In production, we should control the proportions of gray balance dot area in the four key areas, namely the highlight zone, 1/4 tone zone, 1/2 tone zone, and 3/4 tone zone. The gray balance dot area ratio is very strict and must be controlled. accurate. Dark tone due to the black version to join more, the ratio of the three primary colors gray balance area is not very strict, but it should pay attention to the black version of the network area settings and processing.
Gray balance correction of manuscripts
After mastering the gray balance data, the operator can not only perform a quick and convenient scan, but also can effectively correct the color of the manuscript, as long as the grey tone of the manuscript is gray balanced during the correction, there is no need to worry about the correction after the correction. The opposite color shift phenomenon occurs.
When correcting the color shift of the original document, it is necessary to first analyze it correctly, determine the degree of color cast of black, white, and gray in the original, and the distribution area of ​​color cast. In general, there is a general color cast and partial color cast in the original document. Therefore, different color casts of the original should be handled in different forms.
1. High-bright white tone correction
High-gloss white (1% to 10%) is required. Most manuscripts have different degrees of color cast. Use high-light dot settings (H%) for scanning equipment or use photoshop Curve for high-light end , According to the proportion of neutral white area ratio correction. Typical neutral white dot area target values ​​are C5%, M3%. The white of the high-light part of the printed image is thus pure white without color cast, and the texture of the white material can be expressed. If the ratio of C, M, Y three-color dot areas is close, it will become a slightly warmer neutral white color, which is also normal. If M, Y is greater than C, then it is easy to color cast.
2. Correcting gray correction
Middle tone gray (35% ~ 65%) color cast, using the middle of the level curve, will be considered that the color of a certain color curve of 50%, according to the neutral gray dot area value adjustment bias. The target value of the curved neutral gray area is C50%, M40%, and Y40%. There are three conditions that should be taken into consideration when adjusting the correction.
(1) Observe whether the dot area value of the color cast portion is close to the original document density value. If the dot area value of the color cast portion is deeper than the original document density, the color cast may be reduced, such as graying, cold, blue, or Shallow C color version.
(2) If the area of ​​the halftone dot area is shallower than the original density, the darker version can be darkened. Such as gray blue purple, you can deepen the Y color version, that is to achieve the gray balance.
(3) When scanning, slightly increase the darkness of the black version, and extend the starting point of the black version from 50% of the C version of the standard curve to 5% of the black version of the C version to 40% of the C version to the 3% of the black version. Point, so that the dark gray tone has a black version, so that gray is more pure and stable.
3. Shadowing black correction
Shadowing (65% to 90%) and dark-darkness (90% to 99%) color cast should be done using the dark tone dot setting (S%) of the scanning device or the UCR underline removal function to correct deviations. During the post-processing, the dark tone of the photoshop curve was used to correct the proportion of neutral black dot area values. The typical neutral black dot area target values ​​were C95%, M88%, and Y88%.
The focus of dark adjustment is the setting and adjustment of the black version. Because the original manuscript, especially the color reversal film, has a darker color cast, the black version that is set to scan according to the normal dark tone is often shallow, sometimes only. About 60%. Therefore, it is necessary to pay attention to deepen the black plate by about 80% during the dark tone setting or post-processing. As for the proportion of the three primary colors gray balance dot area value of the dark tone black part, it is not necessarily very strict, even if there is a large depth of access will not be cast, because there is about 80% of the black version of the overprint, so the print effect can still reach full Black level.
An excellent pre-press image processing staff must use the theory of printing gray balance to guide, strengthen the awareness of gray balance, and develop the habit of observing the target value of gray balance dot area at any time to ensure the correct reproduction of gray, multicolor and color of the original. This not only makes pre-press image processing more consistent with scientificity and regularity, but also facilitates the printing of the back end, and makes the printing quality stable and improved.
Source: Printing Technology