New screening technology
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Screening is a very important process in printing. The basic function is to convert the processed continuous tone image into a halftone image for printing. The quality of screening technology directly affects the quality and grade of printed products. AM is the most common screening method used now. The position and angle of the dot are fixed, and the layer change and color reproduction are obtained through the change of the size of the dot. The advantage is that the intermediate tone is well reproduced, and the layer transition is smooth and natural; the disadvantage is that it is limited by the printing conditions. Generally, the number of screen lines is limited to 200 lpi or less, and the image is not delicate enough. When the number of high screen lines is used, the highlight and shadow portions are not ideally reproduced. FM screening (or random screening, English is FM) The dot size is fixed, but the position is randomly changed. There is no mesh angle and network cable. The level and color are reproduced by the change of the number of dots in the unit area. The size is to distinguish its accuracy. The dot diameter is 40 microns, 21 microns (equivalent to 2% dot of 175 lpi AM mesh), 14 microns (equivalent to 1% dot of 200 lpi AM net), l0 micron (equivalent to 1% dot of 300 lpiAM net), etc. . With the traditional FM screening method, it can print very fine prints, which can eliminate the moiré of AM screening, can copy the dark tone well and copy the bright tone well, and can output with lower resolution, but The printing dot is enlarged, the high-light part is prone to particle phenomenon, and the printing pressure and ink quantity control are very high. The slight change of the printing condition will affect the tone reproduction of the whole image. Although the FM network has been promoted for many years, due to its harsh printing conditions, there are not many practical applications. Both FM and AM are subject to certain limitations. With the widespread adoption of CTP, the quality requirements of products are getting higher and higher without increasing production costs and reducing production efficiency. Therefore, various companies have researched and introduced a variety of new screening technologies.
Although the new screening methods introduced by different companies are different, in general, the method of combining AM and FM screening is widely used, that is, hybrid filtering using AM and FM. The method (of course not simply mixed together). In addition, some companies insist on adopting an improved FM screening method. This article will introduce some of the new screening technologies of each company.
1 Screen company's "Shibida" screening
"Spekta" screening technology is a new hybrid screening method developed by Japan Screen Company in 2001. It can avoid problems such as moiré and disconnection. VisionPay can significantly improve print quality without compromising productivity and changing conventional printing conditions. If you use the thermal CTP version of the output, the normal 2400dpi VisionPay can achieve the same quality of high-line screening. Vision will be able to take full advantage of the two methods of amplitude modulation and frequency modulation.
Comparison between Vision and Networking and FM AM
Depending on the color density of each image, Vision will use a similar FM or AM screen. In the 1-10% highlight and 90-99% of the dark-tone part, Vision will use the dot size of the FM network to reproduce the level by changing the number of dots. The distribution of the dots is optimized according to the principle of not overlapping and not forming large intervals, so that the particle effect can be effectively controlled. In the 10 to 90% part, the size of the dot changes like the amplitude modulation screen, and the distribution of the dot is randomly changed like the FM screening, so that there is no collision.
For the highlight section, at a output accuracy of 2400 dpi, the minimum dot size can be as small as 10.5 micrometers, but it is difficult to reproduce in actual printing. Vision Bida solves this problem by combining small dots. The method is to combine 2-3 small dots into a larger dot (21 or 32 microns) to improve the printability and stability of the highlight region.
With the Vision Blu-ray, the printing accuracy of 300 lpi can be achieved under the ordinary 2400dpi-175 lpi condition, and the very strict process control like high screen number printing is not required. Like FM screening, the distribution of the dots of the Visiona network is random, there is no mesh angle, the Moir pattern can be completely avoided, and the “net cover” on the fabric and wood grain speakers caused by the corners can be avoided. It can eliminate rose spots that are prone to appear in dark gray areas or black areas. The screening method also makes the reproduction of the midtone portion more vivid and natural.
Vision Technology is directly applied to the thermal plate-making machine of the 霹雳Pressing series of screens, and is supported by the RIP and workflow of the screen to achieve high-quality output of CTP direct plate making.
In summary, the location of the Bida network is random, and in this regard it is like an FM network. In the middle adjustment part, although the size of the dot is variable, there is no fixed center distance and mesh angle of the amplitude modulation screen. By increasing the minimum point, the high-light part of the FM network is difficult to print, and the layer mutation phenomenon is minimized by complex dot positioning and combination technology.
2 Agfa Sublima Jinghua network dot screening technology
Sublima's Crystal Networking Technology combines the advantages of AM and FM to be called Overclocking Network (XM). It is a brand new screening technology introduced by Agfa after the crystal network (the Chinese name of Jinghua outlet is "crystal sublimation").
Sublima achieves high screen line printing with certain printing conditions and no additional cost. The printed images are very delicate, and the net flowers and dots are difficult to identify with the naked eye at 340 lpi.
Sublima uses the AM dot to express the middle part (8-92%), the FM dot to express the bright tone (0-8%) and the dark tone (92-100%). Moiré, rose spots, etc. are basically eliminated.
Sublima uses Agfa's patented XM algorithm. When AM transitions to FM, the random point of FM continues the angle of AM point, which completely eliminates the transition trace of AM to FM. The random point of FM continues the angle of AM point
Sublima adopts the concept of “minimum printable dot” (more than 175 lpi 2% AM dot). When adjusting the transition between light and dark tone in the middle, it is always the minimum dot to meet the requirements of ordinary printing, so that it can be realized in print. %-99% network point restore. At the same time, the calculation of the dot is based on the "step-by-step accurate calculation method", which significantly improves the calculation efficiency.
When outputting Sublima dots of each network cable (210 lpi, 240 lpi, 280 lpi, and 340 lpi), CTP devices can use 2400 dpi output precision to produce high-screen printing plates without reducing output efficiency.
In fact, the overclocking screening technology uses FM nodes in the bright and dark areas, and uses the AM points in the middle part to achieve a smooth transition at the point conversion. For example, when reproducing the bright-adjusted dot, the AM dot will gradually become smaller to the smallest size that can be copied, and then fade out and replace it with the FM dot. Similarly, the dark-adjusted area network also transitions from the AM network to the FM network, leaving no trace at the junction. The dot sizes of the bright and dark areas are the same, and the density is not the same, but it is not a true FM point. The mesh points under the control of the FM mode are used, which are arranged in a line at a certain angle to become a new dot arrangement.
At the 2003 All-Indian Exhibition in Shanghai, Agfa used Sublima outlets + Xcalibur45 CTP machines to produce printed proofs that were not only very delicate, but also very good in color.
The 340 lpi Sublima dot is the same size at 8%, 2% and 1%, and the level is expressed by reducing the density of the dot distribution; the same method is used for 92% to 99% of the dots. 340 lpi Sublima minimum dot size is greater than 175 lpi 2% AM dot. If the printer can copy 175 lpi 2% AM dot, it can completely copy 340 lpi Sublima 1%-99% level.
At the time of printing, the 240 lpi AM highlights have a loss of dots, because the dots are too small for the press to copy; and the 240 lpi Sublima dots can completely replicate the dots of the highlights (which can also completely replicate the dark portions) because the dots remain Printable dot size
3 Esko-Graphics's screening technology
1) Offset printing dots
Monetscreens and highline screens
First and second order monet screens. The first-order and second-order "frequency modulation" screening of Monet's network is currently mainly used for offset printing. You can get images without net flowers, no moiré and unusual sharpness. In order to perfectly match the different needs of each type of print, different sizes of Monet dots can be mixed and used in the same print, so the site is not a simple FM site.
High line number screening technology (highlinescreens)
The feature of the high-line number of dots is that a very high number of screen lines can be obtained at a general output resolution. Esko's high-network-counting screening technology is a new AM screening technology that combines the characteristics of AM and FM screening. It has the advantage of being able to express image details while maintaining stability and reproducibility. 423 Ipi output at 2400dpi accuracy can be achieved using high line counts.
2) Flexo dots
Samba flexscreens (sambaflexscreens)
Samba outlets won the FIexoTech Award in 1999, and Samba outlets combine mid-range AM screening technology with FM screening technology in highlights and shadows. The ideal combination of such different dots is suitable for flexographic printing, corrugated printing and screen printing. Samba outlets provide a smooth transition between AM and FM screening, so there is no change in the intersection of the outlets.
Groovy outlet
The latest direction of flexo screening focuses on improving color contrast and density in dark areas, which is a major focus of flexographic printing. Especially when printing PE materials, density and contrast problems occur. Groovy produces a higher density map and uses less ink for the same print. Print tests have proven to produce better color contrast.
Ec-centric dots for corrugated printing
Although the pre-press of corrugated printing is roughly the same as that before flexo printing, it also has some unique features, including extremely low screen lines, challenging printing materials and printing registration problems. The Eccentric dot is especially used to eliminate the Rosette pattern that is easily seen in the four-color image of the low-wire line. Ec-centric dots can reduce dot gain and smoother tones.
4 Creo Vision Fangjia FM Screening
(Staccoto) FM
Screening combines the advantages of random screening and traditional screening to eliminate problems such as halftone rose spots, screened moiré, grayscale shortage, and hue skipping. Vision's FM screen also enhances the color and halftone stability of the press, ensuring print quality when printing is extremely large, complemented by the precision and consistency of SQUARE spotTM square point thermal imaging technology ( It is precisely with the square dot technology that random screening has really moved to the practical stage of printing). Can produce stable, smooth colors. In traditional FM screening, defects such as particles are often found in areas with less color, and secondary screening can avoid these problems. Staccoto screening uses first-order FM screening in highlights and shadows, while in the mid-tones that are prone to problems, use grids of varying sizes to avoid problems with flat areas. Its second-order FM screening uses a secondary screening method. Vision Fangjia secondary network clustering in the form of rules can effectively reduce low frequency noise and instability, and avoid visible particle patterns brought by other FM screening.
Vision's FM screen can be printed on a very thin ink film, with a wide range of substrates, and the dark portion can be well represented without sacrificing solid density, contrast and color gamut. A thinner ink film means that the drying speed is faster than that of the amplitude modulation screen, which is especially advantageous for double-sided printing.
A frequency-modulated screening uses only a random algorithm. When the midtones of multiple color plates are superimposed on each other, a water-like stripe is generated, which is what we call low-order harmonics. In response to this phenomenon, we will first reorganize the FM network that has been completely dispersed, and then break it up again to get the required secondary FM network.
The usual FM screening has a larger dot expansion because the dot gain only occurs at the edge. The secondary FM screening connects the adjacent small dots when reorganizing the dots, which greatly reduces the total perimeter of the dots, making the expansion of the dots easier to control.
Comparison of traditional AM screening, random FM screening and Vision-friendly FM screening
Co-Re screening technology has achieved breakthroughs in high-net-line network points with lower output accuracy and won the Japan Printing Society Technology Award. The previous technology obtained 175 -200lpi dots with 2400dpi output precision, and Fujifilm realized that the technology achieves 300 lpi screen image or 1200dpi precision output with 2400dpi precision output, and 175 lpi screen image is obtained, and the image quality is not lowered. . Under the premise of using existing software and hardware such as CTP and RIP, the technology can achieve a substantial improvement in image quality at a lower cost (purchasing network software), and the production efficiency is also nearly doubled.
According to conventional printing common sense, in order to reproduce a printed image, each dot needs about 200 tones to express. According to this calculation, if the output precision is 2400 dpi, the number of screen lines is 2400 / √ 200 = 170 lpi, which is theoretically bounded by about 175-200 lpi. It is generally believed that when the number of screen lines is higher than the theoretical limit value, the lack of tone will result in a decrease in quality.
However, from the characteristics of the human eye, a larger area of 145 square micrometers than the 175 lpi area of 145 square micrometers) can be "feeled" to its density by integration, so the percentage is different. The multiple dots are mixed to express the intermediate-level multi-mode technical solution, and a dot composed of 50-60 tones can achieve the same smooth tone effect as the 200 tone dots. In this way, the common sense of printing sites in the past is denied not only in the samples of printed matter, but also in principle.
Another great feature is the in-depth study in theory. In fact, when using 2400dpi output to produce 300lpi dot images, the biggest technical issue is the monochromatic moiré caused by the dot frequency and the scanning interval of the output machine. The elimination of frequency unevenness faults.
This technology is an analog system that takes into account the characteristics of the CTP material, the characteristics of the recording curve of the CTP device, and especially the characteristics of the human eye, and can "record the dots on the printing plate by CTP and visually evaluate them". All the jobs are automatically calculated and processed on the microcomputer.
The site is optionally applied to Fujifilm's thermal imaging CTP, photopolymer CTP, and dot-type DDCP. For print shop users who have obtained a thermal imaging CTP of 300 lpi dot prints at 2400 dpi, they have achieved great results in high-quality and most demanding products such as the high-end monthly magazine of the printing department store. By constructing a simulation system starting from material properties, output optical properties, and visual characteristics, we have developed a technology for producing high-wire-count products with very low resolution. "Simulate the actual situation, consider the visual characteristics, and automatically produce the best. The dot is the idea of the technology and can be used in a variety of output systems.
6 Screening techniques seen on DRUPA 2004
One trend in the prepress field is the new product of screening technology. Many CTP plants are developing FM and AM combined screening technologies. A new generation of FM screening is on the scene to achieve high quality.
1) New FM screening
Large Japanese screen / MTC Ran-dotX FM screening. The screening method is the second-generation FM screening method (HDS screening method), which can reproduce 20 micrometers, 15 micrometers, 10 micrometer dots, no moiré, no disconnection, and achieve high quality. A 25% reduction in ink consumption is achieved by controlling the expansion of the optical dots.
2) AM and FM hybrid screening
Agfa's Sublima Screening (Cross Modulation, Mixed Modulation).
Groovy screening of Esko-Graphics (added to the ordinary AM network, adding a linear pattern in the field to improve the density and coloration of the field).