Screening technology advantages and solutions
As we all know, the AM and FM in the printing industry are not as simple as the wavelength of the radio. The following is the latest development information in this regard. In today's complex fully automated prepress workflow, the hot topics discussed are mainly PDF, JDF, XML, CMS, and ICC. Screening is no longer the technology most concerned by prepress experts. However, recent developments have shown that screen screening and other methods of forming dots are still the top concerns for manufacturers and sellers of prepress workflow and output systems.
1. Important production tools
The advantage of optimizing screening technology is to bring more vivid prints, clearer details, no moire and stability of the process to printing companies, and those who ignore this-technology companies have missed a very important production control tool .
Let us first review the development process of digital screening technology. It evolved slowly from the screening process of glass and contact screens used in the formation of simulated dots. From the early stage of offset printing technology, printing process experts have been experimenting with dot shapes, angles and screen lines, hoping to optimize The effect of the printed matter and the control of the process. Digital screening provides us with a possible way to form dots in a physical manner, so that process constraints are no longer a problem.
When DTP (desktop publishing system, desktop publish-ing) appeared, early PostScriptRip can realize four-color and multi-color digital screening, but the quality is lower than that of simulation screening and special high-file color system. Experienced pre-press operators may remember the extensive and intense discussion of "screening" in the late 1980s.
Later, there was a revolutionary change in the optimization of the network composition, which provided more screen angle options than PostScriptLevel1. At the same time, pre-press equipment manufacturers began to attach importance to PostScriptRip and applied their extensive knowledge of screens to desktop publishing systems.
The real revolution is the use of FM or random screening, although it is not a new idea. In the 1980s, it has been used in digital printing processes that do not require high dot quality. It does not use dots of different sizes to simulate different continuous tones, but uses the same size and relatively small size. The pitch between the dots to reproduce the tone.
FM Random Screening was launched at the time of the most intense discussions in Screening, and received a lot of advertising and excessive expectations. Since then, the traditional screening method has been named AM (Amplitude Modulation) screening to distinguish it from FM screening.
Second, a clearer effect
Compared with AM, the advantage of FM is a clearer effect, because the smallest dots can produce more tones; to ensure that there is no moire between colors and patterns, so that the printing process is more stable. However, before applying FM screening to a wider range of non-special purpose applications, it encountered many obstacles.
The disadvantages faced in the early 1990s were: it was very difficult to handle in a computerto film (ctf) environment, and there was no exposure range of the printing plate; It produces particle patterns; and it is difficult to compensate for chromatic aberrations by using ink thickness variations on printing presses. Operators who adopted this method in the early days were rarely able to persevere.
However, in the past 10 years, a small number of pre-press and printing companies have begun to cooperate with FM screening technology to produce higher-quality prints. Art books and high-gloss catalog products with objects such as textile images, speakers' pupils, and architectural designs that are more prone to moire objects have benefited from FM screening technology and become a technology they are happy to use.
3. Simplify the process
Because CTP technology simplifies the process, it has played an important role in the recovery of FM screening technology. In addition to film, dust and registration problems have become some factors that hinder the development of FM technology.
Since CTP technology is adopted, there is no need to consider film edges (thickness) or dust particles, so smaller FM dots (usually 12 to 30 μm in offset printing and 70 μm in flexo and newspaper printing) can be directly on the printing plate form.
Another advantage of CTP technology is that harder dots can be formed on the thermal plate to obtain better printing results. Particles composed of laser beams can form predictable screen dots in imaging and printing. Any dot edges composed of unfixed layers remaining on the printing plate will not form an irregular printing effect.
Heidelberg's prepress solution applied this technology to their CTF imaging machine a few years ago. Creo combines the company's Staccato screening technology and consulting services to revive FM screening technology again. It advocates controlling on-machine profits, including reducing the amount of ink used, obtaining higher color stability, and making ink easier to achieve balance. .
Better printing process stability has gradually shifted offset printing from 65lpi plus screen lines for newspaper printing to 100 ~ 110lpi (40-44l / cm). In commercial offset printing, the number of screen lines is increased from 133lpi (54l / cm) to 175lpi (70l / cm), and can even reach 200lpi (80l / cm) very high-quality printing.
Four, AM alternative
A method that is similar to FM as an alternative to AM screening technology is to use a very fine screen for screening. This method has been widely popular in Japan, and many professional printing companies in the Western Hemisphere have generally adopted it. This method usually uses 250 ~ 350lpi or even higher line numbers to optimize the printing effect, and achieve a clearer and finer effect through high-density ink. The breakthrough in ultra-high screen lines encountered the same problems as FM, such as harsh process conditions and the need for high-resolution scanning to generate maximum profits.
In many places in Europe and the United States, 300dpi scanning and moderate vignetting masks are often the default settings, while the scanning standard in Japan is set to 350dpi and a slightly higher level of unclear masks to cater to higher screen counts. Claim. Related to the number of ultra-high screen lines is a higher image resolution, which means that more gray levels can be produced. For the ultra-high screen number of 4000dpi, compared with the 2400 or 2540dpi which is more commonly used in the Western world in AM and FM screen, the imaging process is greatly slowed down.
In the East, Fuji has proposed a Co-Res screening method that uses a traditional screening angle, which is comparable to the use of relatively high-resolution image effects. A 1219dpi image can achieve an effect of 175dpi, or a 300lpi effect can be obtained from a plate-making machine where the image resolution is slightly lower and this effect cannot be obtained.
So far, the technology is still limited to applications in Fuji's CelebrantRip and plate-making machines. The most direct advantage is a leap in overall production, because there is less data to be processed, and there is no need to change the operating habits of the printing press, because the screen angle and dots are exactly the same.
A few years ago, companies like Barco and Screen were looking for the ideal way to combine FM and AM screening on the same image. This method uses the most suitable AM ​​screening in flat tones and skin tones. In addition, FM screening is used in areas of fine detail and moire sensitive objects.
Five, interactive mask
The shortcoming of the hybrid screening method is that it requires an interactive mask on a high-end workstation, such as Screen's Taiga-Press, so it has a high labor intensity and is only suitable for high-value printing projects. For packaging applications, printing methods of more than four colors are usually used. For the flexo printing with more rough screen lines, Barco and ArtworkSys-tems have developed a corresponding hybrid screen method, which can not only avoid the appearance of moire, It can also produce more detail in brighter and darker areas, and can be used for clearer and more saturated printing.
This hybrid screening method can provide FM details and continuous tone reproduction of bright and dark areas, and it will not affect most of the flat tone and middle tone granular graphics, because these are achieved by AM screening . In the field of newspaper printing, Agfa has completed testing of the hybrid screening technology Sublima. This technology has been tested in Norway. FMCristal-Raster outlets are used in some regions, and AMABS screening is used in the middle tone. The Screen company has recently launched a new hybrid screening technology Spekta, so that its thermal CTP imaging machine to obtain the best quality. Spekta screening technology combines the advantages of FM and AM screening methods in dot formation, color mixing, moire and easy operation compensation on the printing press.
Like other hybrid screening methods, Spekta uses FM screening in the 0% to 10% and 90% to 99% replication areas, and AM round dot screening in the 10% to 90% range. Since all the dots are randomly distributed within the total dots, there is no restriction on the screen angle between different colors, so there is no problem of moire when the colors are mixed. Compared with other high-screen screening methods, Spekta can provide an optical effect comparable to 300 + lpi, and there is no productivity limit, but the standard image setting area such as 175lpi (70l / cm) should be screened at 2400dpi .
Six, the best screen solution
In general, adding text to an image will achieve better results, such as wine labels and maps. Screen company's Spekta screening technology can eliminate obvious rose spots and moire. Together with ScreenTaiga and Trueflow, it provides users with a unique PlateRite thermal imaging machine, which is a universal and most suitable screening solution. After the discussion of "screening" in the 1980s, the industry experienced a relatively quiet period. New technologies related to thermal CTP imaging technology can now produce clearer, more reproducible dot quality. Based on this, pre-press customers are constantly looking for the best screen-printing mode to obtain maximum productivity, in order to achieve the best copy effect in the easiest way. In the process of printing and copying, the dot is undoubtedly the most important issue. The organic combination of AM and FM will definitely produce better results.
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