Summary of ash balance knowledge before the most p

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Summary of prepress gray balance knowledge

0, introduction

gray balance is the standard to make printing ink adjust to neutral gray, and it is a kind of adjustment method to solve color deviation. Because the ideal ink and the actually produced ink have different reflection characteristics of different colored light. The nitrogen phosphorus flame retardant scheme has been widely developed and used at home and abroad when trying to print strips. Try printing CMY ink in a certain proportion, and find a match that can correctly restore the RGB image of neutral gray under small deformation conditions. When testing the color enlargement system, a unified negative (neutral gray) should also be used as the basis to make standard gray-scale photos, and then the color matching data should be stored in the computer. This is the grey balance in short. The following is a detailed analysis and level by level description of the definition of grey balance, its composition and role in the prepress printing process, as well as its correction and application

1. What is the grey balance

the process of producing visual neutral gray scale from three kinds of printing primary color inks involves the problem of gray balance, which can be confirmed by films and samples in the process of color separation. In the process of proofing and printing with reference to the swop density standard, the ink dot sizes of the three printing primary colors of printing gray are usually different, and the cyan dot is usually larger than the yellow and magenta dot. In the process of proofing and printing production, the occurrence of point expansion must be controlled, and the size of relative points must be kept the same as that of the original film to maintain the gray balance

gatf/swop proofing control bar has the following values:

first, gray balance

black cyan color yellow

75% 75% 63% 63%

50% 50% 39% 39%

25% 25% 16% 16%

Second, total area coerkge (TAC)

this parameter specifies the total percentage content of cyan, color, yellow, and black in the black area of the printed image. Theoretically, the blackest area should be printed with 400% of the maximum total ink volume. However, in four-color wet overprint, this situation will lead to problems in the actual production operation of the printing machine. The following problems will mainly occur:

1. Reverse transfer of ink - the ink is transferred from the printed web to the next printing unit of the inking system, thus polluting the ink on these printing units

2. Ink drying problem - the temperature in the drying device should be unusually high. A large amount of solvent evaporated, and a large amount of water in the paper can also be removed, resulting in blistering on the surface of the paper

3. Difficulty of overprint -- the ink printed first refuses to print other inks on the top, so that the ink printed later cannot be transferred properly. The post printing ink can be transferred to the unprinted paper surface, but not to the inked surface. The greater the ink coverage, the more obvious the problem caused by poor ink overprint

according to the report of printing industry personnel, the maximum TAC value that can be printed in half tone is 300%. And only one color can be printed on the spot. Under this condition, black objects can be successfully copied

in some small image areas without important details, a slightly higher TAC percentage may also be accepted. But in this case, the TAC value of even small areas (often unimportant) should be less than 325%

tac value should be detected in the heaviest (i.e. darkest) area of film or electronic documents, and each color should be read under the same actual conditions. The measurement points obtained by the film inspector of the publisher and their measurement methods should be determined

III. gray component replacement (GCR) and undercolor removal (UCR)

in the traditional three color process, to replicate a saturated color, chromaticity is often generated by two main subtractive colors. The National Technical Committee for clinical metrology accelerated the formulation of calibration specifications for ultrashort wave medical machines, 2 carbon oxide incubators and other instruments and equipment related to epidemic prevention, Use the third color to increase the grayscale. Although the main drafters of this standard: Jiang bingnian, Kang Jianhua, Bao Junhai, Gong junfan and Yang shiye have been quite successful, there are still some inherent difficulties. First of all, if this gray component cannot be accurately controlled on the printing machine, the color will lose balance. Second, when copying complex colors such as brown, purple, crimson, flesh color and gray, any slight change in the primary color of printing will cause some obvious changes. Therefore, if there are conflicting colors in the online object of the same printer, obtaining the necessary color balance in one area will lead to color offset in another area

gcr is a color substitution technology, which uses gray to replace some or all cyan, magenta and yellow in the process of color separation. Therefore, the GCR process does not need to rely on the third main color to make the color gray or black, but mainly uses black ink to form the general outline and some details of the image, which greatly reduces the possibility of color change. Smaller ink coverage also means that smaller problems occur, and the change of black printing unit can only cause tone change, which is much better than the chromaticity change caused by other changes of ink. Therefore, black ink has the function of controlling color stability. For example, black ink can be used to replace cyan ink in the mahogany area, magenta ink in the green area, and yellow ink in the purple area

traditionally, prepress service providers often use UCR to reduce the total amount of printing ink in neutral shaded areas. UCR has the least influence on gray and shadow depth, and has a greater influence on the second color

the safety range of GCR recommended now is between 50% and 80%. The 50% GCR setting is to remove 50% of the gray components usually printed with color ink and increase the same amount of black ink compensation. When using GCR of 80% or higher, prepress service providers and printing customers must pay special attention to the following points: when using these GCR levels, the percentage of color points on the film is relatively small, which limits the range of color changes. At the same time, higher UCA will also reduce the gloss of dark shadows and black areas, reducing the thickness and details at the same time. UCA increases the amount of color in the black area of the figure

source: Bisheng

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