Gray balance and dot expansion principle (five)
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4. Setting of color separation parameters
Using gray component instead of GCR color separation can determine the black version generation, black limit, total ink limit, UCA background color gain in Photoshop software, and can adjust the parameters in "black version generation" and adjust the black curve shape. The establishment of the black version of the starting point and the end point, the scope of the adjustment is large, and can fully meet the requirements of various types of original copying on the black version.
1 Black Generation. This setup has five black generation function curves to choose from.
A. No black: that is, only C, M, Y three-color version of the curve, and no black version is generated. This three-color copying process is generally not used and is used only for special effects. Because the gray color of the three-color overprint is unstable, the density of the dark portion of the image is insufficient, and the contrast is insufficient.
B. Light (Light) black generation: C, M, Y three colors after the overprinting gray, black from the middle to the dark tone are removed, the amount of color ink is relatively large, the removed color part is replaced by a long black version, black The version starts at 35% and the black generation curve is steep.
C. Medium black generation: C, M, Y three-color overprinted gray, black removed from light to dark. The color of the three-color ink is less, and the removed color portion is replaced by a long-tone black version. The black version has a large increase in the dark adjustment area, and the starting point is at 20%. This is a commonly used curve.
D. Heavy black generation: It can be known from the color curve that the gray, black, and black tones of C, M, and Y are greatly removed from the light, the middle, and the dark, and the C, M, and Y color inks. Less, and the black version is correspondingly deeper, working almost throughout the tone, starting at 10%, and the black generation curve is closer to the 45° diagonal.
E. Maximum black color generation: C, M, Y three-color overprinting gray, black areas are all removed, no color ink, are replaced by black ink, black version of the most complete, deepest, plays an important role, the starting point is At the state, the black generation curve is theoretically 45° diagonal.
This method of all-in-one is generally not used because there is currently no such thing as 10. The density of black ink in the field can reach 2.2 or above, which can not reach the density value of 300% superimposed by UCRI art four colors, and can not reach the density value of 340%-360% of the four-color superposition of the traditional process, which will result in The printed products are short in black, lack of contrast, and poor visual effects.
2 black ink total limit. The set value of the black ink limit will affect the amount of C, M, and Y inks in the dark adjustment area. When the black ink limit value is increased, the amount of ink in the C, M, and Y colors will decrease. Conversely, when the black ink limit amount is lowered, the amount of C, M, and Y three-color inks will increase. The default is 100%, and most originals are set to 60% to 70%.
According to the current dot enlargement rule of the gravure electro-engraving printing process and the characteristics of the original mainly for food and seeds, the black ink limit is set to 60%, that is, the black ink limit value should be lower, and the three primary color inks should be more.
3 total ink limit. The setting of the total ink limit is the sum of the C, M, Y, K four-color dot values of the normal black field calibration point. At present, the total amount of ink for offset printing is generally 320% to 360%, and the total amount of ink for printing on gravure cylinders and plastic films is generally 300% to 310%.
5. The difference between GCR and UCR
Both the gray component replacement and the ground color removal replication technology use black ink instead of the color ink, so it is easy to misunderstand that GCR is an extension of the background color removal range, but the two are essentially different.
(1) Color ink removal method Different background color removal is to replace the color (base color) of the dark portion of the image with black ink, while the gray component replacement replaces the ground color with black ink instead of the entire color. There are alternatives to colored areas.
(2) Different color ink removal ranges The background color reproduction technique uses black ink instead of color ink to be limited to the neutral hair area of the dark tone, which acts in a narrow range near the gray axis of the color space. The ash component replacement replication method extends the replacement of the color ink to the entire colored region containing the gray component, and its range of action will extend in the direction of increasing saturation.
(3) Different amounts of color ink removal The amount of black ink used to replace the color ink is generally between 30% and 40%, and the amount of black ink replaced by the gray component can be varied from 0% to 100%.
(4) The black version of the black plate with different background color removal is mainly used to enhance the density contrast of the image and stabilize the intermediate tone to the dark tone color; the black version of the gray component instead of the copy technology not only has to bear the reproduction of the picture tone, but also participates in the composite The color reproduction of the color, that is, the black ink also has a group color effect.
(4) Background color gain (UCA)
The under color gain UCA (Undercolor Add Mon) is another plate making process that, contrary to the under color removal function, increases the amount of color ink in the dark-adjusted area.
The background color gain is along the gray axis of the color space, so it has the greatest effect on neutral gray and is limited to neutral gray components. The background gain is controlled by the background gain strength and the background gain starting point (the background gain from the original density of the original). It can be used to adjust the gray balance of the dark area of the image and to adapt to the color of the dark area. The special requirements have played a role in increasing the black version of the neutral gray area.
The background color gain is an effective means of color reproduction of the electric extension. It can be used to eliminate the color shift caused by the insufficient density of one of the three primary colors in the original image in the dark and dark. It can balance the three colors C, M and Y. .
Use SWOP (Coated) ink paper combination, black generation function Medium, intermediate adjustment dot expansion value of 20%, black ink limit of 100%, ink total limit of 400%, if the background color gain is changed from 0% to 20 %. The color ink is used in the dark adjustment area of the image. When the tone value of the image is lower than 75%, the ink ratio relationship is basically unchanged.