The modern press and publishing industry has already transitioned from the traditional typesetting and printing to the era of computer laser phototypesetting, especially the appearance of the color desktop publishing system, which has made the development of the printing industry undergo a remarkable revolution. In recent years, the number of color newspapers has been increasing. It provides readers with a strong appeal with colorful colors, authentic pictures, and innovative novels. It meets the needs of readers with a high level of appreciation. However, the quality of color newspapers is currently uneven. Some colors Gorgeous, natural, with distinct layers and accurate overprinting: some have dull colors, low definition, and blurred images. In addition to the effects of inaccurate overprinting and uneven ink color during the printing process, improper pre-press processing, especially incorrect pre-press system parameter settings, is also an important reason. At present, almost everyone adopts the Founder or Huaguang color phototypesetting system, and the image processing is done in Photoshop software. Setting the system parameters correctly is of great significance. In order to set the correct pre-press system parameters in Photoshop, we must first understand the characteristics of color newspaper printing. Newsprint printing, due to its characteristics such as fast aging, large quantity, and relatively low requirements for printing materials, determines that it is different from traditional leaflets in terms of image reproduction tone, ink color rendering, and dot changes due to different printing speeds and printing materials. There are many differences in paper offset printing. 1. The whiteness of newsprint is low Whiteness is a physical quantity used to describe the light reflection characteristics of the paper surface. Most newsprints have low whiteness. On the one hand, printing color shifts will occur due to the color shift of the paper; on the other hand, it will cause problems such as large grayscale of the printed matter, small image contrast, and insufficient saturation. 2. Newsprint has low smoothness Newsprint has a rougher surface and lower smoothness than other papers, especially coated paper. The reduction of printed color pictures is based on dots as the basic unit. The transfer rate of ink on rough newsprint is low, and the restored dots are not complete. The color of the ink is relatively sturdy. 3. Newsprint has poor dimensional stability The main component of newsprint is pulp, which has high impurity content, poor water resistance, and poor dimensional stability of paper. It is easy to cause image misalignment when printing in color. Overprint error occurs. This is a fatal weakness of newsprint and an important factor that is extremely difficult to control in printing and seriously affects the quality of printing. 4. Newsprint is highly absorbent The loose pores between the loose-textured fibers of the newsprint are larger, so the absorption of the paper is greater, and the expansion of the ink on the paper makes it easy to cause blurring and gradation in the dark areas of the image. , Causing severe loss of image dark tone levels. 5. The printed dots increase in value The blanket on the printing machine will be deformed by the printing pressure, which will cause the dots to expand. Because newspaper printing uses highly absorbing newsprint and penetrating drying ink, its dot increase value is 20% -30% higher than that of coated paper. 6. The color gamut of printing ink is small Due to the particularity of paper, the color gamut of color printing is smaller than that on coated paper, that is, the number of colors that can be reproduced is small, and the reproducibility is poor. Because of these characteristics. The color newspapers have some quality problems such as inaccurate overprinting, uncolorful colors, short tone levels, uneven ink color, etc. Combining with practical experience in the past few years, referring to a large number of related books, the author summarizes a set of how to set up the prepress system Parameter method. To strengthen the printing quality of color newspapers. scanning 1. The scanning resolution should be twice the number of network cables. For example, the input resolution of 120 lines / inch network cable output of the imagesetter should be 240 lines / inch. 2. Make color corrections and adjustments in RGB and make fine detail adjustments in CMYK. 3. Proceed appropriately. Because the gray scale of newsprint is large, the image should be properly brightened. Also, because the contrast of the image printed on newsprint is small, the contrast should be appropriately increased for the original with a low contrast. The tone duplication range should be properly compressed to reduce the dots in high-keys and to reduce the tone value in dark-tones. Saturation can be properly increased to improve the purity of color. Separation settings 1. Printing ink settings Select the custom CMYK from the CMYK drop-down menu in the Photoshop menu, as shown in Figure 1. A custom CMYK window pops up as shown in Figure 2; Set the following in the ink options: ①Inks Colors. "Printing ink settings" must first set the "ink color" usually choose one of the Swop (web offset printing specifications) settings. ②Dot Gain increase. The dot gain is also called dot gain compensation. The dot gain value indicates the dot gain value at the time of printing at 50%. Since the expansion of the dots is spread along the edge during printing, the sum of the edges of the dots at 50% is the longest, and the expansion value is also the largest. After the halftone dots are expanded and compensated, the intermediate values ​​of the color separation are reduced more to ensure that the image is not too dark after printing. As the dot gain value increases, the corresponding data obtained by color separation decreases. These reductions are to compensate for the expansion of the dots during back-end printing. The later the dot expansion value is larger, the data should be made smaller during color separation, so that the printing can be just right. ③Color separation options (color separation type GCR, UCR). GCR is an achromatic structure, that is, gray component replacement (Gray Component Replacement); UCR is an under color removal (Under Color Removel). GCR allows black ink to replace color ink in the full tone range. Black Generation provides five processing methods for users to choose from which tone to start black substitution, namely None (no black substitution), Light40% (parts with a tone lower than 40% are not subject to black substitution), Maximum (All black replacement) If the low-key part of the image occupies a large area, some gray components should be properly replaced to reduce smearing and gradation loss caused by excessive overprinting during the printing process. ④The black version is the black version tone. The custom black range curve is shown in Figure 3. The black level allows the user to choose the level change of the black level. The customization in the column of black tone allows users to draw the black shape of the image by themselves, including the starting point, the maximum amount and the degree of change in the middle part. Photoshop has done a lot of research on the tone of the black version because the black version plays an extremely important role in image reproduction. Added black to the YMC three primary colors. This makes the darkest gradation of the printed image generally increase the density of 0.4-0.8, which is to open up the overall contrast of the image, increase the gradation and density of the thick color part, and make the image more three-dimensional. The custom black version has the following rules: If it is a dark and dark mixed color original with half color and half achromatic color, the black version can be used from light adjustment, and the starting point is 20% -30% of the blue version. The dark tone is 80% -90%, and the middle tone needs to be changed according to the specific image. If the original is mainly achromatic and supplemented by color, the black version needs to be used from the bright part, and the darkest part can also be deepened to 100% dots. ⑤ Black Ink Limit (Total InkLimit) represents the maximum value of the sum of four color dots. For newspaper printing, the value is usually about 260%. This value is directly determined by the printing process. If the dot expansion is serious during printing, the value must be small. Otherwise, the dark field part will die and the level will be lost. ⑥ Total ink limit (Black InkLimit): Different types of originals should have different values. Usually, the maximum value of the electrical separation process is 70%. In color newspaper printing, we often take 85% because this data can ensure that the black field of the printed matter is sufficiently black, that is, there is enough contrast. ⑦UCA (Under Color Addition) Amonunt background color gain: mainly to increase the amount of CMY data in the dark tone. After setting the color separation parameters, it will be processed in Photoshop according to different manuscripts. There is a fundamental criterion to be observed in the processing: to ensure the gray balance during the copying process. Gray balance is to overprint a certain amount of cyan, magenta, and yellow inks according to printing characteristics to obtain a visually neutral gray color, which is called gray balance. At the same time, the percentages of the dots of cyan, product, and yellow are called the gray balance data of the dot. It can be said that, no matter if making a plate or printing, as long as the gray balance of the ink is carefully controlled, it can be regarded as solving half of the problem. Picture 1 Figure 2 Figure 3
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