Background color removal application
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The black color printed in the past four colors does not replace the part of the gray that is moderately synthesized by the three primary colors, except that a black color is superimposed on the three primary colors. This type of printing is on a monochrome or two-color offset press, and the printing speed is not too fast. If it can be adapted, in today's four-color high-speed offset press, under the wet and wet printing conditions, it is not suitable. In the dark adjustment area, four ink color overprints, the total dot area coverage rate can be as high as 360% or more, especially the third and fourth colors of the post-printing, in the case that the ink of the previous color is too late to be fixed, and then printed again. Going up, when the next printed blanket and the stamp are imprinted, the ink printed on the first sheet of the sheet is likely to be transferred from the surface of the sheet to the ink in the direction of the ink transfer, in the latter one. Serious ink interference in the ink results in contamination of the picture color, which is called reverse transfer. The high coverage of the four color inks is overprinted in today's high-speed four-color wet-wet conditions, forcing people to re-examine the role of the black version. The under color removal technology is promoted in this case.
First, the definition of background removal
The so-called background color does not refer to the black color of the three primary colors, but also the black component contained in the color. From the printing point of view, any color, as long as its brightness is not the highest, or it has a certain degree of darkness, then it must contain a certain black component, this black component is the background color of this color. Any part of the base color overprinted by the three primary colors is replaced by black, which is the background color removal, expressed as UCR (under color remove).
According to the color mixing law of subtractive color method, any two primary colors of the three primary colors yellow, magenta, and cyan are overprinted, and the hue of the generated intermediate color is necessarily the complementary color of the third primary color. According to the law of complementary color, once the third primary color is overprinted with the previous color, it will inevitably produce a neutral black gray. If the coverage of the three primary colors is not equal, then three equal amounts of overprinting, limited to the lowest of the three equals, can be separated therefrom. The result of these three equal amounts of synthesis must be neutral black gray, which is the ground color.
Second, the analysis of the amount of background removal
In the case where the coverage of the three primary color dots is not equal, the background color analysis map of the color synthesized by the three primary colors is superimposed.
First, the coverage of the dot area of each color version of the three primary colors is 25%, and they are equally synthesized into gray. The remaining 65% yellow and 55% magenta are combined into orange-red. The composite color is equivalent to this orange red and 25% gray, so the brightness of the orange color of the three primary colors is not very high.
In this case, the coverage of the dot areas of the two primary colors is equal and low, and the coverage of the dot area of the other primary colors is higher, as shown in FIG. The area coverage of yellow and magenta is 50%, while that of green is 90%. It can be analyzed in this way, 50% of the dot area is also taken out from Qingzhong. At this time, yellow, magenta and cyan form a medium blackness with 50%, and 40% of the cyan is left with this background. In the end, the final result is a dark blue color.
It can be seen from the analysis of the above two cases that the composite color which is synthesized by the three primary colors necessarily contains the ground color, and the synthesized color is the color with lower brightness, and the single primary color and the intermediate color do not contain Background color.
After the ground color is removed, since the coverage of the three color dots is simultaneously reduced, the total coverage of the dot area per unit area is greatly reduced. From the point of view of improving the printability of wet-wet inks, it is advantageous to reduce the total area coverage, but the lower the total coverage, the better. The substrate used now - the surface of the paper cannot be very smooth, always with pits and capillary holes. When the surface of the paper is covered with ink, the ink must first be filled with the recessed holes and the capillary holes, and then a smooth ink film layer can be formed thereon. If the total coverage is too low, it is not enough to form a smooth ink film layer. , it will reduce the highest density of colors and the vividness of colors. The advantages and disadvantages of the comprehensive aspects are generally not 100% of the background color removal, but appropriate control of a removal amount, about 50%. If the paper is smooth, the removal can be as much as 60%; if the paper is smooth, the removal can be as low as 30%.
After the background color is removed, the amount of black ink of the corresponding background color is increased to bear the task of determining the color brightness of the original background color. The higher the percentage of background removal, the longer the tone of the corresponding black version.
Third, the positive significance of the removal of the ground color
1. Good tone reduction If the background color is not removed, the total coverage of the dot area per unit area can not be reduced in the dark part of the picture. The background color is generated by the overprint of three colors or four colors, and the dark-adjusted area is almost the real field, although the contrast of the picture is increased, but the level of the dark tone is not available, and the outline of the subtlety is blurred. With background removal, these problems are easily solved. Due to the enhancement of the tone of the black version of the dark-adjusted area, the level of the dark-adjusted area is mainly represented by the black version, so that the level of the dark-adjusted area of the original is well expressed.
2. Better printability In actual printing, when the total coverage of the dot exceeds 300%, the ink transfer condition will be worse, and the dot enlargement and reverse transfer will be more likely to occur; when the total coverage is less than 200%, In addition, due to the microscopic unevenness of the surface of the paper and the influence of the capillary pores, the ink layer exhibits light scattering, which reduces color density and color vividness. In general, it is better to control the total coverage of four-color printing dots between 200% and 300%. This can be done with a base color removal for better printability.
3. More suitable for the production needs of digital proofing
Today's digital proofing uses economical and practical inkjet printing methods. We know that inkjet imaging has higher requirements on paper ink, so the surface coating of proofing paper is particularly important. It must ensure that the paper can absorb a certain amount of ink, but it must maintain a certain amount of ink droplet diffusion. In fact, each proofing paper has a saturation limit of the amount of absorbed ink. When the ink limit is exceeded, the droplet diffusion will Can not be well controlled, resulting in a large amount of ink on the dark side of the image level, which seriously affects the image accuracy. In this regard, some digital proofing management software such as BlackMagic applied the background removal principle to solve this problem. BlackMagic's total dot coverage is generally controlled within 260% (depending on the proofing ink, but slightly lower than the printed one). By successfully applying the background removal principle, the inkjet method is used to simulate the high-line amplitude modulation network. The problem.
In addition, the application of background color removal increases the stability of neutral gray, saves expensive ink and printing ink, and makes the dot enlargement well controlled. After successful application, it will find that its role is far more than this.