How to Avoid the Shortcomings of Traditional Lithographic Offset to Improve Color Copy Quality (Part 2)

4 outlets - there is a phenomenon of level jump

The role of the outlets are as follows: 1 The task of reproducing hue, lightness, and saturation is responsible for printing; 2 is the minimum unit for sensing and repelling water, and is the basic element of image transmission; 3 is the color, level, and color of images in color synthesis. Contour organizer. The most important problem of outlets is expansion. The amount of expansion is not only related to printing pressure, the number of dots and the number of dots, but also related to the dot shape of the dot. Now the dot shapes commonly used are square dots, circular dots, and chain dots. The square dots are at the 40% angle, and under the influence of the printing pressure, the 50% point has the largest amount of expansion. From the perspective of the level transition, a more obvious level jump is formed at the 50% point; round dots have to reach about 70%. When an edge occurs, an imprint jump will also occur. Only at the level, the level jump will be postponed; the chain points will take two angles, 25% and 75%, respectively. A smaller jump. The generation of level jumps will make the transcription of prints not continuous. Therefore, in the prepress production, we should use different shapes of dots according to the features of the original level. For example, you can use circular dots to represent the screen where the dark tone level is not very important. Use the chain points to represent the theme of the midtones. When making figure figures, it is best to use chain-type dots to avoid the enlargement of 50 percent points because most of the faces are about half of the dots. When making scenery maps, you can use square points or chain points.

5 "Water" - A Double-edged Sword

The main function of the fountain solution is to form a water film that repels ink in the blank part of the printing plate, and to keep the blank part of the printing plate from being dirty. It can be said that there is no fountain solution, and conventional offset printing cannot be discussed. However, the use of fountain solution in offset printing is a double-edged sword. Why do we say that here we do not talk about the various printing failures caused by “small water and large water”, that is, under the condition of “ink balance”? When the fountain solution competes with the ink, “water” will scour and corrode on the basis of the ink, so that the fine dot (especially the small dots below 3%) is difficult to ink, causing this part of the dot in the printing process. Missing, resulting in high light leveling. Therefore, as a printing operator, the amount of water should be controlled, and the amount of water in the layout should be reduced as much as possible without the print being dirty. As a prepress creator, you can't just pursue the exquisiteness of the image. You should consider the actual situation and select the appropriate number of screens, because 3% of 120 lines/inch screens are much larger than 3% of 175 lines/inch screens. Large outlets are easier to locate on plates.

6 Total ink limit

The total amount of ink can be set in the color separation option in PHOTOSHOP's CMYK palette. This parameter specifies the total percentage content of cyan, magenta, yellow and black in the black area of ​​the printed image. The theoretically darkest area should be printed with 400% of the maximum total ink. However, in four-color wet-overprinting, this situation can cause the following problems in the actual production operation of the printing press;

1 It is easy to cause dirt on the back of the printed sheet;
2 ink is not easy to dry;
3 Overprinting difficulties, ink overprinting is not good;
4 ink reverse transfer.

In the wet-overprinting, the total ink limit is not more than 340%. It is better to replace the gray component of the image in newspaper printing. The total amount of ink can also be reduced. The actual situation should be based on the actual situation, and the experience should be summarized to find the right one. The color separation parameter setting value? But under the monochromatic overprinting condition, I think that the gray component substitution is only in the image dark tone, the total amount of ink can be set larger, the other color part should be used to express CMY To increase color richness and image glossiness.

7 stamping problems

In CMYK four-color printing, overprinting is the most basic requirement for color printing. The stability of the machine, the suitability of the raw and auxiliary materials, the temperature and humidity of the workshop, etc. may all lead to misprints, even if all aspects are in good condition. There may still be minor misalignment between two color blocks that are trapped in the printing process, resulting in overprint deviations, which are manifested at the junction of different colors. The missing or overlying color of missing or overprinted edges is now compensated for. The defect method is trapping during color separation. The principle of trapping processing is to appropriately expand the color of the light-colored side to the dark side, and the specific expansion can be set according to the actual conditions of the printing (for example, according to the registration accuracy of the printing press), which is now common in many software applications. With trapping settings, some large companies also have professional trapping software that provides better control over trapping. Trapping processing should pay attention to the use of color, and the final trapping value setting cannot destroy the subtle level of the image or blur the boundary of the image. Sometimes trapping may not be done, such as printing in one color only. In addition, when using CMYK to design color blocks, it is necessary to pay attention to minimize the use of color blocks or texts of M+C=B, because M and C are all strong colors, and they are only slightly inaccurate.

I would like to make some suggestions to printing colleagues who produce newspaper advertisements, and try to do as little as possible prints that have thin lines or hollowed out trumpet characters. I often read newspapers. Due to my professional habits, I often need to double-check the coloring papers. Advertising can rarely register to satisfy people. Therefore, pre-press designers should not only pursue their own design results, but also pay attention to the actual situation of some printing, so that your design work will look better when meeting with the audience.

As a traditional lithographic offset printing, because of the advantages of its product's cost-effectiveness in the printing industry, it will continue to exist. Since there are reasons to exist, we cannot avoid it, including its advantages and disadvantages. The best way to master it is to Fully recognizing the existence of these problems mentioned above, in order to prevent weaknesses in the design and production process, according to the different characteristics of the product, the system printed satisfactory print.

Source: "Printing World"

Author: Wu Ming root Jiangsu Province Press and Publication schools