Frequency modulation (FM) screening

For 125 years, the printing industry has used halftone screens to achieve continuous tone images. This kind of screening is to divide the original image part into a black-and-white net point in the form of a grid, and to reproduce the effect of shadow, color, etc. by changing the size of the dot in the grid. If we look at these outlets as a whole, the images are connected. This is called continuous tuning. This kind of halftone screening we call "AM" screening. AM is the abbreviation of AmplitudeModulated, Chinese means amplitude modulation, that is, the distance between the dots is the same and the dot size is different.

AM screening technology is quite mature, and we are also accustomed to using AM screening. Although AM screening is good, there will still be many problems.

Now, both publishers and printers have begun to use stochastic screening, which is FM screening. This type of screening can solve the problems encountered by AM screening. FM screening does not follow fixed screening angles and meshes. The mesh size is the same, but the number is not equal, which means it appears randomly. This type of screen has no direction and there is no screen angle. The variable distance between outlets means that there is no fixed distance and there is no network line (lpi). In terms of detail rendering, FM screening is represented by the micron-sized dot size. For example, the 21-micron FM screening shows the details equivalent to 400 lpi.

Because FM screening does not have halftone screens and screen angles, there are no rose patches and no common defects in AM screening.

Although FM screening technology appeared in 1980, there are not many printers in use. The main reason is that it is more difficult and inconsistent for FM networks to image on plates. As long as any changes occur in the traditional platemaking process, it will affect the final tuning of FM screening and reduce the reliability of screening.

With the gradual promotion of computer direct plate-making and flexible and stable digital proofing technology, the variable factors affecting FM screening are greatly reduced, and FM screening has been put into practical use. Now, this technology is used in the fields of sheetfed and rotary printing, packaging and printing, magazine printing and direct mail printing. Their experience shows that the use of FM screening increases the quality of offset printing.

However, FM screening is just like other innovations in printing technology. To successfully apply it, it is necessary to upgrade software and hardware, as well as related training and testing. The most important thing is to establish a production control system. In this system, not only the prepress and printing employees must work closely, but also the printers and raw material suppliers should collaborate to ensure that the desired results are achieved.

It should be noted that FM screening may never completely replace traditional AM screening. Since AM screening has been used on offset printing for a long time, the technology is mature, and some specific printing effects can be well performed, it will remain the mainstream of screening in the coming years.

Reprinted from: Chenyi Printing Network