Advantages and solutions of screening technology
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The AM and FM mentioned in the printing industry are not as simple as the wavelength of the radio. Below is the latest development information in this regard. In today's complex automated prepress workflow, the hot topics discussed are mainly on PDF, JDF, XML, CMS and ICC. Screening is no longer the technology that prepress experts are most concerned about. However, recent developments indicate that screening and other ways of forming outlets remain the top concerns for prepress workflow and output system manufacturers and vendors.
First, important production tools
The benefits of optimized screening technology are to bring more vivid prints, clearer details, no moiré and process stability to the printing company, and those who ignore this technology miss a very important production control tool. .
Let us first review the development of digital screening technology. It is a slow evolution of the glass and contact screen screening process used in the formation of simulated dots. From the early days of offset printing technology, printing process experts have been experimenting with dot shape, angle and number of 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 physically form dots, making process constraints no longer a problem.
When DTP (desktop publishing-ing) appeared, early PostScriptRip could implement four-color and multi-color digital screening, but the quality was lower than digital screening for simulated screening and dedicated high file color systems. Experienced prepress operators may recall the extensive and intense discussion of "screening" in the late 1980s.
Later, there was a revolutionary change in the composition of optimized outlets, which provided more screening angle options than PostScriptLevel1. At the same time, prepress equipment manufacturers began to pay attention to PostScriptRip and applied their rich screening knowledge to the desktop publishing system.
The real revolution is the use of FM or random screening, although it is not a new idea. In the 1980s, it was applied to the digital printing process where the quality of the dot is not high. It is not to use different sizes of dots to simulate different continuous tones, but to use the same size and relatively small. The spacing between the dots to reproduce the tone.
The FM random screening was launched at the most intense time of the screening discussion, and received a lot of advertising and gave too many 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 that it has a clearer effect, because the tiny dots can produce more color tones; it ensures that there is no moiré between the colors and the pattern, which makes the printing process more stable. However, it encountered many obstacles before applying FM screening to a wider range of non-specialized applications.
The unfavorable conditions faced in the early 1990s were: it was very difficult to handle in the environment of computer to film (ctf), there is no exposure range of the printing plate; A particle pattern is produced; and it is difficult to compensate for chromatic aberration by using a method of varying the thickness of the ink on the printing press. Operators who used this method early rarely seldom persist.
However, in the past 10 years, a small number of prepress and printing companies have begun to use FM screening technology to produce higher quality prints. Art books and high-gloss catalogues that are prone to moiré objects such as textile images, speakers' pupils, and architectural designs all benefit from FM screening technology and become a technology they are happy to use.
Third, simplify the process
Because CTP technology simplifies the process, it plays an important role in the recovery of FM screening technology. In addition to film, dust and registration problems have become factors that hinder the development of FM technology.
Thanks to the CTP technology, there is no need to think too much about the film edge (thickness) or dust particles, so smaller FM dots (usually 12 to 30 μm in offset printing, 70 μm in flexo and newspaper printing) can be directly on the plate. form.
Another advantage of CTP technology is that a harder dot can be formed on the thermal plate for better printing results. Particles composed of a laser beam can form a screened dot that is predictable in imaging and printing. Any edge of the dot consisting of unfixed layers remaining on the plate will not form an irregular printing effect.
The Heidelberg prepress program applied this technology to their CTF imaging machines a few years ago. Creo combines the company's Staccato screening technology and consulting services to revitalize FM screening technology, which advocates control of machine profit, including reduced ink usage, higher color stability and easier ink balance. .
Better printing process stability has gradually shifted the offset printing from the 65lpi screen line to 100~110lpi (40-44l/cm). In commercial offset printing, the number of screen lines has been increased from 133 lpi (54 l/cm) to 175 lpi (70 l/cm), and even 200 lpi (80 l/cm) very high quality printing is required.
Fourth, AM's alternative
An alternative to FM's approach to AM screening technology is to use very fine screens for screening. This method has been widely used in Japan and has been widely adopted by many professional printing companies in the Western Hemisphere. This method usually uses 250 to 350 lpi or higher to optimize the printing effect, and achieves clearer and more refined effects with high-density ink. The breakthrough in ultra-high screen counts encountered the same problems as FM, such as harsh process conditions and the need for high-resolution scanning to generate maximum profit.
In many places in Europe and the United States, 300dpi scans and moderate virtual masks are often the default settings, while in Japan the scan standard is set to 350dpi and slightly higher levels of unclear masks to cater for higher screen counts. Claim. Associated with the number of super-high screen lines is a higher image resolution, which means that more gray levels can be produced. For the ultra-high screen line of 4000dpi, the imaging process is greatly slowed down compared to the 2400 or 2540dpi, which is more commonly used in Western and FM screening in the Western world.
In the East, Fuji has proposed a Co-Res screening method that uses the traditional screening angle, which is comparable to the image with relatively high resolution. A 1219dpi image can achieve 175dpi effect, or 300lpi can be obtained from a plate-making machine with a slightly lower image resolution.
So far, the technology is still limited to use in Fuji's CelebrantRip and platesetters. The most direct advantage is that there is a leap in overall production because there is less data to process and there is no need to change the operating habits of the press because the screen angle and the dot 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, using the most appropriate AM screening in the flat and skin tones. FM screening is used in fine detail and moiré sensitive object areas.
Fifth, interactive mask
The disadvantage of the hybrid screening method is that interactive masking is required on high-end workstations, such as Screen's Taiga-Press, so it has a high work intensity for the workforce and is only suitable for high-value printing projects. For packaging applications, usually four or more printing methods are used. For the rougher screen lines, Barco and ArtworkSys-tems have developed a corresponding hybrid screening method, which not only avoids the appearance of moiré. It also produces more detail in brighter and darker areas for more sharper, more saturated printing.
This hybrid screening method provides FM detail and continuous tone reproduction of bright and dark areas without affecting most of the flat and midtone grain graphics, as these are achieved through AM screening. . In the field of newspaper printing, Agfa completed testing of the hybrid screening technology Sublima, which has been tested in Norway, using FMCristal-Raster outlets in some areas and AMABS screening in the middle section. Screen has recently introduced a new hybrid screening technology, Spekta, to get the best quality for its thermal CTP imaging machine. Spekta screening technology combines the advantages of FM and AM screening in dot composition, color mixing, moiré and ease of operation compensation on the press.
As with other hybrid screening methods, Spekta uses FM screening in the replication areas of 0% to 10% and 90% to 99%, and AM round dot screening in the range of 10% to 90%. Since all the dots in the total dot range are randomly distributed, there is no restriction of the screen angle between different colors, so there is no problem of moiré in color mixing. Compared with other high-network screening methods, Spekta can provide an optical effect comparable to 300+lpi, and there is no productivity limitation, but 2400dpi screening is required in standard image setting areas such as 175lpi (70l/cm). .
Sixth, the best screening solution
In general, adding text to an image will give you better results, such as wine labels and maps. Screen's Spekta screening technology can eliminate the obvious rose spots and moiré. Together with ScreenTaiga and Trueflow, it provides users with the unique PlateRite thermal imaging machine, which is a universal and suitable screening solution. After the "screening" discussion 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, prepress customers are constantly looking for the optimal screening mode for maximum productivity in order to achieve the best possible reproduction in the easiest way. In the process of printing and copying, the dot is undoubtedly the most important issue. Combining the two technologies of AM and FM will produce better results.