1. The meaning of black and the range of black solid density in printing "Color is the general term for achromatic and colored." Achromatic refers to white to black series in printing. It refers to the contrast range of the maximum whiteness of the printing paper and the effective density of the four-color solid ink layers of yellow, magenta, cyan and black superimposed, that is, the whiteness, light gray, medium gray, dark gray and black of the paper, sometimes Use the defocused concept. In the non-color series, the ideal white is a completely reflective object. There is no 100% reflective object in life. The best coating paper for printing paper has a reflectivity of about 90%, newsprint is only about 50%, and other printing papers ( Offset paper, letterpress paper, and dictionary paper) are in between; the ideal black is an object that completely absorbs the visible spectrum, and there is no object that completely absorbs. Printed with coated paper, the effective density of the four colors superimposed is 1.8 Right and left, general newsprint printing monochrome, black solid density is 1.0-1.2, offset printing monochrome, black solid density is 1.2-1.4. The solid density of coated paper black is 1.4 ～ 1.8. Therefore, it can be said that the density of the black ground is between 1.0 and 1.8. Second, the role of the black version in color reproduction 1. Using the black version can enhance the density contrast of the image. Printing under the current conventional conditions, the effective density of the three primary colors of yellow, magenta, and cyan superimposed, the maximum is about 1.8, and the visual resolution capability can reach 1.8 to 2.0, so the black plate of the appropriate tone is selected to increase the paper The absorption capacity of general absorption increases from 96% to 98%, that is, the effective density is actually increased by 0.2-0.4, thereby increasing the overall image density contrast range, enhancing the three-dimensional sense of the image, the sense of space, and improving the quality of the product. 2. The black version can stabilize the color of the image. The stable range depends on the length of the black tone. The longer the tone of the black tone, the greater the range of stable colors. Generally speaking, most of the color-based images use skeleton black version, mainly to stabilize the medium-dark color and strengthen the image outline. The specific implementation should analyze the characteristics of the image color and tone, and determine the starting point and curve characteristics of the black tone. For ink-based Chinese paintings and neutral tone images, the black tone should be relatively long, but otherwise, the black tone is longer, and the image tone tends to become darker. At present, the image plate-making software has the function of automatically generating a black plate. If the color tone of the original is standard, the result of color separation and screening is generally in line with reality. The problem is that the proportion of the original used for plate making conforms to the standard is very small. Most of the time must be adjusted, generally pay more attention to the color version, and ignore the black version. The starting point and γ value of the black tone should be adjusted according to the characteristics of the original and the printability conditions. Generally speaking, the deviation of the light to mid-tone color can be adjusted by adjusting the size of the dot area, and the dark tone of the screen image, especially 75% of the dots, is limited by the area of ​​the kao dot area, so a considerable number of prints are dark to medium. The color tone is unstable. Judging from the test results of multiple printed products in the Beijing area (using the same paper, the same ink, and the same measurement and control strip), none of them are ideal neutral inks, and most of them use the green filter to measure the highest value, and the purple and blue filter The measured value is second, the measured value of the red filter is low, which means that the dark color of the image is warm, but the dark color of most images is actually cold. Therefore, using the appropriate level of black overlay can be used To stabilize the effect of dark tones, to overcome the warmth of dark tones, to achieve satisfactory results. 3. The black version can enhance the level of dark tones in the image. Due to the limitations of printability and human visual adaptability, the general rule of color reproduction is to maintain bright tones, and some to emphasize slightly; to maintain as much as possible to moderate or slightly compressed, generally compressed dark tones. For example, the background color of most images is removed, and the dark tone of the three color versions reduces the color amount to different degrees. The amount of dark tone is insufficient. In addition, the visual resolution of the dark tone is relatively strong, and only the color overlay is used. , The level of medium to dark tone is obviously not good, the outline or line is falsely mixed, and the tone cannot be pulled apart. Therefore, it is necessary to increase the black version, and some black versions also need to increase the background color, which can enhance or compensate the dark tone level. 4. Images with black and gray as the main tone, such as Chinese paintings with a long history and self-contained systems in the world art field, can also be copied in theory by conventional techniques, but from color separation and screen printing to printing gray balance are very Difficult to master. The product is easy to produce yellow, purple or reddish, and the long-tone black version is much more convenient and the effect is better. If necessary, it is equipped with a special gray version, the reproduction effect is better, and it can reflect the style of traditional Chinese painting. . 5. The use of a black plate with appropriate tone is not only conducive to printing, but also reduces costs. The black can be superimposed by the three primary colors, and the background color removal method (UCR) is used in the plate making. The corresponding parts are subtracted from the three primary colors and replaced by the black version. , Because each of the three primary colors is much more expensive than black ink. Therefore, as long as it does not affect the quality of the product, use the black version as much as possible. [NextPage] 3. Types of black tone In color reproduction, the correctness of the application of the black version directly affects the quality of the product. Therefore, according to the relevant conditions and requirements, the black version should be used reasonably and flexibly. The black version can be roughly divided into three types: 1. Short-cut black version. The tone of the black version is shorter than that of the three primary colors, and it is suitable for images that are mainly colored or have bright tones. The tone of the black version generally starts from the middle tone of the image, mainly in the contour part of the image to the dark tone, so it is also called the outline black version or the skeleton black version. It mainly plays the role of enhancing the image contrast, strengthening the medium to dark tone levels and stabilizing the color. Because the color tone of the original varies greatly, the tone of the short-tone black version is flat and shallow. When the tone starting point is basically unchanged, some of the tone is quite short, and the dot area is about 0 to 5% Slightly exceeded; some are moderate, the dot area is about 0-75%; some are deep brand, the dot area can reach 0-95%. 2. Mid-range black version. Generally refers to the black version produced at a conventional ratio, so it is also called a linear black version. It is suitable for both color and achromatic manuscripts, such as landscape paintings, manuscripts with architectural figures. In order to facilitate the display of the picture, the tone of the black version can be lengthened according to the requirements of the original features and printing suitability. The starting point of the tone can be smaller than the middle tone of the image. About 50% of the map area. 3. Long-tune black version. Applicable to manuscripts that are mainly non-color and supplemented by color. For example, the traditional Chinese painting with ink tone (focus, thick, heavy, light, clear) as the main theme, in order to facilitate the reproduction of the achromatic series, the black tone can be made 0-100%, so it is also called the full tone black version. The dot area of ​​the black version can account for more than 80% of the whole picture, except for the basic color parts, the tone on the three primary color version should be shortened accordingly. The test proves that the long-tone black version is used. Generally, the tone of the yellow and magenta version is 0-50%, and the cyan version is 0-25%. It is not difficult to implement with the software functions of the Desktop Publishing System (DTP). The black plate is divided into three categories according to the general rules above. There are no clear boundaries in practical application. It only proposes the basic principles and application methods. It cannot be applied rigidly. To meet customer requirements. Reproduction of images with bright colors and low density contrast should be based on the three-primary-color version. Short-tone black versions are preferred; images with rich tones, bright colors, and moderate-density contrast should be coordinated. The three primary-color versions should be coordinated with the black version. The black version is better with a medium tone; to copy an image with non-color as an important position, it is better to use a long tone black version. Existing pre-press hardware and software can be used freely in any tone. But be clear: plate making is the means, and printing is the end. When making a plate, not only must analyze the characteristics of the original manuscript, adjust the shortcomings of the original manuscript, but also consider the difference in printability (the comprehensive suitability of paper, ink, printing, printing process and environment), just like a set of printing plates, printed on a single sheet Machine and coated paper printing, the printing effect will be very good. If you still use this set of printing plates, printing with high-speed rotary machines and general paper (newsprint or offset paper), the printing effect may be very poor. Therefore, the latter's plate-making should be adjusted, the basic color tone is relatively sufficient, on the contrary, the color is less, and the network cable is thicker. Because the opposite colors are used infrequently, the black tone is relatively long and deep.
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It should be pointed out that quite a few people have insufficient understanding of the role of black plates. Actually, black plates play a very important role. The understanding of the role of black plates should be improved and attention should be paid to the research on the production and use of black plates. 