The advantages and solutions of screening technology

As we all know, AM and FM in the printing industry are not as simple as the wavelength of a radio. Here are the latest developments in this area. In today's complex, fully automated prepress workflow, the hot topics of discussion focus on issues such as PDF, JDF, XML, CMS, and ICC. Screening is no longer the technology that prepress specialists are most concerned about. However, recent developments indicate that screening and other forms of network formation are still the top concerns for prepress workflow and output system manufacturers and distributors.

First, an important production tool

The benefits of optimizing screening technology are to bring more vivid prints, clearer details, no moiré and process stability to the printing companies, and companies that ignore this technology have missed a very important production control tool. .

Let us first review the development of digital screening technology. It has evolved slowly from the process of glass and contact screen screening used in the formation of analog outlets. From the early days of offset printing, 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 method of physically forming network points, making the process constraints no longer a problem.

When DTP (desktop publishing, desktop publishing) appeared, early PostscriptRip could achieve four-color and multi-color digital screening, but the quality was lower than digital screening of analog screening and dedicated high-end color systems. Experienced prepress operators may remember the extensive and intense discussion of “screening” at the end of the 1980s.

Later, there was a revolutionary change in the configuration of optimized networks, providing more screening angle choices than PostscriptLevel1. At the same time, prepress equipment manufacturers began to pay attention to PostscriptRip, and applied their rich screening knowledge 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 had been used in digital printing processes where the dot quality was not high. Instead of using different dot sizes to simulate different continuous tone, it used the same size and was relatively small. Intervals between the dots reproduce the tone.

FM random screening was launched at the time of the most intense discussion of the Internet and received a lot of advertising and given too much expectation. Since then, the traditional screening method has been named AM (Amplitude Modulation) screening to distinguish it from FM screening.

Second, more clear results

Compared with AM, the advantage of FM is a clearer effect, because extremely small dots can produce more hues; ensuring no moire between colors and patterns, making the printing process more stable. However, it encountered many obstacles before it was applied to a wider range of non-special purpose applications.

The unfavorable conditions encountered in the early 1990s were: it was very difficult to handle in the computer to film (ctf) environment, and there was no exposure range for printing plates; Particle patterns; and it is difficult to compensate for color differences on the press by using ink thickness variations. Operators who used this method early can rarely persist.

However, during the past 10 years, a small number of prepress and printing companies have begun to use the FM screening technology in a tacit understanding to produce higher quality prints. Artistic books and high-gloss catalog products with more prone moire objects, such as textile images, speaker's pupils, and architectural designs, all benefited from FM screening technology and became a technology they were happy to use.

Third, simplify the process

As 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.

Due to the use of CTP technology, there is no need to consider too much film edge (thickness) or dust particles, so smaller FM dots (usually in the offset 12 ~ 30μm, flexo and newspaper printing up to 70μm) 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 laser beams can form screened dots that are predictable in imaging and printing. Any irregularity of the printing effect is not formed by the edges of the dots formed by the unfixed layers remaining on the plate.

Heidelberg's 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 enable FM screening technology to recover again. It advocates control of on-machine profits, including reduced ink usage, higher color stability, and easier ink and ink balance .

Better printing process stability has gradually shifted the offset printing from newspaper printing 65 lpi screen lines to 100 to 110 lpi (40-44 l/cm). In commercial offset printing, the number of screens is increased from 133 lpi (54 l/cm) to 175 lpi (70 l/cm), and even 200 lpi (80 l/cm) can be printed with very high quality requirements.

IV. Alternatives to AM

A method similar to FM that replaces the AM screening technology is to use a very fine screen for screening. This method has been widely used in Japan, and many professional printing companies in the Western Hemisphere have been widely used. This method usually uses 250~350lpi or even higher number of lines to optimize the printing effect, and realizes clearer and more fine effects through high-density ink. Breakthroughs in the number of ultra-high-gauge lines have 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, 300 dpi scanning and modest false light masks are often the default settings, while in Japan the scan standard is set at 350 dpi and a slightly higher level of unclear masks to cater for higher screen lines. Claim. Associated with the number of super-high screen lines is a higher image resolution, which means that more gray levels can be generated. For ultra-high-dual-screen 4000dpi, the imaging process is greatly slowed down compared to the 2400 or 2540dpi more commonly used by the Western world in AM and FM screening.

In the East, Fuji Corporation proposed a Co-Res screening method that uses the traditional screening angle, which can be compared with the use of relatively high resolution image effects. A 1219dpi image can achieve a 175dpi effect, or a 300lpi effect can be obtained from a platemaker that does not have this effect at a lower image resolution.

To date, the technology is still limited to use in Fuji's CzechRip and platesetters. The most immediate advantage is that there will be a leap in the overall production volume, because there is less data to be processed, and it is not necessary to change the operating habits of the press because the screen angle and the dot are exactly the same as the original.

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 best AM screening in both flat and skin tones. In addition, FM screening is used in areas with fine details and moire-sensitive objects.

Fifth, interactive mask

The disadvantage of the hybrid screening method is that it requires interactive masks on high-end workstations, such as Screen's Taiga-Press, so it has a higher work intensity and is only suitable for high-value printing projects. For packaging applications, printing methods with more than four colors are generally used. For the flexo printing with coarser screens, Barco and ArtworkSys-tems have developed a corresponding hybrid screening method to not only avoid the appearance of moiré. You can also produce more detail in lighter and darker areas for more clear, more saturated printing.

This hybrid screening method can provide FM details and continuous tone reproduction of bright and dark areas without affecting most flat tone and midtone grainy graphics because these are implemented using AM screening. . In the field of newspaper printing, Agfa completed the test of the hybrid screening technology Sublima, which has been tested in Norway, using FMCristal-Raster outlets in some regions and AMABS screening in the middle portion. Screen Corporation has recently introduced Spekta, a new hybrid screening technology, to achieve the best quality of its thermal CTP imaging machine. Spekta screening technology effectively combines the advantages of FM and AM screening in dot formation, color mixing, moiré and ease of operation compensation on the press.

Like other hybrid screening methods, Spekta uses FM screening for 0% to 10% and 90% to 99% of the replication area, and uses AM round-net screening for the range of 10% to 90%. Since all the dots are randomly distributed within the total dot area, there is no limitation of the screening angle between different colors, and therefore no problem of moire occurs when colors are mixed. Spekta can provide a comparable optical effect to 300+lpi compared to other high-mesh screens. 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

Under normal circumstances, adding text to the image will give better results, such as wine labels and maps. Using Screen's Spekta Screening Technology eliminates obvious rose spots and moire, along with ScreenTaiga and Trueflow, provides users with a unique PlateRite thermal imaging machine, which is a versatile, most suitable screening solution. After the “screening” discussion in the 1980s ended, the industry experienced a period of relative silence. 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 best screening mode to get the maximum productivity in order to achieve the best reproduction effect in the easiest way. In the process of printing and copying, outlets are undoubtedly the most important issue. The organic combination of AM and FM technologies will produce better results.

Source: Printing Talent Community