Base color removal calculation method - adjust the gray balance

In the analog electronic color separation machine, due to the use of a suitable image processing method for the under color removal, the neutral ash component of the dark tone composite color can be individually extracted, so that the under color removal function can be accurately, quickly and simply realized. .

Back-color removal is essentially a kind of transformation of the composite color region, replacing color with black, reducing the amount of three-color ink, and the calculation method is similar to the black version of the calculation, but more emphasis on the size of the color saturation, usually the back color removal is limited to The image saturation area with small saturation, the simulation operation equation is:

R=S-L-S/K=S-Δ/K

Among them: R - represents the amount of removal of the background L - said max (Vy, Vm, Vc)
S——min (Vy, Vm, Vc)
Δ=L-S indicates the saturation of the composite color, and K indicates the degree of saturation influence on the black plate. The larger K indicates the smaller the influence of saturation on the black plate.

In the actual use of the under color removal, it is necessary to take into account both the under color removal range and the under color removal amount, and the value range thereof is determined by actual work.

The following formula is used in some electronic color separation machines to calculate the amount of under color removal.

R = removal density / replication density range × 100% = DR / Dr × 100%

Among them: DR - removal density Dr - replication density range

In the subtractive calculation of the undercoat color, the value of K is usually taken as 5, so that the effect of the convexity on the removal amount of the under color is enhanced, and the area where the under color removal effect is significant is located at the position where the original is close to the neutral gray. The saturated color or solid color area has little or no background color removal, thereby ensuring that the original image is bright and vivid, and avoiding the phenomenon of darkening or winning due to an increase in the black version, and determining the amount of background removal. At the same time, you also need to choose a suitable background to remove the starting point.

4. Process characteristics of under color removal

When UCR separation mode is selected, its setting is only the black ink limit and the total amount of ink. The general ink amount is limited to about 260%, and the black printing start point is basically fixed at about 50%.

Adjust the black ink limit and the total amount of ink two technical indicators, UCR removal will have different changes, at the same time, UCR removal starting point will also be in accordance with the total ink limit changes.

UCR is suitable for most manuscripts and printing processes. In particular, gravure printing process and manuscripts require bright colors. Therefore, the UCR separation mode is more suitable, and the black ink limit parameter values ​​can be smaller, for example, 60%, three primary colors. Ink is more advantageous.

The disadvantage of UCR is that deeper primaries with more ash components are subject to removal and cause insufficient saturation. Therefore, when you encounter an image with an important deep primary color, you need to use Photoshop tools for local corrections to achieve sufficient saturation.

Source: Bison