"UCR" and "GCR" Separation Process (II)

Second, GCR separation process

The GCR is a way to adjust the amount of black ink used to replace the color ink. The essence is to use a Gamma curve to control the black substitution. In this way, Black Generation can be controlled by Black Generation, which is the black highlight. Black Int Limit is controlled by Black Int Limit, so that the black curve can be defined according to special requirements.

(1) Black Generation

a. None Black, only produces CMY image, can make color map saturation, vividness increase, only suitable for special printing requirement.

b. Light is more than 40% gray balance and part of the color ink is replaced with black ink. Because the human eye can easily see the level within the range of 0-50%, the lighter colors in this tone range are protected from black, which is beneficial to enriching the levels within the tone.

c. More than 20% of medium achieves gray balance. The portion of color ink is replaced with black ink.

d. More than 10% of the heavy gray balance that part of the color ink with black ink instead.

e. Maxium replaces all blacks and only produces images on black channels. CMY has no images and is only used for special processes.

f. Custom custom black generation curve. According to the special requirements of the image and the printing conditions, define a curve that can more accurately reproduce the original and more suitable for its own printing conditions.

Black highlights are set according to the different conditions of the image. For extremely dark images, it is easy to produce a large amount of black and further darkens the tone of the image. For such images, the black highlights can be higher, such as 50%-55%, and the black midtones can also be adjusted to help the poles. Dark images normalize. For very bright images, there are few colors, black produces little or no color, and black highlights can be lower, which can increase some of the black in the image.


(2) Black Int Limit (Black ink limit)

It is a dark tone instead of black, which is the darkest value of the black ink allowed by the dark tone. The general setting is 85%-100%.

(3) Total Int Limit

This setting controls the upper limit of the amount of ink that can be printed on the press. It is determined by the type of printer used and the substrate used. The more ink used in principle, the better the resulting image. However, too much ink will also bring some problems, such as increasing the cost, difficult to dry and so on. Normally set to 350%.

(4) UCAUnrer Color Additon Background Gain)

After replacing the color with a lot of black, there will be a dull tone, missing details, and the black ink will lack luster. The background gain can restore some of the colors in the neutral tone region and add some color ink in the dark tone region, typically set to 0-20%.

UCR color separation process is mostly used in traditional electricity production plate making, GCR color separation process is mostly used in desktop publishing system.

The GCR color separation process has many typical application examples in the actual production, and is now being analyzed by the application in Chinese painting reproduction. Chinese traditional Chinese paintings are dominated by ink and wash, ink follows the water, and water follows paper. It is the charm of ink painting. The rational application of GCR color separation process is a good reproduction of the traces of ink flow and the rich changes in ink color. In the reproduction of Chinese paintings, applying the GCR process, first of all, it is necessary to determine the appropriate total ink volume and black ink volume so that the printed matter can reach a certain range of density requirements to fully accommodate the rich levels of changes in Chinese ink painting. The determination of the total amount of ink and the amount of black ink should be determined after repeated testing according to the performance of the ink used and its printing conditions. In the use of domestic four-color inks and the current printing conditions, the total amount of ink used in the GCR process was 242%; the black ink was 97%; and the gray component replacement amount (black generation) was 53%. With the GCR process, the adjustment of the black level curve becomes even more important when a suitable density range is achieved. Because the gray substitution process reduces the amount of yellow, blue, and green inks, that is, the area percentage of the dots is reduced, the levels of the tones reproduced by the yellow, cyan, and cyan plates are greatly reduced. Therefore, in the GCR process, the black edition not only compensates for the reduction of the ink volume of the three-color edition, but also the good reproduction of the print level must be mainly done by the black edition. The key to the level reproduction of ink painting is the traces of watermarks formed by heavy ink, thick ink, and ink bleeding. However, in the case of color reproduction, heavy ink and dark ink are high-density areas, and the percentage of halftone dots is larger. It is easy to paste the printing version when printing, and the level reproduction is difficult. It is easy to make the heavy ink and dark ink in the printed matter lack level changes and be copied. The blunt black block results in a lack of vitality in the entire picture. Therefore, it is necessary to strengthen the processing of high-density areas. Through Black Generation, as shown in Fig. 5, the adjustment of the dark tone region is used to enhance the level of the dark and intermediate tone region, so that the printed matter can better represent the artistic characteristics of the Chinese ink painting application. The ink marks in the ink painting are in the bright-toned area of ​​color reproduction, and the level of the area will be compressed. If the black version is no longer compensated and strengthened for the level of the area, the ink marks in the original ink will disappear. The ink rhyme of the print will appear exhausted and lifeless. Through the Black Generation, as shown in Fig. 6 , the adjustment of the bright-sounding region makes the level of the light-colored ink rhyme well reproduced, so that the subtle changes formed by the infiltration of ink in the original work are ideally reproduced.

Here are some typical separation settings classified by printed material:
Coated Case Coated Stock
Separation Type Separation Type) GCR
Black Generation: Limit
Black Limit: 90 to 100%
Total Int: 290 to 340% (reel presses lower, sheetfed presses higher)
UCA0 to 10%
Offcoated Stock (Uncoated Stock
Separation Type Separation Type) GCR
Black Generation: Limit
Black Limit: 90 to 100%
Total Int: 270-300% (web press lower, higher sheetfed presses)
UCA0 to 10%
Newsprint (newspaper or letterpress paper)
Separation Type Separation Type) GCR
Black Generation Black Generation): Medium
Black Limit: 90 to 100%
Total Int: 290 to 340% (reel presses lower, sheetfed presses higher)
UCA0 to 10%
Newsprint (newspaper or letterpress) (another method)
Separation Type Separation Type) UCR
Black Limit: 70~80%
Total Ink: 290 to 340% (web presses lower, sheetfed printers higher)

In our actual work, we must apply a good color separation process according to the actual conditions of each picture and the printing conditions in order to better restore the original and produce beautiful and accurate colors.

Source: "Printing World"
Author: Wang Yongmei Yunnan Yuxi Printing Co., Ltd.

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