How to Deal with Color Reproduction of Neutral Gray Balance in Printing and Copying

First, the concept of neutral gray balance

The reproduction work of the printed matter is color restoration, tone reduction, texture restoration, and resolution restoration. The so-called tonality is the color classification by lightness, the color is three variables, the neutral gray is a three-dimensional color space, the neutral gray is composed of Y, M, C three colors, the three variables of the color (hue, saturation, lightness ) Hv/c indicates that neutral ash has no hue and saturation and only one-dimensional variable has lightness.

We know that the three primary colors R, G, and B of the shade transition to the white field, and the three primary colors Y, M, and C of the pigment transition to the black field. In addition, four-color printing is subject to two conditions: one is that only four colors of Y, M, C, and K can be used; and the other is that the ink layer on each sheet is evenly distributed.

Neutral ash refers to a series of colors such as Y, M, and C. They absorb R, G, and B light in equal amounts. Only lightness changes without changes in hue and chroma.

When the three primary colors Y, M, and C of the pigments are overprinted in the proper proportions on the spot or halftone, the neutral gray scale can be completely reproduced. Then, the three primary colors of Y, M, and C are said to have reached a neutral gray balance. The monochromatic density of the three primary colors that achieves gray balance is called the equivalent neutral gray density.

Second, emphasize the significance of neutral gray balance

1. Correctly copy the original gray.

2. At the time of plate making and printing, the neutral gray balance is used as a measure of the appropriateness of the ratio of the three primary color inks for color separation and printing.

Third, the background removal and neutral gray balance

1. The concept of background removal. The so-called under color removal (UCR) refers to the removal of a portion of the neutral ash formed from the three primary colors of Y, M, and C, that is, the approximately black background formed by the superposition of the three primary colors Y, M, and C of the toner, and the black ink. instead.

For example: Let a color be overprinted by Y, M, C three-color, Y dot area is 80%, M dot area is 80%, C dot area is 100% (field), if according to neutral gray balance, 80% Y and 80% of M can overlap with 90% of C to form black ink equivalent to 90% of dot area. Then:

C =80%Y +80%M+100%C =80%Y+80%M+90%C +10%C =90%K +10%C

2. The need for background removal.

1 Improves printing adaptability: Under normal circumstances, it is used in dark tone. In the dark tone area, if three primary colors Y, M, and C are used for printing, the dot area is often very high. When high-speed multi-color printing is performed, a process problem easily occurs. If the background color is removed, the amount of ink is greatly reduced and the printability is improved.

2 is conducive to control the neutral gray balance when printing.

3 is conducive to ink drying, reducing the Y, M, C trichromatic color inks overprinting.

4 As the amount of Y, M, C color inks is reduced, the amount of black ink is increased, thereby reducing the cost, and black ink is relatively inexpensive.

5 The use of high-speed multi-color printing presses, the biggest problem affecting the speed and quality of high-speed printing presses is the ink drying problem, which means that ink drying speed will directly affect the speed and quality of high-speed multi-color printing presses. There are many ways to solve this problem, such as changing the composition and structure of the ink, and improving the drying method of the printing machine. The other is to improve the process, improve the concentration and gloss of black ink, and reduce the three primary colors of Y, M, and C. The amount of ink in the non-colored areas, which effectively thins the ink layer to speed up the drying, is the fundamental reason for using UCR in color reproduction.

3. Points to note when subtracting the ground color.

1 Undercolor removal generally works in midtones, shadows neutral gray and near-neutral gray areas.

2 Correctly control the removal amount.

3 master the control of the removal point, which is to remove the scope of control.

Fourth, the relationship between the dark lines and the amount of background removal

The depth of the black plate and the amount of background removal are closely related to each other. The amount of background removal is large, and the black version should be deep. On the contrary, the amount of background removal is small, and the black version should be shallow. At the same time, the length of the black tone should be determined by the length of the dark tone density range of the original. Dark tone density range is long, black version should be long, dark tone density range is short, black version should be short. Neutral gray balance is an important condition for copying and restoring a manuscript. It is also a technique difficult to master in plate making and printing because Y, M, and C inks have a certain degree of difficulty in reproducing the neutral gray balance.