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The dot is the most basic element of Lu's image tone and color. It is a small number of dots with the same center distance, the same density, and the same area. Offset uses the dot area in the unit area to express the times. Regardless of whether it is 90% of the site or 30% of the site, the density of the center-to-center distance between every two dots is the same, but the percentage of the area per square meter of the Internet is 90% and 30%, respectively. If the surface of the substrate in the graphic part is completely covered with ink, which is equivalent to 100% of the dot, it is called ground.
11. What is flat network, hierarchical network?
An image is composed of the same size of dots. The set of dots is called flat screen. An image is composed of dots of different sizes, and the collection of such points is called a hierarchical network.
12. Why does offset printing need to reproduce the picture through wind spots?
1) Continually adjusting the film During the process of copying, the density transmission is difficult to control, and the image copy quality is difficult to guarantee.
2) Since the principle of lithography of offset printing plates is very different from the principle of silver sensitization, the printing plates that are printed out have only two states of ink and non-inking. The result of printing only has two levels, colored and non-colored, and cannot be like silver. The salt sensitization material can change the gradation by changing the density of silver particles.
3) Even if a continuous-tone plate can be developed, the offset press cannot control the density of the image through accurate ink layer thickness, thereby completing the image-level reproduction.
Therefore, the continuous tone image of the original document must be invaded into its own independent dot. The density value of each dot is the same, but the dot area is not the same according to the difference of the four colors and the depth of the tone. Dark shadows, large dots, printing only need to provide the same thickness of the ink layer, the amount of ink is not, copy the product color is dark; bright tone, small dot, although the ink thickness and dark tone of each dot is the same However, due to the small dot area and the low amount of ink, the color of the copied product is light, and thus the color changes in shades of light.
13. What is the size of the outlets?
In the prepress stage, the depth of the manuscript is expressed by dividing the continuous adjustment image of the manuscript into dots of different sizes. The size of the outlet is equal to the ratio of the area of ​​the dot in the unit area to the unit. It is represented by 0-100%. 0 is blank, 100% is the actual site, and 50% is the area and non-network part of the wind within the unit area. The area is half of the area.
14. What is the number of screens?
The number of screen lines is the number of Internet sites per unit length, usually expressed as how many lines per line or as many lines per line. The center distance between every two dots is equal to the reciprocal of the dot lines. For offset printing, the higher the number of lines and the same percentage of outlets, the smaller the number of outlets, the finer the level of performance, and the stronger the ability to express levels, but the more serious the network expansion during the printing process; the lower the number of lines, the lower the number of outlets. If the percentage is the same, the larger the network, the worse the performance of the subtle level, but the network expansion during the printing process is lighter.
15. What are the factors to consider when determining the number of screens?
1) Determined according to the competence of the print. Ordinary offset printed packaging products are generally to be enjoyed under normal viewing distance conditions, and higher screen lines should be used.
2) Consider the influence of the substrate material. The coated paper with a higher smoothness is suitable for a higher screen number, and the offset paper with a lower smoothness is suitable for a lower screen number. The smoothness of the cardboard used to make the carton is usually between the two, and the number of screens used should also be between the two.
3) Consider the effect of the printing process used by the printer used. The high precision of the printing press adopts rigid liners, air-cushioned rubber blankets, and relatively small dot gains. Finer network cables can be used; the accuracy of the presses is poor, and soft liners and common blankets are used. A thicker cable should be used. In order to achieve a balance in the level of fine-grained replication and the control of network expansion, the number of screens commonly used in offset printing is 150 lines per inch, which is then increased or decreased according to specific conditions.
16. What are the requirements for the arrangement of dot offsets in offset printing?
The common square and circular meshes in offset printing are arranged vertically in the structure, and the dot angles can be expressed as 0-90 degrees. In multi-color printing, dots with more than two colors are superimposed on one another. Dots of different colors intersect each other at different angles. The smaller the angle of intersection and the larger the pattern, the larger the pattern will destroy the original tone of the image. When the angle of intersection is larger, the flower spinning is smaller and has less influence on the reproduction of the tone. (To be continued)
How much is the packaging offset?(2)
10. What is an outlet or field?