Close contact with printing outlets (5)

Dot printing.

There are two kinds of dot printing that represent the color image hierarchy:

1.1 AM Screen Printing

In the unit area, the dark and light shades of the image are represented by the size of the dot, but it has a weakness that is prone to moire.

AM Screening

At present, the traditional network used in color printing is called AM Screening. The original text is called Amplitude Modulation Screening (Figure 1). This includes square networks, chain networks, and circular networks. In the case where the position and arrangement angle of the halftone dot are fixed, the depth of the image is represented by the size change of the halftone dot.

Need to control the density of the network cable and the screen angle (net angle: the angle between the connection between the center of the adjacent network point and the reference line is called the screen angle). The screen angles of the two color versions must be 30 degrees or more to avoid collision. The C version is usually placed at 15 degrees, the M version is at 45 degrees, the K version is at 75 degrees (the M version or the BK version is exchangeable), and the Y version is placed at 90 degrees. In this case, the Y version is combined with other color versions. Only 15 degrees apart, because it is shallower than the other three colors, even if there is collision will not be obvious.

On the one hand, AM Screening can achieve stable print reproduction, and at the same time, it is easy to produce Rosettes, Moires between image textures, Tone jumps, and reproducibility of text and subtle levels. . In addition, extremely high overlay accuracy is also required in printing.

1.2 FM network screen printing

With the increase of computer computing capabilities, FM mesh screening technology has emerged. FM screening technology is consistent in the size of the network within the unit area. The number of mesh points is used to represent the dark and light levels of the image. The FM network is basically solved. The problem of moire.

The above two screening methods use offset printing, gravure printing, embossing, or screen printing. If you want to represent the level of the image, you cannot leave the outlets. Look at the printed matter with a magnifying glass, whether it is the AM screening technology or the FM network. Thanks to the screening technology, outlets are clearly visible on the replicas, so they are certainly replicas, and they cannot be made in any way.

FM Screening

A few years ago, each Image setter manufacturer developed a type called FM Screening, the full text of which is Frequency Modulation Screening (Figure 2). The diameters of these fine dots range from 8 to 30 μm. The size of each fine dot is the same. The expression of dark and light colors is different from the amplitude modulation dots. The intensity of the image is expressed in terms of density. The greater the density of the dots, the darker the color. The method is to distribute this fine point randomly.

FM Screening has the advantages:

1. Will not hit the net and net flower.

2. The resulting small outlets can show more details.

3. Eliminate the Tone jump in the midtones.

4. Registration issues will not affect the color balance.

Disadvantages of FM Screening:

1. The level of light and peace network are prone to rough, grainy.

2. The density of halftone dots is extremely high, and the dot gain rate is difficult to control.

3. High-precision and harsh printing conditions are required.

4. Film output stability, fine point reproducibility and clarity.

5. When printing, the light position is easy to lose, deep position is easy to block.