Black tone setting and print quality
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The setting of the black tone tone directly affects the color effect of the image, the density of the dark tone and the overall copy quality, which plays an important role in improving the quality of the print.
The color image is decomposed and synthesized by color, and should be able to reproduce all the tones of the original image. However, due to the defects of the chromaticity characteristics of the actual ink, the overprinting is insufficient, and the influence of plate making on the compression of the image tonality makes the color and tone reproduction of the color prints less than ideal, especially the density of the dark part of the image is insufficient, resulting in insufficient image contrast; The neutral gray of the color reproduction is also prone to color cast. Therefore, in color printing reproduction, a black version must be added to compensate for the lack of printing and deviation to improve the quality of the printed product.
1. The role of black version in color printing reproduction
1 Increasing the density and contrast of the printed matter, increasing the maximum density from about 1.7 to about 2.0, improving the reproduction and reproduction of the image tone level and color.
2 Stabilize and enhance the color and level of the middle tone to the dark tone, and stabilize the reproduction of the neutral gray.
3 Reduce the amount of color ink, meet the requirements of printability, reduce printing failures, save costs, improve production efficiency and print quality.
4 can also print text. Color printing is developing in the direction of illustration and text. The text in the picture is printed with black ink, which has the best visual effect. It is not advisable to use three-color ink to overprint the text.
2. black version of the coordination settings
In the color separation, the black version should be used in a targeted manner according to the characteristics of the original and the printing conditions.
2.1, short-tune black version: the original tone of the original color is bright, neutral gray black and achromatic level (30%), using a short black version. The short-tone black version starts from the middle tone, and the dark part can increase the density by 0.4-0.7, and the dot area can reach 60%-80%. The effect is to strengthen the tone contrast of the middle tone to the dark tone, emphasizing the most dark tone level, making the level The skeleton, which highlights the outline of the image hierarchy, is also known as the skeleton black version. As shown by the curve 1 in Fig. 1, the steeper the darkness is. It should be noted that when using the short black version, the three primary color version of the layer curve is not removed as a background color.
2.2, the middle version of the black version: medium and dark color, when the area of the decolorizing layer is about half, it is best to use the black version. The black version of the tone can be extended to a high-profile, with a black version at about 20% tone, which can stabilize the medium-tone gray reproduction and increase the darkness of the dark level. The medium black version can increase the density above 0.6 in the darkest tone, and the maximum dot size can reach 80%-95%. The printing density gradation curve is mostly straight, also called linear black version. As shown by curve 2 in Figure 1. When using the medium black version, based on the short black version, a small amount of background color removal is applied to the three primary color plates to reduce the amount of overprinting of the three primary color dots in the middle and dark tone.
2.3, full black version: such as mechanical drawings, Chinese painting originals, the middle and dark tone is mainly based on achromatic level, when the black and gray level is more than 70%, the full black version is also used, also known as the long black version. This kind of manuscript uses a black version from the high-profile of the image, which can stabilize the printing reproduction of the full-tone neutral gray and improve the overprinting suitability of the four-color dot in the dark part. The full-tone black version can increase the density by 1.0-1.5 in the dark tone, and the dot area can reach 85%-100%, as shown by curve 3 in Figure 1. When using the full-tone black version, based on the short-tone black version, the background color removal of the full-order reconciliation (30%-60%) is performed.
If the conditions of paper, ink, printing equipment, etc. are poor, you should use “Bottom Removal” or “Gray Component Replacement”. Since black to color ink replacement is used for the entire tone, a full black version should also be used.
3. the black version of the production
3.1. Generation of black version: The black version signal is not the result of scanning color separation. It should be generated according to the length and depth of the original layer and the overprinting requirement of printing. In the photographic color separation process, the red and green color filters can be used to separate the light, or the amber color filter can be used to form a black plate. In the electronic color separation mechanism process, the black plate is calculated by the three-color separation signal calculation. In the color desktop publishing system, the processing of the black version is different from that of the electric extension. It has a separate black version setting and has the function of separately adjusting the black version. According to the needs of copying, you can arbitrarily adjust the parameters in "Black version generation", adjust the shape of the black version curve, and determine the starting point and ending point of the black version.
And the maximum dot value, etc., the adjustment range is large, the range is wide, can meet the requirements of various types of manuscript copying on the black version.
3.2. The production of black version in Photoshop software: In Photoshop software, the black version is calculated according to the chroma conversion. The black version will have different types due to the different settings of the color separation, as shown in Figure 2. In the case of color separation, the image can be divided into black, gray, black, black, black, black, and black.
We know that if the neutral gray color is represented by a pure black version, it is a Maxium type black version; if it is a neutral gray color by yellow, magenta, and blue, then the black version of the Internet point is 0%, and the black version is None; If the neutral gray color is represented by four colors of yellow, magenta, cyan, and black, the black version of the Internet point size will change, such as Light, Medium, Heavy, and other types of black version.
For example, the color R163G163B163 can be separated according to the following conditions:
When the black version is Light, the color separation result is C40%M33%Y33%K1%:
When the black version is Medium, the color separation result is C37%M30%Y30%K7%:
When the black version is Heavy, the color separation result is C26% M20% Y20% K22%.
Although there is a big difference between the color separation results, the printing results should be similar. The above is the result of color separation for neutral gray color. In fact, the black version also has different effects on the complex color in the image, because the complex color contains gray components, and the gray component also has how to distribute yellow and magenta. The ratio of the ratio of green and black.
4. the black version and the background color removal
As the black tone is deepened and lengthened, in order to reduce the total amount of four-color dot overprinting of the image, a background removal process is required. The removal of the underlying color is only carried out on the three primary color plates, only in the visible neutral gray areas. Areas with high color and high saturation are not removed with or without background color. The amount of background removal can be set separately, but the starting point must be the same. The key is to ensure the printing gray balance of the three primary color plate level curves after the base color is removed.
As shown in Fig. 3, the starting point of the background color removal can be selected at the full tone level point, and the same amount of removal can be played in different tone ranges. In order to make the three primary color plate level copy curve smooth, there is no obvious turning point, and the image level is not flattened. Except for special needs, the removal range should generally be increased with the increase of the amount of background color removal. In particular, when a large amount of background color is removed, the background color removal of the full-tone range should be performed.
5. the conclusion
Color printing needs to use the black version to cover the lack of printing and color cast, improve the density of the middle and dark levels, and stabilize the reproduction of gray balance.
1 The choice of the black version of the tone has both regularity and flexibility, which restricts the printing reproduction of the image tone level (especially the dark tone) to a large extent.
2 Change the length and depth of the black version of the tone, you need to use the short-tone black version as the benchmark to remove the corresponding background color of the three primary color version of the dot-level copy curve.
3 Effectively use the black version, not only to add black to the three primary colors, but to reduce the amount of the three primary colors in the black part, so as to use the black version to open the dark level, and use the black version to enhance the image contrast.
The combination of the black version of the gradation transformation and the background color removal is also an integral part of the image level adjustment and gray balance reproduction, mainly in the dark adjustment.
At present, most electric and desktop operators do not pay much attention to the black version. They do not realize the importance of the black version. As a result, many products are too dark in the black version, causing the image to be dark and dark; the second is that the black version is too shallow. The image has no contrast and no intensity. In fact, using the black version can enhance the image contrast, enhance the dark tone level, make the dark part have strength, and have a strong sense of form, which is one of the keys to enhance the image beauty and improve the image quality.