The Setting up of the Gradation of Black Plate and the Quality of Press Product LIU Xiao-xia,DING Yi
(shanxi University of Science and Technology, Xianyang 712081, China)
Abrstract: The black plate is used not only in the gray adn black part of pictuer, but also in all the compound color part.Therefore, the sutting up or the gradation of black plate will affect the color effect of press product, thd density fo Shade tone and the quality of duplicating.
Key words: Black plate; Gradation; Under color removal

After the color image is decomposed and synthesized, it should be able to reproduce all the gradations of the original image. However, due to the defects of the actual ink's color characteristics and the lack of overprinting, and the influence of plate-making on the compression of the image tone, the color and tone reduction of the color printing product is not ideal, especially the dark part of the image is not dense enough, resulting in an image. Insufficient contrast; three-color reproduction of neutral gray is also prone to color cast. Therefore, in the color printing and copying, a black version must be added to compensate for the lack of printing and deviations to improve the quality of printed products.

1 The role of Black Edition in color printing reproduction

a. Increase the density and contrast of prints, increase the maximum density from about 1.7 to about 2.0, and improve the reproduction and reproduction of image tone levels and colors; b. Stabilize and enhance the tone and gradation of the midtones to the tone, and stabilize the reproduction of the neutral gray; c. Reduce the amount of color ink to meet the printability requirements; d. At the same time, text printing can be carried out. The text in the figure is printed in black ink, and the visual effect is best. Overprinting text with three colors of ink is not desirable.

2 Black tone settings

In the color separation, the black version should be used in a targeted manner according to the characteristics of the original document and the printing conditions, as shown in FIG.
2.1 Short-tune black version of the original color of the main tone, neutral gray and black tone level (≤ 30%), the use of short-term black version. Short-term black version starts from the middle tone, the dark part can increase 0 density 0.4-0.7, the dot area can reach 60%-80%. Its role is to enhance the contrast between the tone of the intermediate tone and the dark tone, emphasize the darkest tone, make the level of the skeleton, highlight the outline of the image level, as shown in curve 1 in Figure 1. The steeper the darker tone. It should be noted that when using a short tone black version, the three primary color level curves are not removed.

2.2 In the medium- and dark-toned color version of the medium-tone version, half of the tone level area is suitable for the black version. The black tone can be extended to a high profile, and the black version can be used at about 20% tone, which can not only stabilize the reproduction of grey tone, but also increase the sense of darkness. The dark tone in the tone can increase the density in the darkest tone above 0.6, the largest dot up to 80% -95%, and its printing density level curve is mostly a straight line, as shown in curve 2. When using the medium tone black version, a small amount of background color removal is required for the three primary color versions based on the short tone black version to reduce the overprinting amount of the three primary color dots in the dark shades of the mixed tone deletion.
2.3 Fully adjusted black editions such as mechanical drawings and manuscripts of Chinese manuscripts, with a dark tone in the achromatic level, when the dark gray level area exceeds 70%, it is appropriate to use a full-tone black version. This kind of manuscript starts from a high-profile image and uses a black version, which can stabilize the reproduction of full-graded neutral grey prints and improve the overprintability of the dark four-color dots. The full tone black version can increase the density by 1.0 to 1.5 in dark tone. The dot area can reach 85% to 100%, as shown by curve 3. When using the full-tone black version, based on the short-distance black version, the full-scale blend is used to remove more background color (30% to 60%).
If the conditions of paper, ink, printing equipment, etc. are poor, "back-color removal" or "ash component replacement" should be used. Since there is a replacement of color ink for black in the entire tone, a black-tone version should also be used.

3 Generation of Black Edition

3.1 Generation of Black Edition The black version of the signal is not the result of scanning and separation. It should be generated according to the length and depth of the tonality of the original document and the overprint requirement of the printing. In the photographic color separation process, the red and green color filters can be used separately, or the black color plate can be formed by one exposure using an amber color filter. In the electronic color separation mechanism process, the black version is obtained by calculating the three-color separation signal. In the color desktop publishing system, there is a separate black edition setting and adjustment function. According to the need of copying, various parameters in "black generation" can be arbitrarily adjusted: the shape of the black edition curve is adjusted, the starting point and the ending point of the black edition, and the maximum dot value are determined. The scope of adjustment is wide and wide, and it can meet the requirements of various versions of manuscripts for copying.
(To be continued)