A method for improving printing ink color matching based on controlling base color gradient

Abstract

The application discloses a method for improving printing ink color matching based on control of base color gradient, which comprises the following steps: (1) obtaining a base color ink series ladder ruler; (2) obtaining reflectivity coefficients of the base color ink series ladder ruler; (3) selecting the reflectivity coefficients that can be used to calculate the absorption and scattering coefficient ratio of the base color ink; (4) calculating the absorption and scattering coefficient ratio of the base color ink; and (5) formula calculation. The application increases the control of the reflectivity coefficients of the base color ink mixed with the diluent in the formula model, selects all the reflectivity coefficients that can be used to calculate the absorption and scattering coefficient ratio of the base color ink yellow, improves the accuracy of the absorption and scattering coefficient ratio of the base color ink, improves the stability and accuracy of the difference between the predicted target spectrum and the target spectrum, and has important significance for the development and application of the ink automatic color matching system.

Description

Technical Field

[0001] The invention belongs to the field of printing ink color matching, and in particular relates to a method for improving printing ink color matching based on controlling base color gradient. Background Art

[0002] A computer color matching method based on the Kubelka-Munk theory (KM theory) employs the following principles: a series of primary ink scales are obtained by mixing a base ink with a diluent, and the absorption and scattering coefficient ratios (i.e., K / S) of the base inks are calculated using the reflectivity coefficients of the base ink scales. Furthermore, the absorption and scattering coefficient ratios of the target ink are calculated based on the reflectivity coefficients of the target ink. Finally, the base ink formula for the target ink is calculated from the absorption and scattering coefficient ratios of the target ink and the base ink. However, in practical applications, a new batch of base inks may differ (spectrally or in color) from the previous batch. To match the new batch of base inks with the original target ink, the reflectivity coefficients of the series of base ink scales of the new batch of base inks must be re-entered. However, when the formula is obtained after re-entry, the formula accuracy may be low. Consequently, when this computer color matching method is applied or developed into color matching software, it can be unstable and sometimes unstable during use. Summary of the Invention

[0003] The purpose of the present invention is to provide a method for improving the color matching of printing inks based on controlling the base color gradient, so as to solve the above problems.

[0004] The present invention provides a method for improving printing ink color matching based on controlling base color gradient, comprising the following steps:

[0005] Step (1): Obtaining the initial base color ink series ladder

[0006] Select a base color ink and mix the base color ink with diluent in a ratio of c i :(1-c i ), i=1,2,…,n mixture, n is the number of base color ink series scales; c i is the percentage of base ink in the i-th gradient sample made by mixing base ink and diluent, where c1 is the maximum percentage of base ink in the matching group;

[0007] Step (2): Obtaining the reflectivity coefficient of the base color ink series gradient color sample

[0008] According to the ratio of step (1), the mixed ink is spread on paper to obtain a series of n scale color samples. The reflectivity coefficients of the series of scale color samples are measured to obtain n groups of reflectivity coefficients. The ratio is c i :(1-c i) is the reflectivity coefficient of the sample i (λ);

[0009] Step (3): Select the first set of reflectance coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink.

[0010] The reflectivity coefficient of the series of gradient color samples of C1 base color ink and 1-C1 diluent is the first group, which can be used to calculate the absorption and scattering coefficient ratio of yellow base color ink, that is, The first group is the reflectance coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink;

[0011] Step (4): Select the remaining reflectance coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink, and select the formula:

[0012]

[0013] Among them, count(·) is a statistical function, which counts the changes in this function with the wavelength λ. If R2(λ) meets the conditions in the selected formula, then R2(λ) is the second set of reflectivity coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink. If R2(λ) does not meet the conditions in the selection formula, continue to judge whether R3(λ) is According to this method, we can judge R i Is (λ)(i=2,…,n) a reflectivity coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink until all R n (λ) is judged to be is the last reflectivity coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the primary color ink; wherein m is the number of groups of reflectivity coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the primary color ink;

[0014] Step (5), calculate the absorption and scattering coefficient ratio of the base color ink

[0015] The m group obtained in step (4) can be used to calculate the reflectivity coefficient of the absorption and scattering coefficient ratio of the primary color ink, and the absorption and scattering coefficient ratio of the primary color ink is calculated;

[0016] Step (6), setting the primary color ink to include yellow ink, magenta ink and cyan ink, repeating steps (1) to (5) respectively, and obtaining the absorption and scattering coefficient ratios of yellow ink, magenta ink and cyan ink respectively. and and the m values ​​of yellow ink, magenta ink, and cyan ink;

[0017] Step (7), formula calculation

[0018] Select the target ink, match the target ink, and calculate the formula for matching the base inks yellow, magenta and cyan and

[0019] As a further preference of the above scheme:

[0020] The calculation formula for calculating the absorption and scattering coefficient ratio of the primary color ink in step (5) is:

[0021]

[0022]

[0023] In the formula, is the ratio of the absorption coefficient to the scattering coefficient of the paper portion of the scale color development sample; is the ratio of the absorption coefficient to the scattering coefficient of the i-th (i=1,…,m) scale color sample made by mixing the base color ink and the diluent; k(λ) is the absorption coefficient; s(λ) is the scattering coefficient.

[0024] As a further preference of the above scheme:

[0025] The calculation formula of the absorption and scattering coefficient ratio of the base color ink is:

[0026] By the formula Calculated, R p (λ) is the reflectivity coefficient of the paper part in the gradient color sample.

[0027] As a further preference of the above scheme:

[0028] The calculation formula of the absorption and scattering coefficient ratio of the base color ink is:

[0029] By the formula Calculated, where is the reflectivity coefficient of the i-th gradient sample obtained by mixing the base color ink and the diluent after steps (3) and (4).

[0030] As a further preference of the above scheme:

[0031] The calculation formula of the formula in step (7) is:

[0032]

[0033]

[0034] in, is the ratio of the sample absorption and scattering coefficients of the target ink; is the ratio of the absorption coefficient to the scattering coefficient of the paper portion of the target ink sample.

[0035] As a further preference of the above scheme:

[0036] The calculation formula of the formula Depend on Calculated, R t (λ) is the reflectance coefficient of the target ink sample obtained by measurement.

[0037] As a further preference of the above scheme:

[0038] In the step (4), 2≤m≤n.

[0039] As a further preference of the above scheme:

[0040] The n value of the yellow ink, magenta ink and cyan ink is 12, the m value of the yellow ink is 6, the m value of the magenta ink is 12, and the m value of the cyan ink is 11.

[0041] The beneficial effects of the present invention are as follows:

[0042] The present invention adds control over the reflectance coefficient of the color development sample of the mixed base ink and diluent in the formula model, selects all the reflectance coefficients in this series that can be used to calculate the ratio of the yellow absorption and scattering coefficients of the base ink, improves the accuracy of the absorption and scattering coefficient ratio of the base ink, and improves the stability and accuracy of the difference between the predicted target spectrum and the target spectrum, which is of great significance to the development and application of the automatic ink color matching system. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0044] Figure 1 is the ratio of the absorption and scattering coefficients of the yellow primary color ink before and after the control of the reflectivity coefficient obtained in the embodiment, which can be used to calculate the absorption and scattering coefficient ratio of the yellow primary color ink;

[0045] Figure 2 is the ratio of the absorption and scattering coefficients of the magenta primary color ink before and after the control of the reflectivity coefficient obtained in the embodiment, which can be used to calculate the absorption and scattering coefficient ratio of the magenta primary color ink;

[0046] Figure 3 is the ratio of the absorption and scattering coefficients of the cyan primary color ink before and after the control of the reflectivity coefficient obtained in the embodiment, which can be used to calculate the absorption and scattering coefficient ratio of the cyan primary color ink;

[0047] Figure 4 In the embodiment, for target formulation #1, the reflectance coefficient of the base color oil yellow absorption and scattering coefficient ratio can be used to calculate the spectral reflectance coefficient reconstructed by the absorption and scattering coefficient ratio of the base color ink before control, the spectral reflectance coefficient reconstructed by the absorption and scattering coefficient ratio of the base color ink after control, and the spectral reflectance coefficient of target formulation #1;

[0048] Figure 5 It is for the #2 target formula in the embodiment, and can be used to calculate the reflectance coefficient of the absorption and scattering coefficient ratio of the primary color ink to reconstruct the spectral reflectance coefficient of the absorption and scattering coefficient ratio of the primary color ink before control, and the spectral reflectance coefficient of the absorption and scattering coefficient ratio of the primary color ink after control, as well as the spectral reflectance coefficient of the #2 target formula. DETAILED DESCRIPTION

[0049] The present invention will be further described below with reference to specific embodiments. These embodiments are intended only to illustrate the present invention and are not intended to limit the scope of the present invention. The structural features of the present invention will now be described in detail with reference to the accompanying drawings.

[0050] The present invention will be further described below with reference to specific examples. These examples are intended to illustrate the present invention only and are not intended to limit its scope. In this example, the spectrophotometer model is an X-Rite SP64, the measurement wavelength range is 400-700 nm, and the wavelength interval is 10 nm. The base ink and diluent are yellow, magenta, and cyan from Siegwerk's fold-resistant series, respectively. The paper is white cardboard specifically used for cigarette packaging, and the color development instrument model is SM-225. It should be noted that the present invention is not limited to the above-mentioned inks, paper, and measuring equipment, and is equally applicable to other types and brands of inks, white paper, and measuring equipment.

[0051] Example

[0052] This embodiment provides a method for improving printing ink color matching based on controlling base color gradient, comprising the following steps:

[0053] Step (1): Obtaining the initial base color ink series ladder

[0054] Select yellow ink as base ink, mix yellow base ink with diluent in the ratio of c i :(1-c i ), i = 1, 2, ..., n mixture, n is the number of yellow base color ink series scales; c iThe percentage content of the yellow base ink in the i-th gradient sample made by mixing the yellow base ink with the diluent; in this embodiment, the yellow base ink of Shengweike obtains n as 12, and the ratios are 100%:0%, 87.5%:12.5%, 75%:25%, 62.5%:37.5%, 50%:50%, 40%:60%, 30%:70%, 25%:75%, 20%:80%, 15%:85%, 10%:90% and 5%:95% respectively;

[0055] Step (2), obtaining the reflectance coefficients of the series of gradient color sample sheets of the base ink

[0056] According to the ratios of step (1), the mixed ink is respectively color developed on paper to obtain a series of n series of gradient color sample sheets, and then the reflectance coefficients of the series of gradient color sample sheets are measured to obtain n groups of reflectance coefficients, that is, the reflectance coefficients of the sample sheets with the formula of step (1) as c i :(1-c i ) are R i (λ).

[0057] Step (3), selecting the first group of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the base ink

[0058] Suppose that c1 is the maximum percentage of the base ink in the series of formulas of c1,…,c n (preferably 100%, 87.5%, 75%, 62.5%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5% in this embodiment), and the reflectance coefficients of the series of gradient color sample sheets of the c1 yellow base ink and 1-c1 diluent are the first group of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the yellow base ink, that is, The first group of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the yellow base ink;

[0059] Step (4), selecting the remaining reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the base ink

[0060] The selection method uses the following formula:

[0061]

[0062] Wherein, count(·) is a statistical function, that is, the number of changes with wavelength λ in this function; if R2(λ) meets the condition in formula (1), then R2(λ) is obtained as the second group of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the base ink If R2(λ) does not meet the condition in formula (1), then it is determined whether R3(λ) is R i (i = 2,..., n) are reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the primary ink, until all R n (λ) are judged whether they are is the last reflectance coefficient that can be used to calculate the absorption and scattering coefficient ratio of the yellow primary ink; wherein m is the number of groups of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the yellow primary ink (corresponding to the series of color spread samples in which the primary ink accounts for 100%, 87.5%, 75%, 62.5%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5%, respectively), and 2≤m≤n;

[0063] Step (5), calculating the absorption and scattering coefficient ratio of the primary ink

[0064] Using the m groups of reflectance coefficients that can be used to calculate the absorption and scattering coefficient ratio of the yellow primary ink obtained in step (4), the absorption and scattering coefficient ratio of the yellow primary ink is calculated, and the calculation formula is as follows:

[0065]

[0066]

[0067] In formula (2), is the absorption coefficient and scattering coefficient ratio of the paper part of the color spread sample, which is calculated by formula R p (λ) is the reflectance coefficient of the paper part of the color spread sample;

[0068] In formula (2), is the absorption coefficient and scattering coefficient ratio of the i-th (i = 1,..., m) gradient (i.e. the i-th primary ink series of color spread gradient) sample made by mixing the primary ink and the diluent, which is calculated by formula , wherein is the reflectance coefficient of the i-th (i = 1,..., m) gradient (i.e. the i-th primary ink series of color spread gradient) sample made by mixing the primary ink and the diluent after steps (3) and (4). In this embodiment, the yellow primary ink of Shengweike obtains m = 6, wherein the percentage of this yellow primary ink is 100%, 50%, 25%, 15%, 10%, 5%, respectively;

[0069] Step (6), selecting the magenta ink as the base ink, repeating steps (1) to (5) to obtain the absorption and scattering coefficient ratio of the magenta base ink; in this embodiment, the magenta base ink of Shengweike obtains n=12 and m=12, wherein the percentages of the magenta base ink are 100%, 87.5%, 75%, 62.5%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, and 5%, respectively;

[0070] Step (7), selecting the cyan ink as the base ink, repeating steps (1) to (5) to obtain the absorption and scattering coefficient ratio of the cyan base ink; in this embodiment, the cyan base ink of Shengweike obtains n=12 and m=11, wherein the percentages of the cyan base ink are 100%, 75%, 62.5%, 50%, 40%, 30%, 25%, 20%, 15%, 10%, 5%, and 0%, respectively;

[0071] Step (8), formula calculation

[0072] Selecting the target ink, matching the color of the target ink, and calculating the formula for matching the color of the target ink with the base ink, and the formula calculation formula is:

[0073]

[0074]

[0075] wherein, are the absorption and scattering coefficient ratios of the yellow, magenta, and cyan inks calculated in steps (1) to (6) above, is the absorption and scattering coefficient ratio of the target ink sample, which is calculated by t is the reflectance coefficient of the target ink sample obtained by measurement, is the absorption and scattering coefficient ratio of the paper part in the target ink sample, which is calculated by the formula are the predicted matching ratios of the yellow ink, the magenta ink, and the cyan ink calculated, i.e., the aforementioned formula; if the percentage matching ratio of the diluent is

[0076] Comparative Example

[0077] In order to verify the effectiveness of the method of the present application, two target colors are configured in this comparative example, and the absorption and scattering coefficient ratios of the base inks are obtained without controlling the spectral reflectance coefficient of the base ink series ladder, and the absorption and scattering coefficient ratios of the base inks obtained by the color matching method of the present application are compared, and the spectral difference and color difference of the color matching effects obtained by the two methods are compared after the spectral reflectance is reconstructed, and the specific process is as follows: ​​

[0078] Step (1): Select a target ink and use the method in the above embodiment to obtain the percentage of yellow base ink. Base color ink percentage And the percentage of cyan base ink As an actual formula, the base color ink formula is mixed to obtain the target ink after color matching, and the color is spread on the target paper to form a color matching sample;

[0079] Step (2): Measure the reflectivity coefficient R of the color matching sample M (λ)

[0080] Step (3): Measure the reflectivity coefficient R of the target sample t (λ);

[0081] Step (4), calculate the spectral difference

[0082] Calculate R using the formula M (λ) and R t (λ) spectral difference, calculated as:

[0083] SE=||R t (λ)-R M (λ)||2

[0084] Where ||·||2 is the l2 norm, SE is the spectral difference;

[0085] Step (4), calculate color difference

[0086] Calculate R under standard light source D50, CIE1931, 2 degree field of view M (λ) and R t (λ) DE2000 color difference between them.

[0087] The comparison results are shown in Table 1 below:

[0088] Table 1 Comparison of spectral difference and chromatic aberration

[0089]

[0090] As shown in Table 1 above, in the operation of matching target color No. 1, the base color ink series gradient scale gradient reflectance coefficient is not controlled, and the calculated base color ink absorption and scattering coefficient ratio is combined with the formula of target color 1. The spectral difference between the reconstructed spectrum and the actual spectrum of target color 1 is 0.3695, while the base color ink series gradient scale gradient reflectance coefficient is controlled by the method of the present invention. The spectral difference obtained is 0.0478, which is smaller and reduced by 87.06% compared with the uncontrolled method; under D50 light source, the color difference of the reconstructed spectral difference under the uncontrolled method is 10.9416, while the color difference obtained by controlling the base color ink series gradient scale gradient reflectance coefficient by the method of the present invention is 1.8705, which is smaller and reduced by 82.9% compared with the uncontrolled method;

[0091] As shown in Table 1 above, in the operation of matching target color No. 2, the gradient reflectance coefficient of the base color ink series scale is not controlled, and the absorption and scattering coefficient ratio of the base color ink is calculated. Combined with the formula of target color 1, the spectral difference between the reconstructed spectrum and the actual spectrum of target color 1 is 0.1592, and the spectral difference obtained by controlling the gradient reflectance coefficient of the base color ink series scale by the method of the present invention is 0.0492. The spectral difference of the present invention is smaller and is reduced by 69.1% compared with the uncontrolled method; under the D50 light source, the color difference of the reconstructed spectral difference under the uncontrolled method is 7.5332, and when the gradient reflectance coefficient of the base color ink series scale is controlled by the method of the present invention, the color difference obtained is 1.5810. The color difference of the present invention is smaller and is reduced by 79.01% compared with the uncontrolled method; therefore, the present invention can achieve the consistency of the color matching ink and the target ink color matching, and the stability is higher.

[0092] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiment. All technical solutions based on the concept of the present invention are within the scope of protection of the present invention. It should be noted that for those skilled in the art, various improvements and modifications that do not depart from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A method for improving printing ink color matching based on controlling base color gradient, characterized in that: The following steps are involved: Step (1): Obtaining the initial base color ink series ladder Select a base color ink and mix the base color ink with diluent in a ratio of c i :(1-c i ), i=1,2,…,n mixture, n is the number of base color ink series scales; c i is the percentage of base ink in the i-th gradient sample made by mixing base ink and diluent, where c1 is the maximum percentage of base ink in the matching group; Step (2): Obtaining the reflectivity coefficient of the base color ink series gradient color sample According to the ratio of step (1), the mixed ink is spread on paper to obtain a series of n scale color samples. The reflectivity coefficients of the series of scale color samples are measured to obtain n groups of reflectivity coefficients. The ratio is c i :(1-c i ) is the reflectivity coefficient of the sample i (λ); Step (3): Select the reflectance coefficients of the series of gradient color samples of the first set of reflectance coefficients c1 primary color ink and 1-c1 diluent that can be used to calculate the absorption and scattering coefficient ratio of the primary color ink as the first set that can be used to calculate the absorption and scattering coefficient ratio of the yellow primary color ink, that is, The first group is the reflectance coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink; Step (4): Select the remaining reflectance coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink, and select the formula: Among them, count(·) is a statistical function, which counts the changes in this function with the wavelength λ. If R2(λ) meets the conditions in the selected formula, then R2(λ) is the second set of reflectivity coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink. If R2(λ) does not meet the conditions in the selection formula, continue to judge whether R3(λ) is According to this method, we can judge R i Is (λ)(i=2,…,n) a reflectivity coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the base color ink until all R n (λ) is judged to be is the last reflectivity coefficient that can be used to calculate the ratio of the absorption and scattering coefficients of the primary color ink; wherein m is the number of groups of reflectivity coefficients that can be used to calculate the ratio of the absorption and scattering coefficients of the primary color ink; In the step (4), 2≤m≤n; Step (5), calculate the absorption and scattering coefficient ratio of the base color ink The m group obtained in step (4) can be used to calculate the reflectivity coefficient of the absorption and scattering coefficient ratio of the primary color ink, and the absorption and scattering coefficient ratio of the primary color ink is calculated; Step (6), setting the primary color ink to include yellow ink, magenta ink and cyan ink, repeating steps (1) to (5) respectively, and obtaining the absorption and scattering coefficient ratios of yellow ink, magenta ink and cyan ink respectively. and and the m values ​​of yellow ink, magenta ink, and cyan ink; Step (7), formula calculation Select the target ink, match the target ink, and calculate the formula for matching the base inks yellow, magenta and cyan and 2. The method for improving printing ink color matching based on controlling base color gradient according to claim 1, characterized in that: The calculation formula for calculating the absorption and scattering coefficient ratio of the primary color ink in step (5) is: In the formula, is the ratio of the absorption coefficient to the scattering coefficient of the paper portion of the scale color development sample; is the ratio of the absorption coefficient to the scattering coefficient of the i-th (i=1,…,m) scale color sample made by mixing the base color ink and the diluent; k(λ) is the absorption coefficient; s(λ) is the scattering coefficient.

3. The method for improving printing ink color matching based on controlling base color gradient according to claim 2, characterized in that: The calculation formula of the absorption and scattering coefficient ratio of the base color ink is: By the formula Calculated, R p (λ) is the reflectivity coefficient of the paper part in the gradient color sample.

4. The method for improving printing ink color matching based on controlling base color gradient according to claim 2, characterized in that: The calculation formula of the absorption and scattering coefficient ratio of the base color ink is: By the formula Calculated, where is the reflectivity coefficient of the i-th gradient sample obtained by mixing the base color ink and the diluent after steps (3) and (4).

5. The method for improving printing ink color matching based on controlling base color gradient according to claim 1, characterized in that: The calculation formula of the formula in step (7) is: in, is the ratio of the sample absorption and scattering coefficients of the target ink; is the ratio of the absorption coefficient to the scattering coefficient of the paper portion of the target ink sample.

6. The method for improving printing ink color matching based on controlling base color gradient according to claim 5, characterized in that: The calculation formula of the formula Depend on Calculated, R t (λ) is the reflectance coefficient of the target ink sample obtained by measurement.

7. The method for improving printing ink color matching based on controlling base color gradient according to claim 1, characterized in that: The n value of the yellow ink, magenta ink and cyan ink is 12, the m value of the yellow ink is 6, the m value of the magenta ink is 12, and the m value of the cyan ink is 11.

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