Why FM network screening technology is currently difficult to popularize
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FM screening, also known as random screening (usually called "FM screening"), that is, all halftone micro dots have very small and the same size, each dot is as small as a single element of the recording device, is a graphic recorder or The smallest point a printer can produce, but the average number (or frequency) of points in the surface area of the image varies with the value of the copied tonal value. In addition, their spatial distribution is carefully assigned by an algorithm, and the dots are distributed according to the statistical estimates of the hue and the details of the adjacent portions of the image, without significant accumulation or unwanted accumulation of micro-dots. In fact, the dot location is based on "calculated randomness." In the conventional AM screening method (usually called "AM Screening") method, the distance between the dots is the same and the dot size is different; the FM screening changes the distance between the centers of the dots according to the brightness and blackness of the input pixels, and the dot size is the same.
The concept of FM screening has been proposed many years ago, but it was not until 1993 that lithographers could get their commercial products. Since the first manufacturer announced its FM products in the spring of 1993, many new manufacturers have also launched themselves. The corresponding product. Although the advantages of FM screening are commendable, the actual use of this technology is very slow. Many printers are interested in FM screening, but few printers and plate makers regard this process as a fixed part of production. .
As a newer technology that emerges later than the AM screening technology, FM screening technology has many advantages:
1 Very small dot images produced by FM screening look smoother, enhance the boundary definition and show more details;
2 image file size is 25% of the amplitude modulation screen file. (the same image quality);
3 no screen turtle pattern will appear, the color definition is clearer;
4 low-end scanning and lower output resolution;
5 Faster on the press without adjustment;
6 easier to maintain ink and water balance;
7 thicker ink coverage can get a higher dynamic range;
8 drying time is short;
9 more uniform distribution of ink in thinner layers;
10 sets of quasi-problems do not affect the color balance;
(11) The spot color version of the screening and the original color version will not appear in the turtle pattern, and high-fidelity color (HiFi color) and spot color printing plate can be realized to improve the color gamut of the printed matter;
(12) The tone jump of the middle tone is eliminated.
Because of these advantages, FM screening technology is considered to be a better way to replace traditional AM screening. However, looking at the actual situation in China, we will find that the application of FM screening technology is still thunder and small, and the raindrops are small. To fully utilize the potential advantages of FM network technology, it still takes a long time to explore, due to the algorithm of FM screening itself. The reason, as well as other factors, make FM screening technology difficult to popularize:
1. The outlets are expanding. The dot gain occurs around the dot, but a large dot is divided into small dots, the perimeter and area ratio increase, and the larger the perimeter, the more the dot gain increases, and the perimeter in the FM network for any given dot density. It is larger than the circumference in the traditional screen. The extra dot gain is an inherent feature of the small dot, and the midtone dot is larger than the quarter turn, so the dot is enlarged. In the 200l screen, 40% of the perimeter of the dot is increased by 1μm, and the dot size is increased by 1%.
The range of dot gain is 18%-25% in the halftone image according to SWOP (web offset press standard). Images using FM screens will have a particularly large dot gain, from 25% to 35% on coated paper and up to 50% on uncoated paper. This problem is difficult to overcome with FM screening, although some printing machinery manufacturers provide software-based conversion curves to enable their equipment to compensate for the expected dot gain, which changes the reproduction curve of the imagesetter itself, and This is only a link in the expansion of the network. The basis of the compensation curve is only "expected", and it is always impossible to compensate according to the specific characteristics of each original and the specific printing machine, resulting in errors and errors.
2. Has a grainy feel. The appearance of "grain" or sandpaper is the result of random distribution of FM dots, especially in the 1/4-order region of the screen. The amplitude modulation network is regular, so the noise generated is easily filtered out, and the FM network is Random, random noise is not filterable. The dots in the 1/4 tone region are easily noticed, producing a grainy appearance, but not yet merged to each other, which is more likely to occur in image regions where the dot size is larger than 20 μm and very smooth.
Combining an AM network with an FM network in one image may be the best way to reduce graininess in the future. The smooth tone region of the FM image is preferably an amplitude modulation network to maintain the smooth appearance of the screen. The tone transition region preferably uses an FM network to replicate as much detail as possible, especially in the highlight portion and about 25% of the tone. Since there is no special standard for the manuscripts adapted to these two screening techniques, this method of integration is not a professional, and according to some professionals, the output errors caused by this combination are more difficult to troubleshoot.
3. The tolerance of the entire production process becomes smaller. Due to the expansion of the outlets and the smaller outlets, the FM outlets cannot tolerate dust in the working environment at the output, and the latitude is usually small. The problems caused by dust and dirt in the AM screening process are small, and in the FM screening, Causes a big problem. The entire work area must be kept clean to avoid the appearance of fine particles during replication. When the entire system uses small-sized dots, small dust particles will cause defects that cannot be ignored. The micro-points in the FM network are equal to or less than the dust in the AM network. In the traditional way, over-exposure plates can eliminate them, which is very obvious during FM screening and cannot be eliminated by excessive exposure, because this It will cause the small dots to be exposed together. The printing plate needs consistent and uniform vacuum pressure to ensure the consistency between the printing plates and the entire printing plate. The slight change of the vacuum pressure will cause “hot spots”, which is better than that in the AM network. The same "hot spots" that are obtained are more compelling. The environment of the printing shop is also very important when printing on the upper plate. Paper wool falling from the paper, particles in the air, and flying fibers may cause the printing plate or the blanket cylinder to be dirty and the printed product to be noticeable. Defects.
Because the effect of increasing the thickness of the ink film on the size of the FM dot is not as significant as that of the AM screen, the image with poor color separation is difficult to improve the quality of the ink on the printing machine; the ink is compensated for by scanning during the printing process. Defects are simply impossible, because the dots are too small, it is difficult to print according to normal printing, and it is easy to paste. If you want to improve the density caused by scanning by adding ink, it is very easy to adjust by printing during AM screening because The AM network has large dots, large dot spacing, and adjustable space, while the FM network does not. Speaking of this, I can't help but want to mention a little about the working environment. I have been to a lot of pre-press, printing, and post-press processing. The pre-press working environment is acceptable, but printing and finishing are difficult. Compliment, there are not a few printing and finishing operations in a large workshop, nearly ten machines such as printing presses, paper cutters, die-cutting machines, laminating machines, binding machines, etc., dust, smoke, The strange smell of chemical gas, static electricity, noise, etc., can not be imagined here to stop the dirty and the resulting uneven color of the ink and other problems how to make the printing press master burnt, the same for other operators.
Although this is a digression, at least such a "bad" environment uses high-speed printing of plates with amplitude-modulated screen printing, but it is not difficult to use the environmentally demanding FM-printed plates. . It's like having a high-speed car without a highway, and the speed of the car is still not fast. The printing industry is facing the challenge of environmental problems while adopting new processes and new equipment. This is also a serious topic of global concern.
4. Film characteristics. High contrast film is critical to suppress dot gain because there may be partial exposure areas around the fine FM network. All films have a partially exposed transition area around the fully exposed dots, which will result in a larger dot size. The FM network itself is small, and its slight expansion will cause significant results. The use of high contrast film can reduce the area of partial exposure, thereby reducing the potential for dot enlargement of the process during this phase. Due to the inherent latitude inherent in the FM network replication process, the film with the widest exposure range provides the best dot reproduction. However, at present, DuPont, Kodak and other films are not satisfactory when using FM screening, but these manufacturers are gradually improving their product performance.
5. Proofing. At present, the proofing technology is a conventional proofing technology using analog materials, which is used to accurately reflect the changes in the structure and size of the amplitude modulation dot on the printing machine. The behavior of the amplitude modulation dot is fundamentally different from the behavior of the frequency modulation dot. The current proofing technology cannot reflect the frequency modulation dot on the printing press. behavior. Accurate FM network proofing is difficult to achieve, and users cannot adjust the traditional proofing system to reflect the behavior of FM sites. Accurate proofing of FM screen images is still an unsolved problem, because the existing proofing system can not reproduce the very small dot size or reflect the excessive dot expansion. Only the corresponding proofing method is developed. Screen technology can be recognized. Some analog systems are more accurate than other systems in predicting the behavior of FM sites. However, the granular toner used in these simulation systems is too large to reproduce the fine printed dots used in FM screening and cannot be accepted as a contract proof. The future of FM network proofing lies in electronic proofing, because electronic meshless proofing and FM screens are similar in the way of placing the dots on the substrate, which may produce good results, but the electronic proofing technology is still not perfect.
6. The dot size is too small. The FM screen processing method provided by the imagesetter manufacturer generally allows only one or two fixed dot sizes for a given output resolution. These dots are used for uncoated paper and newsprint or for screen printing. It seems too small at the time, and the expansion of outlets that occur at this time is difficult to control. Too small a dot is also one of the causes of noise interference in low-contrast images, but the increase in dots makes the graininess of the image stronger, and the smallest micro-dot size is too small, and many printers cannot reproduce correctly. Even if you get a small dot on the plate, it is difficult to accurately transfer the ink to the paper, because the small dot size is only used on a new, expensive press, operated by an experienced operator. This kind of replication is feasible.
7. The views of printers and customers. For printers, the use of FM screening technology means buying RIP with the ability to calculate and randomly place outlets, requiring an additional investment, and the accompanying additional harsh working conditions, environment and staff The improvement in quality requirements has increased investment, and printers have also considered whether these additional investments can bring them greater profits when investing. They will not be easy when there are no fixed customers who require FM screening. Investing. Even if the printer invests the money, the investment costs usually exceed the customer's extra cost due to the advantages of random screening output. Because the quality required by most customers can be met by the high-quality output of the AML technology above 200LPI, they will not pay extra for the method that does not bring them much benefit. Even if the customer is willing to pay extra funds, it is not the same image. The final structure of the FM screening output is better than that of the AM screening. For example, when printing large-area flat-toned solid colors, the results of FM screening are used. The feeling of showing stains is not available when printing with amplitude modulation screening.
The above is an analysis of the potential shortcomings of FM screening technology and why it cannot be popularized. Actually, there are many other factors, such as the economic situation of the country and the quality of the entire national. Although there are so many defects and factors in using FM screening technology. It affects its popularity, but as a new technology, it has the superiority that traditional screening methods can't match. However, there are many external conditions that affect its use. It has many things to be perfected, such as There are still many people studying better screening algorithms. These algorithms are based on the advantages of combining amplitude modulation and frequency modulation networks. Some algorithms have been applied locally, such as those used in screen printing. Wait.
We have reason to believe that the FM screening technology that is currently difficult to popularize will be recognized by the majority with the development of science and technology, especially the development of printing technologies such as waterless offset printing and direct plate printing.