3. Influence of printing pressure and process conditions on dot gain In general, the greater the printing pressure, the more serious dot gains will be. Offset press produces certain deformation of the blanket, which can also cause dot gain. Any problem on the same press can affect the tone value of the image. For example, if the printing offset is too loose, dot doubles (DOT DOuBlInG) are usually generated, which looks like a serious dot gain problem, or there are too many scratches on the paper and the paper slips slightly relative to the impression cylinder, usually also DOT SluR problem. This dot gain will vary depending on the printability of the press, the type and status of the press, and the ink brand. Therefore, according to the different printing conditions to trim the state of the level of the curve, will be helpful to the level of printing quality performance. Generally, according to the increase of printed dots, the appropriate reduction in the middle will enhance the printability of prepress production.
4. Influence of paper condition on dot gain After the ink is transferred to the substrate, due to the absorption of the paper, the ink spreads around when it penetrates, which is one of the reasons for the dot gain. Therefore, the amount of ink and the viscosity of the ink should be changed according to the nature of the paper at the time of printing. Coated paper (coating paper) has good gloss, whiteness, and light reflection ability. It has a good printability: the ink printed on coated paper is less diffused, the dot type is better, and dot gain can be controlled. About 15% can reflect a good level and contrast. Therefore, when printing, high-grade printing paper is used to print pictures and samples. In addition, in prepress operations, color proofing is generally performed using coated paper to check the image quality of prepress jobs. To this end, the holders use proofs of coated paper as basis for adjusting the basic curve. When offset paper (non-coated paper) is printed, the tightness and flatness of the paper are inferior to that of coated paper. In order to achieve a certain ink density for the print, more ink and more pressure are needed.
Therefore, in the printing process of offset paper, the dot gain will increase, especially in the midtone region will be much larger than other regions, and the shadowy region will often cause "sticking" phenomenon due to improper printing. In addition, due to the poor flatness of the paper in high-profile areas, too small 2% dots cannot be reflected on the paper at all. The dot gain is controlled at around 22%. Therefore, the mid-level adjustment of the level curve is about 5% to 7% lower than normal, so that the print can have a suitable picture contrast. The printability of newsprint is even worse, and dot gains are even more serious. Poor smoothness directly affects the color drift of the printing ink; the low surface whiteness results in a small print contrast; the smoothness is low and the ink diffusivity is strong; the dot gain is increased by 30% to 40%. On the other hand, special glossy papers can sometimes cause blurs in the dots, and its effects are similar to dot gains, because premium grades are printed. There will be a slight slide in the machine.
5. The effect of the number of network lines on the increase of network points When the number of network lines increases, it is easy to blur halftone dots and cause dot gain. Because:
1 Dot gain occurs in the edge area of ​​the dot: When the number of lines increases, it means that the edge area increases and the possibility of dot gain increases.
2 When the number of network lines is high, the outlets are too close to each other, so that any increase in outlets can fill up the small gaps between the outlets, resulting in image hierarchy. But how can we know how high the number of network lines can avoid these problems? The main factors that need to be considered are output resolution, output method, printing method and paper.
6. Effect of dot shape on dot gain The dots with different shapes have different influences on dot gain in the printing process: dots with the same size, different shapes, and different perimeters. The larger the perimeter, the bigger the dot gain. In the process of growing from small to large, there are always sites where overlapping starts, as shown in Figure 1. At this point, the overlap of the dots will cause a sudden increase in the density of the printed matter, destroy the continuity of the print, and cause some loss of tone levels, such as a gradient, which will cause excessive unevenness due to the density jump. Figure 1 In the three types of outlets, square outlets are overlapped at 50%, circular outlets are overlapped at about 70%, and chain outlets are overlapped at 25% and 75%. In contrast, the image quality of the chain-shaped dot is better, because its overlapping parts avoid the midtones, and the overlap is divided into two, weakening the degree of density jump. Because of this, if the image contrast is small and soft, such as character images, chain-shaped dots can be used; if the contrast is large, square or circular dots can be used. (to be continued)
4. Influence of paper condition on dot gain After the ink is transferred to the substrate, due to the absorption of the paper, the ink spreads around when it penetrates, which is one of the reasons for the dot gain. Therefore, the amount of ink and the viscosity of the ink should be changed according to the nature of the paper at the time of printing. Coated paper (coating paper) has good gloss, whiteness, and light reflection ability. It has a good printability: the ink printed on coated paper is less diffused, the dot type is better, and dot gain can be controlled. About 15% can reflect a good level and contrast. Therefore, when printing, high-grade printing paper is used to print pictures and samples. In addition, in prepress operations, color proofing is generally performed using coated paper to check the image quality of prepress jobs. To this end, the holders use proofs of coated paper as basis for adjusting the basic curve. When offset paper (non-coated paper) is printed, the tightness and flatness of the paper are inferior to that of coated paper. In order to achieve a certain ink density for the print, more ink and more pressure are needed.
Therefore, in the printing process of offset paper, the dot gain will increase, especially in the midtone region will be much larger than other regions, and the shadowy region will often cause "sticking" phenomenon due to improper printing. In addition, due to the poor flatness of the paper in high-profile areas, too small 2% dots cannot be reflected on the paper at all. The dot gain is controlled at around 22%. Therefore, the mid-level adjustment of the level curve is about 5% to 7% lower than normal, so that the print can have a suitable picture contrast. The printability of newsprint is even worse, and dot gains are even more serious. Poor smoothness directly affects the color drift of the printing ink; the low surface whiteness results in a small print contrast; the smoothness is low and the ink diffusivity is strong; the dot gain is increased by 30% to 40%. On the other hand, special glossy papers can sometimes cause blurs in the dots, and its effects are similar to dot gains, because premium grades are printed. There will be a slight slide in the machine.
5. The effect of the number of network lines on the increase of network points When the number of network lines increases, it is easy to blur halftone dots and cause dot gain. Because:
1 Dot gain occurs in the edge area of ​​the dot: When the number of lines increases, it means that the edge area increases and the possibility of dot gain increases.
2 When the number of network lines is high, the outlets are too close to each other, so that any increase in outlets can fill up the small gaps between the outlets, resulting in image hierarchy. But how can we know how high the number of network lines can avoid these problems? The main factors that need to be considered are output resolution, output method, printing method and paper.
6. Effect of dot shape on dot gain The dots with different shapes have different influences on dot gain in the printing process: dots with the same size, different shapes, and different perimeters. The larger the perimeter, the bigger the dot gain. In the process of growing from small to large, there are always sites where overlapping starts, as shown in Figure 1. At this point, the overlap of the dots will cause a sudden increase in the density of the printed matter, destroy the continuity of the print, and cause some loss of tone levels, such as a gradient, which will cause excessive unevenness due to the density jump. Figure 1 In the three types of outlets, square outlets are overlapped at 50%, circular outlets are overlapped at about 70%, and chain outlets are overlapped at 25% and 75%. In contrast, the image quality of the chain-shaped dot is better, because its overlapping parts avoid the midtones, and the overlap is divided into two, weakening the degree of density jump. Because of this, if the image contrast is small and soft, such as character images, chain-shaped dots can be used; if the contrast is large, square or circular dots can be used. (to be continued)
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