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If the printed product is a book, picture book, etc. for reading, the observation distance is close, and the number of high-quality screen lines should be used. If the printed product is used for outdoor posters or advertising paintings, the observation distance is far, the number of available low-reduction lines can be used, and the effect is good. And easy to print. Its theory is based on the visual principle of the available dots. Table 2 shows the number of dot lines applicable for different line of sight.
Table 2 Relationship between different line of sight and line number The viewing distance (cm) 212529334373 The outlet (line/cm) 807060544025 The number of lines (line/inch) 20017515013310060
2. Determine the number of screens according to the paper type
When we choose the number of screens, we should consider the paper used. The recommended data is as follows:
The coated paper has a smooth surface with 175 lines/inch (ie, 70 lines/cm) and above.
For non-coated paper, 125-170 lines/inch (ie, 50 lines/cm or more) screens are used.
Newsprint uses 100 lines/inch (ie 40 lines/cm) and below for the number of screens.
3, according to the resolution of the scanner to determine the number of screen lines
When the scanner scans a continuously tuned original, it converts the optical information on the original into computer-usable digital information, that is, pixels. When printing, the pixels are arranged into a desired halftone image.
The higher the resolution of the scanner, the smaller the pixels, and the more pixels that express the image, the more realistic the reproduction of the original. The size of the pixel is consistent with the number of screens of the screen printing product. The higher the screen number, the finer the screen. Therefore, the resolution of the scanner is proportional to the number of screens added to the image. According to the scanning characteristics of the scanner and the four-color printing, the dot angles of the four versions of yellow, magenta, cyan and black are known:
The number of screen lines = scanner resolution * 2/3 means that when continuously adjusting the image to be screened, the number of input screens should be lower than the scanner resolution.
4, laser photosetter output resolution to determine the number of screen lines
Studies have shown that the gray level of the image = (output resolution/number of screen lines) 2+1.
In order to make the gray level of the image delicate, ie, the screen level of the screen is rich, the output resolution is higher, but the number of screens for the image is smaller.
For example, a laser imagesetter with an output resolution of 2400 dots per inch (2400 dpi), when the number of screen lines is 150 lines/inch (150 lpi), the generated mesh can be reproduced (2400/150)2+1=257 At this level, a mesh unit contains exactly 16x16 laser print points; but if the number of screen lines is 200 lines/inch (200 lpi), the generated mesh can only be reproduced (2400/200) 2+1= At 145 levels, one mesh unit contains exactly 12*12 laser print points.
Therefore, the resolution of the laser image-setter must be determined according to the requirements of the gray level of the image, and the appropriate number of screen lines should be determined. The larger the line density, the better.
5, according to other factors determine the number of screen lines
The number of screens is also related to the overlay accuracy of the printing press. Only through high-quality printing presses, high-quality rigid blankets, high-quality dampening fluid control, and high-quality machine adjustment, can we achieve a high number of screens. Adjust prints. The same half-net points, high dot lines, and small black dots, if the machine is not good, the pressure is not uniform, the deformation of the blanket is large, and the dot slip is serious, these small black spots are easily lost, resulting in serious layer defects. .
Based on the above analysis, when determining the number of screen lines for the halftone image, all factors should be taken into consideration as a whole and summarized in the following table:
The factors affecting the number of outlets in Table 3: Influencing Factors Loiter Range Paper Type Scanner Resolution Imagesetter Output Resolution Printer Quality Printing Quality High Screen Numbers Far Coating Paper High High High School Wire Numbers Middle Non-Coated Paper Mid-to-Low Net Lines Near Newsprint Low Low Low (to be continued)
Formation of printing dots in printing manuscripts and production mechanism 6
1. Determine the number of screens according to the purpose of printing