How to correctly set the prepress system parameters of color newspapers
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The modern news publishing industry has already transitioned from the traditional typesetting to the era of computer laser phototypesetting, especially the emergence of the color desktop publishing system has made the printing industry experience a remarkable revolution. In recent years, the number of color newspapers has increased. It has a strong appeal to the readers with colorful colors, realistic pictures and creative novels. It satisfies the readers' high level of appreciation. However, the quality of color newspapers is currently uneven. Gorgeous, natural, well-defined, accurate overprinting: some are dim, low definition, and blurred images. In addition to the effects of inaccurate overprinting and uneven color of the printing process, improper prepress processing, especially the pre-press system parameter setting is also an important reason.
At present, almost everyone uses the Founder or Huaguang color photo system, and the image processing is done on Photoshop software. It is of great significance to correctly set the system parameters. To set the correct prepress system parameters on Photoshop software, you must first understand the characteristics of color newspaper printing.
Because of its fast time-consuming, large quantity, and relatively low requirements on printing materials, newsprint printing determines its traditional leaflets in terms of image reproduction, ink coloring, dot changes, etc. due to different printing speeds and printing materials. There are many differences in offset printing on paper.
1. News paper has low whiteness
Whiteness is a physical quantity used to describe the reflective properties of a paper surface. Most of the news paper has low whiteness. On the one hand, it will produce printing color cast due to the color cast of the paper; on the other hand, it will cause problems such as large gray scale of the print, small contrast of the image, and insufficient saturation.
2. Newsprint has low smoothness
Newsprint is much rougher than other papers, especially coated paper, with low smoothness. The reduction of the printed color picture is based on the dot as the basic unit. The ink has a low transfer rate on the rough newsprint, and the restored dot is relatively incomplete.
3. Newsprint dimensional stability is poor
The main component of newsprint is the slurry, which has high impurity content and poor water resistance, and the dimensional stability of the paper is poor. It is easy to cause image misalignment during color printing. An overprint error is generated. This is an Achilles heel of newsprint and an important factor in printing that is extremely difficult to control and seriously affects print quality.
4. News paper is highly absorptive
The capillary pores between the loose fibers of the news paper are relatively large, so the absorption of the paper is large and the expansion of the ink on the paper makes it easy to cause the dots to be smeared and graded in the dark portion of the image. , causing serious loss of image darkness level.
5. Printed dot gain value is large
The blanket on the printing press is deformed by the printing pressure, causing the dot to expand. Because newspaper printing uses absorbent paper and osmotic ink, the dot gain is 20%-30% higher than that of coated paper.
6. The color gamut of printing ink is small
Color printing Because of the particularity of the paper, the color gamut of the ink is smaller than the color gamut on the coated paper, that is, the number of colors that can be reproduced is less reproducible.
Due to these features. Some color problems such as inaccurate overprinting, inconspicuous color, short tone level, uneven ink color, etc., combined with years of practical experience, refer to a large number of related books. The author summarizes a set of how to correctly set up the prepress system. The method of the parameter. To enhance the quality of color newspaper printing.
Scan
1. The scan resolution should be twice the number of hanging lines. If the screen is 120 lines/inch, the input resolution should be 240 lines/inch.
2. Make color corrections and adjustments in RGB Make subtle detail adjustments in CMYK.
3. Process properly. Since the gray scale of the newsprint is large, the image should be properly illuminated. Moreover, since the contrast of the image printed on the newsprint is small, the contrast of the small contrast is appropriately increased, and the tone copying range is appropriately compressed to appropriately reduce the halftone dot in the high key, and the halftone tone value is lowered in the dark tone. The saturation improvement treatment can be appropriately performed to improve the purity of the color.
Color separation setting
1. Printing ink setting
In the Photoshop menu, select the custom CMYK from the CMYK drop-down menu, as shown in Figure 1.
Pop up the custom CMYK window as shown in Figure 2;
Set the following in the ink options:
1 ink color (Inks Colors). The "ink color" is first set in the "printing ink setting". Usually one of the Swop (web offset printing) settings is used.
2 dot gain (Dot Gain). The dot gain is also called the gain gain of the dot gain compensation dot, which means that the dot is 50% in the middle, and the dot gain value at the time of printing. Since the enlargement of the dot is spread along the edge portion at the time of printing, the edge of the dot at 50% is the longest and the enlargement value is the largest. After the dot gain is expanded, the value of the color separation is reduced in the middle to ensure that the image after printing is not too dark. As the value of the dot gain increases, the corresponding data obtained by the color separation is reduced. These reductions are meant to compensate for the expansion of the dot size during the back end printing. If the value of the dot gain in the back is large, the data should be made smaller when the color separation is performed, so that the printing can be just right.
3 color separation options (separation type GCR, UCR). GCR is a non-colored structure, that is, Gray Component Replacement; UCR is Under Color Removel.
GCR allows black ink to replace color ink in the full tone range. Black Generation provides 5 processing methods for users to choose from which tone to start black substitution, namely None (no black substitution), Light40% (the part below the 40% tone is not black substitute), Maximum (All black substitutions) If the low-profile portion of the image occupies a large area, a partial gray component replacement should be appropriately set to reduce the drag and gradation loss caused by excessive overprinting during printing.
4 black version produces the black version of the tone. The custom black version range curve is shown in Figure 3. The black version of the tone allows the user to choose the black version of the tone change. The customization in the black tone tone column allows the user to draw the black version of the image to include the starting point, the maximum amount, and the degree of change in the middle portion. Photoshop software 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. Black has been added to the YMC three primary colors. This makes the darkest level of the printed image generally increase the density of 0.4-0.8, which is to open the overall contrast of the image, increase the layer and density of the thick color part, and make the image more stereoscopic. There are the following rules in the custom black version:
If it is a dark and dark mixed tone original of color and achromatic color, you can use the black version from the light, starting at 20% - 30% of the green version. The dark tone is between 80% and 90%, and the midtones need to be changed according to the specific image.
If it is achromatic, the color is the auxiliary, the black version needs to be used from the bright part, and the darkest part can be deepened to 100%.
5 Black InkLimit Indicates the maximum value of the sum of the four color dots. For newspaper printing, the value is usually about 260%, which is directly determined by the printing process. If the dot is enlarged during printing, the value must be small. Otherwise, the dark field will be dead and the level will be lost.
6 Black InkLimit: Different types of originals should have different values. Usually, the maximum value of the electric 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 black enough, 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.
After setting the color separation parameters, it is also processed in Photoshop according to different originals. Follow a fundamental guideline in your processing: ensure gray balance during the copying process. The gray balance is to superimpose a certain amount of cyan, magenta, and yellow inks according to the printing characteristics to obtain the visual neutral gray color, which is called achieving the gray balance. At the same time, the percentage of dots of green, yellow and yellow is referred to as the gray balance data of the point. It can be said that regardless of the plate making or printing, as long as the gray balance of the ink is carefully controlled, it is half the problem solved.