How to Decrease the Moire on the Screen in the Making of Web Template (I)

In halftone dot color printing, different shapes of interference patterns (hereinafter collectively referred to as moiré patterns) are often generated on an image, and the existence of these patterns destroys the visual effect and the color effect on the image, and thus must be “eliminated”. Or weaken as much as possible. So, in general, what are the reasons for the occurrence of moire on printed materials in the production process of the online template? How can we avoid and weaken the moire? It is discussed from the following aspects:

1. Characteristics of two screening methods: Everyone knows that there are two screening methods for halftone dot printing :

1.1 AM printing features: The sizes of the dots are different. The color shades of the halftone dot printing are determined by the size of the dot network of the color image. That is, the dot area of ​​the high profile part is small, and the dot area of ​​the low profile part is large; meanwhile, the amplitude modulation Dot printing is based on the same center distance between adjacent dots in the same screen number. The resolution of the pattern and the printable fineness (number of lines) are determined by the size of the center of the dot. Since the center distance between dots is different with the printing accuracy, there are regular changes. In screen printing, regular dots on a stencil are attached by a regular woven screen, so that the overlap between the two “rules” (printed images and screens) interfere with each other and interfere with each other. :

1.1.1 In the case of halftone halftone color printing, the effect of producing a moiré pattern to interfere with the color reproduction of the image is unavoidable, and the moiré pattern on the pattern can only be reduced (less) by various technological measures.

1.1.2 In AM screening, because two overlapping rule patterns produce interference patterns, we use this principle to make a ruled line pattern film with a regular pattern from wide to fine, with equal spacing to test the screen. The number of meshes. From this it can be seen that when two regular patterns overlap each other and rotate with each other, there will be various degrees of mutual interference, but the overlapping positions are different, and the size, number, and degree of appearance of the moiré are different. . Therefore, it must be noticed when screen making.

It is further explained that in the halftone amplitude modulation dot printing, the generated moiré pattern can be weakened and cannot be eliminated, which is a congenital defect in amplitude modulation dot printing.

1.2 FM network printing: FM network printing is the same size of the outlets, and the distance between two adjacent outlets is randomly changed. The depth of the color of the image is determined by the degree of density of the Internet. In the highlight part of the image, the dots are loose, and the color is light; the dots in the low-key part are tight, and the color of the expression is deep. In the image, the fineness of the dot represents the high, low, and delicate color of the image. Since the outlets are random, there is no regular change in the outlets. Therefore, there is no interference between the irregular dots on the image and the screen with regular weaving. Because the dots on the image are arranged randomly, the moiré caused by dot deviations of the various colors does not exist in the FM screen printing. Therefore, FM screen printing can eliminate moiré generated by halftone dot printing, and is a new method of copying and restoring originals of color images.

Compared with the amplitude modulation screening, the FM screening printing can make the image sharper, the color reducibility is higher, the nesting error sensitivity is small in the printing, and the impact on the color is less. Since the FM screen printing is not limited by the screen angle (screen angle) in the color printing, the FM screen printing can print R, G, and B other than the normal four colors so that the color images can be reproduced from the original. The Y, M, C, K four-color development of R, G, B, seven-color print, so that the color reproduction of the image more realistic, more distinct levels. Middle tone levels are excessive, and it is not easy to produce dot density jumps.

However, FM screening printing is not perfect, but it still exists:

1.2.1 Due to the small size of the FM network (approximately 8-30um in diameter) and the high density, the number of outlets per unit area is greatly increased. Therefore, the number of outlets in the screen printing is limited by the number of screen meshes, resulting in an increase in the loss of outlets. , And when the network is very detailed, the screen printing screen template production can not be achieved. Under normal circumstances, in the plate-making printing, the high-light spot on the screen plate can easily be lost, and the dark tone network site is easy to be blocked.

1.2.2 Screening stencils and screen printing conditions are strictly required, such as the density of the film, the number of screen meshes, the diameter of the wire, the size of the openings, and the thickness of the photosensitive layer, as well as the degree of cleanliness of the plates and the printing environment. Fine-grained reproduction will have an impact, so high and demanding printing condition guarantees are required. In view of the above, FM screen printing still has poor uniformity and fine dot, and it is more difficult to print than AM dots. At the same time, there is still insufficient stability of the output of the negative film. Therefore, the printing is mainly based on AM printing.

(to be continued)