In the printing process, the continuous blending of halftone images is adjusted by the density of the dots. By mixing CMYK four-color dots, you can display an infinite number of colors. There are two main types of outlets currently used in the printing process: amplitude modulation (AM) and frequency modulation (FM).

AM outlets

AM sites are currently the most widely used network. Its density of dots is fixed, and the shades of color are expressed by adjusting the size of the dots, thus achieving the transition of tone. In printing, the use of AM sites mainly needs to consider the size of outlets, the appearance of outlets, the angle of outlets, and the accuracy of network lines.

Network size

The dot size is determined by the coverage rate of the dot. It is also called the ink rate. Generally speaking, it is customary to use “Cheng” as a unit of measure. For example, a 10% coverage rate is called a “10% outlet”, and a 20% coverage rate is called a “20% outlet”. In addition, the coverage rate is 0%. The outlets are called "absolute nets," and outlets with a coverage rate of 100% are called "on the ground."

The tone of printed matter is generally divided into three levels: bright tone, mid tone, and dark tone. The coverage rate of the outlets of the bright-tuning department is about 10% to 30%; the coverage rate of the outlets of the intermediate-tone department is about 40% to 60%; and that of the shadow recording department is 70% to 90%. The net and field sectors are further divided.

Network shape

The appearance of dots in printing is not merely a kind of circular shape that everyone imagines. It is divided into four types: square, round, and rhombus according to the shape of the dots displayed in the case of 50% ink.

The square dots are in a chessboard shape at a 50% coverage rate. Its granules are relatively sharp, and its ability to express levels is strong. Suitable for lines, graphics and some hard-coded images.

No matter if the circular spot is still in the midtones, the outlets are independent, and only the dark tone is connected to the department. Therefore, the performance level for the mining level is poor, and it is rarely used in four-color printing.

The diamond-shaped dots integrate the hard-tone of the square dots and the soft-adjustment of the circular dots. The color transition is natural, which is suitable for the performance of general images and photos.

Network point of view

In the printing plate making, the choice of dot angle has a crucial role. Choosing the wrong dot angle will cause interference fringes.

The common dot angles are 90 degrees, 15 degrees, 45 degrees, and 75 degrees. The 45-degree network has the best performance, it is not chaotic and does not appear dull; the angle between 15 degrees and 75 degrees is not worse than the angle, but the visual effect is not rigid; the angle of 90 degrees is the most chaotic, but The visual effect is too rigid and there is no beauty.

If two or more mesh points are put together, there will be mutual interference. When the interference is severe enough to affect the appearance of the image, the commonly known “rhizard pattern” is thrown up.

In general, when the angle difference between the two types of dots is 30 degrees and 60 degrees, the overall interference fringe is still more beautiful; the dot angle difference of 45 degrees is next; when the angle difference between the two dots is 15 degrees and 75 degrees When the interference fringes can damage the image.

Dot number

The number of screen lines determines the fineness of the image, similar to the resolution. The common line number is applied as follows:

Line 10-120: Prints with low quality, distant printed posters, posters, and other large-scale printed materials are generally printed using newsprint paper or offset paper, and sometimes use low-gram sub-paper and coated paper.

150 lines: Normal four-color printing generally use this accuracy, all types of paper have.

Line 175-200: exquisite albums, pictorials, etc., mostly printed on coated paper

250-300 lines: The most demanding albums, etc., are mostly printed on premium coated paper and specialty paper.