Color box packaging products often have color reduction problems in actual production, such as neutral gray color cast, etc., which affects product quality. In addition to the problems of the equipment itself and the technical level of the production personnel, the key issue is that the enterprise does not Effective color management and proper application of inks.
The concept and necessity of color management
Color management is to manage people's perception of color. The purpose is to realize the conversion between different colors in the entire process of image reproduction to ensure that the appearance of the image color from the input display to the output is matched as much as possible. Harmony with the color of the reproduction.
Image reproduction needs to undergo multiple stages of image acquisition, processing, color separation, printing, etc. At each stage, the color information will be expressed according to the coloring principle and color description characteristics of the currently used equipment. Different scanning and display devices will have different color representations for the same original. In addition, the color rendering ability between the RGB three-color display and the four-color printing ink is different. In addition, different application software converts RGB data into CMYK, which lacks consistency and uses different papers and inks. The printed matter obtained is also different. Therefore, color management techniques must be used to control color reproduction on various devices and media in a production system.
Color management content
Establishing the device's color profile is the core of color management. The description file has representative color features of each device, such as chromaticity characterization curve, output color gamut characteristic curve, etc. The color management system uses these representatives. Sexual color features enable matching and conversion of color space of each device.
For color management, a series of prescribed operating procedures must be followed to achieve the desired results. Color management is divided into three steps in principle, referred to as "3C", that is, calibration, characterization, and conversion.
Calibration: In order to ensure the stability, reliability and sustainability of the color information transmission process, the input, display and output devices are required to be calibrated to ensure that they are in standard working condition. The input correction includes the brightness, contrast, and correction of the black and white field of the scanner or the like. To ensure that the same image can be obtained for the same original regardless of when it is scanned.
By displaying the brightness, contrast, color temperature of the display, and the Gamma value of the entire display system, it is possible to accurately display the color. Output corrections include calibration of printers, imagesetters, printers, and proofers, and their characteristics are corrected so that the device can be output according to factory-standard features.
Characterization: Recording the calibrated characteristics of all devices is the process of characterization. These profiles are bridges from device color space to standard device-independent color space (PCS).
Conversion: Based on the calibration of the system equipment, the device description file is used to implement the correct conversion between the color spaces of each device by using the standard device-independent color space as the medium. Since the color gamut of the output device is narrower than the color gamut of the original, the scanner, and the display, the color gamut needs to be compressed during color conversion, and the color gamut compression has absolute color method, relative color method, and ICC protocol. Highlight the four methods of saturation and sensory.
Implementation of color management
In general, for a packaging printing company to do color management, you need a standard ambient light source; high-quality color characteristics file generation software; advanced color management system; standard measuring instruments and testing tools; standard color target Standard print management; standard remote digital proofing color management; standard scan and restore, digital camera color management; standard display correction and screen soft proofing. In the specific implementation process of color management, the following aspects should be done: carefully standardizing, standardizing, and data-based production management of all processes in the whole process of printing, which is the premise and basis for applying ICC color management.
Enterprises must strictly formulate quality standards for fine products, standards for raw materials and equipment such as paper and ink, standards for measuring tools and environmental light sources, and develop standardized management documents, etc., and require everyone to strictly follow the standards. Display, soft proofing, ICC file of the printer, various parameters of the printing machine, etc. should be standardized, and quantified within the standards and specifications. In all places where data can be expressed, the data can be summarized and summarized by means of testing. The three complement each other and depend on each other to ensure stable high quality and efficient production.
Prepress image processing technology is the basis and key link of print copy quality. The display should be professional, the scanning of the original and the processing of the digital original should be unified with the four basic standards of copy quality (grey balance, tone reproduction, color correction, sharpness enhancement) to guide the work, and standardize the four standard parameters through experiments. . After the scanning of the documents is completed, it is necessary to adjust and process the defects of the non-adapted originals to make the printed matter more rich and better than the original. For off-site printing companies, remote digital proofing profile management ensures that the color of the digital proofs in both places is the same.
Color management system selection
There are many color management systems on the market, such as Adobe's Photoshop color management system, Apple's ColorSync color management system, and Kodak's color management system. Different color management systems have different color management capabilities for devices and have their own expertise, so companies must first determine which devices need to have consistent colors for selection.
Secondly, it is necessary to determine the self-describing file in the color management system and whether to support the creation of the description file in the open system; in the case of a closed system, the manufacturer must create a description file, so that it is necessary to determine whether it can withstand the creation of the description file. The cost required. The system should be compared and tested according to the company's own situation, such as system reliability, equipment support capability, scalability, compatibility and ease of use. The same color manuscript can be used for testing to observe which system is specific. In the operating environment, the effect that matches the original is obtained.
Effective color management is the guarantee of the entire copy quality, but the final product is achieved through ink. As one of the five major elements of printing, ink has an important influence on the printing process and quality. Proper and reasonable use and blending of inks is the key to ensuring accurate color reproduction. Ink use problem
Composition and properties of ink: Water-based inks are processed from water-soluble resins, advanced pigments, solvents and additives. The hue depends on the nature of the pigment, and the pigment is generally required to have a bright color, a suitable tinting strength and hiding power, good resistance and a high degree of dispersion. In order to obtain good printability of ink, various ink additives are often used to adjust the fluidity, dryness and viscosity of the ink according to different conditions. There are many factors that determine the quality of ink, and improper use will bring a series of quality problems. When purchasing and using, you should pay attention to analysis, judge its pros and cons, and make adjustments according to the situation to ensure its excellent printability. .
In printing, the ink has a certain viscosity which is a necessary condition for maintaining normal transfer and transferring ink. Therefore, the viscosity of the high-grade ink is generally controlled to about 20 ± 5 seconds, and the difference in viscosity causes the difference in the color of the printing. In the actual production process, depending on the material and temperature, the PH value of the ink on the machine can be adjusted or controlled between 8.0 and 9.5.
Ink blending: Ink blending mainly refers to the color blending of inks. In the printing of packaging products, the color of the ink is mainly applied in the spot color of the spot color, achieving the dual effects of vision and anti-counterfeiting.
These different spot colors cannot be overprinted by four colors of green, yellow, black, and black. They are often not directly used. It is necessary for technicians to adjust the original ink according to the production conditions. .
The color matching of the ink is based on the principle of subtractive color method, that is, any color can be blended by using different proportions of the three primary colors, and considering the three basic properties of hue, brightness and saturation. In the color matching, the ink used should be determined according to the actual printing process, the thickness of the ink layer, the printing substrate, and the like, and the hue, gloss, tinting strength, hiding power and the like of the ink itself are considered.
Color matching process
Analysis of original color: Toning is performed on the color of the original. In order to reduce the blindness of the color, the original color must first be analyzed to determine the hue and scale of the primary ink. The analysis of the manuscript is mainly a combination of instrument color measurement and human eye colorimetry. It is simple and practical to determine the ratio of the three primary color inks by printing chromatography, and the three primary color inks and white ink content can be calculated according to the percentage of the primary color dot area marked in the chromatogram.
Color matching: According to the calculated ratio, a small amount of primary color ink is first weighed for blending. Note that the ink color is compared with the original color. When the two colors are close, the adjusted ink can be compared on the scraping paper, and then repeated until the two colors are completely consistent. When colorimetric, the ink should be evenly distributed, and the thinner the ink layer, the better. In order to ensure the accuracy of the hue of the color sample, the paper should be the same as the paper used for printing. The adjustment of brightness and saturation is achieved by adding white ink and black ink. When white and black inks need to be added, special attention should be paid to the accuracy of weighing.
After the ink to be dispensed reaches the original requirement, the batch ink can be dispensed in proportion. The amount of ink used in a batch of jobs is usually determined by the type of paper, the image area, the number of prints, and the amount of wear, and is carried out on a principle that is less or less.
Record: When the preparation is completed, the ratio of the inks of various colors used for ink adjustment, ink oil, dry oil, ink type, quantity, manufacturer and other information will be registered in detail, which is convenient for future ink distribution.
Other precautions: When analyzing the original and colorimetric, it is best to carry out the standard light source or the light source close to daylight, and pay attention to the color film after drying, to reduce the visual error. Try to use a color that is close to the original color ink or other single color. If the color is too much, the brightness and saturation will be worse, which will affect the printing effect. Therefore, the less the number of inks in color matching, the better, it is best to choose the same manufacturer's ink products.
When grading, it is necessary to fully understand the daily printing speed and printing pressure of the equipment of the factory, and control the viscosity of the ink. Different printing speeds and pressures will produce different shades of printed products. Therefore, the inks that are dispensed at low speeds must be re-checked with the originals after the printing speed is turned to the normal speed to avoid chromatic aberration and waste.
After the ink is transferred out, if it is found that the color sample printed on the machine is in error with the original, it should be corrected in time. When changing colors, the ink fountain and ink roller should be cleaned to avoid the color change caused by unclean cleaning. For the spot color ink remaining after printing, it can still be adjusted according to the hue of the new manuscript, but the saturation is often gray, especially the remaining ink retrieved from the ink fountain, which may have been emulsified or the printability has changed.
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