Printing Screening Process Talk - FM Networking (4)

13. Virtual Light Mask

The fine details kept in the FM network reduce the need for virtual masks. In some cases, the use of false light masks in FM network images can create additional problems by emphasizing noise in the image; noise can be removed in conventional images. The result of overemphasizing the details is that it will get nasty rough. In general, it is recommended to use the same or a small amount of false light mask.

Virtual Light Masking (USM), Underlying Color Removal (UCR) and Gray Component Replacement (GCR) are not affected by FM screening and can be used in the same way as AM.

However, making some adjustments may further improve the image quality. In some cases, traditional virtual masks may make full use of some of the advantages of the FM network in terms of detail, resulting in a higher image quality than the best in traditional images.

14. Image details

The AM-tone halftone screen prints are generally considered to be continuous in casual observation, but the particles can be seen when carefully observed with the naked eye. The smaller the printed dots used, the more detail that can be reproduced, and the printer can achieve this effect by using a high number of screens on a waterless offset press. FM screening does not smoothly reduce sampled color mixing or sharpen poor scanning.

The details in the FM network are not limited by the amplitude modulation screening, and the details obtained in some scans can be duplicated. Because of the many details that can be reproduced by the FM network, the effects of false light masks are significantly possible for the AM network. FM screening can benefit from high-resolution scanning because it can deliver more detail without having to limit the scanning resolution by the number of screens. The amount of virtual masking applied and the required scanning resolution depend on the desired image quality and the specific image characteristics. If the scan parameters are adjusted properly, the potential for increasing the number of image details exceeds all possibilities in the screen of the AM screen. More details can be found in the FM screening technology. It is the best way to copy line drawings and text in scanned images.

15. Smaller file storage

The image file size used for the FM network is smaller than the conventional color separation image with the same detail quality because the FM network method can obtain more detail with the same file size, and the smaller file achieves the same detail with the larger conventional file. . FM network vendors claim that a scan ratio of 1:1 is sufficient. In other words, in order for the FM network to achieve the same detail as a conventional 150-screen screen scanned at 2:1, the scanning resolution of the FM network only needs to be equal to the number of screen lines that it wants to match the details. However, the user does not get satisfactory results with such a low resolution scan unless the image details are very soft. Many FM network users still scan or even higher at a 2:1 ratio to copy more detailed images.

16. Scanner resolution

The Nyquist theory shows that if the scanning resolution exceeds twice the number of screen lines, an increase in the resolution will not increase the image quality of the AM network. Using the same scanning resolution, the FM network has more details than the AM screening. Therefore, the FM network is not limited by the constraints in the theory. Some FM network users reported that higher scanning resolution than traditional screening will further increase the range of detail displayed in the FM network. Few users use scan resolutions higher than 3.5:1.

Using a low scanner resolution in randomly screened images is possible compared to traditional screened images. According to the Nyquist theory, the recommended scanner resolution for AM networks is twice the number of network lines. However, many dispersers use a ratio of 1.5 times the number of screen lines to obtain a qualified screening.

The image of the FM network requires less resolution to achieve the same visual effect. The simple rule among them is: use a conventional color separation scan with the same details to half the resolution. Because of the different scanning resolutions, the resulting file size is 25% of the traditional file size.

Users of some stochastic screening techniques reported that they noticed that when the scanning resolution is slightly lower than the scanning resolution used in traditional technology, the image details will be reduced. The FM network has no screen lines, so the scanning resolution becomes the only parameter that requires output quality determination. Although some observers claim that the FM network can use a lower scanning resolution, it is not possible to select a lower scanning resolution when the user wants more details. Images with rich detail require high scan resolution to maintain image quality.

The advantage of higher resolution depends in part on the image. Originals with high detail may benefit from high scanning resolution, while soft images are not affected. Other users reported that when the images scanned at 225 pixels/inch and 300 pixels/inch were printed with 21 μm dots, the former looked better than the latter.

However, there are some users who reported that according to image sharpness, there is no significant image degradation as long as it is not lower than 140 dpi.

Dots are generated by the laser spot of the telegraphic recorder and are usually combined into a 3x3 or 2x2 grid. The dot size of the laser spot at 3600 dpi is 7.5 μm. In order to obtain 14 μm dots, 2×2 laser dots are required to be combined.

A single printing dot is a tiny dot with a specific laser resolution (dpi). In quarter tone regions, they join to form a worm and fill up as the tone increases.

(to be continued)

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