Neutral gray balance in color reproduction (top)

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 means that neutral ash has no hue and saturation, and there is only one-dimensional variable brightness.

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, neutral gray balance is used as a measure of the appropriateness of the ratio of the three primary color inks used in color separation and printing.

Third, the background removal and neutral gray balance

1. The concept of background color removal, the so-called under color removal (UCR) refers to the removal of a portion of the three primary colors of Y, M, and C to form a neutral gray background, that is, the approximately black bottom of the color materials Y, M, and C. Color, and replaced with black ink.

For example: suppose a certain color is 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 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 to remove the ground color, 1 improves the printing applicability: in general under the dark tone, in the dark tone area if you use the three primary colors Y, M, C printing, the dot area is often very high, in high-speed multi-color printing, It is prone to process problems. 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 the ink drying speed will directly affect the speed and product quality of high-speed multi-color printing presses to solve this There are many ways to solve the 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 black ink concentration and gloss, and reduce the Y, M, C trichromatic ink in the achromatic color. The amount of ink at the site, which effectively thins the ink layer to speed up the drying process, is the fundamental reason for using UCR in color reproduction.

3. Background removal should pay attention to several points

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.