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From traditional printing to desktop publishing (DTP) to today's CTP and digital printing, the printing industry has undergone a process of constant change. However, no matter how the printing industry changes, people are concerned only with the transmission and reproduction of graphic information. Therefore, it is always extremely important to evaluate the quality of the reproduction of graphic information and use effective means to detect and control the quality. So, when the printing industry moves from DTP and CTP to full digital network production, how should we conduct quality inspection and control? This article will discuss this issue.
Main printing production process
The DTP technology that emerged in the 1970s and 1980s has caused great changes in the printing platemaking process. At the beginning, DTP was mainly based on the word processing system, and it solved part of the pre-press process; by the early 1990s, the printing industry entered a more mature color desktop publishing stage, and desktop publishing in this period has gradually developed into a set of processes Process. CTP is an extended form of pre-press digitization at the output. With the continuous decline in the price of CTP plate materials and the continuous maturity of related technologies, the CTP system has entered a practical stage by the mid-1990s. "Digital printing" is essentially an extension of pre-press digitization to printing and post-press. For the definition of digital printing, there is no unified statement. Broadly speaking, the so-called digital printing is a printing method in which data such as characters and images stored in a computer are recorded on a certain medium in a digital form, and then the information is transferred to the substrate by this medium. At present, digital printing can be divided into two ways. One is to completely eliminate the printing plate and use electronic imaging or inkjet technology to directly image the digital printing on the medium, such as the digital printing press launched by HP Indigo and Xeikon; the second is the semi-digital printing press with printing plate , Such as Heidelberg's DI (Digital Direct Imaging System) printer. The latter can also be summarized as on-machine CTP.
According to the different levels of digitization, the existing printing technology can be divided into the following four workflows.
1. CTF process: DTP → CTF → traditional printing machine → printed matter
2.CTP process: DTP → CTP (offline computer direct plate making) → traditional printing machine → printed matter
3. Semi-digital printing process: DTP → semi-digital printing machine (computer-to-machine direct plate making) → printed matter
4. Full digital printing process: DTP → digital printing machine → printed matter We call the first CTF process as the traditional printing process, and the latter three as the digital process.
Print quality control elements and control tools
Print quality refers to the comprehensive effect of various appearance characteristics of printed matter. From the perspective of copying technology, print quality should be based on "faithful reproduction of the original". Whether in the traditional printing process or in the digital process, the printed matter must be faithfully copied to the original. There are 4 control elements for printed matter: color, gradation, clarity, consistency.
1. Color is the basis of product quality, which directly determines the quality of the product. Color control or management is always the research and analysis of printing professionals.
2. The gradation is the gradation, which refers to the change of the gradation of the color recognizable by the image. It is the basis for accurate color reproduction.
3. Clarity refers to the clarity of image details, including three aspects, the clarity of the subtle levels of the image, the clarity of the edges of the image outline, and the clarity of the image details.
4. Consistency is uniformity, which includes 2 aspects. On the one hand, it refers to the consistency of the ink volume of different parts of the same batch of printed matter, that is, different ink areas. It is generally measured by the consistency of the vertical and horizontal solid density of the printed matter. It reflects the stability of different parts of the printed matter printed at the same time. On the other hand, it refers to the consistency of the density of different batches of printed products in the same location, which reflects the stability of the printing press.
For printed matter, as long as these four aspects are well controlled, that is, the color, gradation, clarity, and consistency of the printed matter can be well controlled, you can get high-quality printed matter.
One of the methods of printing quality control is to use conventional signal strips, test strips, control strips, ladders, and test instruments and charts to scientifically and quantitatively control printing quality (including printing quality and printing engineering quality). At present, there are many types of signal strips and test strips used in various countries, such as the GATF system in the United States, the Brunner system in Switzerland, the Fogra system in Germany, and the Glinda system. In China, the signals and test strips of GATF and Brunner of Switzerland are mostly used.
Common testing tools for printing include signal strips, test strips, control strips, and ladders. The signal bar is mainly used for visual evaluation, the function is relatively single, and it can only express the appearance quality information of the printed matter. Such as the sun ladder, GATF code signal bar, color signal bar, etc. The test strip is a multi-functional marking element mainly based on density meter detection and evaluation. It is a test strip combining visual identification and density meter test, and numerically calculating with the help of charts and curves. The control bar is a multifunctional control tool that combines the visual evaluation and test evaluation of the signal bar and the test bar. Such as Brunel's third generation control strip. The ladders have unequal density or dots, which are used to control the printing and printing quality.
The printing process mentioned above needs to use signal bars and control bars to record data in the operation of its main links to lay the foundation for standardized production. Quality inspection and control generally find problems through proofing. In the traditional printing process, traditional proofing is used, that is, proofing by round flattening. In the digitalization process, digital proofing has gradually replaced traditional proofing. The digital files to be printed can be directly output to the proofing machine to see whether there are problems with the text, specifications, and images. Since film is no longer used in the digitalization process, and even printing plates are no longer used, quality evaluation and control largely depend on the digital proofing. So, in today's digital and networked environment, what factors are restricting its printing quality in the digital process? What are the difficulties and advantages of quality inspection and control?
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