Using Screening New Technology to Improve Print Quality

Although the "digital revolution" has made a tremendous change in the prepress field. Unfortunately, there is no change in the quality of prints. Although the colors and forms of printed materials, such as brochures, posters, and magazines, are all very fresh, they are still used. The 1751pi AM screening method (AM) of the “Analogue era.” The quality of printed products only stays on the technical level of accurate overprinting and good color reproduction, but it cannot fundamentally meet the requirements for photo-level effects under close observation. The reason is that in the prepress-making process, high-resolution image information produced or scanned cannot be displayed on the PS plate or CTP plate in an advanced, reasonable, and operable screening mode. Caused by printing.

Recalling the history of the development of the screening technology, every change in the screening method has provided the impetus for the improvement of the quality of printed matter, but at the same time, it has, to a certain degree, constrained the continuous improvement of the quality of printed products. Therefore, under the existing productivity and technological conditions, we urgently need to use a new screening technology to replace the original traditional screening methods in order to fully improve the quality of printed products.

First, the drawbacks of traditional screening methods

1. The limitations of the traditional “amplitude screening” have brought confusion to the printing industry. The traditional "amplitude screening method" is to change the level and color of an image by changing the size of the dot. At present, the vast majority of printing processes use this screening method. Its advantage is that the pitch and the angle of the dot are fixed, and the gradation change of the image can be stably expressed.

However, the AM screening method has disadvantages that cannot be ignored. Since the halftone dots have a fixed pitch and angle, if each color plate has a strict registration, or the screen angle conflicts with the scene texture in the picture. It is easy to cause the appearance of moire. When using this screening method, jaggies and breaks in the lines, or jumps in the tone of the gradient areas, are typical problems. Even more troubling is that such problems are unpredictable before printing. In the prepress area, the process of moving toward a fully digital workflow, which includes the activation of CTP technology and the rationalization of digital proofing processes, has played a stumbling block.

If you try to achieve higher print quality with higher AM screens, you will encounter additional problems: For the printing process, more stringent print quality management is required. It is more difficult. Because of this, only a handful of printers dare to try to print more than 3001pi.

Although powerful graphics and image processing software allows us to easily obtain high-precision digital information, the printing industry can only “print finer graphic images” because only 175 lpi AM screening is usually available. Wang Yang sighed.

2. FM screening technology can only be shelved due to process constraints.

We once pinned our hopes on FM technology, hoping that it could replace AM screening. FM screening is made on the color separation is a very small idea. The dense changes of these small ideas can represent the level changes of the image. This technology can not only avoid the problem of moiré and thread breakage, but also can achieve ink coverage of 250, which is also beneficial to improve the print resolution. But things are not as perfect as people expected. FM screening also has some serious drawbacks. It is very demanding on the printing process. To meet these requirements, the cost of printing production will be greatly increased. In addition, in the printing process, the levels of the intermediate tone and dark tone levels are not easy to grasp, and the quality fluctuates greatly, and the graininess of the highlights and shades is very serious. and so. Although FM screening is superior to AM screening in some aspects, it has not been widely adopted because of these more serious drawbacks.

Second, the digital era gave birth to new technologies

In the perplexed and difficult trade-offs, the printing industry ushered in the digital revolution, and a large number of new screening technologies that can meet the requirements of productivity development and graphic arts have emerged, and have come out of the theoretical and experimental stages, and are fully applied to prepress. stage. At present, there are a variety of screening methods in the printing industry, which can be divided into the following four categories from the principle of screening:

1. High-LPIAN: This is a so-called high-precision traditional screening method. The number of screens is finer than the industry standard (200 lpi for commercial printing or 150 lpi for newspaper printing). For example, Creo's Prinergy AM Prinergy FM, Cypress's Brisque Turbo Winning Scroll Plus, Fujifilm Co-Res Plus, and Artworks Paragon Plus.

2 . High-LPI hybrid AM: It is a variant of the traditional high-line AM screening. Creole Corporation

MaxtoneT "Catalyzed, Agfa's Sublima Plus and Esko's Sambatlex Plus.
3 . First-order FM: This is the initial FM random screening. Examples include Creo's Caccato 20.1, Agfa's CristalRaster and Heidelberg's Diamond Diamond Screening. All these systems have a common drawback: they have visible particles, and they are difficult to screen. Therefore, such screening technologies have basically been abolished.

4. Second-order FM: This type of screening is also referred to as hybrid FM screening or hybrid screening. It is a variant of FM screening. Examples include Creo's Vision Plus screening technology, Screen Spekta/Fairdot's Sprite Plus, Heidelberg's Satin screening, and Peking University’s EagleFam screening.

Among the above four types of screening methods, hybrid screens are the most popular among the screens for mixed frequency modulation and screening, and have the fastest development speed. In just a few short years, it has been widely used in the screening of commercial printing. The application technology of the screening technology has emerged in the form of a variety of screening formats, and the mixed screening technology has emerged as the dominant one. The combination of stick and FM screens has brought new changes to the platemaking process, providing technical assurance for the overall improvement of the quality of printed products.

Third, the principle and advantages of hybrid screening technology

As we all know, AM screening is to reconstruct the tone and gradation of an image by changing the dot size by fixing the dot spacing, which has obvious advantages for the restoration of intermediate tone. FM screening is to reconstruct the tone and gradation of an image by fixing the dot size and changing the dot spacing to restore the details of the image. The hybrid screening method combines all the advantages of AM screening and FM screening technologies. For the first time in the history of printing technology, it can be used to select AM screening or FM screening according to changes in screen colors and levels. Screening method. Although there are many kinds of hybrid screening technologies in the market, and the screening names are different, their screening principles are roughly the same. That is, in the shadow area where the percentage of mesh points is 1% to 10% and the percentage of mesh points is 90% to 99%, the mixed screening uses fixed-size ideas in the FM screening method, and uses these ideas. Density to indicate the color and gradation of the image. In the range of 10% to 90% of the percentage of outlets, it can adjust the size of outlets according to the color and gradation of the image.

However, the location of all outlets is still random, which is similar to FM screening. This means that the "net-line angle" parameter is no longer present, and the low-frequency components are reduced to reduce the picture graininess, and the high-frequency components are reduced to improve the printing stability. In this way, the hybrid screening avoids the moiré phenomenon that occurs in the AM screening process because each color version does not have strict registration or the network line angle conflicts with the texture of the scene in the picture. In addition, the minimum dot is slightly reduced. Bigger, and avoiding the disadvantages of the difficult printing of FM outlets. It also uses sophisticated network positioning and combination techniques to reduce the level of mutation to the slightest degree. The problem of long-delayed Gradient Web Jumping can also be easily solved.

The hybrid screening technology is suitable for the existing printing conditions and operation levels. Under the conventional production conditions of 2400 dpi/175 Ipi, screening can achieve a super-fine screening quality equivalent to 300 Ipi or more, and the lines it produces are not jagged or Breaking phenomenon. At the same time, it can provide more medium tone, more stable color performance, faster ink drying and better color synthesis when overprinting is not allowed, so that it can easily achieve super 3001pi picture quality, reflecting the picture The rich details make print quality easy to achieve photo-quality effects, while ignoring the harsh conditions that traditional high-line-number screening processes require.

IV. Prospects of Hybrid Screening Technology

Hybrid screening technology has been widely used in prepress printing. After the interpretation of the RIP through the built-in hybrid screening technology, the information of the graphic image file is reflected in the form of dots to the film (made into the PS version) or directly output to the CTP plate, which is provided to the back end printer. The perfect combination of hybrid FM screening technology and CTP's advanced photo/thermal imaging technology ensures the production of flawless, rich, high-quality printing plates. At present, CTP direct plate-making machines that are loaded with networked sharpener-hybrid frequency modulation screening technology have settled in thousands of households. Such technologies as the Creo high-performance serial products otemT Omnipotent and Trendsetter. Omni-CTP and screen publishing 神 8800/8600 series CTP products are built-in.

Nowadays, most merchants consider whether or not to support the new outlet technology as an important indicator when they choose an image-composing device and a CTP plate-making machine. It can be foreseen that with the increasing popularity and utilization of hybrid screening technology, it will be an important factor in promoting the overall improvement of the quality of printed matter.

Source: Shanxi Datong Railway Tongbao Printing Company Meng Hongri