Printing Screening Process Talk--Frequency Modulation (5)

17. Increased network

As the tone value increases, more and more ideas are added. Each pip stays separate from its neighbors until they are forced to join. All the printed dots are separated by an algorithm to avoid accumulation when the density is lower than the intermediate density. A completely random pattern will get a random and unwanted accumulation. At higher density levels, several dots are joined together at once. Because the FM network screen has no abrupt connection at all specific levels, the tone change is smoother than that of the AM screen.

18. Network size

The 3600dpi image recorder has a laser spot size of 7 [mu]m and a 2400 dpi dot size of 10.5 [mu]m. The 2*2 grid of these two dots forms the basic printing dots of 14 [mu]m and 21 [mu]m, respectively.

The size of a 14 μm dot is approximately 1% dot size for a 200 line/inch screen, and the size of a 21 μm dot is 1% dot size for a 133 line/inch screen. Development conditions will affect the actual dot size on the film, and some manufacturers use a dot size of 70 μm.

19. Output time

Although FM network screening calculations are more complex than AM network screening calculations, smaller file storage can offset the increased processing time. The use of telegraphic recorder resolutions lower than those of conventional screens results in faster output speeds, that is to say images with higher resolution can be obtained with lower resolution outputs. This is likely to be a reduction in processing time, although the results will be based on the actual production situation.

20. FM, traditional screen and text on the same page

Many vendors promote the ability to rasterize two types of images on the same page. This ability to rasterize traditional and FM network screens in different parts of the same page is provided by the RIP vendors. Postscript level has the ability to use multiple screening algorithms on the same page.

At approximately 1000 dpi, the electronically-imaged text began to look good. If a telegraphic recorder with a resolution below this threshold is used to image on the page, the text appears to be more or less jagged, whether the image is being screened in a random or traditional manner.

twenty one. Scanning resolution and positioning accuracy of graphic recorders

In the traditional screening, the simple rule is: When the printing machine can print 256 color tones, the resolution of the graphic recorder should be 10 to 16 times the number of lines. In a random manner, 8-bit image data can always generate 256 levels of gray regardless of the resolution of the teletext recorder.

22. Film properties

High-contrast film is critical for suppressing dot gain because there may be partially exposed areas around the tiny FM dot. All films will have some partially exposed transitions around the fully exposed dots, which will result in larger dots. The FM network is very small, and its slight expansion will cause significant results. Using high-contrast film can reduce the area of ​​partial exposure, thereby reducing the potential for dot gain at this stage of the process.

Since the inherent latitude in the FM network replication process is small, the use of the widest exposure range of the film gives the best dot reproduction.

23. Traditional process control

The tiny size of the basic printing dots expands all the deficiencies in the current proofing technology. The latitude is usually smaller, and the problems caused by the dust and dirt in the AM screening process are not significant. In the FM screening process, it will cause great problems. The proof area must be kept clean to avoid fine particles during copying. When the entire system is using small-sized dots, small dust particles will cause defects that cannot be ignored. The printed micro-dots in the FM network are equal to or less than the dust in the AM network. Excessive exposure of the plates in the traditional way can eliminate them.

A consistent and uniform vacuum pressure is required to ensure consistency between the plates and the entire plate. A slight change in vacuum pressure will cause hotspots, which is more noticeable than the same hot spots obtained in the amplitude modulation network.

24. Electronic proofing outlets

Accurately copying the proofs of the FM mesh micro points only needs to reveal the motif moire that exists in the image. The observer judges that the method of final printing of the image product is performed at a normal reading distance. Therefore, if the proof is only indicative of the appearance of the final print, no dot is required.

25. Plate resolution

In order to print high-resolution dots in the range of 14 to 25 μm, the plate must be able to resolve 4 to 6 μm images. When the plate is exposed, it must be able to correctly reproduce the 6 to 8 μm signal bars to reproduce the smallest dot correctly.

The microplate signal strip should be used to determine the resolution of the plate. The plate resolution is determined by finding the bars that appear to be the same in the yin and yang sections. If 8 μm of the Yin and Yang line signal bars have the same thickness, the plate resolution is 8 μm.

The plate must be able to reproduce the individual FM dots of highlights and shadows. If a single cell is lost, all details in the 0% to 20% and 80% to 100% regions may be lost. (The tonality of these areas is completely reproduced by a single micro-dot being spread over a suitable distance.) According to the conventional standard, in order to correctly reproduce the highlights and highlights, it is necessary to reduce the exposure of the printing plate according to the conventional standard. Reducing the exposure may reduce plate life and increase duplication of the dots.

The post-exposure process is used to densify the dots to increase the plate life. In order to prevent duplication of the dots on the plate, it is necessary to pay attention to the cleanliness of the plate. In order to reduce the variable factors in the printing process, a high-quality printing machine is required, and the poor printing opportunities generate hot spots, which make the entire printing plate and the printing plate unevenly exposed. Rough-surfaced plates can increase the degree of adsorption but may sacrifice resolution. (to be continued)