Offset printing lithographic plate high-saturation packaging color-reducing printing method, device, equipment and medium

Abstract

The invention relates to the technical field of package printing, in particular to an offset printing lithographic plate high-saturation package color reduction printing method, device and equipment and a medium, and the method comprises the following steps: obtaining a standard Lab color value of a large-area intermediate color in a target image based on an international standardized color management system; separating an intermediate color in a target image to a user-defined spot color layer according to the standard Lab color value, and determining an overprinting proportional relation between basic CMY three colors and the intermediate color according to the user-defined spot color layer; screening optimization processing is carried out on an area corresponding to the overprinting proportional relation so as to reduce interference of basic CMY three colors on an intermediate color; and generating a standardized printing file containing the spot color layer and the basic CMY color, and finishing printing through an offset printing process. The offset printing method has the effect of solving the problems of insufficient color saturation and poor color stability in existing offset printing package printing.

Description

Technical Field

[0001] The present application relates to the technical field of packaging printing, and in particular to a method, device, equipment and medium for offset lithographic high-saturation packaging subtractive printing. Background Art

[0002] Offset printing technology, characterized by its delicate graphics and high printing precision, is widely used in the packaging and printing industry. However, the traditional four-color separation method employed by offset printing can suffer from issues such as insufficient color saturation and unstable overprinting when rendering large areas of color and intermediate colors. In particular, intermediate color areas often require the addition of spot color sets to compensate for the lack of saturation, leading to increased equipment modification and production costs.

[0003] Flexographic printing, with its thick ink layers and numerous color sets, offers advantages in producing highly saturated images. However, due to differences in process principles between flexographic and offset printing, it is difficult to directly replace offset. To address this issue, this technology draws on the multi-spot color separation process of flexographic printing and combines it with the process characteristics of offset printing. By optimizing the color separation method and screening process, this technology proposes a subtractive color printing method that improves the saturation and color stability of offset-printed images without adding additional color sets. Summary of the Invention

[0004] In order to solve the problems of insufficient color saturation and poor color stability in existing offset packaging printing, the present application provides an offset lithographic high-saturation packaging subtractive printing method, device, equipment and medium.

[0005] The above-mentioned invention objective of this application is achieved through the following technical solutions: A high-saturation packaging subtractive color printing method for offset lithography is characterized in that the high-saturation packaging subtractive color printing method for offset lithography comprises: Obtain the standard Lab color value of the large area intermediate color in the target image based on the international standardized color management system; Separating the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determining the overprint ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer; Performing screening optimization processing on the area corresponding to the overprint ratio relationship to reduce interference of the basic CMY colors on the intermediate colors; A standardized printing file containing the spot color layer and the basic CMY colors is generated and printing is completed through an offset printing process.

[0006] By adopting the above technical solution, the color saturation of printed products can be improved. By separating the intermediate colors and optimizing the screening process, the interference of the basic CMY colors on the intermediate colors can be reduced, and the saturation and vividness of the intermediate colors in a large area can be significantly improved; the color stability can be improved, and the Lab color value and △E2000 color difference formula are used for precise measurement. In combination with standardized color separation and screening optimization technology, the color consistency of printed products in different batches can be significantly improved; the production cost can be reduced, and high-saturation printing can be achieved without adding color groups or adding spot color groups, avoiding the additional cost investment of equipment modification and spot color ink; the process applicability can be enhanced. This method is suitable for most offset printing equipment and can be widely used in the field of high-end packaging printing, especially for products that require high saturation and high visual impact.

[0007] In a preferred example, the present application may be further configured as follows: separating the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determining the overprinting ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer, specifically including: Establishing an image color separation channel, and performing intermediate color separation on the target image according to the image color separation channel to obtain a target intermediate color; Iteratively correcting the target image according to the target halftone, so that the ΔE2000 color difference value of the target halftone is controlled within a preset threshold, thereby obtaining the automatic spot color layer; The standard Lab color value of the automatic spot color layer is obtained, and a regression equation is constructed based on the basic CMY three-color ink density values and the standard Lab color value to obtain the overprinting ratio relationship.

[0008] By adopting the above technical solution, an image color separation channel is established to perform intermediate color separation on the target image to obtain the target intermediate color, and the intermediate color can be accurately separated; the target image is iteratively corrected according to the target intermediate color, so that the △E2000 color difference value of the target intermediate color is controlled within the preset threshold to obtain a custom spot color layer, which can ensure the color accuracy of the custom spot color layer; the standard Lab color value of the custom spot color layer is obtained, and a regression equation is constructed based on the basic CMY three-color ink density value and the standard Lab color value to calculate the overprint ratio relationship, which can accurately determine the overprint ratio of the basic CMY three colors and the intermediate color, and realize accurate separation and overprint optimization of the intermediate color, thereby improving the color saturation of the printed product, improving color stability, and avoiding the additional cost investment of equipment modification and spot color ink.

[0009] In a preferred example, the present application may be further configured as follows: performing screening optimization processing on the area corresponding to the overprinting ratio relationship to reduce interference of the basic CMY colors on the intermediate colors, specifically including: The dot angles of the three basic colors CMY are set accordingly, and are arranged asymmetrically with the 90° dot angle of the intermediate color area; Through the composite dot structure of square dots superimposed on circular dots, the dot gain rate compensation parameters of the intermediate color area are calculated according to the preset ratio.

[0010] By adopting the above technical solution, the screen angles of the basic CMY three-color dots are set and arranged asymmetrically with the 90° screen angle of the intermediate color area, and a composite dot structure of square dots superimposed on circular dots is used to compensate the dot expansion rate parameters of the intermediate color area according to a preset ratio. This can reduce the interference of the basic CMY three colors on the intermediate colors, ensure the stability and high saturation of the intermediate colors in a large area, and improve the color saturation and color stability of the printed products.

[0011] In a preferred example, the present application may be further configured as follows: generating a standardized printing file including the spot color layer and the basic CMY colors and completing printing through an offset printing process specifically includes: Acquire reflectance spectrum data of the intermediate color area through a multispectral sensor; When the deviation between the measured Lab value and the standard value exceeds a threshold, an instruction is generated and triggered to the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller; The reflectance spectrum data of the intermediate color area is convoluted and corrected using a surface texture feature library to eliminate the influence of the printing substrate structure on color difference detection, and a standardized printing file is generated according to the correction result.

[0012] By adopting the above technical solution, the reflectance spectral data of the intermediate color area is obtained through a multispectral sensor. When the deviation between the measured Lab value and the standard value exceeds the threshold, the ink supply pressure of the ink fountain roller is adjusted to ensure color stability and consistency during the printing process; the convolution correction of the reflectance spectral data using the surface texture feature library can eliminate the influence of the printing substrate structure on color difference detection, thereby making the generated standardized printing files more accurate, and ultimately helping to improve the color saturation and color stability of printed products and reduce production costs.

[0013] In a preferred example, the present application may be further configured as follows: using the surface texture feature library to perform convolution correction on the reflectance spectrum data of the intermediate color area to eliminate the influence of the printing substrate structure on color difference detection, and generating a standardized printing file based on the correction result, specifically including: The standardized printing file includes the CIELAB absolute coordinate values and XYZ colorimetric parameters of the spot color layer, and a logic tree diagram of the overprinting priority of the basic CMY three colors and the spot color layer is established according to the XYZ colorimetric parameters; Obtain a color compensation matrix under a preset standard light source, and obtain current lighting data of the printing workshop, trigger a corresponding compensation mode according to the color compensation matrix and the current lighting data, and generate the standardized printing file after correction according to the compensation mode.

[0014] By adopting the above technical solution, the reflectance spectral data of the intermediate color area is convoluted and corrected using the surface texture feature library, which can eliminate the influence of the printing substrate structure on color difference detection; the standardized printing file contains the CIELAB absolute coordinate value and XYZ chromaticity parameters of the spot color layer, and a logical tree diagram of the overprinting priority of the basic CMY three colors and the spot color layer is established according to the XYZ chromaticity parameters, which is conducive to clarifying the overprinting order; the color compensation matrix under the preset standard light source and the current lighting data of the printing workshop are obtained, and the corresponding compensation mode is triggered for correction to generate a standardized printing file, which can reduce the impact of lighting differences on printed colors and further improve the color stability and color saturation of printed products.

[0015] The second object of the present invention is achieved through the following technical solutions: An offset lithographic high-saturation packaging subtractive color printing device, the offset lithographic high-saturation packaging subtractive color printing device comprising: The standard color value acquisition module is used to obtain the standard Lab color value of the intermediate color of a large area in the target image based on the international standardized color management system; An overprint ratio acquisition module is used to separate the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determine the overprint ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer; An intermediate color optimization module is used to perform screening optimization processing on the area corresponding to the overprint ratio relationship to reduce the interference of the basic CMY colors on the intermediate colors; The printing control module is used to generate a standardized printing file containing the spot color layer and the basic CMY three colors and complete the printing through an offset printing process.

[0016] By adopting the above technical solution, the color saturation of printed products can be improved. By separating the intermediate colors and optimizing the screening process, the interference of the basic CMY colors on the intermediate colors can be reduced, and the saturation and vividness of the intermediate colors in a large area can be significantly improved; the color stability can be improved, and the Lab color value and △E2000 color difference formula are used for precise measurement. In combination with standardized color separation and screening optimization technology, the color consistency of printed products in different batches can be significantly improved; the production cost can be reduced, and high-saturation printing can be achieved without adding color groups or adding spot color groups, avoiding the additional cost investment of equipment modification and spot color ink; the process applicability can be enhanced. This method is suitable for most offset printing equipment and can be widely used in the field of high-end packaging printing, especially for products that require high saturation and high visual impact.

[0017] The third objective of this application is achieved through the following technical solutions: A computer device comprises a memory, a processor and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps of the above-mentioned offset lithographic high-saturation packaging subtractive color printing method are implemented.

[0018] The fourth objective of this application is achieved through the following technical solutions: A computer-readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the above-mentioned offset lithographic high-saturation packaging subtractive color printing method.

[0019] In summary, this application includes at least one of the following beneficial technical effects: 1. By separating intermediate colors, determining the overprint ratio, and optimizing the screening process, the interference of the three basic CMY colors on the intermediate colors is reduced, thereby improving the color saturation of the printed product. 2. Use standard Lab color values and precise measurement methods, combined with standardized color separation and screening optimization technology, to improve the color stability of printed products; 3. High-saturation printing can be achieved without adding color sets, reducing the additional cost of equipment modification and spot color ink investment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a method for offset lithographic high-saturation packaging subtractive color printing in one embodiment of the present application; Figure 2 This is a principle block diagram of an offset lithographic high-saturation packaging subtractive color printing system in one embodiment of the present application; Figure 3 It is a schematic diagram of a device in one embodiment of the present application. DETAILED DESCRIPTION

[0021] The present application is further described in detail below with reference to the accompanying drawings.

[0022] In one embodiment, if Figure 1 As shown, the present application discloses a high-saturation packaging subtractive color printing method for offset lithography, which specifically includes the following steps: S10: Obtain the standard Lab color value of the intermediate color of a large area in the target image based on the international standardized color management system.

[0023] Specifically, accurate color rendering is crucial in today's printing industry. For offset lithographic high-saturation packaging printing, accurately obtaining the standard Lab color values of large areas of intermediate colors in the target image is the cornerstone of the entire process.

[0024] The internationally standardized color management system provides a unified and accurate color measurement standard. The Lab color space offers unique advantages, offering a more intuitive reflection of the human eye's color perception and a precise mathematical description of color. Based on this system, a target image is measured using a color measurement device. During measurement, the device collects color data for a large area of intermediate colors. This data is then analyzed using the △E2000 color difference formula. This formula calculates the differences between colors and determines the standard Lab value for the large area of intermediate colors in the target image. For example, when faced with a packaging image containing multiple colors, this formula can be used to filter out the large area of intermediate colors from the numerous colors and accurately determine their standard Lab value.

[0025] This method provides basic data for subsequent color separation and screening optimization. With accurate standard Lab values, subsequent operations have a clear reference basis, which can ensure color accuracy and consistency throughout the entire printing process.

[0026] S20: Separating the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determining the overprinting ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer.

[0027] Specifically, after obtaining the standard Lab color value, the intermediate colors in the target image are separated and the overprint ratio relationship is determined.

[0028] First, we use image processing software like Adobe Photoshop and Adobe Illustrator, combined with the Esko Inktools plug-in, to perform intermediate color separation, enabling detailed analysis and processing of the target image. The Esko Inktools plug-in provides a more professional and efficient tool for intermediate color separation.

[0029] During the separation process, based on the acquired standard Lab color values, the specific functions in the software are used to accurately separate the intermediate colors in the target image and generate a custom spot color layer. In other words, specific colors can be selected from a colorful picture and extracted separately.

[0030] Next, determine the overprint ratio of the primary CMY colors and the intermediate colors, and calculate this based on the actual requirements of the offset printing process. This is done by taking into account various factors, including the performance of the offset press, the characteristics of the ink, and the printing material. For example, different offset presses have varying ink absorption and transfer capabilities, so the overprint ratio must be adjusted accordingly. Furthermore, different inks exhibit varying color performance after mixing, requiring experimentation and calculation to determine the optimal overprint ratio.

[0031] In this way, the overprinting relationship between the intermediate colors and the three basic colors can be optimized, so that the intermediate colors can be presented more accurately during the printing process, avoiding color deviation or insufficient saturation.

[0032] S30: performing screening optimization processing on the area corresponding to the overprinting ratio relationship to reduce interference of the basic CMY colors on the intermediate colors.

[0033] Specifically, after the overprinting ratio relationship is determined, in order to further improve the printing quality, it is necessary to perform screening optimization processing on the area corresponding to the overprinting ratio relationship.

[0034] Screening is a crucial step in the printing process, directly impacting the color rendering and clarity of printed products. In traditional printing, the overlay interference of the primary CMY colors on intermediate colors is a common problem, resulting in reduced color saturation and poor color stability.

[0035] To address this issue, the dot angles for the three primary colors (CMY) are first adjusted accordingly, creating an asymmetrical arrangement with the 90° angles of the intermediate colors. This asymmetrical arrangement effectively reduces interference between the three primary colors (CMY) and the intermediate colors, allowing the intermediate colors to appear more clearly. Secondly, a composite dot structure of square dots superimposed on circular dots is used to compensate for the dot gain ratio in the intermediate colors according to a preset ratio. Square and circular dots have different properties: square dots better render detail, while circular dots create more natural color transitions. By superimposing the two and applying dot gain compensation, the saturation and stability of the intermediate colors can be further improved.

[0036] These screening optimization processes can improve the stability and high saturation of large-area intermediate colors during the printing process, making the colors of printed products more vivid and lively, and improving the quality and visual effects of printed products.

[0037] S40: Generates standardized printing files containing spot color layers and basic CMY colors and completes printing through offset printing process.

[0038] Specifically, generating standardized printing files is a critical step, directly impacting the final quality of printed products. Optimized color separation image files are collated and converted to generate standardized printing files (PDFs) containing spot color layers and the basic CMY colors. These files contain accurate color information and printing parameters, ensuring consistent printing results across different offset printing devices.

[0039] During the process of generating standardized printing files, a multispectral sensor acquires reflectance spectral data for the mid-tone area. The multispectral sensor accurately measures the spectral characteristics of the mid-tone area, providing a basis for subsequent color adjustments. When the measured Lab value deviates from the standard value by more than a threshold, the system automatically generates and triggers a command to the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller. This allows for timely correction of color deviations during the printing process, ensuring color stability in printed products.

[0040] At the same time, a convolution correction is performed on the reflectance spectrum data of the intermediate color region using a surface texture feature library to eliminate the influence of the printed substrate structure on color difference detection. The surface texture of the printed substrate can interfere with color difference detection, but convolution correction effectively eliminates this interference, making color difference detection more accurate. Based on the correction results, standardized printing files are generated, ensuring that the color information contained in the files is more accurate and reliable.

[0041] During the offset printing process, densitometers and colorimeters are used to monitor the overprinting of the primary CMY colors and intermediate colors in real time. Densitometers measure ink density, while colorimeters measure color differences. This real-time monitoring allows for timely identification of printing process issues and adjustments to ensure color stability and consistency, ultimately resulting in highly saturated, color-stable prints.

[0042] In one embodiment, in step S20, the intermediate colors in the target image are separated into custom spot color layers according to the standard Lab color values, and the overprint ratio relationship between the basic CMY colors and the intermediate colors is determined according to the custom spot color layers, specifically including: S21: establishing an image color separation channel, performing intermediate color separation on the target image according to the image color separation channel, and obtaining a target intermediate color.

[0043] Specifically, after obtaining the standard Lab color values of large-area intermediate colors in the target image based on the international standardized color management system, the image color separation channels are first established. Through image processing software such as Adobe Photoshop and Adobe Illustrator, combined with the Esko Inktools plug-in, appropriate color separation channels are accurately created based on the color characteristics of the image and the standard Lab color values.

[0044] For example, many packaging designs often include large areas of intermediate colors like orange, purple, green, and pink. Using these tools to create image color separation channels allows for detailed segmentation based on the distinct characteristics of each color. For example, for orange, pixels associated with it might be identified from the entire image and assigned to a specific channel based on its specific range in the Lab color space. This approach effectively separates the intermediate colors within the target image, ultimately yielding the desired intermediate color.

[0045] This method of separating intermediate colors offers significant advantages. In traditional offset printing, due to a lack of precise color separation methods, the rendering of intermediate colors over large areas is often unsatisfactory, with insufficient color saturation and unstable overprinting. By establishing image color separation channels for intermediate color separation, intermediate colors can be clearly extracted from the complex image color system, providing a clear target for subsequent color processing and optimization. This allows for more targeted color adjustments and printing processes, effectively improving the rendering of intermediate colors in printed products and resulting in more vivid and realistic colors for printed packaging products.

[0046] S22: Iteratively correcting the target image according to the target mid-color, so that the △E2000 color difference value of the target mid-color is controlled within a preset threshold, and automatically obtaining a spot color layer.

[0047] After obtaining the target midtone, iterative correction of the target image is crucial for ensuring color accuracy and stability. Specifically, the ΔE2000 color difference of the target midtone must be kept within a preset threshold. The ΔE2000 color difference formula is an internationally recognized standard for measuring color differences, and it more accurately reflects the human eye's perception of color differences.

[0048] During the iterative correction process, a stepwise approximation approach is employed. First, based on the initial state of the target midtone, the ΔE2000 color difference between it and the standard Lab color value is calculated. If this color difference exceeds a preset threshold, the target image is adjusted accordingly. This adjustment can involve changing relevant color parameters in the image, such as brightness and saturation. After each adjustment, the ΔE2000 color difference is recalculated, and further adjustments are made based on the new calculation results. This process is repeated until the color difference meets the preset threshold.

[0049] This iterative correction process significantly improves color accuracy and consistency. In actual packaging printing, color consistency across batches of printed products is a crucial metric. Excessive color variations can severely impact the overall image and quality of the product. This iterative correction approach minimizes color errors in the target midtones, ensuring high color consistency across batches and meeting the high-quality requirements of packaging printing. Ultimately, after multiple iterations of correction, a custom spot color layer is created, featuring highly accurate and stable midtones.

[0050] S23: Automatically obtain the standard Lab color value of the spot color layer, construct a regression equation based on the basic CMY three-color ink density value and the standard Lab color value, and obtain the overprint ratio relationship.

[0051] Specifically, after obtaining a custom spot color layer, the standard Lab color values for that layer are obtained. A regression equation is constructed based on the density values of the basic CMY inks and the standard Lab color values to calculate the overprint ratio between the basic CMY inks and the intermediate colors. Professional ink density measurement equipment is used to accurately measure the density values of the basic CMY inks under different conditions. Simultaneously, the standard Lab color values of the custom spot color layer are combined to establish a mathematical relationship between the two, known as the regression equation.

[0052] Constructing a regression equation requires collecting a large amount of data samples, including the color effects corresponding to different combinations of the basic CMY ink densities, as well as various variations in custom spot color layers. By analyzing and fitting this data, the most appropriate regression equation is found. Once the regression equation is determined, it can be used to calculate the optimal overprint ratio between the basic CMY inks and the intermediate colors.

[0053] In one embodiment, in step S30, the area corresponding to the overprint ratio relationship is subjected to screen optimization processing to reduce the interference of the three basic CMY colors on the intermediate colors, specifically including: S31: The dot angles of the three basic colors CMY are set accordingly, and are arranged asymmetrically with the 90° dot angle of the intermediate color area.

[0054] Specifically, during offset printing, the dot angle setting affects the quality and color rendering of the printed image. In traditional four-color printing, dot angles are typically set according to specific rules. However, when processing intermediate colors, interference may occur between the basic CMY dot angles and the intermediate color dots, resulting in problems such as moiré, which affects the clarity and color uniformity of the printed product. By setting the dot angles of the basic CMY colors accordingly and arranging them asymmetrically with the 90° angle of the intermediate color area, this interference can be effectively avoided, allowing the intermediate colors to be presented more clearly and stably.

[0055] First, the dot angles of the basic CMY colors must be accurately measured and analyzed. In practice, professional printing testing tools, such as a dot angle tester, can be used to obtain the current dot angle data for the basic CMY colors. Then, based on the characteristics of the offset printing process and the properties of intermediate colors, combined with extensive experimental data and experience, the optimal dot angle settings for the basic CMY colors are determined. Generally speaking, these settings should form a suitable asymmetric angle difference with the 90° screen angle for the intermediate color area.

[0056] For example, the cyan (C) dot angle can be set to 15°, the magenta (M) dot angle to 75°, and the yellow (Y) dot angle to 0°. This creates a distinctly asymmetrical arrangement of the basic CMY dots with the 90° angle of the intermediate color areas, significantly reducing the possibility of interference between dots.

[0057] When setting the dot angle, consider the performance and characteristics of your printing equipment. Different offset presses may have varying degrees of accuracy and stability in dot angle control, so fine-tuning is necessary based on the specific equipment.

[0058] This asymmetrical arrangement of dot angles significantly reduces interference between the primary CMY colors and intermediate colors. During the printing process, intermediate color areas are free from blurring, unevenness, or moiré patterns caused by dot interference, thereby improving the clarity and color quality of printed products. This effect is particularly pronounced when printing large areas of intermediate colors, resulting in brighter, richer intermediate colors and a significantly enhanced visual quality. Furthermore, the reduced dot interference reduces scrap during the printing process, improving production efficiency and economic benefits.

[0059] S32: Using a composite dot structure of square dots superimposed on circular dots, a dot enlargement rate compensation parameter is applied to the intermediate color area according to a preset ratio.

[0060] Specifically, during the offset printing process, dot gain can be a problem. When ink is transferred to the printed substrate, the dots expand to a certain extent due to factors such as ink fluidity and the paper's absorbency. This dot gain can affect the color reproduction and layering of the printed product, especially in mid-tone areas, where dot gain can cause color distortion or loss of layering. By adopting a composite dot structure consisting of square dots superimposed on circular dots and applying dot gain compensation parameters to the mid-tone areas according to a preset ratio, this problem of dot gain can be effectively addressed, improving the color accuracy and layering of printed products.

[0061] First, it's important to understand the respective characteristics of square and circular dots. Square dots better capture detail in highlights and shadows, while circular dots provide a smooth transition effect in midtones. Overlaying square and circular dots can fully leverage their respective strengths, achieving even more nuanced color rendering.

[0062] When creating printing plates, specialized platemaking software combines square and circular dots according to specific rules. For example, square dots can be placed in highlights and shadows, while circular dots are placed in midtones, and then the two can be superimposed. Simultaneously, a preset dot gain compensation parameter is determined based on the characteristics of the midtone area and the requirements of the printing process. This parameter can be determined through extensive experimentation and data analysis, taking into account factors such as ink type, printing speed, printing pressure, and paper type.

[0063] During the printing process, the printing equipment adjusts the dot size of the midtone areas based on preset dot gain compensation parameters. For example, if the dot gain is detected to be outside the preset range, the equipment will automatically reduce the dot size of the midtone areas to compensate for the effect of dot gain. This adjustment can be made automatically by the printing equipment's control system or manually by the operator based on real-time monitoring data.

[0064] A composite dot structure combining square and circular dots, along with dot gain compensation parameters for mid-tone areas, effectively improves color accuracy and layering in printed products. In these mid-tone areas, colors appear more vivid and realistic, with more natural transitions, avoiding color distortion and loss of layering caused by dot gain. This composite dot structure also enhances the runnability of printed products and extends the life of printing plates. The combination of square and circular dots disperses ink pressure, reducing dot wear and deformation, thereby ensuring consistent quality throughout the entire printing process.

[0065] In one embodiment, in step S40, a standardized printing file including a spot color layer and basic CMY colors is generated and printed using an offset printing process, specifically including: S41: Acquire reflectance spectrum data of the intermediate color region through a multispectral sensor.

[0066] Specifically, a multispectral sensor acquires reflectance spectral data for intermediate color areas. During the printing process, the color performance of intermediate color areas is crucial to the overall print quality. Multispectral sensors accurately capture reflectance spectral data for intermediate color areas because different colored materials have different reflective properties for different wavelengths of light. Multispectral sensors cover a wide spectral range, from visible light to near-infrared light, comprehensively capturing spectral information for intermediate color areas. This precise spectral data acquisition provides an accurate basis for subsequent color analysis and adjustments. For example, when printing a packaging design containing multiple intermediate colors, a multispectral sensor can scan intermediate color areas such as orange and purple to generate corresponding reflectance spectral curves. This curve contains detailed information about the color, such as color purity and brightness. Using this reflectance spectral data, the actual performance of the intermediate colors during the printing process can be accurately determined.

[0067] S42: When the deviation between the measured Lab value and the standard value exceeds a threshold, an instruction is generated and triggered to the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller.

[0068] Specifically, when the measured Lab value deviates from the standard value by more than a threshold, a command is generated and triggered to the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller. The Lab color space is an internationally recognized color representation method that more accurately reflects the human eye's perception of color. During the printing process, standard Lab values for the mid-tone area are pre-set based on design requirements and product quality standards. The reflectance spectrum data acquired by the multispectral sensor can be converted into measured Lab values. When the deviation between the measured Lab value and the standard value exceeds a pre-set threshold, it indicates that the color representation of the mid-tone has significantly deviated during printing, potentially resulting in the color being too dark, too light, or having a shift in hue. At this point, the system generates an adjustment command and sends it to the servo motor. The servo motor is connected to the corresponding ink fountain roller and can precisely control the roller's rotation speed and force, thereby adjusting the ink supply pressure. For example, if the measured Lab value indicates a light mid-tone, indicating insufficient ink supply, the servo motor will increase the ink supply pressure on the ink fountain roller, delivering more ink to the printing plate and darkening the mid-tone. Conversely, if the intermediate color is too dark, the servo motor will reduce the ink supply pressure, reducing the ink supply. This real-time feedback and adjustment mechanism can effectively ensure the color accuracy and stability of the intermediate color, avoiding color deviation caused by improper ink supply.

[0069] S43: Using the surface texture feature library, convolution correction is performed on the reflectance spectrum data of the intermediate color area to eliminate the influence of the printing substrate structure on the color difference detection, and a standardized printing file is generated according to the correction result.

[0070] Specifically, a convolution correction is performed on the reflectance spectrum data of the mid-tone region using a surface texture feature library to eliminate the influence of the printed substrate structure on color difference detection. A standardized printing file is then generated based on the correction results. The surface structures of printed substrates vary, with some being smooth and others being rough. These varying surface structures affect light reflection, which in turn affects the accuracy of color difference detection. The surface texture feature library stores surface texture information for various common printing substrates. By convolving the reflectance spectrum data of the mid-tone region with the data in the surface texture feature library, the influence of the printed substrate surface structure on the reflectance spectrum data can be identified. These influences are then corrected to remove interference caused by the printed substrate surface structure. For example, for rough paper, light will diffusely reflect from its surface, resulting in irregular fluctuations in the reflectance spectrum data. By performing convolution correction with the surface texture feature library, these fluctuations caused by diffuse reflection can be eliminated, ensuring that the reflectance spectrum data more accurately reflects the actual color of the mid-tone. This correction results in more accurate and reliable data. Finally, a standardized printing file is generated based on the corrected results. This standardized printing file contains accurate color information for the spot color layer and the basic CMY colors, as well as other relevant printing parameters such as dot size and ink concentration. It can provide precise guidance for the offset printing process, ensuring that accurate color and stable quality prints can be reproduced under different printing equipment and environmental conditions.

[0071] In one embodiment, in step S43, the reflectance spectrum data of the intermediate color region is convoluted and corrected using the surface texture feature library to eliminate the influence of the printing substrate structure on the color difference detection, and a standardized printing file is generated based on the correction result, specifically including: S431: The standardized printing file includes the CIELAB absolute coordinate values and XYZ colorimetric parameters of the spot color layer, and a logic tree diagram of the overprinting priority of the basic CMY three colors and the spot color layer is established according to the XYZ colorimetric parameters.

[0072] Specifically, during the printing process, the structure of the printed substrate significantly impacts color difference detection. Different substrates, such as paper and plastic film, have varying surface textures. These surface textures scatter light, causing deviations in reflectance spectral data, which in turn affects the accuracy of color difference detection. Therefore, utilizing a surface texture feature library to perform convolution correction on the reflectance spectral data in the intermediate color region is crucial.

[0073] First, a surface texture feature library must be constructed. Samples of various common printed substrates are collected and scanned and analyzed with high precision to extract surface texture features, such as texture roughness, orientation, and spacing. These features are digitized and stored in a database, forming the surface texture feature library. This process requires extensive data collection and processing to ensure the comprehensiveness and accuracy of the feature library.

[0074] Next, we acquire reflectance spectral data for the mid-tone area. Using a multispectral sensor, we scan the mid-tone area of the printed product and accurately measure its reflectance at different wavelengths, generating reflectance spectral data. This data forms the basis for subsequent corrections, and its accuracy directly impacts the effectiveness of these corrections.

[0075] Next, convolution correction is performed. The acquired reflectance spectral data is matched with features in the surface texture feature library and convolved. Convolution is a mathematical operation that simulates the scattering effect of surface texture on light. Specifically, a corresponding convolution kernel is generated based on the matched surface texture features. This convolution kernel is convolved with the reflectance spectral data to eliminate the influence of surface texture on the reflectance spectral data. This results in corrected reflectance spectral data that more realistically reflects the color information of the intermediate color region.

[0076] Furthermore, the CIELAB color space is an internationally recognized color representation method that accurately describes the lightness, hue, and saturation of colors. XYZ colorimetric parameters are another important color representation method, and they can be converted between each other. Representing the color information of a spot color layer using CIELAB absolute coordinates and XYZ colorimetric parameters provides a precise color reference for subsequent printing.

[0077] When generating standardized printing files, precise color measurement and analysis of the spot color layer is required. Using a professional color measurement instrument, such as a spectrophotometer, the spot color layer is measured to obtain its absolute coordinate values in the CIELAB color space. The corresponding XYZ colorimetric parameters are calculated based on the measurement results. Accurately recording this data in the standardized printing file ensures accurate reproduction of the spot color layer during the printing process.

[0078] Furthermore, during the printing process, the overprinting order and priority between the base CMY colors (cyan, magenta, and yellow) and the spot color layers are crucial. Different overprinting orders can produce different color effects and may even lead to color deviation. Therefore, it is necessary to establish an overprinting priority logic tree based on XYZ colorimetric parameters.

[0079] First, we conduct a thorough analysis of the XYZ colorimetric parameters of the base CMY color matrix and the spot color layer. We compare differences between them, such as brightness and purity. Based on these differences, we determine their overprinting priority. Generally speaking, brighter colors are likely to be overprinted first to avoid being overwritten by other colors and affecting the overall color quality.

[0080] Next, a logical tree diagram is constructed. The base CMY color matrix and spot color layers are used as nodes, connected according to overprinting priority. The root node of the logical tree diagram is typically the first overprinted color, with branch nodes representing subsequent overprinted colors. This method clearly demonstrates the overprinting order and priority relationships between colors. During the printing process, operators can accurately control the printing sequence based on this logical tree diagram, ensuring color accuracy and stability in printed products.

[0081] S432: Obtain a color compensation matrix under a preset standard light source and obtain current lighting data of the printing workshop, trigger a corresponding compensation mode according to the color compensation matrix and current lighting data, make corrections according to the compensation mode, and generate a standardized printing file.

[0082] Specifically, different light sources affect color perception. In the printing industry, a standard light source, such as D65, is often used as a benchmark for color measurement and comparison. A color compensation matrix is calculated based on this standard light source and a specific color model. It can be used to correct color deviations caused by light source differences.

[0083] First, obtain the color compensation matrix under a preset standard light source. This matrix is usually calculated by professional color experts based on extensive experimental data and theoretical calculations. This matrix is stored in the system and can be called up when needed.

[0084] Next, obtain the current lighting data for the printing room. Light sensors are used to monitor parameters such as light intensity and color temperature in real time. This data reflects the current lighting conditions in the printing environment and may differ from the preset standard light source.

[0085] Furthermore, based on the acquired color compensation matrix and current lighting data, the system triggers the corresponding compensation mode. If the current lighting data differs significantly from the standard light source, the system adjusts the color data based on the color compensation matrix. For example, if the current lighting is yellowish, the system will appropriately increase the blue component to balance the color deviation.

[0086] The specific correction process involves applying a color compensation matrix to previously acquired color data (such as CIELAB absolute coordinates and XYZ colorimetric parameters). Through matrix operations, the color data is corrected so that it accurately displays the expected color effect under the current lighting conditions.

[0087] Finally, the corrected color data and information such as the overprint priority logic tree are integrated to generate a standardized printing file. This file contains all the key information required for printing, such as color data and overprint order. Operators can use this file to perform printing operations, ensuring the desired color saturation and stability of the printed product.

[0088] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.

[0089] In one embodiment, a high-saturation offset lithographic packaging subtractive color printing device is provided, and the high-saturation offset lithographic packaging subtractive color printing device corresponds to the high-saturation offset lithographic packaging subtractive color printing method in the above embodiment. Figure 2 As shown, the offset lithographic high-saturation packaging subtractive color printing device includes a standard color value acquisition module, an overprint ratio acquisition module, a halftone optimization module, and a printing control module. The functional modules are described in detail as follows: The standard color value acquisition module is used to obtain the standard Lab color value of the intermediate color of a large area in the target image based on the international standardized color management system; The overprint ratio acquisition module is used to separate the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determine the overprint ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer; The intermediate color optimization module is used to perform screening optimization on the areas corresponding to the overprint ratio to reduce the interference of the basic CMY colors on the intermediate colors; The printing control module is used to generate standardized printing files containing spot color layers and basic CMY colors and complete printing through offset printing process.

[0090] Optionally, the overprint ratio acquisition module includes: The target intermediate color separation submodule is used to establish an image color separation channel, perform intermediate color separation on the target image according to the image color separation channel, and obtain the target intermediate color; The layer iteration submodule is used to iteratively correct the target image according to the target intermediate color, so that the △E2000 color difference value of the target intermediate color is controlled within the preset threshold value, and the spot color layer is automatically obtained; The proportion relationship calculation submodule is used to automatically obtain the standard Lab color value of the spot color layer, construct a regression equation based on the basic CMY three-color ink density value and the standard Lab color value, and obtain the overprint proportion relationship.

[0091] Optional, mid-tone optimization module includes: The intermediate color arrangement submodule is used to set the screen angles of the three basic colors CMY and form an asymmetrical arrangement with the 90° screen angle of the intermediate color area; The compensation parameter acquisition submodule is used to use a composite dot structure of square dots superimposed on circular dots to compensate the dot enlargement rate parameters of the intermediate color area according to a preset ratio.

[0092] Optionally, the printing control module includes: The spectral data acquisition submodule is used to acquire the reflectance spectral data of the intermediate color area through a multispectral sensor; The pressure command trigger submodule is used to generate and trigger the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller when the deviation between the measured Lab value and the standard value exceeds a threshold; The printing control submodule is used to perform convolution correction on the reflectance spectrum data of the intermediate color area using the surface texture feature library, eliminate the influence of the printing substrate structure on color difference detection, and generate standardized printing files according to the correction results.

[0093] Optionally, the printing control submodule includes: A logic diagram construction unit is used to standardize the CIELAB absolute coordinate values and XYZ colorimetric parameters of the spot color layer included in the printing file, and to establish a logic tree diagram of the overprinting priority of the basic CMY three colors and the spot color layer based on the XYZ colorimetric parameters; The printing control unit is used to obtain the color compensation matrix under the preset standard light source and the current lighting data of the printing workshop, trigger the corresponding compensation mode according to the color compensation matrix and the current lighting data, and generate a standardized printing file after correction according to the compensation mode.

[0094] The specific definitions of the offset lithographic high-saturation packaging subtractive color printing device can be found in the definitions of the offset lithographic high-saturation packaging subtractive color printing method described above and will not be further elaborated here. Each module in the offset lithographic high-saturation packaging subtractive color printing device described above can be implemented in whole or in part through software, hardware, or a combination thereof. Each of these modules can be embedded in or independent of a processor in a computer device in hardware form, or stored in a computer device memory in software form, allowing the processor to call and execute the corresponding operations of each module.

[0095] In one embodiment, a computer device is provided. The computer device may be a server, and its internal structure diagram may be as follows: Figure 3 As shown. The computer device includes a processor, memory, a network interface, and a database connected via a system bus. The processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program, and a database. The internal memory provides an environment for the operation of the operating system and computer program in the non-volatile storage medium. The network interface of the computer device is used to communicate with an external terminal via a network connection. When executed by the processor, the computer program implements a method for offset lithographic high-saturation packaging subtractive color printing.

[0096] In one embodiment, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the following steps are performed: Obtain the standard Lab color value of the large area intermediate color in the target image based on the international standardized color management system; Separate the intermediate colors in the target image into a custom spot color layer based on the standard Lab color value, and determine the overprint ratio between the basic CMY colors and the intermediate colors based on the custom spot color layer; Perform screening optimization on the areas corresponding to the overprint ratio to reduce the interference of the basic CMY colors on the intermediate colors; Generate standardized printing files containing spot color layers and basic CMY colors and complete printing through offset printing process.

[0097] In one embodiment, a computer-readable storage medium is provided, on which a computer program is stored. When the computer program is executed by a processor, the following steps are implemented: Obtain the standard Lab color value of the large area intermediate color in the target image based on the international standardized color management system; Separate the intermediate colors in the target image into a custom spot color layer based on the standard Lab color value, and determine the overprint ratio between the basic CMY colors and the intermediate colors based on the custom spot color layer; Perform screening optimization on the areas corresponding to the overprint ratio to reduce the interference of the basic CMY colors on the intermediate colors; Generate standardized printing files containing spot color layers and basic CMY colors and complete printing through offset printing process.

[0098] Those skilled in the art will understand that all or part of the processes in the above-mentioned embodiments can be implemented by instructing the relevant hardware through a computer program. The computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to memory, storage, database or other media used in the embodiments provided in this application may include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM) or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in many forms such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), Synchronous Link DRAM (SLDRAM), Rambus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0099] Those skilled in the art will clearly understand that for the sake of convenience and brevity of description, only the division of the above-mentioned functional units and modules is used as an example. In actual applications, the above-mentioned functions can be distributed and completed by different functional units and modules as needed, that is, the internal structure of the device can be divided into different functional units or modules to complete all or part of the functions described above.

[0100] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A high-saturation offset lithographic packaging subtractive color printing method, characterized in that: The offset lithographic high-saturation packaging subtractive color printing method comprises: Obtain the standard Lab color value of the large area intermediate color in the target image based on the international standardized color management system; Separating the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determining the overprint ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer; Performing screening optimization processing on the area corresponding to the overprint ratio relationship to reduce interference of the basic CMY colors on the intermediate colors; A standardized printing file containing the spot color layer and the basic CMY colors is generated and printing is completed through an offset printing process.

2. The offset lithographic high-saturation packaging subtractive color printing method according to claim 1, characterized in that: Separating the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determining the overprinting ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer specifically includes: Establishing an image color separation channel, and performing intermediate color separation on the target image according to the image color separation channel to obtain a target intermediate color; Iteratively correcting the target image according to the target halftone, so that the ΔE2000 color difference value of the target halftone is controlled within a preset threshold, thereby obtaining the automatic spot color layer; The standard Lab color value of the automatic spot color layer is obtained, and a regression equation is constructed based on the basic CMY three-color ink density values and the standard Lab color value to obtain the overprinting ratio relationship.

3. The offset lithographic high-saturation packaging subtractive color printing method according to claim 1, characterized in that: The performing of the screening optimization process on the area corresponding to the overprinting ratio relationship to reduce the interference of the basic CMY colors on the intermediate colors specifically includes: The dot angles of the three basic colors CMY are set accordingly, and are arranged asymmetrically with the 90° dot angle of the intermediate color area; Through the composite dot structure of square dots superimposed on circular dots, the dot gain rate compensation parameters of the intermediate color area are calculated according to the preset ratio.

4. The offset lithographic high-saturation packaging subtractive color printing method according to claim 1, characterized in that: Generating a standardized printing file including the spot color layer and the basic CMY colors and completing printing by an offset printing process specifically includes: Acquire reflectance spectrum data of the intermediate color area through a multispectral sensor; When the deviation between the measured Lab value and the standard value exceeds a threshold, an instruction is generated and triggered to the servo motor to adjust the ink supply pressure of the corresponding ink fountain roller; The reflectance spectrum data of the intermediate color area is convoluted and corrected using a surface texture feature library to eliminate the influence of the printing substrate structure on color difference detection, and a standardized printing file is generated according to the correction result.

5. The offset lithographic high-saturation packaging subtractive color printing method according to claim 4, characterized in that: The method of performing convolution correction on the reflectance spectrum data of the intermediate color area by using the surface texture feature library to eliminate the influence of the printing substrate structure on the color difference detection and generating a standardized printing file according to the correction result specifically includes: The standardized printing file includes the CIELAB absolute coordinate values and XYZ colorimetric parameters of the spot color layer, and a logic tree diagram of the overprinting priority of the basic CMY three colors and the spot color layer is established according to the XYZ colorimetric parameters; Obtain a color compensation matrix under a preset standard light source, and obtain current lighting data of the printing workshop, trigger a corresponding compensation mode according to the color compensation matrix and the current lighting data, and generate the standardized printing file after correction according to the compensation mode.

6. An offset lithographic high-saturation packaging subtractive color printing device, characterized in that: The offset lithographic high-saturation packaging subtractive color printing device comprises: The standard color value acquisition module is used to obtain the standard Lab color value of the intermediate color of a large area in the target image based on the international standardized color management system; An overprint ratio acquisition module is used to separate the intermediate colors in the target image into a custom spot color layer according to the standard Lab color value, and determine the overprint ratio relationship between the basic CMY colors and the intermediate colors according to the custom spot color layer; An intermediate color optimization module is used to perform screening optimization processing on the area corresponding to the overprint ratio relationship to reduce the interference of the basic CMY colors on the intermediate colors; The printing control module is used to generate a standardized printing file containing the spot color layer and the basic CMY three colors and complete the printing through an offset printing process.

7. The offset lithographic high-saturation packaging subtractive printing device according to claim 6, characterized in that: The overprint ratio acquisition module includes: A target halftone separation submodule is used to establish an image color separation channel, perform halftone separation on the target image according to the image color separation channel, and obtain a target halftone; A layer iteration submodule is used to iteratively correct the target image according to the target halftone, so that the ΔE2000 color difference value of the target halftone is controlled within a preset threshold value, thereby obtaining the automatic spot color layer; The proportion relationship calculation submodule is used to obtain the standard Lab color value of the automatic spot color layer, and to construct a regression equation based on the basic CMY three-color ink density value and the standard Lab color value to obtain the overprint proportion relationship.

8. The offset lithographic high-saturation packaging subtractive color printing device according to claim 6, characterized in that: The intermediate color optimization module includes: A halftone arrangement submodule is used to set the dot angles of the three basic colors CMY accordingly, and to form an asymmetrical arrangement with the 90° dot angle of the halftone area; The compensation parameter acquisition submodule is used to use a composite dot structure of square dots superimposed on circular dots to compensate the dot enlargement rate parameters of the intermediate color area according to a preset ratio.

9. A computer device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the computer program, the steps of the offset lithographic high-saturation packaging subtractive printing method according to any one of claims 1 to 5 are implemented.

10. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the steps of the offset lithographic high-saturation packaging subtractive printing method according to any one of claims 1 to 5 are implemented.

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