Automatic screening method for primary color printing ink

Abstract

The invention discloses an automatic screening method for primary color ink. The method comprises the following steps: (1) preparing a training sample sheet and a target ink test sample sheet; calculating a basic spectrum matrix of the target ink and a mixing parameter vector of primary color ink in the target mixed ink, and selecting a basic spectrum vector corresponding to a non-zero parameter; (2) manufacturing a primary color ink sample page to obtain a reflectivity vector of pure primary color ink; (3) calculating an included angle between adjacent vectors of the reflectivity vectors of the pure primary color ink, and completing preliminary screening through the included angle; and (4) calculating an included angle between a vector in each basic spectrum matrix and each primarily screened primary color ink reflectivity spectrum vector, and finishing final screening according to the included angle. According to the method, before the formula is calculated by using the color matching method, the primary color ink contained in the prepared ink can be automatically selected.

Description

Technical Field

[0001] The invention relates to the technical field of printing ink color matching, and in particular to an automatic screening method for base color ink. Background Art

[0002] In the printing, coating and other industries, companies often mix new color inks with existing base color inks (also called basic color inks). In the process of configuring new color inks, it is usually necessary to rely on professional operators to determine which base color inks are contained in this color ink. Although in some color matching methods (such as color matching methods based on KM theory), even if the operator has no experience and makes arbitrary choices, in most cases these methods can still calculate the percentage of each base color ink in any color ink, that is, the formula. However, these methods have the risk of failure. For example, if the base color ink of a certain color ink is not selected, the accurate formula of this color ink cannot be obtained. For example, if multiple similar base color inks are selected, the final formula may contain the percentage of these two similar base color inks at the same time, increasing the complexity of mixing. Summary of the invention

[0003] The purpose of the present invention is to provide a method for automatically screening primary color inks to solve the above problems.

[0004] The present invention provides a method for automatically screening primary color inks, comprising the following steps:

[0005] Step (a), select m base color inks, select two different base color inks in turn and mix them, prepare N training samples, and calculate the reflectivity of the pure ink on the training samples

[0006] Step (ii), confirm the target ink, prepare the target ink test sample, and obtain the pure target ink reflectivity R on the sample tc (λ);

[0007] Step (3): According to and R tc (λ) Calculate the basic spectrum matrix of the target ink A = [a1 … a k … a m ] T , and the mixing parameter vector of the base color ink in the target mixed ink The calculation formula is:

[0008]

[0009] In the formula, h represents the positive rule parameter; X=[x1 … x j … x Nx t ] T , x j =[x j1 … x jk … x jm ], Vector a in the basic spectral matrix A k =[a k (400) a k (410) … a k (690) k (700)], det() is the determinant of the calculation matrix;

[0010] The calculated basic spectrum vectors are combined into a matrix, which is the basic spectrum matrix A of the target ink; the corresponding basic spectrum vectors of non-zero parameters are selected in the mixed parameter vector;

[0011] Step (iv), making a base color ink sample and calculating the reflectivity of the pure base color ink on the sample Get the reflectivity vector of the pure base color ink pass The angle with the x-axis, rearrange Numbered from 1 to k;

[0012] Step 5: Calculation The angle α between adjacent vectors k-1 and α k+1 , through the angle α k-1 and α k+1 Determine the reflectivity vector of pure base color ink Whether the corresponding base color ink is a mixed member of the target ink, after screening, the spectral vector corresponding to the base color ink set is

[0013] Step (six): Based on, repeat step (V) until all similar base color inks are screened out and the corresponding reflectance spectrum vector is obtained P≤P1≤m;

[0014] Step (seven), calculate the vector a in each basic spectrum matrix obtained in step (three) k ∈(a1 … a O ) and the reflectance spectrum vector of each primary color ink selected in step (six) The angle θ between i ; Determine the vector a in the primary color spectrum matrix k ∈(a1 … a O ) Whether it contains the reflectance spectrum of the base color ink, the judgment principle is:

[0015]

[0016] Where, subscript k = 1,…,Q, and Q ≤ P, The corresponding base ink is the base color ink finally screened out.

[0017] As a further preference of the above scheme:

[0018] The preparation method of the training sample in step (i) is: select two different primary color inks from m primary color inks in sequence, and use c i :1-c i Mixed in proportion, 0<c i <1, i=1,…,n, n represents the number of mixtures of two base color inks with different percentages; the mixed inks are printed on white paper to prepare a total of N training samples.

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

[0020] The reflectivity of pure ink on the training sample in step (a) The calculation formula is:

[0021]

[0022] in,

[0023] In the formula, subscript j=1,…,N, and They represent the absorption coefficient and scattering coefficient of the pure mixed ink on the j-th training sample, respectively, where the superscript c represents the pure mixed ink.

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

[0025] In the step (ii), the target ink is spread on a white paper to prepare a test sample; and then the reflectivity R of the test sample is measured. t (λ) and the reflectivity R of the paper in the test sample p (λ); Calculate the pure target ink reflectivity R tc (λ).

[0026] As a further preference of the above scheme:

[0027] The pure target ink reflectivity R tc The calculation formula of (λ) is:

[0028]

[0029] in,

[0030] Among them, Ktc (λ) and S tc (λ) respectively represent the absorption coefficient and scattering coefficient values ​​of pure target ink on the target ink test sample, and the superscript tc represents pure target ink.

[0031] As a further preference of the above scheme:

[0032] The principle for determining the mixed members in step (V) is:

[0033] If α k-1 <10, and α k+1 <10, then and The corresponding base color ink is removed. The corresponding base color ink is used as one of the optional base color inks;

[0034] If α k-1 <10, and α k+1 ≥10, then The corresponding base color ink is removed. and The corresponding base color ink is used as one of the optional base color inks;

[0035] If α k-1 ≥10, and α k+1 ≥10, then and The corresponding base color ink is used as one of the optional base color inks.

[0036] As a further preference of the above scheme:

[0037] Step (VII) Angle θ i The calculation formula is:

[0038]

[0039] Beneficial effects of the present invention: The proposed method for automatically screening primary color inks can automatically select the primary color inks contained in the matched inks before using the color matching method to calculate the formula, as follows:

[0040] The present invention first uses an orthogonal regularization optimization method to obtain a basic spectrum matrix of a target ink, and then uses vectors in the basic spectrum matrix to select a base color ink that constitutes the target ink from existing base color inks. The present invention is aimed at operators without any background knowledge, and before formula calculation, the existing base color inks are automatically screened. The screened base color inks are the base color inks necessary for mixing to obtain the target ink, thereby reducing the risk of failing to obtain an accurate formula due to insufficient selection, and reducing the complexity of formula calculation due to excessive selection, which is of great significance to the development and application of an automatic ink color matching system. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with specific examples. These examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0042] The present invention is further described below in conjunction with specific embodiments. These embodiments are only used to illustrate the present invention and are not used to limit the scope of the present invention. Now in conjunction with the specification, the structural features of the present invention are described in detail. In this embodiment, the measuring instrument is a spectrophotometer, model SP64 of X-Rite, the measuring wavelength range is 400-700nm, the wavelength interval is 10nm, the base color inks are yellow, magenta, cyan, orange, red, blue, dark blue, and green of the Siegwerk folding series, the paper is white cardboard specially used for cigarette packs, 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, papers and measuring equipment, and is also applicable to other types and brands of inks, papers and measuring equipment.

[0043] Example

[0044] The present embodiment provides a method for automatically screening primary color inks, comprising the following steps:

[0045] Step (1), preparing training samples;

[0046] Select m kinds of primary color inks, select two different primary color inks from the m kinds of primary color inks in sequence, and use c i :1-c i (0<c i <1) mixing to obtain mixed ink, i=1, ..., n, n represents the number of mixtures of two base color inks with different percentages; using a color development instrument to print the mixed ink on white paper, to prepare a total of N=n×(m-1)m / 2 training samples;

[0047] In this embodiment, the selected m primary color inks refer to the number of primary color inks currently owned by the enterprise; 8 primary color inks are selected, namely m=8, which are yellow, magenta, cyan, orange, red, blue, dark blue, and green; firstly, the yellow and magenta primary color inks are mixed, and three different proportions are mixed, namely i=3, and the mixing ratios of yellow and magenta are respectively: c1:1-c1=0.2:0.8, c2:1-c2=0.5:0.5, c3:1-c3=0.8 :0.2; and so on, in this embodiment, the mixing ratio of each other two different color base inks is also: c1:1-c1=0.2:0.8, c2:1-c2=0.5:0.5, c3:1-c3=0.8:0.2, and a total of N mixed inks are obtained; the mixed inks are placed on white paper using a colorimeter to prepare a total of N=n×(m-1)m / 2=3×(8-1)×8 / 2=84 training samples; that is, in this embodiment, N=84;

[0048] Step (ii), measuring the reflectivity of the training sample;

[0049] Use the spectrophotometer SP64 to measure the reflectivity R of the N training samples obtained in step (a) j (λ), j = 1, ..., N; and measure the reflectivity R of the paper in the training sample p (λ), λ represents the wavelength, λ∈[400,700], and the wavelength interval is 10nm;

[0050] Step (iii), calculating the reflectivity of the pure mixed ink on the training sample;

[0051] According to the reflectivity R of the training sample obtained in step (2) j (λ) and the reflectivity R of the paper in the training sample p (λ), the reflectivity of the pure mixed ink on the training sample is calculated using the following formula (1):

[0052]

[0053] in,

[0054] In formula (1), subscript j=1, ..., N, in this embodiment, N=84; and They represent the absorption coefficient and scattering coefficient of the pure mixed ink on the jth training sample, respectively, where the superscript c represents the pure mixed ink;

[0055] Step (iv), prepare a target ink test sample, and obtain the pure target ink reflectivity R on the test sample tc (λ);

[0056] First, confirm the target ink, which can be any mixed ink; then, use a colorimeter to develop the mixed ink on white paper to prepare a test sample, which is the sample of the target ink; then use the measuring instrument SP64 to measure the reflectivity R of the test sample t (λ), and the reflectivity R of the paper in the test sample p (λ); Finally, the pure target ink reflectivity R is calculated tc (λ);

[0057] The reflectivity R of the pure target ink on the above test sample tc (λ) is calculated as follows:

[0058]

[0059] in,

[0060] Among them, K tc (λ) and S tc (λ) respectively represent the absorption coefficient and scattering coefficient values ​​of pure target ink on the target ink test sample, and the superscript tc represents pure target ink;

[0061] It should be noted that the method of the present invention can be applied to any target ink, that is, a mixed ink obtained by mixing any base color ink in any ratio; in the art, the aforementioned target ink is usually any one base color selected in any ratio. Proportioned mixing to obtain the target ink, in practical application, It is unknown, so it is necessary to determine which base color inks the target ink is mixed with;

[0062] Furthermore, in the actual application of the method of the present invention, generally, when a printing enterprise continuously produces a product, some target ink produced last time will remain. This target ink is the mixed ink formed by mixing the primary color inks that can be determined by the method of the present invention. In addition, if there is no remaining target ink, the printed product that has been printed with the target ink is used as a target ink test sample, and the reflectivity of the printed product and the reflectivity of the printed product paper can be directly calculated using formula (2) to obtain the reflectivity of the pure target ink. Furthermore, in order to facilitate the verification of the effectiveness and accuracy of the method of the present invention, in this embodiment, yellow and magenta primary color inks are selected and mixed at a ratio of 0.75:0.25 to obtain a target ink.

[0063] Step (V): Extract the basic spectrum matrix A in the target ink = [a1 … a k … a m ] T and the mixing parameter vector of the base color ink in the target ink

[0064] The reflectivity of the pure mixed ink (the mixing ratio of the ink is known) on the training sample obtained in step (iii) is used to and the reflectivity R of the pure target ink (the mixing ratio of the ink is unknown) on the test sample obtained in step (iv) tc (λ), calculate the basic spectrum matrix of the target ink A = [a1 … a k … a m ] T , and the mixing parameter vector of the base color ink in the target mixed ink

[0065] In this embodiment, m=8, namely yellow, magenta, cyan, orange, red, blue, dark blue, and green primary color inks respectively;

[0066] The basic spectrum matrix A in the target ink is A = [a1…a k a m ] T , and the mixing parameters of the base color ink in the target ink The calculation is as follows:

[0067]

[0068] In formula (3), h represents the normal rule parameter, The regularization term can ensure that the differences between the vectors in the basic spectral matrix are greatly differentiated, so that the vector a in the basic spectral matrix k There is no similarity in main features between them, so that similar base color inks can be avoided when selecting base color inks based on the basic spectrum matrix;

[0069] In formula (3), X=[x1 … x j … x N x t ] T , x j =[x j1 … x jk … x jm ], The basic spectrum matrix A is a k =[a k (400) a k (410) … a k (690) k (700)], det() means to calculate the determinant of the matrix;

[0070] The basic spectrum vectors calculated above are combined into a matrix (i.e., basic spectrum matrix) A, which is expressed as follows:

[0071] A=[a1 … a k … a m ] T , a k It is composed of different λ (λ∈[400,700], with a wavelength spacing of 10nm), that is, a k =[a k (400) a k (410) … a k (690)a k (700)];

[0072] Step (six): Select the mixing parameters of the base color ink in the target ink. The corresponding basis spectral vectors for non-zero parameters in The selection principles are as follows:

[0073]

[0074] Among them, O represents the basis The number of remaining basis spectral vectors after non-zero filtering of the mixing parameters;

[0075] In this embodiment, two basic spectrum vectors are calculated, that is, O=2;

[0076] Step (VII): Making a base color ink sample and calculating the reflectivity of the pure base color ink on the base color ink sample

[0077] The m primary color inks selected in step (i) are respectively developed on white paper using a color development instrument to obtain primary color ink samples, and then the reflectivity of the primary color ink samples is measured using a measuring instrument. and the reflectivity R of the paper in the base color ink sample p (λ), where k = 1,…,m; calculate the reflectivity of the pure base color ink

[0078] In this embodiment, yellow, magenta, cyan, orange, red, blue, dark blue, and green primary color inks are respectively applied on white card paper to prepare 8 primary color ink samples; the reflectivity of pure primary color ink on the primary color ink sample is The calculation is as follows:

[0079]

[0080] in, and They represent the absorption coefficient and scattering coefficient of the pure primary color ink on the kth primary color ink sample, and the superscript b represents the pure primary color ink

[0081] Step (eight), calculating the angle between the reflectance spectrum vectors of the pure primary color ink;

[0082] Using the reflectivity vector of the pure base color ink obtained in step (VII) pass The angle with the x-axis, rearrange Number from 1 to k, and then calculate The angle α between adjacent vectors k-1 and α k+1 ;

[0083] Angle α k-1 and α k+1 The calculation is as follows:

[0084]

[0085] In formula (6), the operator · represents the inner product of vectors;

[0086] Step (IX), preliminarily judging whether the base color ink is a mixed member of the target ink according to the included angle;

[0087] Through the angle α k-1 and α k+1 Determine the reflectivity vector of pure base color ink Whether the corresponding base color ink is a mixed member of the target ink in step (iv);

[0088] The principles for judging the base color ink are as follows:

[0089] If α k-1 <10, and α k+1 <10, then and The corresponding base color ink is removed. The corresponding base color ink is used as one of the optional base color inks;

[0090] If α k-1 <10, and α k+1 ≥10, then The corresponding base color ink is removed. and The corresponding base color ink is used as one of the optional base color inks;

[0091] If α k-1 ≥10, and α k+1 ≥10, then and The corresponding base color ink is used as one of the optional base color inks;

[0092] Finally, after screening, the spectrum vector corresponding to the base color ink set is The subscript p1 represents the number of primary color inks remaining after the existing m primary color inks are initially screened;

[0093] Step (10): Based on this, reread steps (eight) and (nine) until all similar base color inks are screened out and the corresponding reflectance spectrum vector is obtained. (P≤P1≤m), the subscript p represents the amount of base color ink remaining after screening in step (10);

[0094] In this embodiment, after screening, seven primary color inks, namely yellow, magenta, cyan, orange, red, blue and green, remain;

[0095] Step (XI): Calculate the vector a in each basic spectrum matrix obtained in step (VI): k ∈(a1 … a O) and the reflectance spectrum vectors of each primary color ink preliminarily screened out in step (10) The angle θ between i ;

[0096] Angle θ i The calculation is as follows:

[0097]

[0098] In formula (7), the operator · represents the inner product of vectors;

[0099] Step (12), determine the vector a in the primary color spectrum matrix k ∈(a1a O ) whether it contains the reflectance spectrum of the base color ink;

[0100] According to the angle θ k Determine the base color ink contained in the mixed ink in step (iv)

[0101] The principles for judging the base color ink are as follows:

[0102]

[0103] In formula (8), subscript k = 1, ..., Q, and Q ≤ P, The corresponding base ink is the base color ink finally screened out;

[0104] In this embodiment, after the second screening, two primary color inks, yellow and magenta, remain.

[0105] Comparative Example

[0106] In order to verify the effectiveness of the method of the present invention, the target ink in the comparative example of the present invention is obtained by mixing the yellow and magenta primary color inks in the above embodiment at a ratio of 75%:25%, and the color matching primary color inks are selected in the following ways: wrongly selecting the primary color ink (i.e. selecting the yellow and cyan primary color inks), selecting multiple primary color inks (i.e. selecting 8 primary color inks of yellow, magenta, cyan, orange, red, blue, dark blue, and green), and selecting the primary color ink of the present invention. After selecting the primary color ink, the ink formula is obtained by the method of the prior art "a printing ink color matching method based on KM theory, publication number CN113910796A", and the ink formula accuracy and calculation time obtained by the color matching method of the present invention are compared, and the comparison results are shown in Table 1 below.

[0107] Table 1 Comparison of formula and formula calculation time

[0108]

[0109] Referring to Table 1, by calculating the spectral difference between the predicted spectrum of the formula and the original target measured spectrum, it can be known that the spectral difference in the case of incorrectly selecting the primary color ink is 3.237, the spectral difference in the case of multiple selections of the primary color ink is 0.9921, and the spectral difference in the case of selecting the primary color ink according to the present invention is 0.4121. It can be seen that according to the method of screening the primary color ink according to the present invention, the spectral difference is significantly smaller and the accuracy is higher.

[0110] Furthermore, by calculating the color difference between the predicted spectrum of the formula and the original target measured spectrum, it can be seen that the color difference in the case of incorrectly selecting the primary color ink is 6.573, the color difference in the case of multiple selections of the primary color ink is 1.181, and the color difference in the case of selecting the primary color ink of the present invention is 0.9152. It can be seen that the color difference is significantly reduced and the color matching accuracy is higher according to the method of screening the primary color ink according to the present invention. In addition, it can be seen from Table 1 that in the color matching process of the same color matching method, from the time used to calculate the formula, the primary color ink selected by the method of the present invention is used for color matching, and the time used is also the shortest, and the color matching efficiency is higher.

[0111] The present invention has been described in detail with reference to the aforementioned embodiments. For those skilled in the art, it is still possible to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for automatically screening primary color inks, characterized in that: The following steps are involved: Step (a), select m base color inks, select two different base color inks in turn and mix them, prepare N training samples, and calculate the reflectivity of the pure ink on the training samples Step (ii), confirm the target ink, prepare the target ink test sample, and obtain the reflectivity R of the pure target ink on the sample tc (λ); Step (3): According to and R tc (λ) Calculate the basic spectrum matrix of the target ink A = [a1 … a k … a m ] T , and the mixing parameter vector of the base color ink in the target mixed ink The calculation formula is: x jk ≥0,a k (λ)≥0 And for the jth mixed ink, If the percentage of the kth primary color ink mixed is 0, Then the corresponding x jk =0 In the formula, h represents the positive rule parameter; X=[x1 … x j … x N x t ] T , x j =[x j1 … x jk … x jm ], Vector a in the basic spectral matrix A k =[a k (400) a k (410) … a k (690) k (700)], det(·) is the determinant of the calculation matrix; The calculated basic spectrum vectors are combined into a matrix, which is the basic spectrum matrix A of the target ink; Selecting the corresponding basic spectrum vector of the non-zero parameter in the mixing parameter vector; Step (iv), making a base color ink sample and calculating the reflectivity of the pure base color ink on the sample Get the reflectivity vector of the pure base color ink pass The angle with the x-axis, rearrange Numbered from 1 to k; Step 5: Calculation The angle α between adjacent vectors k-1 and α k+1 , through the angle α k-1 and α k+1 Determine the reflectivity vector of pure base color ink Whether the corresponding base color ink is a mixed member of the target ink, after screening, the spectral vector corresponding to the base color ink set is Step (six): Based on, repeat step (V) until all similar base color inks are screened out and the corresponding reflectance spectrum vector is obtained Step (seven), calculate the vector a in each basic spectrum matrix obtained in step (three) k ∈(a1a O ) and the reflectance spectrum vector of each primary color ink selected in step (six) The angle θ between i ; Determine the vector a in the primary color spectrum matrix k ∈(a1…a O ) Whether it contains the reflectance spectrum of the base color ink, the judgment principle is: Where subscript k = 1,,Q, and Q ≤ P, The corresponding base ink is the base color ink finally screened out.

2. The method for automatically screening primary color inks according to claim 1, characterized in that: The preparation method of the training sample in step (i) is: select two different primary color inks from m primary color inks in sequence, and use c i :1-c i Mixed in proportion, 0<c i <1, i=1,,n, n represents the number of mixtures of two base color inks with different percentages; the mixed inks are printed on white paper to prepare a total of N training samples.

3. The method for automatically screening primary color inks according to claim 1, characterized in that: The reflectivity of pure ink on the training sample in step (a) The calculation formula is: in, In the formula, subscript j=1,…,N, and They represent the absorption coefficient and scattering coefficient of the pure mixed ink on the j-th training sample, respectively, where the superscript c represents the pure mixed ink.

4. The method for automatically screening primary color inks according to claim 1, characterized in that: In the step (ii), the target ink is spread on a white paper to prepare a test sample; and then the reflectivity R of the test sample is measured. t (λ) and the reflectivity R of the paper in the test sample p (λ); Calculate the pure target ink reflectivity R tc (λ).

5. The method for automatically screening primary color inks according to claim 4, characterized in that: The pure target ink reflectivity R tc The calculation formula of (λ) is: in, Among them, K tc (λ) and S tc (λ) respectively represent the absorption coefficient and scattering coefficient values ​​of pure target ink on the target ink test sample, and the superscript tc represents pure target ink.

6. The method for automatically screening primary color inks according to claim 1, characterized in that: The principle for determining the mixed members in step (V) is: If α k-1 <10, and α k+1 <10, then and The corresponding base color ink is removed. The corresponding base color ink is used as one of the optional base color inks; If α k-1 <10, and α k+1 ≥10, then The corresponding base color ink is removed. and The corresponding base color ink is used as one of the optional base color inks; If α k-1 ≥10, and α k+1 ≥10, then and The corresponding base color ink is used as one of the optional base color inks.

7. The method for automatically screening primary color inks according to claim 1, characterized in that: The angle θ of step (VII) i The calculation formula is:

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