Adjustment of ash balance in the reproduction proc

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Adjustment of gray balance in the printing reproduction process 1. The concept of printing gray balance

the reproduction process of printing is to ensure the reproduction of gray tone, tone, color and clarity of the original. Color science divides color into two systems: one is gray system, namely black, white and gray system (multicolor or cubic color also belongs to gray system); The second is the color system, namely yellow, orange, red, green, blue, purple, etc

the grey system of three-dimensional color space has no hue and saturation, only the lightness of one-dimensional variable, and is only a white dot on the chromaticity map. The color system has three attributes, namely hue, saturation and lightness. All colors contain these three attributes, and these variables are different for each color

we know that the three primary colors R, G and B of color and light transition to the white field, and the primary color light will turn gray when mixed in the same amount. While the three primary colors C, m and y of the pigment transition to the black field. After the three primary colors are combined and overprinted according to the ratio of different point area values, they can completely duplicate different neutral gray. In the industry, it is called that the three primary colors C, m and Y reach the neutral gray balance. The monochromatic density of the three primary colors that achieve the neutral gray balance is called the equivalent neutral gray density

the role of gray balance in reproduction

one of the key technologies of color reproduction is how to correctly reproduce the gray in the original, which is the basis for realizing tone reproduction and color reproduction

1. grey balance is a measure of the tone of prepress image processing, the scale of color reproduction, color printing midpoint and ink volume change, which runs through the whole process of prepress and printing process. It is a unified standard for printing reproduction color management, standardization and data quality management, and also a common criterion for all processes

2. gray balance is also the standard to check whether the gray tone of the scanned color separation film is correct, and is also the basis to judge and correct whether the original and printed matter are biased

theoretically speaking, the color correction based on gray balance reproduction is the key to determine whether the hue can be correctly reproduced. Only the gray tone in the original is reproduced accurately can the color be reproduced accurately. If the gray scale ratio composed of the area values of the three primary colors C, m and Y is not correct, the color reproduction will be biased, and the West Red Hangzhou color may be copied in orange. Therefore, the premise of color reproduction is to establish a gray balance curve and its parameter set of the combination of area values of different points of C, m and Y primary colors, which can be adjusted as the internal setting value before scanning and color separation

the author has summed up a rule in practice. As long as the proportion of gray balance point area value established by the electric extension and scanner is correct, and the standard color correction amount established on this basis is correct, the gray tone in the image can be reproduced. At the same time, all multicolor (tertiary color and composite color) in the image can also be reproduced in this way, There is no need to adjust the area ratio of the three primary colors of the multicolor plate during scanning or post-processing, because the multicolor belongs to the gray system

in terms of color, grey tone 1 refers to neutral grey (pure grey); Second, it refers to the composite color with gray degree. The composite color is formed by combining three or more colors. Therefore, there are tens of thousands of color gray, such as yellow gray, green, gray, blue gray, red gray and so on, all of which belong to the gray tone. According to the determination of scientists, among the more than 100000 colors that can be identified, more than 80000 are gray colors

practice has proved that as long as the gray balance curve and its point area ratio set by the electric extension and scanner are correct. Then, after the correct Black/white field calibration, the gray tone in the original and the thousands or thousands of multi colors contained in the image can be reproduced. Because color belongs to gray system, it belongs to the category that scanning should be restored

the gray and multicolor of some originals need to be adjusted. First, adjust the defects that the original image is too bright and too dark. This adjustment should be deepened or lightened at the same time by using the four-color hierarchical curve; Second, adjust the color deviation of the original gray tone, and use the monochrome hierarchical curve to correct the deviation

combination of gray balance point areas

1. definition of printing gray balance

printing gray balance refers to the combination of C, m and Y primary color plates according to the area percentage of different points, and neutral gray is generated in the printing that the left and right alignment of the sample is guaranteed by the fixture. Specifically, under certain printing suitability conditions (paper, ink, printing machine, etc.), C, m and Y primary plates are combined and overprinted according to a certain percentage of point area from light to deep, Get different shades of gray (the process of white, light grey, medium grey, dark grey and black is called printing grey balance.

2. combination of grey balance

combination of grey balance means that after the neutral grey scale is scanned for color separation, both RGB mode and cnyk mode have their own proportional values. In RGB mode, from the theory of color light additive method, R, G and B light will become grey when mixed in the same amount. As shown in Table 1.

but in CMYK mode, C, m and y will become grey when mixed in the same amount The primary color ink can not get neutral black when overprinted with the same amount of field density, but red and warm black. When overprinted with the same amount of point area percentage, it can not become gray, but red and warm compressive strength is gray when an iron ore pellet is completely broken

from the color theory of pigment subtraction, the overprint of the maximum saturation of the three primary colors should be black, and the overprint of the same amount of three primary colors with different saturation should be gray with different lightness

then, why does the three primary color ink overprint in the same amount but not get neutral gray and become red and warm gray? It is mainly affected by two factors

(1) ink error

due to the different light absorption and reflectivity of the three primary color inks, there are color deviation and gray components, that is, components with other ink hues in one ink. For example, C ink contains some magenta components, and M ink contains some yellow components, which causes color deviation and gray components. As shown in Figure 1

the author measured and calculated the proofing experiment of dic-graf-g ink, and the color is the least. Therefore, the gray balance three primary color dot area percentage combination is obtained through experiments according to the characteristics of the ink used and the printability conditions such as paper. Practice has proved that as long as the printability of ink and paper is stable, the area percentage of gray balance point can be fixed

(to be continued)

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