Prepress: The production and application of the black version
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First, the meaning of black and the range of black solid density in printing
"Color is a general term for achromatic and colored." Achromatic color refers to a series of white to black in printing. It refers to the contrast between the maximum whiteness of the printing paper and the effective density of the yellow, magenta, cyan, and black solid ink layers, ie the whiteness of the paper, light gray, medium gray, dark gray, black, sometimes Use the concept of burnt black.
In the non-color series, the ideal white is a completely reflective object. There is no 100% reflection in life. The best coated paper for printing paper has a reflectivity of about 90%, and newsprint has only about 50%. Other printing papers ( Offset paper, letterpress paper, dictionary paper) between the two; the ideal black is an object that completely absorbs the visible spectrum, and the completely absorbed object does not exist. It is printed on coated paper, and the effective density of the four colors is 1.8. Left and right, the general newsprint prints monochrome, the black solid density is 1.0-1.2, the offset paper prints monochrome, and the black solid density is 1.2-1.4. The solid density of the coated paper black is between 1.4 and 1.8. Therefore, it can be said that the black solid density is between 1.0 and 1.8.
Second, the role of the black version in color reproduction
1. Use the black version to enhance the density contrast of the image. According to the current conventional conditions, the effective density of yellow, magenta and cyan primary inks is up to 1.8, and the visual resolution can reach 1.8 to 2.0. The absorption capacity generally increases from 96% to 98%, that is, the effective density of 0.2-0.4 is actually increased, thereby increasing the range of image density contrast, enhancing the stereoscopic effect of the image, the sense of space, and improving the product quality.
2. The black version can stabilize the color of the image. The range of stability depends on the length of the black version of the tone, the longer the black version of the tone, the greater the range of stable colors. Generally speaking, most of the color-based images use the skeleton black version, which mainly stabilizes the dark and dark colors and enhances the image outline. The specific implementation analyzes the characteristics of the image color and tone, and determines the starting point and curve characteristics of the black tone. For black ink-based Chinese paintings and neutral tones, the black tone should be relatively long, but in addition, the black tone is long and the image tones are grayed out. At present, the image plate making software has the function of automatically generating a black version. If the original color tone is standard, the result of color separation and screening is generally in line with the actual problem. The problem is that the original used for plate making conforms to the standard is small, color separation and screening Most of the time must be adjusted, generally paying more attention to the color version, but the black version is ignored. The starting point and gamma 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 color to the middle can be adjusted to adjust the size of the dot area, and the darkness of the net image, especially 75% of the spot point, the adjustment of the area of the kao dot is limited, so a considerable amount of prints are toned The color tone is unstable. From the results of many printing products testing in Beijing (using the same paper, the same ink, the same measuring strip), none of them is an ideal neutral ink, most of which have the highest value measured with green filter, purple 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 warmer, but the actual dark color of most images is cold. Therefore, the black version of the appropriate tone can be used. To stabilize the color to dark tone, overcome the problem of dark warmth and achieve satisfactory results.
3, the black version can enhance the level of the image to the dark tone. Due to limitations in printability conditions and human visual adaptability, the general rule of color reproduction is to maintain a bright tone, with some emphasis; to maintain a moderate or slight compression as much as possible, usually a dark shadow. For example, most of the images are removed from the background, and the three color shades are reduced to a different degree. The amount of dark adjustment is insufficient. In addition, the resolution of the visual contrast is relatively strong, and only the color overlay is used. The medium to dark level is obviously not good, the outline or the line is mixed, and the tone cannot be opened. Therefore, it is necessary to add a black version, and some black versions also need a background color gain, which can strengthen or compensate the level of the dark tone.
4. Images with black ash as the main color, such as Chinese paintings with a long history and self-contained in the field of world art, can also be copied in theory by conventional techniques, but from the color separation, the printing to the printing gray balance are very Hard to master. The product is prone to yellowing, purple or reddish, but it is much more convenient to use the long black version, and the effect is good. If necessary, it is equipped with a special gray version, the copying effect is better, and the Chinese painting style is better. .
5, the use of the appropriate tone of the black version is conducive to printing, but also reduce costs. Black can be superimposed by three primary colors. In the plate making process, the background color removal method (UCR) is used to replace the corresponding parts in the three primary color plates, and the black plate is replaced, which can meet the requirements of image color tone, save color ink and reduce cost. Because the three primary colors of ink are each much more expensive than black ink. Therefore, the black version should be used as much as possible without affecting the quality of the product.
It should be pointed out that quite a few people have insufficient understanding of the role of the black version. The actual black version plays a very important role. It should raise the understanding of the role of the black version and pay attention to the research on the production and use of the black version.
Third, the type of black tone
In color reproduction, the correctness of the black version application 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 black version. The black version is shorter than the three primary color gradations and is suitable for images that are dominated by color or bright colors. The tone of the black version generally starts from the middle of the image, and mainly acts on the contour part of the image to the dark tone, so it is also called the outline black version or the skeleton black version. Mainly to enhance the image contrast, strengthen the middle to dark tone level and stabilize the color. Since the tone of the original is varied, the tone of the short black version has a flat and a shallow depth. When the starting point of the tone is basically unchanged, some of the tones are quite short, and the dot area is about 0 to 5%. Slightly exceeded; some moderate, the area of the dot is about 0-75%; some deep, the dot area can reach 0-95%.
2, the middle version of the black. Generally speaking, it is a black version made according to the conventional ratio, so it is also called a linear black version. It is suitable for manuscripts with both color and non-color, such as landscape paintings, manuscripts with figures in architectural paintings, etc. In order to facilitate the performance of the picture, the tone of the black version can be lengthened according to the characteristics of the original and the requirements of the printability. The starting point of the tone can be smaller than the middle adjustment of the image, the tone is longer than 70%, and the dot area can occupy the whole About 50% of the area of the map.
3, long black version. Applicable to non-color-based, color-assisted manuscripts. For example, Chinese paintings based on ink (focus, thick, heavy, light, and clear) are reproduced in order to facilitate the reproduction of non-color series. The black tone can be made 0-100%, so it is also called full-tone black version. The area of the black dot can account for more than 80% of the whole picture. In addition to the basic color, the tone of the three primary colors should be shortened accordingly. The test proves that a long black version is used. Generally, the yellow and magenta version has a tone of 0 to 50%, and the green version can reach the requirement of 0 to 25%. It is not difficult to implement software functions using the Desktop Publishing System (DTP).
According to the general rule, the black version is divided into three categories. There is no clear boundary in practical application. Only the basic principles and application methods are proposed. The application cannot be used as a hard copy. It should be controlled according to different manuscripts and different printability conditions. To meet customer requirements. Copying images with bright colors and small contrast contrast should be based on the three primary colors. It is better to use the short black version; the copy is rich in color, the color is bright, and the density contrast is moderate. The three primary colors and the black version should be well coordinated. The black version is better for the middle one; copying the image with the non-color occupying the important position will be better with the long black version.
Existing prepress hardware and software, the black version of the tone can be used freely. But be clear: plate making is the means, printing is the purpose. In the plate making process, it is necessary not only to analyze the characteristics of the original, to adjust the shortage of the original, but also to consider the difference in printability (paper, ink, printing, printing process and overall compatibility of the environment), like a set of plates, printed on a single sheet of paper. Printing on machine and coated paper will make the printing effect very good. If you use this set of plates, printing on high-speed rotary presses and general paper (newspaper or offset paper), the printing effect may be poor. Therefore, the latter's plate making should be adjusted, the basic color is relatively more used, the opposite color is less used, the network cable is thicker. Because the opposite color is used less, the black version of the tone will be relatively longer and deeper.