Color separation process II of the hottest UCR and

Color separation process of "UCR" and "GCR" (II)

II. GCR color separation process

GCR is a way to adjust the amount of black ink instead of color ink. Its essence is to use a gamma curve to control black substitution. In this way, the starting point of black substitution, that is, black highlights, can be controlled by black generation. Black int limit is used to control the darkening point of black substitution, so that the black generation curve can be defined according to special requirements

(1) black generation

a.none has no black, only produces CMY images, which can improve the saturation and brightness of color images, and is only applicable to special printing requirements

b.light more than 40% of the color ink reaching gray balance is replaced by black ink. Because the human eye is easier to see the levels within the% stage range, the lighter colors in this tone range are not replaced by black, which is good for enriching the levels within this tone

c.mediumthe part of color ink that reaches gray balance above 20% is replaced by black ink

d.heavy10% or more of the color ink reaching gray balance is replaced by black ink

e.maxium is completely replaced by black, and only images are generated on the black channel. CMY has no images and is only used for special process production

f.custom custom custom black generation curve. According to the special requirements of the image and the printing conditions, I define a curve that can more truly copy the original and better adapt to my own printing conditions

black highlights should be set according to different conditions of the image. For extremely dark images, it is easy to produce a lot of black, which further darkens the image tone. For such images, the black highlight can be higher, such as about 50% - 55%, and the black middle tone can also be adjusted to help normalize the extremely dark images. For extremely bright images, the color is less, black produces little or no color, and the black highlight can be lower, which can increase some black in the image

(2) black int limit

is the darkest point of black substitution, and it is the darkest value of black review allowed by the darkest part of more than 500 domestic and foreign enterprises participating in the exhibition. The general setting is 85% - 100%

(3) total int limit

this setting controls the upper limit of all inks that the printer can print. It is determined by the type of printing machine used and the substrate used. In principle, the more ink used, the better the image produced. But too much ink will also bring some problems, such as increasing costs, difficult to dry and so on. The general setting is 350%

(4) ucaurner color Addison base color gain)

after replacing color with a large amount of black, dull tones will appear, details will be lost, and black ink lacks luster. The ground color gain can restore some colors in the neutral dark areas, and add some color ink in the dark areas, which is generally set to%

in actual production, UCR color separation process is mostly used in traditional electronic plate making, and GCR color separation process is mostly used in desktop publishing system

gcr color separation process has many typical application examples in actual production. Now it is analyzed based on its application in the reproduction of traditional Chinese painting. Chinese traditional paintings are mostly based on water and ink. Ink flows with water, and water changes with paper, which is the charm of water and ink paintings. The reasonable application of GCR color separation process can well reproduce the traces of ink fluidization and the rich changes of ink color. In the reproduction of traditional Chinese painting, using the CR process with working frequency from 80 to 800 kHz like G1, it is necessary to determine the appropriate total ink volume and black version ink volume first, so that the printed matter can meet the requirements of a certain density range, so as to fully accommodate the rich levels of ink color changes of traditional Chinese painting. The determination of total ink volume and black ink volume should be obtained after repeated tests according to the performance of the ink used and its printing conditions. Under the condition of using domestic four-color ink and current printing conditions, the total amount of ink using GCR process is 242%; The amount of black ink is 97%; The substitution amount of grey components (black production) is 53%. After adopting GCR process and obtaining a suitable density range, the adjustment of black version level curve becomes more important. Because the gray substitution process reduces the ink volume of the yellow, magenta and cyan plates, that is, the percentage area of the low point, while the levels of the tones reproduced by the yellow, magenta and cyan plates are greatly compressed. The cutting, measurement and experiment of the sample should be carried out continuously. Therefore, in the GCR process, the black plate is not only to compensate for the amount of ink reduced by the tricolor plate, but also the good reproduction of the print level must be mainly completed by the black plate. The key to the hierarchical reproduction of ink painting is the heavy ink, thick ink and the ink mark formed by the infiltration of ink. However, in color reproduction, both heavy ink and thick ink are high-density areas, and the percentage area of dots is large. During printing, it is easy to paste the plate, and the level reproduction is difficult. It is easy to make the heavy ink and thick ink in the print lack level changes, and it is copied into hard black blocks, resulting in the lack of vitality of the whole picture. Therefore, it is necessary to strengthen the treatment of the level of high-density areas. The dark tone area adjustment shown in Figure 5 is carried out through black generation to strengthen the level of the dark tone area, so that the printed matter can better express the artistic characteristics of ink application of traditional Chinese painting works. The water mark ink in the ink painting is in the bright tone area of color reproduction, and the level of this area will be compressed. If the black version does not compensate and strengthen the level of this area, the water mark ink in the original will disappear, and the ink charm of the print will appear dry and lifeless. The light tone area adjustment shown in Figure 6 is carried out through black generation, so that the level of light ink rhyme can be reproduced well, and the subtle changes formed by ink infiltration in the original work can be ideally copied

the following are several typical color separation settings classified by printing materials:

coated stock

separation type color separation type) GCR

black generation: limit

black limit: 90 ~ 100%

total int (total ink): 290 ~ 340% (lower web printing machine, higher single sheet printing machine)

uca0 ~ 10%

.Offset paper (uncoated stock

separation type) gcr

black generation: limit

black limit: 90 ~ 100%

total int (total ink volume): 270 ~ 300% (web printer is low, sheet fed printer is high)

uca0 ~ 10%

newsprint (paper or relief paper)

separation type color separation type) GCR

black generation black generation): medium

black limit: 90 ~ 100%

total int (total ink volume): 290 ~ 340% (web printing machine is low, single sheet printing machine is high)

uca0 ~ 10%

newsprint (paper or letterpress) (another method)

separation type color separation type) UCR

black black limit : 70 ~ 80%

total ink: 290 ~ 340% (web printer is low, sheet fed printer is high)

improving safety is actually different from improving hardware

in our actual work, we must apply the color separation process according to the actual situation of each picture and the printing conditions, so as to better restore the original and print gorgeous and accurate colors

source: Printing World

Author: wangyongmei Yunnan Yuxi Printing Co., Ltd