Causes and Solutions of Chromatic Aberration in Image Replication (Part 2)

The color manuscript is color-decomposed into a single-color screen to make a printing plate of different printing methods, and then it is reproduced through the four-color basic color ink (black-Bk, yellow-Y, product-M, blue-C). The tone level and color of the image. Trichromatic inks are colorants for subtractive color images. Its color characteristics have a big flaw. The ink is to be overprinted on the substrate. The surface properties of the substrate and its effect on the color of the ink after it is combined with the ink increase the defects of the ink. Due to the different printing methods, complicated printing processes are required, and the color synthesis will also evolve, which will cause printing color differences.

1. Inaccuracy of color reproduction due to ink color performance and other factors

Ink and printing processes produce different inks or pigments with different color purities, the addition of resins and excipients, and the combined effects of pigment particle dispersion and other factors, which have greater defects in the absorption and reflection of the spectrum, reducing the ink Chromaticity of the color causes defects in the color characteristics of the ink and cannot be compensated by adjustment means. In the CIE chromaticity diagram, the color of the ink colorant is complementary to the three primary color filters used in color decomposition or the three primary color channel colors, and the wavelength distribution position on the chromaticity diagram should be the theoretical equidistant fixed color phase. However, in fact, the color of the ink pigment is much lower than that of the color film transparent pigment, and due to the increase of the gray scale, the color saturation and the deviation of the hue are reduced, the color efficiency of the color mixture is weakened, and the color reproduction of the reproduction color is caused. The error.

2. The main influencing factors of color reproduction in printing process

Different printing methods determine the differences in the printing process. In the printing process, the color inks are stacked one after another, and a variety of different color sequences can be arranged. Such as offset printing, gravure and other different printing methods, and sometimes the same type of printing, the color sequence is not the same, such as the gravure printing and printing. Due to the opacity of the ink, changes in the order of the upper and lower layers of the ink inevitably affect the color appearance after color mixing.

The change in ink supply will affect the thickness and density of the ink layer. Different densities will have different absorption of colored light and the colors will be different.

The pressure of printing will affect the effect of network transfer. Excessive pressure will inevitably cause the expansion of outlets, which means that the proportion of colors will be changed and the reproduction of colors will also be affected.

3. Solution

a. Color difference caused by ink

The color characteristics of the ink cannot be compensated by adjustment methods, but we use a uniform description standard to require our visual effects to standardize the three-primary inks for daily printing with the chromatogram manual that best expresses the approximate standard, so that it can meet our copy requirements. demand. PANTONE chromatography as referenced by printing inks.

b Color difference caused by the printing process

The choice of printing color sequence varies according to different printing methods, but the general principle is that plain printing is usually from light to dark, and gravure printing is the opposite. The factors affecting ink supply include printing pressure, printing plate dot size, ink viscosity, and ink color density. Take gravure as an example, gravure printing has characteristics such as fast and high efficiency, thick ink and vivid color reproduction. The gravure ink supply is mainly determined by factors such as ink viscosity, embossing force, squeegee position and angle, printing plate dot shape, size, and the like. So in the process of batch copying. Keep the same batch of jobs in one hue. Must control the above several aspects of the elements. That is, to maintain the stability of the ink viscosity of the entire production team, the left and right balance of the imprinting force, the moderate hardness of the imprinting roller, the smaller adjustment range of the squeegee angle, and the accurate overprinting, etc., can maintain the color difference to the minimum.

(author/dairy rite)

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