On FM screening technology

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On FM plus technology

point is the most basic unit of graphics and text on the printing plate, which plays the role of reproducing the tone, level and image outline of the original. According to the action principle of points, it can be divided into amplitude modulation points and frequency modulation points. The former can be widely used because of its simple processing, fast and good imaging effect. At the same time, people have also clearly recognized its shortcomings, such as the impossibility of absolutely eliminating moire, etc., so with the development of printing technology, people began to turn their attention to another type of dot tone, which makes 3D printing really practical

FM plus theory has been produced for some time. At the beginning of 1993, Agfa company and Linotype hell company officially launched FM plus technology. In August 1993, Founder Company of Peking University also developed its own FM plus technology

frequency modulation plus technology is a technical method to understand the contribution of advanced material technology to sustainable development by displaying the density and level of the image through the number and density of points, that is, the frequency of points, which are randomly distributed in different spaces with the same size of points when the image is scanned, input and processed through the output device. Therefore, the fineness of the image it represents is no longer explained by the number of black-and-white lines per centimeter, but by the size of dots. The smaller the dot size, the higher the accuracy and sharpness of the image it can represent

the image generated by this technology is closer to the photographic effect. Due to the different intensity of exposure during photography, the number of silver salt particles in the same area is different. After development, there are few silver salt particles in the places with low density on the image; Where the density is high, there are many silver salt particles, and the density change is determined by the number of silver salt particles in different regions. The AM point is different. It is expressed in point size (percentage), so it cannot be close to the effect of photography

at present, various companies have different point structures and point names, such as "crystal" in Agfa company, "diamond" in Linotype hell company, and "Randot" in big Japan screen company. They are all different in algorithm. Therefore, the number and position of printing points in each unit of image area are different, but they all belong to FM plus

the point size of FM plus depends on the output resolution and plus parameters. If the output resolution is 2400dpi and the plus parameter is 2x2 laser points as a point, the plus dot diameter is 21 μ m; Add 3x3 laser points as a point, and the sub point diameter is 32 μ m。

in the whole process, the most critical factor is the conversion and adjustment of frequency modulation. The core is to select the appropriate random dots to match the laser beam diameter. The newly generated frequency modulation points are smooth and solid, with uniform size and few isolated spots, which is the key to quality control. The new imagesetter meets this requirement, and the laser beam diameter can be adjusted according to the point size. In addition, in order to cooperate with the next process, it should also pay attention to select the dot gain, which can generally be controlled within the range of 5%. In addition, the washing of phototypesetting film should pay attention to the temperature, speed, pH value and other values, and use fast high-temperature washing film to ensure the quality of the dots. In printing, because there is no angular limitation in frequency modulation, the overprint accuracy of the equipment is not high, and the usually used color ink is also acceptable

printing is an easy to ignore link, but it also has a great impact on product quality. First of all, because the diameter of the frequency modulation point is small, there is no need for secondary exposure, otherwise there will be a lot of point loss, and some or even all 2% points will be sacrificed. Therefore, only one exposure is needed, and the time and light intensity should be controlled well

in general, compared with am, FM has the following advantages:

1) due to the random distribution of points, moire will not appear after overprint

2) due to the equal size of the dot, the intermediate tone will not jump due to the large dot expansion value during printing

3) the detail definition is good, and some thin lines of the image will not form refraction or burr due to addition

4) it can show delicate levels, which is suitable for the needs of high-precision printing

5) the dots on the printing plate are micronized, so the fountain solution is also micronized and dispersed, making offset printing easy to stabilize

6) the extremely small dots are fully dispersed, which makes the printing sheet and the blanket easy to separate, and reduces the back rubbing of the printing sheet

everything has its advantages and disadvantages. At present, there are still some problems in FM plus:

1) revision cannot be carried out after image output

2) there are some difficulties in copying

3) do not use points with very low resolution, otherwise aliasing will occur

4) when the image has no nested compliance line, overprinting is very difficult, so the image edge contour is sometimes not clear

5) low printing resistance

in view of these problems, some people have proposed a multiple plus image replication technology using FM plus and am plus at the same time. This multiple addition is an addition method to solve the contradiction between the traditional amplitude modulation plus printing with good adaptability but easy to appear "moire", while the emerging frequency modulation plus does not appear "moire" but it is difficult to grasp the printing adaptability. Different addition methods are used in different areas of the same image with computer processing. For example, frequency modulation plus is used in the area where "moire" is easy to appear in the middle tone, and amplitude modulation plus is used in the area of high light and dark tone, so each takes its own advantage, Avoid their shortcomings

at present, FM plus technology is widely used in the field of flexographic printing, such as printing some high-precision product packaging boxes, cigarette boxes, etc. it is believed that with the deep application of computer technology in the printing field, FM plus technology will also be continuously promoted in other printing fields

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