Printing knowledge

Why pre-press image screen?

    printing process decided to print only the dot original continuous tone levels, as shown in Figure 1-2, if this picture to enlarge, you'll find is made up of many different sizes of outlets. We see the dot size is different, but they all occupy the same amount of space, this is because the original image once after the screening, regular arrays of image into countless networks, that is, continuous tone image information into discrete dot image information. Points larger, darker, darker; smaller outlets, color lighter, brighter, as shown in Figure 1-3. Each node has a fixed position size is decided by the screen line number, for example, add dot mesh 150lpi are one inch in length or in width of 150 outlets. Dot and dot size, spatial location are two different concepts, such as representative of C50% dot space occupied is the meaning of dot size 50%,100% refers to the location of dot size all network spatial location, print that "site", 0% because there is no dot, only the dot position, so there is no ink to be printed on the place. Obviously Hung, and aim higher, the position the smaller outlets, can describe the level, the more, the more delicate. In fact, the original levels and color through this screening method is reproduced.

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