Analysis of gray balance in the hottest four-color

2022-08-21
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Analysis of gray balance in four-color printing (Part 2)

III. realization of gray balance in color separations

after the establishment of the three primary color theory 150 years ago, there were many methods to eliminate color to gray. At first, Gray was obtained by mixing the same amount of green, magenta and yellow materials, but people found that the result of their superposition was fuzzy brown, not gray. Why? Theoretically, equal amounts of three primary colors are superimposed into neutral gray, but in fact, the ink raw materials are impure. No kind of pigment can completely absorb the three primary colors of red, green and blue in the additive method as theoretically. The presentation of color is the result of absorbing its complementary color. Cyan pigments absorb red light and reflect the complementary color of red to people's eyes. The problem is that the most accurate cyan, magenta and yellow materials absorb different amounts of light. Because the three color materials are not as perfect as theoretically read, it is necessary to accurately calculate the amount of each color material to achieve the ideal neutral gray balance

we use the percentage of error and chromaticity to express the amount of impurities in each eye material. Measure the printed sample with a very precise densimeter. The common hue error and gray scale percentage in silk color printing are: the hue error of yellow deviation products is 2% - 5%, and the gray scale is 2% - 5%; The error of yellow image is 8% - 26%, and the gray scale is 18% - 26%

it was found in printing that even if the ink proportion was accurately adjusted every time, neutral gray was not successfully superimposed every time. Black cannot be obtained by simply mixing a certain color with its complementary color. To solve this problem, printers use color ink to print black with tone changes, just like the CMYK color map we use today. The disadvantage of adding black to the color is that it can't accurately copy the tonal part of each color, and the tonal part in the color separations tends to be black without color components. Most prints don't care about this loss, but artists and designers will argue about the matching of colors

IV. gray scale printing

in order to measure the accuracy of color separations, some rulers need to be printed as reference standards. The three key scales are the field scale, the lightest ink scale and the neutral gray scale. If these three scales are not printed on each printing sheet, it is like shooting in the dark. You don't know whether the color deviates or is balanced

a good printer often checks against the printing color code. If the ink matches the printed sheet, and the ink color is correct and consistent with the gray ladder color code, the image reproduction is good

the choice of ink and printing color sequence will affect neutral gray and color balance. Neutral gray is the skeleton of the color separations, and all color printing should be based on neutral gray

in order to obtain gray balance, three characteristics of ink should be considered. The first is the color of ink. Any two sets of three primary color inks will not be exactly the same. If the ink is not measured during color separation, the printing will definitely encounter the problem of color matching. If the color separation volume is the same, take out the seal to be printed, let the color separation worker see it, and measure the color density. Do not change the brand of the ink after the color separator is finished, unless it has been measured with a color divider and a reflection densitometer to ensure that the replaced ink is consistent with that on the sample. The second is the color density of ink. The uniformity and blackest degree of the printing gray scale depend on the color density of the ink. The density of each color ink should maintain the correct relationship to obtain the neutral gray balance

the optical density of the blackest part in the color separation sheet is 2.0, that is, almost 99% of the light irradiated on this part is absorbed, and the density of the blackest part in silk printing is greater than 2.0. When the color increases, its density conforms to a logarithmic relationship, that is, after the superposition of two colors with density of 1.0, the density is not equal to 2.0. In order to obtain an ideal gray scale, it is recommended to use the following range for the density of each color: Yellow 0.85--1.0 product 1.15--1.3 green 1.25--1.4 black 1.35--1.6

select the density range according to the ink used. If the density is set low or high, the density of the ink should also be low or high. When each color is superimposed and printed, the final density is nearly 2.0. If the density of each color is different, the color of the ladder will be biased. The color density of that color is high, and the gray ladder will correct the deviation to that color. For example, the green density is 1 45, then the color of the gray ladder rule tends to cyan. If the density of a certain color is low, the gray scale color will be biased towards the complementary color of that color. If the density of cyan is too low, the gray scale color will be biased towards red or orange

the final influence on the balance of ink characteristics is the transparency of the ink. If the transparency of the ink is not good, the gray scale wine will show the colors superimposed in turn. To a good three primary color ink is very good. If you save money on buying ink, it will cost time and money on Printing adjustment

the public benefit of non colored gray balance is that the color of the tone part is completely eliminated. In order to make up for this defect, it is recommended to print black patterns first, and then print color ink on the black. This can have two advantages. First, it provides a black background for the tone part, on which the color ink looks more natural. Second, for UV ink printing, the coverage of black ink is small. Printing black first. The color displayed on the imitation dial of this kind of experimental machine can reduce moire. If black is on the top, the image looks rough and unbalanced compared with other colors

v. in order to optimize the industrial structure and version variables,

it is very important to play with the version in order to obtain a good gray ladder. A good printing plate should be able to print the smallest point, with correct ink accumulation and accurate registration

anqing first built a first-rate industrial carrying platform to print 65 line halftone images, with light peaking of 5% and dark setting of 95%. To obtain the gray balance of the highlight part, the ink percentage is y=5%, m=5%, c=8%, which means that if you want to print 5% dots, otherwise yellow will be lost with red gray, the balance will be destroyed, and the color of the ladder ruler will be biased towards cyan

the selection of silk is very important. The more we know about the silk lattice parameters, the easier it is to select silk for color image printing in a certain range of tones. The number of wire mesh, the size of wire diameter, and the form of wire braiding are the physical characteristics of the wire. They determine the thickness of the whole wire and the porosity of the wire. They affect the printing and ink transfer at the minimum point. The color of death affects the quality and time of general exposure. The photosensitive film is also very important

if the variables of silk and plate are controlled correctly, a good color separation effect can be obtained. Make some color codes on the variable surface of the printing material, and you can check whether the minimum point is highlighted. The 65 line/inch halftone image is printed with 355 line/inch plain woven silk with a wire diameter of 34 microns, and the polished part point is 4%. The smaller the wire diameter, the smaller the dot coverage. Of course, it is still necessary to print color codes on the printing materials, otherwise you will not know whether all the inks to be printed have been printed

VI. conclusion

in color separation, it is the key to correctly grasp the gray balance color reproduction. Each set of three primary color inks and color separation chips correspond to a gray balance state. Indiscriminately transforming them into impact ink brands and colors will destroy the entire color balance and gray balance of the image. Keep in touch with color separation to ensure the relationship between ink density and several colors of ink, which is the key to achieve gray balance. If the gray balance is not well mastered in color separation, all work such as silk plate making, moire control, dot expansion, etc. will be in vain. Each piece should be printed with a color code with light, dark and gray gradient changes, which is only necessary for printing high-quality images

information source: silk printing

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