Electronic screening technology question and answer
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Q: What are the differences, advantages and disadvantages between AM and FM?
Answer: The dot is the basic way to reproduce the color continuous tone original. The dot size is responsible for the thickness of the ink layer, the tone level change and the color organization of the reproduced image. At present, there are two kinds of screening methods for color original copying, namely amplitude modulation (AM) screening and frequency modulation (FM) screening. AM filtering is a periodic screening method, which is a common process in four printing; FM screening It is a non-periodic screening method, which is a new high-fidelity color reproduction technology proposed by Agfa and Lennon-Hair in 1993.
1. AM screening is a screening method that allows continuous adjustment of originals to form an ordered array of small squares on the film by screening. Each small square represents a basic unit, called a mesh, with a laser-exposed dot in each mesh, distributed at the center of the grid. Because the small square is very small, the human eye can not distinguish the size of the dot in the mesh within a certain line of sight, and can only see the depth of the tone level. AM screening is the use of changes in the area of the dots in each small square to represent the original level.
2. FM network points are also called random network points (diamond dots). Laser points with a very small pixel unit of 7~35μm are randomly distributed in a specific unit area. The size of the network points is the same, and the distribution of dots is different. To represent the shades of the image, the smaller the dots, the more colorful layers and colors can be copied. Its advantage is that because the dots are randomly distributed, there will be no moiré after overprinting. High-definition, uniform reproduction, low-resolution imagesetters can use FM technology to output high-quality images. Conducive to multi-color reproduction and improve production efficiency.
3. The difference between the two screening technologies: the traditional AM filtering parameters include the number of screen lines, the screen angle, the tone range, and the dot shape. FM screening has only one parameter, namely the dot size. FM screening does not produce moiré. The difficulty of AM screening is directly related to the moiré, especially textile patterns, woodgrain patterns, fine art, Chinese painting, etc. Once the printed moiré products appear, they will be scrapped. The moiré is the product of the periodic structure interaction, while the FM screening does not have the number of screen lines and the screen angle. The distribution of the dots is random and random. Several plates are overprinted together, even if the printed matter, textiles, etc. are not copied. There will be moiré. In terms of clarity, even if the AM screening technology is good, it can only avoid large moiré, and small markings (snow, star, rose) can not be eliminated. The speckles copied by amplitude modulation are the result of light diffraction, which cannot be avoided. These markings are the root cause of the image roughness. The FM screening has no markings, which makes the image more precise and clear, with strong stereoscopic effect and extremely rich layers.
4. The level of the FM network is uniformly reproduced. Since there is no dot structure, the density jump in the adjacent direction will not occur when the level is increased, the layer reproduction transition is naturally harmonic, the level is beautiful, the printed matter is close to the original, and the high-fidelity effect is achieved, which is beneficial to multi-color printing. . When printing from 5 to 7 colors, AM screening will increase the difficulty of the technical arrangement of the screening angle. The use of FM screening technology has fundamentally solved the generation of moiré, provided conditions for multi-color printing, met some special copying requirements, expanded the color reproduction range of printed matter, and achieved high fidelity printing requirements.
Q: Can I use the FM screening process for screen printing?
A: At present, there are still some problems in the use of FM screening technology for screen printing. The FM screening technology realizes the FM screening technology through the computer's dynamic ability. However, in practical applications, there are still some difficulties in prepress, screen printing process equipment and materials and related technologies.
1. The FM screening network is too small, 7~35μm, and the 20μm dot is only equivalent to 2% dot of 100 line print or 5% dot of 200 line print. Because the outlets are too small, it is difficult to reproduce the dots in the printing plate, and the level is lost.
2. The frequency-added network points have a high expansion value, and the FM network point expansion value is 20% to 40% higher than that of the conventional network.
3. There are certain difficulties in revision and copying. The size of the conventional negative film dot can be treated by chemical repair such as external thickening and thinning, while the frequency modulation negative dot is too small to be processed, and the printing ink dot is too small to be copied and transmitted easily.
4. At present, the number of screen lines in the screen printing process is 60-80 lines/inch, and the tone range of the screen is 10%~85%. The printing process is adopted, and the small dots are not easy to print.
5. The screen printing of FM screening is low, and the printing quality is not stable.
FM screening technology is in the development stage of experiments and applications. For example, the combination of two different sizes of FM networks or the combination of AM and FM points has gradually been applied in four major printing applications. The emergence of FM screening technology has improved and promoted color reproduction technology. Some domestic flexographic printing companies have adopted FM screening technology. At present, it is difficult to use FM screening technology in screen printing from material equipment to screening technology. Therefore, in the color network copying and copying, in addition to using FM film to enlarge and copy, FM screening can not replace the traditional AM screening technology.