Quality control in the hottest digital printing pr

2022-08-12
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Quality control in the process of digital printing

from traditional printing to desktop publishing (DTP) to today's CTP and digital printing, the printing industry has experienced a continuous process of change. However, no matter how the printing industry changes, people focus on the transmission and reproduction of graphic information. Therefore, it is always of great importance to evaluate the quality of graphic information reproduction and use effective means to detect and control the quality. Then, when the printing industry from DTP, CTP to full digital network production, how should we carry out quality inspection and control? This paper will discuss this problem. The main printing production process

DTP technology, which rose in the 1970s and 1980s, has greatly changed the printing plate making process. DTP initially focused on word processing system, which solved part of the prepress process; By the early 1990s, the printing industry has entered a relatively mature stage of color desktop publishing, during which desktop publishing has gradually developed into a set of technological processes. CTP is an extended form of prepress digitization at the output end. With the continuous decline of CTP plate prices and the continuous maturity of related technologies, by the mid-1990s, CTP system has entered the practical stage. In essence, digital printing is also an extension of pre press digitization to printing and post press hydrostatic time measurement of pipes. There is no unified definition of digital printing at present. In a broad sense, the so-called digital printing is a printing method that records the text, image and other data stored in the computer in a digital form on a certain media, and then the media transfers the information to the substrate. At present, digital printing can be divided into two ways. First, completely eliminate the printing plate, and adopt electronic imaging or inkjet technology to directly image the digital printing with full significance on the medium, such as the digital printing machine launched by HP indigo and Xeikon; The second is semi digital printing machine with printing plate, such as Heidelberg di (digital direct imaging system) printing machine. The latter can also be summarized as on-board CTP

according to the degree of digitalization, the existing printing technology can be divided into the following four workflow

f process: DTP CTF traditional printing press prints

p process: DTP CTP (offline computer direct plate making) traditional printing press prints

3 Semi digital printing process: DTP semi digital printing machine (in machine computer direct plate making) printed matter

4 Full digital printing process: we call the first CTF process as traditional printing process and the last three as digital process for DTP digital printing machine

printing quality control elements and control tools

printing quality refers to the comprehensive effect of various appearance characteristics of printing. From the perspective of reproduction technology, the printing quality should be based on the faithful reproduction of the original. Whether in the traditional printing process or in the digital process, the printed matter should be faithful to the reproduction of the original. There are four control elements for printed matter: color, level, sharpness and consistency

1. Color is the basis of product quality, which directly determines the quality of products. Color control or management has always been the focus of printing professionals' research and analysis/P

2. Level refers to the change of color gradient that can be recognized in the image. It is the basis of accurate color reproduction

3. Sharpness refers to the clarity of image details, including three aspects: the clarity of image fine levels, the clarity of image contour edges and the clarity of image details

4. Consistency is uniformity, which includes two aspects. On the one hand, it refers to the consistency of ink volume in different parts of the same batch of printed matter, that is, different ink areas. Generally, it is measured by the consistency of vertical and horizontal field density of printed matter, which reflects the stability of different parts of printed matter printed at the same time. On the other hand, it refers to the consistency of the density of different batches of prints in the same part, which reflects the stability of the printing press

for printed matter, as long as these four aspects are well controlled, that is, the color, level, clarity and consistency of printed matter can be well controlled, high-quality printed matter can be obtained

one of the methods of printing quality control is to use conventional signal strips, test strips, control strips, ladders, together with testing instruments and charts, to scientifically and quantitatively control the printing quality (including the quality of printed matter and printing engineering quality). At present, there are many kinds of signal strips and test strips used in various countries, such as GATF system in the United States, Bruner system in Switzerland, freguer system in Germany, and gelinda system. China mostly adopts the signals and test strips of GATF and Bruner, Switzerland

commonly used detection tools for printing include signal strip, test strip, control strip and ladder. The signal bar is mainly used for visual evaluation. Its function is relatively simple, and it can only express the appearance quality information of printed matter. Such as exposure ladder, GATF code signal strip, color signal strip, etc. The test strip is a multi-functional marking element based on densitometer detection and evaluation, which combines visual identification with densitometer testing, and carries out numerical calculation with the help of charts and curves. Control strip is a multifunctional control tool that combines visual evaluation and test evaluation of signal strip and test strip. Such as Bruner's third generation control strip. A ladder with equal differential density or points, which is used to control the printing quality

the printing process mentioned above needs to use signal strips and control strips to record data in the operation of its main links, so as to lay a foundation for standardized production. Quality inspection and control usually find problems through proofing. In the traditional printing process, traditional proofing is used, that is, proofing by round flattening. In the digital process, digital proofing has gradually replaced the traditional proofing. The digital documents to be printed can be output directly to the proofing machine, so as to see whether there are problems with words, specifications, images, etc. Since film and even printing plates are no longer used in the digital process, the evaluation and control of quality largely depend on the digital proofing. Then, in today's digital and networking environment, what factors restrict the printing quality in the digital process? Where are the difficulties and advantages of quality inspection and control

methods of printing quality detection and control in digital environment

1 The transmission of data flow in the digital process

the digital production process makes the data flow and control flow in the actual production less intuitive than the traditional process. What we see is only the input layout elements, the layout information displayed by the display device, and the final output color digital proofing and CTP printing plate. In that case, the pre tension will fluctuate greatly, and the information will exist in the form of data. Any small error or small error will cause the failure of data transmission or abnormal output results, and will also exceed the control ability of the operator. It is difficult or impossible to check the problem at all, so these variables have become uncontrollable factors in the prepress operation. In order to ensure the correct and smooth flow of data, we must find a set of practical data flow control methods

in the production of printing industry, there are two kinds of information flows in printing parts, namely, graphic information flow and production control information flow. Graphic information flow solves the problem of what to do; The control of information flow solves the problem of how to do and what to do. In the digitalization process, these two kinds of information are digitalized, which can be stored, recorded, processed and transmitted by computers. The control nodes of data flow in the digital process are document pre inspection, print output, PDF standardized digital collage, and rip post output

2. Color management under open system

color reproduction is an important measure of image reproduction quality. The color control in the traditional process is based on the theory of the definition and description of color attributes with density control as the core, and carries out color recognition and correction through a closed-loop system. The specific control methods include gray balance, color correction, optimal printing density control, point transfer and its control, etc

digital printing process is an open system. Input, processing and output equipment may come from different manufacturers. Various devices have different ways of predicting the impact of color description and expression. With the increase of the number of times of use, the same device will also lose, and the expressiveness of color will also be different, which increases the difficulty of color reproduction. And because of the emergence of networks and the need of information exchange, the designed color images or color image files are no longer limited to local publishing and printing; Often need to watch or copy in different places. The color information of color image not only needs to be transmitted in different devices, such as computer monitors (even the same device, the ability of color display of devices produced by different manufacturers is also different), but also needs to be transmitted between different media

this requires a system whose function is to make the transmission results of colors between all media basically consistent without aliasing. That is, what you see is what you get. This system is called color management system. The international color organization ICC has developed a standard iccprofile to describe the color performance of devices. Using iccprofile feature files can realize cross platform color communication, so that when other computers add color management functions, these files can be converted at will. Color management is carried out through property files. Color management system is an application system, including computer hardware, computer software and color measuring equipment. Its goal is to form an environment so that various devices and materials supporting this environment can match each other in color information transmission and realize undistorted transmission

the new color control method with color space transformation as the core color management makes the technical process in the field of printing and communication enter a new digital production stage, and solves many problems of color benchmark and conversion in the production of printing media. New technologies and equipment such as digital proofing, CTP, digital printing and digital production process continue to appear, and move towards the goal of what you see is what you get

3. Data transmission and management

with the deepening of digitization, the amount of data increases exponentially. Although there is a fast network, it is still necessary to optimize the transmission and management of data on. To this end, two related specifications have been formulated in the prepress field: OPI (openprepressinterface) specification and DCS (desktop color separation) specification. OPI specification allows the replacement image with low resolution to be used when making up, and the corresponding high-resolution image will be automatically replaced by the OPI server when color separation output, so as to reduce the transmission volume of files in the network. DCS specification is an extension of EPS file format, which can manage the whole color separation process of desktop publishing system, which is conducive to shortening production time and reducing the requirements for equipment. In the printing process, data flows in all links. Therefore, it is extremely important to ensure that data files are not missing in the transmission process and that different platforms interpret the files consistently. Otherwise, the files transferred to the back end will be destroyed due to data loss

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