Analysis of color management solutions for newspaper printing
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In the printing of newspapers, usually the layout of the advertising theme is produced by the advertising company. The layout of the news theme is produced by the prepress department of the newspaper. After the printing company obtains the digital files of different layouts, it is printed on the large version and printed on the printing plate. . Since the color decomposition of the prepress process and the color synthesis of the printing process are respectively produced by different companies, there is a lack of communication between them, which makes the entire production process of the color newspaper often lack effective color management, resulting in quality disputes such as color cast and smudging. Therefore, how to effectively manage the color of the newspaper printing process is the focus of every newspaper printing factory.
Problems with newspaper printing
1. Problems in prepress plate making
In the pre-press process, due to the lack of in-depth understanding of color management by some prepress producers, when converting picture mode from RGB to CMYK, Photoshop software's default printing paper printing characteristic file is often used (such as Japan, which is often used). Color 2001 Coated.icc, etc.) is the target property file for color separation. Take Japan Color 2001 Coated.icc as an example, the color space represented by it is very different from the color space printed by newspapers. In the case of a picture that is separated in this case, the color cannot be accurately restored during the printing process. The more obvious drawback is that the total amount of ink specified by Japan Color 2001 Coated.icc is as high as 350%, that is, after the black part of the picture is separated, the sum of the dot area ratios of the CMYK four-color ink is close to 350%. This is not only a waste of ink for newspaper printing, but also a printing failure such as smearing when the paper is delivered due to the inability of the ink to dry in time.
In addition to using the printing property document of the coated paper as the target property file for color separation, some prepress producers also use the printing property document of newsprint (such as ISOnewspaper26v4.icc) as the target property file for color separation. Taking ISOnewspaper26v4.icc as an example, the specified black ink starting point value is 0%, the maximum value is 95%, and the color separation option selects the maximum gray component substitution (GCR). In this case, the color separation picture, after printing, the black ink replacement amount is too much, which tends to cause the density and gloss of the intermediate adjustment and brightness adjustment parts to be lowered, the level loss is serious, and the color saturation is poor. At the same time, due to the large amount of black ink replacement, black becomes the main color, and the domestic newspaper printing factory often uses square dots when coloring and screening the prepress documents, and the dot angle of the CMYK four-color printing plate is set to 15°. 45°, 90°, and 75°, in which the black plate is not arranged in the 45° direction as the main color plate, resulting in a colored portion overprinted by four-color ink, especially in the middle and the bright and bright parts. The grain, which causes the picture to be rough and the layer to be lost.
Therefore, we believe that the default print profile of Photoshop software and the print profile of newsprint are not suitable for use in domestic newspapers for color separation. It is necessary for domestic newspaper printing factories to generate printing characteristic files according to their own process characteristics after printing and calibration, for use in pre-press separation, proofing and setting color block colors.
2. Problems in the printing process
In the actual production process of newspaper printing, because most newspaper printers either have no density meter, or because there are no test strips in the newspaper, or because the printer does not develop the habit of controlling the amount of ink by detecting density, the printing process The control of the amount of ink is mainly based on the long-term experience accumulated by the printing workers. In addition, because photo editors and prepress producers are accustomed to using the color seen by the monitor as a measure of the printing effect, it is always felt that the color after printing is not bright enough. Therefore, in order to meet the requirements of photo editors and prepress producers, some newspaper printers intend to increase the amount of ink in the printing process of newspapers, so that the actual density values of the four basic colors of CMYK clearly exceed the international standard ISO 12647-3 for newspaper printing. And the standard density values of the four basic colors of CMYK recommended by the national standard GB/T 17934.3.
In addition, due to differences in paper, ink, ink and water balance control, etc., there are large differences in the chromaticity values of the newspaper printing basic color CMYK and the intermediate color RGB and the CMYK dot gain value. The dot gain of most newspaper printing houses is 17% to 21%, which is much smaller than the international standard ISO 12647-3 and the national standard GB/T 17934.3.
Color management control for newspaper printing
1. Standardization of printing process
Should newspaper printing adjust the printing process to meet international or national standards as much as possible? According to the characteristics of the printing dot of most newspaper printing houses, if the value of the dot gain is up to 26% as specified by international standards or national standards, it is generally necessary to positively compensate the dot gain in RIP. When the printing plate is output, it is intentionally to increase the dot size of the digital file with an area ratio of 50% to compensate for the shortage of the dot in the subsequent printing process. For documents that have been separated by the printing characteristics of the coated paper, the pre-separation is based on a dot gain of about 15%, and if we deliberately compensate the dot gain in RIP. The actual dot gain of the reprinted file is about 26%, and the intermediate process has more than 10% dot gain, which will inevitably result in the level and loss of the middle and dark levels of the image.
Considering that the actual dot gain of most newspaper printing houses is not as high as 26%, we believe that newspaper printing companies should not compensate the dot gain according to the requirements of the international standard ISO 12647-3 or the national standard GB/T 17934.3. 26%. Instead, CTP linearizes the output plate, that is, 50% of the dots displayed on the computer are output to the plate or 50%, so that the dot gain is 17% to 21% when printing. Under this condition, a test version containing CMYK solid color patches, RGB intermediate color patches, CMY trichromatic overprint patches, and CMYK four-color ladders is printed, which is convenient for later use of newspaper printing property file settings. When printing the test version, refer to the national standard CMYK solid density, that is, the density value of paper white in the T response state (C is 0.94, M is 0.94, Y is 0.90, K is 1.10) to control CMYK. The amount of ink is adjusted in light of the customer's demand and the reproduction of the gray balance until a satisfactory sample is obtained.
2. Setting of newspaper property files
Considering that when printing newspapers, it is difficult to print the color of the picture evenly. If the test characteristic file such as IT8.7/3 on the printed sheet is printed to produce the printing characteristic file, there will be problems such as tone jump, so it is recommended to use CMYK. The test version of the solid color block, the RGB intermediate color block, the CMY three-color overprint color block and the CMYK four-color step ruler, the Lab value of each color block is collected, and the print characteristic file is preferably set by Photoshop. Although this method is less accurate, it can guarantee the continuity and smoothness of the tone change.
The specific steps are as follows: First, the Lab value of the paper white, the CMYK solid color block, the RGB intermediate color block, and the CMY three-color overprint color block on the printed test plate is measured by a densitometer, and the ink shown in FIG. 1 is filled in. Color settings panel. In Figure 2, for the general picture, set the "black version generation" option to "medium", and appropriately limit the black ink replacement amount of the bright adjustment part; the "black ink restriction" option is set to "95%" to ensure the dark adjustment part. There is enough black ink to replace the black version; the "Total ink limit" option is set to "270%", and the actual total amount of ink that can be achieved is about 260%, which can fully meet the characteristics of low speed of domestic web offset presses. Helps the ink to dry in time.
After setting each option according to the above method, the newspaper printing factory can use Photoshop software to generate a printing characteristic file suitable for its own process characteristics, and send it to the pre-press production department of the newspaper for use in image separation. Judging from the use of many newspaper printing factories, when the printing characteristic files set by the above methods are used for production, the overall effect is good, and there is no problem of dark-adjusting paste, printing and smudging, and it is more convenient for the printing operator. Actual operation.