is registered. As described above, since the color and gradation reproducibility change when the viscosity is different, for example, if there are three types of viscosity values used in printing, the above-mentioned cases of the three viscosity values are described above. These four coefficient values must be measured and registered in DB4. The same applies to M color ink, Y color ink, and medium.

  In addition, even if the process color ink and medium used for blending are the same and the viscosity is the same, if the printing conditions such as doctor conditions, printing pressure conditions, drying conditions, and original fabric types are different, the color Since the gradation reproducibility differs, even when the values of each of these printing conditions are different, the coefficients of the above four variations are obtained for each of the process color inks and media, and the DB4 However, in order to avoid complexity, only the viscosity value is taken up here.

  The operation will be described below. When performing toning, the operator first specifies each process color ink and medium used for blending and inputs them from the input means 2. Further, the operator inputs the given printing conditions from the input means 2. Here, the viscosity value is input from the input means 2.

Next, the operator measures the target color and inputs the colorimetric value. The colorimetric values may be input by inputting numerical values of L ^* , a ^* , b ^* from the input means 2, and a colorimeter is connected to one of the I / Fs 5a, 5b, 5c. If the colorimetric value can be automatically taken in from the colorimeter, it may be taken in from the colorimeter.

  Next, the blending amount of each process color ink and medium in the test ink prepared in step S2 of FIG. 1 is input. This blending amount may be numerically input by the operator from the input means 2, and for example, if a scale is connected to any of the I / Fs 5a, 5b, 5c, It is also possible to measure the ink and the medium, and to automatically take the measured value into the control means 1.

  Next, a developed color of the test ink is created, the color is measured, and the colorimetric value is input. The operator may input numerical values from the input unit 2 as numerical values, or may be automatically taken into the control unit 1 from the colorimeter via the I / F.

When the colorimetric value of the target color and the colorimetric value of the test ink developed color are taken in this way, the control means 1 uses the above equations (1) to (4) to express ΔL ^* , Δa ^* , Δb ^* and ΔE are calculated and these values are compared with respective threshold values registered in advance. If these four values are all equal to or less than the threshold values, step S5 in FIG. Is determined as YES, and the display means 3 displays that the test ink achieves the target color.

  In this case, since the ink that can achieve the target color has been toned, the composition of each process color ink and medium of this ink and the measurement, together with data that can specify this ink, such as the name or ID number, are measured. The color value is registered in DB4. This completes the toning work.

^{However, △ L *, △ a *} , △ b *, △ if they also exceed the threshold value in one of four values of E, in the test ink is determined that it is impossible to achieve the target color ( The determination in step S5 is NO), and the correction amount obtained by calculating the correction amount ΔC, ΔM, ΔY, ΔMe of the blend of the process color ink and the medium from the test ink according to the above equation (6). The values of ΔC, ΔM, ΔY, ΔMe are displayed on the display means 3.

  At this time, the control means 1 selects 16 variation coefficients constituting the 4 × 4 matrix used in the calculation of the equation (6) from among the variation coefficients registered in the DB 4. , It is the coefficient of variation for the process color ink and medium used for the previously input toning, and the coefficient of variation for which the printing conditions match, here the coefficient of variation for which the viscosity values match Is used for calculation.

  As a result, the operator can know the correction amounts ΔC, ΔM, ΔY, and ΔMe of each process color ink and medium from the test ink. Ink is prepared, and the process from step S2 onward in FIG. 1 is repeated using this as a new test ink.

  As described above, according to this toning apparatus, the process color ink and the medium composition of the ink that achieves the target color when printed under predetermined printing conditions are not obtained from the beginning, but appropriate. Since the correction amount of each process color ink and medium for achieving the target color from the test ink created by the method is obtained, the calculation is also a simple calculation of equations (1) to (4) and (6 ) Is a simple determinant, so that not only can it be performed easily and with high precision, but a special computer system is not required for this purpose, and a widely used personal computer system may be used. Can be configured at low cost.

  As described above, according to the toning method according to the present invention, the amount of correction of each process color ink and medium from the test ink, the colorimetric value of the target color, and the colorimetric value of the developed product of the test ink Therefore, the accuracy of the correction amount can be improved, and the number of corrections of the blending can be reduced, thereby improving the efficiency of the toning process. And a toning method capable of reducing the cost of the ink used to create the ink for achieving the target color, and according to the toning device according to the present invention, Each process to achieve the target color from the test ink prepared by an appropriate method, rather than from the beginning to determine the blend of each process color ink and medium that achieves the target color when printed under printing conditions Process color in And the amount of correction of the medium is calculated, so that the calculation is only a simple calculation and not only can be easily performed with high accuracy, but also a special computer system is not required for this purpose. Therefore, a toning device that can be configured at low cost is provided.

It is a flowchart which shows embodiment of the toning method which concerns on this invention. It is a figure which shows one Embodiment of the toning apparatus which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Control means 2 ... Input means 3 ... Display means 4 ... Database (DB)
5a, 5b, 5c ... Interface (I / F)

Claims (2)

In a method for blending all or part of cyan, magenta and yellow process color inks and medium,
Based on the difference between the colorimetric value of the target color and the colorimetric value of the developed product of the test ink and the color difference between these two colorimetric values, each process color ink and medium from the test ink formulation A toning method characterized by obtaining a correction amount of the color. Based on the difference between the colorimetric value of the target color and the colorimetric value of the developed product of the test ink and the color difference between these two colorimetric values, each process color ink and medium from the test ink formulation A toning device comprising control means for obtaining a correction amount of the color.

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