Neutral gray balance in color reproduction (top)
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First, the concept of neutral gray balance
The copying work of the printed matter is color restoration, tone reduction, texture restoration, and resolution reduction. The so-called tone is that the color is classified by brightness, the color is three-variable, the neutral gray is a three-dimensional color space, the neutral gray is composed of three colors of Y, M, and C, and the three variables of color (hue, saturation, brightness) Hv / c means that neutral gray has no hue, saturation, only the brightness of one-dimensional variables.
We know that the three primary colors R, G, and B of the color light transition to the white field, and the three primary colors Y, M, and C of the color material are transition to the black field. In addition, four-color printing is limited by two conditions: one is to use only four colors of Y, M, C, and K; the other is that the ink layers on each sheet are evenly distributed.
Neutral gray refers to a series of colors such as Y, M, and C. They absorb the R, G, and B colors in equal amounts, and only the change in brightness has no change in hue and chroma.
When the three primary colors Y, M, and C of the color material are overprinted in an appropriate ratio, the neutral gray scale can be completely reproduced. Then, the three primary colors of Y, M, and C are said to reach a neutral gray balance. The monochromatic density of the three primary colors that achieve the gray balance is called the equivalent neutral gray density.
Second, emphasize the significance of neutral gray balance
1. Correctly copy the gray of the original.
2. At the time of plate making and printing, the neutral gray balance is used as a measure of whether the ratio of the three primary colors of ink in the separation and printing is appropriate.
Third, the background color removal and neutral gray balance
1. The concept of background color removal, the so-called background color removal (UCR) refers to the removal of a part of the neutral color from the three primary colors of Y, M, C, that is, the almost black bottom formed by the superposition of the three primary colors Y, M, C. Color and replaced with black ink.
For example, if a certain color is overprinted by Y, M, and C, the area of Y dot is 80%, the area of M dot is 80%, and the area of C dot is 100% (in the field). If it is balanced according to neutral gray, 80%Y and 80% of M can overlap with 90% of C to form a black ink equivalent to 90% dot area, then: C = 80% Y + 80% M + 100% C = 80% Y + 80% M + 90% C + 10% C = 90%K +10%C
2. The necessity of removing the ground color, 1 improves the printability: in general, it is used in the dark tone. If the three primary colors Y, M, and C are printed in the dark adjustment area, the dot area is often high. In high-speed multi-color printing, Easy to create process problems. If the base color is removed, the amount of ink is greatly reduced, and the printability is improved. 2 Conducive to controlling neutral gray balance during printing. 3 is conducive to the drying of the ink, reducing the amount of overprinting of the three primary color inks of Y, M, C. 4 Because the amount of Y, M, C color ink is reduced, the amount of black ink is increased, thereby reducing the cost, and the price of black ink is relatively cheap. 5 After adopting high-speed multi-color printing machine, the biggest problem affecting the speed and quality improvement of high-speed printing machine is ink drying problem, which means that the speed of ink drying will directly affect the speed and quality of high-speed multi-color printing machine. The solution to the problem is multi-faceted, such as changing the composition and structure of the ink, improving the drying method of the printing press, and improving the process, improving the concentration and gloss of the black ink, and reducing the Y, M, and C primary color inks in achromatic colors. The amount of ink in the part, which effectively thins the ink layer to speed up the drying, which is the root cause of UCR in color reproduction.
3. Points to note when removing the ground color
1 Background color removal generally works in intermediate, dark-adjusted neutral gray and near-neutral gray areas.
2 Correct control of the removal amount.
3 master the control of the removal point, which is to remove the scope of control.