A color matching method for spot color ink printing

Abstract

The invention belongs to the field of printing technology, and specifically relates to a color adjustment method for spot color ink printing, which solves the problems of long time in reaching the target color and difficulty in determining the direction of ink fine-tuning in the process of spot color printing color tracking, and the method is simple, easy to implement and low-cost.

Description

Technical Field

[0001] The invention belongs to the technical field of ink printing, and in particular relates to a color adjustment method for spot color ink printing. Background Art

[0002] Among the daily printing jobs of printing companies, a large part of them need to be printed with spot color inks, and spot color inks often need to be mixed. Among the current mainstream ink mixing technologies, one is to use a special ink mixing room, use specific ink mixing software, and use a color display machine to first display the adjusted color samples to confirm that the color difference value is within the customer's color difference requirement range; the other is to rely on the personal experience of the printing machine leader, fully mix the original ink in a certain proportion on site, print directly on the designated material on the machine, and continuously reduce the Delta E process until the color is determined before printing in large quantities. The former uses universal coated paper for color display, which is different from the actual material. During actual printing, due to differences in information such as the pressure system of the printing press, the machine status, and the ink absorption characteristics of the actual printing material, the pre-adjusted ink still has deviations, and some even have Delta E>4, leading to unacceptable conditions. The latter will also take up a certain amount of machine time and have a slightly lower efficiency. However, no matter which ink adjustment method is used, there will be a problem. When the color is constantly approaching the target color, if the ink is adjusted simply by experience or a colorimeter, it will take a long time and the direction of ink adjustment is difficult to judge. What's worse, the wrong direction of ink adjustment will cause ink waste, and even the adjusted ink will be scrapped, and it will have to be adjusted again. Summary of the invention

[0003] In order to solve the problems existing in the prior art, the present invention provides a color matching method for spot color ink printing.

[0004] The technical solution of the present invention is achieved in this way:

[0005] A color matching method for spot color ink printing comprises the following steps:

[0006] S1: measure the target LAB value of the color;

[0007] S2: Convert the target LAB value to CMYK value;

[0008] S3: Measurement and conversion of machine color matching and sample color;

[0009] S4: Determine the color adjustment direction and adjust the ink by adding or subtracting ink;

[0010] S5: Repeat the above steps and print the product according to the adjusted ink.

[0011] Furthermore, in step S1, M1, Lab, D50, and 2 degree field of view are selected as all measurement conditions involving LAB values ​​to obtain the LAB value of the reference target color.

[0012] Furthermore, step S2 further includes the following steps:

[0013] Convert the target LAB into CMYK values ​​that can be expressed by ordinary black, blue, red and yellow basic inks, select relative chromaticity as the mapping method, and record the obtained CMYK values ​​in a unified form.

[0014] Furthermore, step S3 includes the following steps:

[0015] According to the process of adjusting spot colors, adjust the color to be close to the target color, use the color measuring equipment to measure the LAB value of the current spot color, measure the LAB value of the printed spot color according to the above step S1, and calculate the Delta value with the target color, according to step S2, get the CMYK value corresponding to the printed spot color, get the Delta value of CMYK, and judge the color adjustment direction of the ink; then add or subtract ink from the spot color ink until the Delta value between it and the target color is less than the target 1.

[0016] Furthermore, in step S4, the direction of ink adjustment is determined according to the Delta difference of CMYK obtained in step S3. The Delta value is the inverse of the difference between the sample value and the target value. If the Delta value is negative, ink reduction is performed, and if the Delta value is positive, ink addition is performed.

[0017] Furthermore, in step S1, M1, Lab, D50, and 2-degree field of view are selected as all measurement conditions involving LAB values ​​in the present invention, and the values ​​at multiple positions are measured and averaged to be the LAB value of the target color.

[0018] Furthermore, in step S3, the CMYK values ​​corresponding to the printed spot colors, ie, the values ​​of DeltaC, DeltaM, DeltaY, and DeltaK are obtained.

[0019] Furthermore, in step S4, the direction of ink adjustment is determined according to the Delta value of CMYK obtained in step S3, and the first preliminary adjustment is performed. Ink is added or subtracted according to the obtained Delta C, Delta M, and Delta Y values. The adjusted color is measured again to obtain color sample 2, and optimization and adjustment are performed again according to the Delta value by thinning the ink layer or by adding white ink to dilute the ink. After the operation is completed, color sample 3 is measured to obtain a color sample 3, and so on, until Delta < 1.

[0020] The beneficial effects of the present invention are as follows:

[0021] Compared with the prior art, the color matching method for spot color ink printing of this scheme has the following advantages:

[0022] This solution uses the LAB value to reverse the CMYK value. Since it is easy to calculate the corresponding CMYK value between two different LABs within the same color system, the difference calculation is performed to obtain the distance between the two colors, which can intuitively determine the direction of color adjustment. The ink adjustment process of this solution is simple and efficient; this method is particularly effective when the direction of the ink is unclear when approaching the target color. It can avoid the problems of low efficiency, large errors, high costs, etc. caused by over-reliance on manual experience in color adjustment during actual operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 A schematic flow chart of a color matching method for spot color ink printing according to the present invention;

[0024] Figure 2 The present invention is a schematic diagram of color determination of a color matching method for spot color ink printing. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0026] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0027] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0028] like Figure 1 As shown, a color matching method for spot color ink printing comprises the following steps:

[0029] S1: measure the target LAB value of the color;

[0030] S2: Convert the target LAB value to CMYK value;

[0031] S3: Measurement and conversion of machine color matching and sample color;

[0032] S4: Determine the color adjustment direction and adjust the ink by adding or subtracting ink;

[0033] S5: Repeat the above steps and print the product according to the adjusted ink.

[0034] Further: for step S1: measuring the target LAB value of the color, there are many methods and equipment for measuring the LAB of the color. To ensure the accuracy and versatility of the measurement, the color measuring device used in this example is X-rite i1Pro2. The measurement bar is based on the latest ISO12467-2 standard, and M1, Lab, D50, and 2-degree field of view are selected as all measurement conditions involving LAB values ​​in the present invention to obtain the LAB value of the reference target color. For some situations with higher accuracy requirements, the values ​​of multiple positions can be measured and averaged to be used as the LAB value of the target color. For example, the target colors actually measured are l81.77, a-15.05, and b56.18.

[0035] Further, S2: Convert the target LAB value to CMYK value, and use the common online LAB to CMYK conversion tool in the prior art to convert the target LAB into a CMYK value that can be expressed by ordinary black, blue, red and yellow basic inks. In most cases, it is required to print on coated materials. In the ICC selection process, select the ISO standard ICC, CoatedFogra39 ICC. If you encounter uncoated materials, you can choose uncoatedFogra29.icc to get better results. Select relative chromaticity as the mapping method. The target color (L81.77 a-15.05b56.18) used in this example is filled in, and the calculation results show that the CMYK values ​​are: (C29 M4 Y78 K0), and the obtained CMYK values ​​are filled in the "Color Adjustment CMYK Determination Table" ( Figure 2 ) (hereinafter referred to as the table) waiting for calculation.

[0036] Further, S3: measurement and conversion of machine color matching and sample color; the machine adjusts the color to be close to the target color according to the process of adjusting the spot color, and the color measuring device can be used to measure the LAB value of the current spot color. According to the above step S1, the LAB value of the printed spot color can be measured, and the color sample 1 in the table is input, and the Delta value with the target color is calculated to be 3.8, which fails to meet the requirements and needs to be further optimized to <1. According to step 2, the CMYK value corresponding to the currently printed spot color can be obtained, and the obtained CMYK value is filled in the table ( Figure 2 ), DeltaC, DeltaM, DeltaY, and DeltaK are automatically calculated. With this CMYK Delta value, you can intuitively judge the ink color mixing direction. Add or subtract ink from the spot color ink in this direction, and repeat the operation, color sample 2, color sample 3, until the Delta E value between the color sample 2 and the target color is less than target 1.

[0037] Further, S4: determine the direction of color adjustment, and perform ink addition or subtraction adjustment; determine the direction of ink adjustment based on the Delta difference of CMYK calculated from the table. The calculation formula in this table is written to facilitate the ink adjustment master to make an intuitive judgment. The Delta value is the opposite of the difference between the sample value and the target value. The advantage of this is that when the machine operator sees a negative Delta value, it is an ink reduction operation, and when he sees a positive value, it is an ink addition operation. He does not need to react again in his brain, making the result more intuitive. Take the target green to be followed in this example. The first initial adjustment shows that Delta C, Delta M, and Delta Y are all positive values. According to the original ink, a certain amount of C ink, M ink, and Y ink are added to achieve the target color. However, considering that the target color is green, the M value is small, and the difference is only 1, so in actual operation, M ink is not added first, only C ink and Y ink are added. The improved color is measured again to obtain color sample 2, Delta. E has dropped, but there is still a difference of 2.13 from the target color, so it needs to be optimized again. According to the ink addition and subtraction instructions obtained from color sample 2, the ink needs to be reduced. Ink reduction is not as good as ink addition. It is impossible to extract relevant ink from the adjusted ink (each color component has been fully mixed into one color). It can only be done by thinning the ink layer or by adding white ink to dilute the ink. In actual production, it is achieved by lightening the ink (lowering the ink output by the ink key). After the operation is completed, color sample 3 is measured and the DeltaE of color sample 3 reaches 0.84. The calculated CMYK value only indicates an increase of 1 blue. Because the color has reached the standard, there is no way to continue to optimize it. Just print the goods according to the adjusted ink.

[0038] This solution follows the most intuitive CMYK color overlapping principle in the printing industry. The process of obtaining the ISO12647-2 standard ICC is actually to mix thousands of color blocks with different CMYK color ratios, measure the LAB value corresponding to each color block, and then perform mathematical calculations to obtain the characteristic curve ICC of the device. The present invention uses the LAB value to reversely infer the CMYK value. Since it is easy to calculate the corresponding CMYK value between two different LABs within the same color system, the difference calculation can easily obtain the distance between the two colors.

[0039] This solution provides a more efficient and concise method of adding and reducing ink, which can overcome the situation of insensitivity to color and inaccurate adding and reducing ink during manual operation, and can intuitively indicate the addition and subtraction of each color to improve the efficiency of ink adjustment. At the same time, the amount of ink added can also be determined by the addition and subtraction of CMYK indicated in the table. This solution can intuitively grasp the color adjustment process in the process of viewing the color, avoiding errors and omissions.

[0040] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution of the present invention, which should be included in the scope of the claims of the present invention.

Claims

1. A color matching method for spot color ink printing, characterized in that: The following steps are involved: S1: measure the target LAB value of the color; S2: Convert the target LAB value to CMYK value; S3: Measurement and conversion of machine color matching and sample color; S4: Determine the color adjustment direction and adjust the ink by adding or subtracting ink; S5: looping the above steps, printing goods according to the adjusted ink; In the step S1, M1, Lab, D50, and 2 degree field of view are selected as all measurement conditions involving LAB values ​​to obtain the LAB value of the reference target color; The step S2 further includes the following steps: Convert the target LAB into CMYK values ​​that can be expressed by common black, blue, red and yellow basic inks, select relative chromaticity as the mapping method, and record the obtained CMYK values ​​uniformly in a table; The S3 step includes the following steps: According to the process of adjusting spot colors, adjust the color to be close to the target color, use the color measuring device to measure the LAB value of the current spot color, measure the LAB value of the printed spot color according to the above step S1, and calculate the Delta value between the spot color being printed and the target color, and according to step S2, obtain the CMYK value corresponding to the spot color being printed, obtain the Delta value of CMYK, and determine the color adjustment direction of the ink; then add or subtract ink from the spot color ink being printed until the Delta value between the spot color being printed and the target color is less than the target 1; In step S4, the direction of ink adjustment is determined according to the Delta difference of CMYK obtained in step S3.

2. The color matching method for spot color ink printing according to claim 1, characterized in that: In the step S1, M1, Lab, D50, and 2 degree viewing field are selected as the measurement conditions of the LAB value, and the values ​​of multiple positions are measured and averaged to be the LAB value of the target color.

3. The color matching method for spot color ink printing according to claim 2, characterized in that: In the step S3, the CMYK values ​​corresponding to the spot color being printed, namely, the values ​​of DeltaC, DeltaM, DeltaY, and DeltaK are obtained.

4. The color matching method for spot color ink printing according to claim 3, characterized in that: In step S4, the direction of ink adjustment is determined according to the Delta value of CMYK obtained in step S3, and the first preliminary adjustment is performed. The operation of adding or subtracting ink is performed according to the obtained values ​​of DeltaC, DeltaM, and DeltaY. The adjusted color is measured again to obtain color sample 2, and optimization adjustment is performed again according to the Delta value, by thinning the ink layer or by adding white ink to dilute the ink. After the operation is completed, color sample 3 is measured to obtain color sample 3, and so on, until Delta<1.

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