Abstract: This paper introduces the color management of printing based on ICC. It is believed that the key to the full color management of printing lies in the standardization and standardization of printing production, the digital transmission of color information, and the automatic detection and correction of color during printing. The closed-loop color management system (Close-Loop CMS), image control system, machine vision system and other color control systems are introduced.
Keywords: printing full color management color control image control system machine vision system
In recent years, color management technology has made great progress, and there are more applications in printing companies. The current color management technology is mainly based on the ICC color management model. Its work process is to record the color characteristics of the various environments and equipment in the printing process after calibration and standardization, and to generate characteristic documents (ICC files), and The standard color space performs color conversion, and eventually achieves the consistency of color reproduction at various device terminals. With the development of printing technology and the ever-increasing competition in the printing industry, the production methods of printing companies gradually move from traditional simulation methods to digitalization, networking, and integration. The application of technologies such as CTP technology, digital proofing, and digital workflow shows this. a little. The digital production method means the digitalization of information transmission in production, the informationization of management, and automation of printing process control. At the same time, the scope of application of color management has also changed, it is no longer limited to a certain part of the printing process, but runs through the entire printing process.
In addition, the transfer and control of color management information is also more intelligent. The printing industry has realized this, and some powerful printing companies have begun to accept new color management ideas, started to introduce advanced color detection, digital workflow and other technologies, and apply color management to the entire printing process. The whole process of color management has a role in promoting printing production. At the same time, it also puts forward higher requirements for printing production. For example, the entire production process of printing should be in a stable state. The printing process should be digital, standardized, standardized and intelligent. Color control technology. This article describes its color control technology from the perspective of the basic principle and application of color management throughout the printing process.
First, printing the whole color management
1.ICC color management principles
In the printing process, the color description capabilities of various types of devices and materials used in color image processing vary widely, and color information is transmitted between them and causes great losses. In order to avoid these losses, the ICC color management mode records their color characteristics and converts them to a standard color space for processing, so that the color signal transmission is not affected by the color characteristics and color gamut of various devices and materials. The color information of the color image is retained as much as possible so that the color information can be transmitted and reproduced without distortion. In the output of color information, the best color gamut matching method is used to make maximum use of the color gamut of the output gamut, so that the color image can have the best output effect. The process of ICC color management is device calibration, device characterization, and color space conversion. Throughout the entire color management, through the real-time collection, analysis, feedback and correction of color information, the cycle of equipment calibration, device characterization and color space conversion process is realized.
2. Influencing factors of full color management
Factors that affect the effectiveness of full-scale color management include: characteristics of equipment before printing and printing; features of printed materials such as paper, ink, and blankets; methods of color detection, accuracy and other properties of test instruments; and standardization and standardization of printing production. Degree and so on.
3. The key to color control in full color management
The basic idea of ​​color management throughout the printing process is that color management is applied to the entire printing process. The core of the color management is the more efficient, accurate, and intelligent color information transmission. Color control is an important measure to ensure the effective implementation of color management. The key to color control lies in the standardization and standardization of printing production, the digitalized transmission of color information, and the automatic detection and correction of color during the printing process. Based on this, the real-time collection, analysis, feedback, and correction of color information in the printing process can be achieved to achieve color control. the goal of.
Second, color control technology
1. Standardization and standardization of printing production
The standardization and standardization of printing production is the premise of digital printing and the basis of color control. By standardizing all aspects of printing production, the equipment status and material properties are stable, and standardized data is established, thereby stabilizing the various factors of color management.
2. Digitalization of color information
The color characteristics of each device in ICC color management are recorded, transferred and converted in a digital manner. In the entire printing process, prepress is the earliest realization of digital information processing, image color information can be recorded and transmitted by TIFF, PS, EPS, PDF and other documents, the color characteristics of the device information recorded in the ICC file; before printing to printing Machine link, image color information is recorded and transmitted through the printing plate, and the ink data related to the image to restore the image color can be transmitted through analog or digital methods. However, in the full color management, the ink data should be generated from before printing. And digitally passed to the press.
3. Digital workflow
The basic idea of ​​the digital workflow is to integrate prepress, printing, postpress and management into a whole, and to realize digital recording and processing of graphic information, production control information and management information. Color control information in color management can be transmitted and processed through a digital workflow. The current digital workflow is mainly based on the PDF and JDF standard processes, in which the PDF standard is used to record graphic information, and the JDF standard is to record management information. The ink data from the prepress to the printer can be passed by the PPF standard.
4. Automatic color control in the printing process
The automatic color control of the printing process, including the real-time collection of color data, data analysis, feedback and correction, must be done by the color automatic control system. Such systems mainly include closed-loop color management systems, image control systems, and machine vision systems.
(1) Closed Loop Color Management System (Close-Loop CMS)
Closed loop color management is a color management idea proposed by GretagMacbeth. Its core is to reduce human influence factors in color management, making the color management system easier to use and more automated. Most closed-loop color management systems (Close-Loop CMS) are online or on-line, that is, the regulation of colors is completely automated, and the entire process is not subject to manpower. Devices that install a closed loop color management system will measure the color space of the printed sheets in real time. If they deviate from the predetermined color space, the system will instruct the device to make corresponding adjustments.
(2) Image Control System
The function of the image control system is to compare and measure the printed sheets so as to realize the online control of print colors, such as the online online image control system of CPC24 in Heidelberg. The system can accurately detect defects, color values, or overprint errors in printed images at the same time. The CPC24 system uses a specially designed high-resolution CCD monitor scan head to scan and sample the entire print sheet, and transmits the sampled data to a dedicated computer. Processing and comparison with preset values ​​°CPC24 can perform supervisory control on certain key areas of the printed sheet to achieve the color control of the printed sheets. When the CPC24 system finds color deviations of the printed sheets, it immediately proposes corrections.
(3) Machine Vision System
Machine vision is the use of machines instead of the human eye to make measurements and judgments. A typical industrial machine vision application system includes the following parts: light source, lens, CCD camera, image processing unit (or image capture card), image processing software, monitor, communication (input and output unit), and the like. The machine vision system converts captured targets into image signals through machine vision products (ie, image capture devices, sub-COMS, and CCD) and transmits them to a dedicated image processing system. Based on pixel distribution, brightness, color, and other information, it is converted into Digital signals; image systems perform various operations on these signals to extract the characteristics of the target, and then control the on-site device actions based on the results. The advantage of the machine vision system is that the detection speed is fast and the precision is high. In the color management, the machine vision system can be used to detect the print color difference and the color uniformity, which greatly improves the efficiency. At present, the application of machine vision systems in the printing industry has only just begun, but it has very good prospects.
With the continuous development of color control technology, the industry has deepened its understanding of color management technology, and the use of color management will be better and better, and will bring greater benefits.
Yang Genfu Peng Bo Zhou Yicheng School of Press and Publication, Hangzhou Dianzi University
Reprinted from: Chinese Packaging