Hottest printing ash balance adjustment 1

Printing gray balance adjustment

(I) black plate function

the chromaticity of ideal color reproduction requires only the superposition of Y, m and C primary color inks, which can combine thousands of colors and achromatism of different brightness. This is the theory of three primary color reproduction. However, the three primary color ink can not print the ideal neutral gray and can not reach the required density (shown in Figure 4-4-2). The field density of four-color printing is higher than that of three color printing, which is due to the use of black plate compensation. In multi-color printing, it is in the state of wet pressing and wet printing. When the ink layer is thick, it is not easy to dry, and it is easy to produce poor overprint and other phenomena. You must subtract the amount of inks in the three primary colors of dark tone, so you need to use black ink instead

the black plate is used to compensate the ink hue defects and adapt to the needs of multi-color high-speed printing machine, so that the printing can be carried out smoothly, which plays an important role in improving the product quality

① it can enhance the density contrast of the image. According to the current conventional printing conditions, the density of Y, m and C inks after superposition is 1.6 ~ 1.7, while the visual resolution can generally reach 1.8 ~ 1.9. Therefore, the black version with appropriate tone is selected to strengthen the absorption capacity of the paper, so as to increase the total density range of the image, increase the dark contrast and three-dimensional sense of the image, and improve the product quality. The whole system adopts digital design

② stable to dark color. Theoretically, the yellow, magenta and cyan inks in the proportion of corresponding points can be superimposed to produce the required color, but the printing volume is large, and the printing conditions are unstable, such as the difference in the performance of paper inks, the variability of machine accuracy, etc., and the adjustment from medium to dark is limited, especially at the area of 70% - 100% points. Therefore, most products tend to be tawny from medium to dark, and the color is unstable. In fact, most of the originals are dark and biased towards cold color, which is inconsistent with the requirements. Proper black version superposition can stabilize the color and overcome the dark and biased color

③ strengthen the middle tone to the dark tone level. In color reproduction, the general rule is to keep the bright tone or slightly emphasize it, keep the middle note or slightly compress it, compress the dark tone layers to many, and there is a flattening phenomenon in the medium and dark tone layers. On the other hand, only the yellow, magenta, and cyan primary color plates are superimposed, and the outline of the medium to dark tones is weak, and the layers cannot be pulled open. The black version is used with clear outline, clear layers, and obvious grading of dark tone details

④ improve the printability and reduce the cost. With the emergence of high-speed multi-color printing machine, the overprint time of each color is very short, and too thick ink brings many faults to printing. Therefore, it is necessary to reduce the amount of color ink in the neutral hair area of the dark part of the picture, and replace it with black ink, so as to reduce printing failures and improve the printability. At the same time, black ink is cheap and the cost is reduced

⑤ solve the problem of developing text printing and color reproduction to both pictures and texts, such as picture descriptions, advertising introductions, pattern labels, and the text of the calendar should be copied in black. In terms of visual requirements, black characters have the best effect. It is unrealistic to overprint words with three color plates

(II) background color removal (UCR)

background color removal, also known as UCR (under color remove), refers to a process that appropriately reduces the amount of ink in the dark composite color area of a print and replaces it with black ink

background color removal process comes from the requirements of wet press wet printing of modern high-speed printing machines and the reproduction of original dark tone levels. It is conducive to rapid overprint, saving expensive color ink (that is, by removing a certain amount of Y, m, C ink and replacing it with a small amount of black ink), and is conducive to neutral gray balance and neutral gray reproduction

1. principle of background color removal

theoretically, if the ideal y, m and C inks are dissolved in equal amounts, the ideal neutral gray can be formed, that is, the minimum value of the three colors composed of Y, m and C inks is the neutral gray component, as shown in figure 4-4-3. In other words, the composite color overprinted by the three primary color inks of Y, m and C has the same visual effect as the composite color overprinted by the two color inks of Y, m and C and black ink. The reason is that the black ink can correctly reproduce the neutral gray, so that the color ink constituting the neutral gray in Y, m and C of the thin-walled material shown in Figure 5 is removed and replaced by the black ink, and the reproduction of the same color achieves the same visual effect

with the development of modern desktop prepress system and image reproduction process, the background color removal function has been continuously improved and developed, and a new process pattern of coexistence of background color removal and ash replacement process has been formed. Ash replacement can not only complete all the work of background color removal, but also maximize the use of black ink to replace y, m, C and other color inks, and maintain the high quality of printed copies

2. The purpose of background color removal

(1) improve the printability and the dryness of ink. In printing, neutral and color are usually reproduced through y, m, C overprint. In order to compensate for the lack of level density from the middle to the dark part, a black version is added. However, for today's multi-color high-speed printing with fast printing speed, it is necessary to overprint the next color of ink before the first printing ink is dry, resulting in that the post printing ink cannot be completely transferred to the first printing ink, resulting in inaccurate overprint, uneven ink color, and even the first printing ink is taken away by the later printing ink. They are particularly obvious in the dark areas with a large amount of superimposed ink of four-color wet press wet overprint. Nowadays, multi-color printing machines generally require that the total area of overprint points of dark tone parts with good printing adaptability must be limited to 250% - 270%. Therefore, in order to meet the requirements of the printing process and improve the above adverse conditions, we must adopt the background color removal process to reduce the overall amount of ink, speed up the ink drying time and improve the printability

(2) reduce production costs. The prices of Y, m, C and BK four-color inks used in printing vary. When the background color is removed, pass 2 The test space is adjustable and can be used to test the requirements of different heights With good rigidity, small deformation, accurate measurement data, the base and beam adopt an integral casting structure, which is reasonable in structure, the workpiece is rigid, and the external decoration is beautiful, ensuring the safety and reliability of all parts A total of about 50% - 80% of the dots can often be removed, and only about 15% of the black version needs to be added, which can replace the printing effect of about 50% - 80% of the yellow, magenta and cyan printing, thus saving a lot of color ink. For mass printing, its economic benefit after cleaning is very obvious. Generally, adding 50% of the background color removal can reduce the ink cost by 10% - 15%

(3) color deviation compensation in the original copy of color image, even if the gray balance of the image from highlight to intermediate tone is good, it often loses balance in the dark part and presents a certain color deviation. If it is necessary to meet the conditions that its color composition is unchanged and can compensate for color deviation, the method of removing the background color is very effective to solve this problem. As shown in figure 4-4-3, there is an original with dark tone and partial redness, and the composition of dark tone color is Y7, M9, C6. To remove the dark tone and partial redness, the background color can be removed, and y, m, C can be removed by equal or unequal amount, and the color composition can be changed to realize gray balance reproduction. For example, if y, m and C are removed in equal quantities, their color composition will change to Y5, M7 and C4. Obviously, 7:9:65:7:4. As long as the appropriate proportion composition of Y, m and C is determined, the color deviation can be corrected

(4) emphasize solid color background color

removal only works on neutral hair areas, so changing the setting of dark tone through background color removal can achieve the purpose of using background color removal to emphasize solid color

generally, when emphasizing pure colors as a whole, it is better to use the background color removal. If only one or two colors are emphasized, it is better to use the color correction method. Figure 4-4-3 also illustrates the emphasis of background color removal on pure colors from another angle

(5) keep the balance of neutral gray stable. In ordinary color printing, y, m and C are often used to reproduce neutral gray. However, there are many unstable factors in the printing process, such as different ink concentrations, different ink volumes, and inaccurate overprinting of various colors. When reproducing the originals with gray tones such as machines and cameras as the main content, it is difficult to copy, which is easy to cause local color deviation. Therefore, using an appropriate amount of background color removal to remove the ink amount of Y, m and C superimposed with gray from y, m and C, and increasing the black version to make up for the lack of background color can obtain a satisfactory effect and keep the neutral gray balance stable