4. Setting of color separation parameters
Using the gray component instead of GCR color separation can determine the black version generation, black version limit, total ink limit, UCA background color gain in Photoshop software, and can arbitrarily adjust various parameters in "black version generation" to adjust the black version curve shape To establish the starting point and end point of the black version, and the range of adjustment is large, which can fully meet the requirements of various types of original copying for the black version.
â‘ Black Generation. There are 5 kinds of black generating function curves to choose from in this setting.
A. No black: there are only C, M, and Y color curves, and no black version is generated. This three-color reproduction process is generally not used, and is only used for special effects. Because the gray of the three-color overprint is unstable, the density of the dark part of the image is insufficient, and the contrast is not enough.
B. Light black generation: C, M, Y three-color overprinted gray and black are removed from the medium to dark tone, the amount of color ink is relatively large, the removed color part is replaced with a long-tone black version, black The start of the edition is at 35%, and the black generation curve is relatively steep.
C. Medium (Medium) black generation: C, M, Y three-color overprinted gray and black are removed from light to dark tones. The amount of tri-color ink is less, and the removed color part is replaced with a long-tone black version. The black version has a larger increase in the dark area, and the starting point is at 20%. This is a commonly used curve.
D. Heavy (Heavy) black generation: It can be seen from the color curve that the gray and black after the three-color overprinting of C, M, and Y have a large amount of removal from bright, medium, and dark tones, and the amount of C, M, and Y color ink Less, while the black version is correspondingly deepened, and works almost throughout the tone. The starting point is 10%, and the black generation curve is closer to the 45 ° diagonal.
E. Maximum (maximum) black generation: The gray and black areas of C, M, and Y overprinting are all removed. There is no color ink, and all are replaced by black ink. The black tone is the most complete and deepest. It plays an important role. The starting point is At the state level, the black generation curve is theoretically 45 ° diagonal.
This all-to-remove method is generally not used because there is currently no one. % Of the black ink density on the ground can reach 2.2 or more, which can not reach the density value of 300% superimposed by the four colors of UCRI art, and even less than the density value of 340% to 360% superimposed by the traditional technology four colors. The printed products are black and light, lack of contrast, and poor visual effects.
â‘¡The total amount of black ink is limited. The set value of the black ink limit will affect the amount of C, M, and Y ink in the darkened area. When the black ink limit value is increased, the amount of C, M, and Y ink will decrease. Conversely, when the amount of black ink is reduced, the amount of C, M, and Y ink will increase. The default value is 100%, and most originals are set to 60% to 70%.
According to the current dot-growing rule of the gravure electro-engraving printing process and the characteristics of the original food and seeds, the black ink limit is preferably set to 60%, that is, the black ink limit value should be lower, and the amount of tri-primary ink should be more.
③ Total ink limit. The setting of the total ink limit is the sum of the C, M, Y, and K color dot values ​​of the normal black calibration point. At present, the total amount of ink for offset printing is generally 320% to 360%, and the total amount of ink for gravure engraving cylinder and plastic film printing is generally 300% to 310%.
5. The difference between GCR and UCR
The gray component replacement and background color removal and replication technologies use black ink instead of color ink, so it is easy to misunderstand that GCR is an extension of the background color removal range, but there is an essential difference between the two.
(1) Different ways of removing color inks The background color removal is to replace the dark colors of the image (background color) with black ink, and the gray component replacement not only replaces the background color with black ink, but also the entire color of any composite color. The colored areas are replaced.
(2) Removal range of color inks Different background color de-reproduction technology The use of black ink instead of color ink is limited to the dark-tone neutral hair area, and it acts on a narrow range near the gray axis of the color space. The replacement method of the gray component will extend the replacement of the color ink to the entire color area containing the gray component, and its action range will extend in the direction of increasing saturation.
(3) The amount of removal of color ink is different. The amount of black ink used to replace color ink for background color removal is generally between 30% and 40%, and the amount of black ink replaced by gray components can vary from 0% to 100%.
(4) The role of the black version The black version 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; Color reproduction of colors, that is, black ink also has a color-forming effect.
(4) Background color gain (UCA)
UCA (Undercolor Add Mon) is another plate-making process. It is opposite to the undercolor removal function, which is to increase the amount of color ink in dark areas.
The background color gain proceeds along the gray axis of the color space, so the effect on neutral gray is the largest and limited to the neutral gray component. The background color gain is controlled by the background color gain intensity and the background color gain starting point (from which level of the original density is the background color gain), which can be used to adjust the gray balance of the dark area of ​​the image and adapt to the color of the dark area The special requirements have played a role in increasing the black level of neutral gray areas.
The background color gain is an effective method for color reproduction of electrical extensions. It can be used to eliminate the color shift caused by the lack of density of one of the three primary colors in the original in the dark and dark areas of the image. It can balance the three colors of C, M, and Y. .
When using SWOP (Coated) ink-paper combination, black generation function Medium, mid-tone dot expansion value of 20%, black ink limit of 100%, and total ink limit of 400%, if the background color gain is changed from 0% to 20 %, You can get the results shown in Figure 4-4-4. It can be seen from the figure that the color ink is used in the dark tone area of ​​the image. When the tone value of the image is lower than 75%, the ink ratio relationship is basically unchanged.
How to apply and store sunscreen
Apply 15 minutes before you go outside. This allows the sunscreen (of SPF 15 or higher) to have enough time to provide the maximum benefit.
Use enough to cover your entire face and body (avoiding the eyes and mouth). An average-sized adult or child needs at least one ounce of sunscreen (about the amount it takes to fill a shot glass) to evenly cover the body from head to toe.
Sunscreen
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