Electronic screening technology question and answer

Q: What are the differences and advantages and disadvantages of AM screening and FM screening?

Answer: The dot is the basic method for reproducing a color continuous tune original. The dot size is responsible for the ink layer thickness of the reproduced image, the shading change of the tone level, and the organization of the color. At present, there are two kinds of screening methods for copying color originals, namely amplitude modulation (AM) screening and frequency modulation (FM) screening. AM screening is a periodic screening method, and is a common process in the four major printing technologies; FM screening It is a non-periodic screening method and is a new high fidelity color reproduction technology proposed by Agfa and Lenno-Hair in 1993.

1. Amplitude screening is a screening method that makes continuous adjustment of originals form an orderly array of small squares on the film through screening. Each small square represents a basic unit called a mesh, and in each mesh there is a dot exposed by a laser, distributed in the center of the grid. Because the small squares are very small, the size of the halftones can only be seen by the eyes of people within a certain viewing distance. AM screening is to use the variation of dot area in each small square to represent the original level.

2. FM network is also called random network (diamond network). Laser dots with a very small pixel unit of 7~35μm are randomly distributed in a specific unit area. The dot size is the same, which is based on the density of different dot distributions. The lower the number of dots, the smaller the dots can reproduce more and more rich layers and colors. Its advantage is that due to the random distribution of dots, there is no moiré after overprinting. An image-setter with a high resolution, uniform level reproduction, and low resolution can output high-quality images using FM technology. It is conducive to multi-color reproduction and increase production efficiency.

3. The difference between the two screening technologies: The traditional AM screening parameters include the number of screens, screen angle, tone range, and dot shape. FM screening has only one parameter, namely the dot size, and the FM screening will not produce moire. The difficulty of AM screening is directly related to the moire, especially textile patterns, wood patterns, fine art, Chinese painting, etc. Once the printing moire products are about to be scrapped. Moire is a product of cyclical structural interactions. FM screening does not include screen lines and screening angles. Dot distribution is random, random, and several plates are superimposed on one another. Even copying prints, textiles, etc. Moire will appear. In terms of definition, even if the AM screening technology is no better, it can only avoid large moire, and small stripes (snowflake, star flower, rose spot) can not be eliminated. Patches of AM screening are the result of light diffraction and cannot be avoided. These markings are the root cause of rough images. The FM screening does not have markings, making the images more detailed and clear, with a strong sense of three-dimensionality and an extremely rich level.

4. The level of the FM network is uniformly reproduced. Because there is no dot structure, when the layer is increased, no density jump occurs when the adjacency is connected. The level reproduction transition is naturally harmonized and the level is beautiful. The printed matter is fully close to the original and the high fidelity effect is achieved, which is favorable for multi-color printing. . When printing at 5~7 colors, AM screening will increase the difficulty of the technical arrangement of the screening angle. The adoption of FM screening technology fundamentally solved the occurrence of moiré, provided conditions for multi-color printing, met some special reproduction requirements, expanded the scope of color reproduction of printed matters, and achieved high-fidelity printing requirements.

Q: Can screen printing use FM screening technology?

A: At present, there are still some problems in screen printing using FM screening technology. The frequency modulation screening technology is achieved through the computer's dynamic capability to achieve FM screening technology. However, in practical applications, there are still some difficulties in the prepress, screen printing process equipment and materials and related technologies.

1. FM screening sites are too small for 7~35μm, while 20μm sites are only equivalent to 2% of 100-line prints or 5% of 200-line prints. Since the outlets are too small, the drying of the dots in the prints does not come out, the loss of levels, and the difficulty in reproducing the dark tone levels.

2. The value of the FM screening network expansion is high, and the frequency expansion value of the FM network is 20%~40% higher than that of a normal conventional network.

3. There are certain difficulties in revision and copying. The conventional negative film dot size can be subjected to chemical retouching such as external thickening and thinning, while the FM negative film dot is too small to handle, and the printing ink dot is too small to reproduce and teleport difficultly.

4. At present, the number of screens in the screen printing process is more than 60 to 80 lines/inch, and the tone range of the screens is 10% to 85%. By using the miss printing process, small dots are not easily printed.

5. The mesh screen of FM and screen printing has low resistance to printing and the printing quality is not stable.

FM screening technology is in the development stage of experiment and application. For example, the combination of two different sizes of FM network points or the use of AM and FM network dots has gradually been applied in the four major printing applications. The emergence of FM screening technology has played an important role in enhancing and promoting color reproduction technology. Some domestic manufacturers of flexographic printing have partially adopted FM screening technology. At present, the use of frequency modulation screening technology in screen printing from the material equipment to the screening technology is still a certain degree of difficulty. Therefore, in the color mesh screen printing copy, in addition to using FM film amplification, FM screening can not replace the traditional AM screening technology.