Detailed discussion on color reproduction of the h

2022-09-20
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Detailed discussion on color reproduction of packaging and printing (Part 1)

color box packaging products often have color reduction problems in actual production, such as neutral gray color deviation, which affects product quality. In addition to the problems existing in the equipment itself and the technical level of production personnel, the key problem is that enterprises fail to carry out effective color management and the reasonable application of ink

the concept and necessity of color management

color management is to manage people's sense of color, and the purpose is to realize the conversion between different colors in the whole process of image reproduction, so as to ensure that the image color rises linearly from the production order to the display to the output, and the appearance shown in the output matches as much as possible, and finally achieve the harmony and consistency of the color of the original and the replica

image reproduction needs to go through many stages, such as image acquisition, processing, color separation, printing, etc. in each stage, the color information will be represented according to the color rendering 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 expression ability between the display screen with RGB three color rendering and the printing ink with four color rendering is different. In addition, different application software will convert RGB data. However, at present, we mainly focus on the conversion of epoxy resin into CMYK, which is also lack of consistency. Using different papers and inks, we will get different prints. Therefore, color restoration on various equipment and media in the production system must be controlled through color management technology

content of color management

establishing a device's color description file (profile) is the core of color management. The description file contains the representative color features of each device, such as the characterization curve of chromaticity, the output color gamut characteristic curve, etc. the color management system uses these representative color features to realize the matching and conversion of the color space of each device

for color management, a series of specified operation processes must be followed in order to achieve the desired effect. Color management is divided into three steps in principle, referred to as 3C for short, namely calibration, characterization and conversion

calibration: in order to ensure the stability, reliability and sustainability in the process of color information transmission, it is required to calibrate the input, display and output devices to ensure that they are in a standard working state. Input correction includes the correction of the brightness, contrast and black-and-white field of the scanner. To ensure that the same image data can be obtained for the same original no matter when it is scanned

by setting the brightness, contrast, color temperature of the display and the gamma value of the whole display system, it can accurately display the color. Output correction includes the correction of printers, imagesetters, printers and proofing machines. After correcting their characteristics, the equipment can be exported according to the standard characteristics at the factory

characterization: recording the corrected characteristics of all equipment is the process of characterization. These characteristic description files are the bridge to transform from equipment color space to standard equipment independent color space (PCS)

conversion: Based on the calibration of the system equipment, use the equipment description file to realize the correct conversion between the equipment color spaces with the standard equipment independent color space as the medium. Because the color gamut of output devices is narrower than that of originals, scanners and displays, it is necessary to compress the Passover growth gamut of per capita consumption of plastic flexible packaging in the Middle East and Africa during color conversion. There are four methods of color gamut compression in ICC protocol: absolute chromaticity method, relative chromaticity method, prominent saturation method and sensory method

implementation of color management

generally speaking, a packaging and printing enterprise needs standard environmental light sources to do a good job in color management; High quality color feature file generation software; Advanced color management system; Standard measuring instruments and test tools; Standard color target; Standard printing management; Standard remote digital proofing color management; Standard scanning restore, digital camera color management; Standard display calibration and screen soft proofing. In the specific implementation process of color management, the following aspects should be done well: carefully do a good job in the standardization, standardization and data production management of all processes in the whole printing process, which is the premise and foundation of the application of ICC Color Management

enterprises should strictly formulate quality standards for fine products, standards for the integrity of raw and auxiliary materials such as paper and ink and equipment, standards for measuring tools and environmental light sources, formulate standardized management documents, and require everyone to strictly follow the standards. The ICC documents of the display, soft proofing, printer and parameters of the printing machine should be standardized, and quantified within the standards and specifications. In all places that can be expressed with data, the data that can ensure the quality should be summarized by means of testing. The three are complementary and interdependent, so as to ensure stable high-quality and efficient production

prepress image processing technology is the basis and key link of printing reproduction quality. The display should be professional. The scanning of originals and the processing of digital originals should be guided by the four basic standards of reproduction quality (gray balance, tone reproduction, color correction, sharpness enhancement), and the parameters of the four standards should be standardized through experiments. After scanning the document, we should adjust and artistic process the defects of the unsuitable original, so as to enrich the printing level and achieve the effect better than the original. For enterprises printing in different places, the profile file management of remote digital proofing can ensure that the color of digital proofs in the two places is consistent

choice of color management system

at present, there are many color management systems on the market, such as Adobe's Photoshop color management system, Apple's colorsync color management system, Kodak's color management system, etc. Different color management systems have different color management capabilities for devices and have their own advantages. Therefore, enterprises must first determine which devices need to obtain consistent colors for selection

secondly, it is necessary to determine the self description file in the color management system and whether it supports the establishment of the description file in the open system; If it is a closed system, the manufacturer must establish the description document, so it needs to determine whether it can bear the cost of establishing the description document. According to the enterprise's own situation, the system's reliability, equipment support ability, scalability, compatibility, ease of use and other performance should be compared and tested. During the test, the same color manuscript can be used to observe which system can achieve the best effect with the manuscript under the specific operating environment. (to be continued)

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