Dots in printing play a very important role. Dots can transfer the gradations, levels, and colors of the image. Any reflections or transmissions are made up of pigment particles or silver particles to form a continuous blooming tone. This blooming tone and layer must be photographed or other methods to segment the image into large and small dots.
Dots are the most basic unit of graphics on the plate, and they are responsible for reproducing the tones of the original, the organizational hierarchy, and the outline of the image. According to the principle of the network, it can be divided into two types of amplitude-modulating network and frequency-modulating network. The former has been widely used. The use of various methods (glass screens, contact screens, and electrical separation technologies) can achieve this type of outlets, which can be widely used due to its simple, fast, and good imaging results. At the same time, people also clearly recognized its deficiencies, such as the absolute elimination of moire, so with the development of printing technology, people began to turn their attention to another type of network – FM network outlets.
The frequency modulation screening theory has been produced for some time. In early 1993, the Agfa Division and Linotype-Hell Corporation officially launched the FM network screening technology. In August 1993, China Founder Beijing University also developed its own FM screening technology.
FM screening technology is the image is scanned and input, after processing, through the output device when the same size points are randomly distributed in different spaces, the number of points and density, that is, the frequency of appearance of the network point, in order to express the image Density and hierarchy of technical methods. Therefore, the fineness of the image it represents is no longer explained by the number of black and white lines in each centimeter, but is defined by the size of the dots. The smaller the dot size, the higher the accuracy of the image that can be represented. The better.
The technology produces images that are closer to photographic effects. Due to the different exposure levels in the photographic process, there are differences in the amount of photosensitive silver salt particles in the same area. After the development, there are few silver salt particles at the low density on the image, and there are many silver salt particles at the high density, and the density change is determined by the number of silver salt particles in different regions. This is similar to the FM network, and the amplitude of the AM sites is different. They are expressed in dot size (in number), so they cannot achieve the effect of close to photography.
At present, companies have introduced different dot structures and given different names, such as Agfa’s “Crystal Network”, Linotype-Hell’s “Diamond Network”, Dainippon Screen’s “RANDOT”, etc. Therefore, the number and location of printing dots in each image area unit are different, but all belong to FM screening.
The mesh size of the FM screening depends on the output resolution and the screening parameters. For example, if the output resolution is 2400 dpi, and the screening parameter is 2×2 laser dots as a network point, the screen diameter is 21 μm; the screening parameters are With 3×3 laser dots as a dot, the dot diameter is 32 μm.
In the whole process, the most crucial factor is the conversion and adjustment of the FM network. The core is to select the appropriate randomness and laser beam diameter. The newly generated FM network points are smooth and solid, uniform in size, and have little isolated light spots, which is the key to control quality. The new typesetting machine satisfies this requirement. The laser beam diameter can be adjusted according to the dot size. In addition, in order to cooperate with the next process, attention should also be paid to selecting the dot gain, which can generally be controlled within the range of 5%. In addition to the above, the photographs of the photographs should be washed with attention to temperature, speed, and pH values, and they should be washed with high-speed hot stamps to ensure the quality of the ideas. In terms of printing, due to the fact that there is no limit to the screen angle in frequency modulation, the accuracy of equipment overprinting is rather low, and the color inks that are usually used are also acceptable.