The use of GCR color separation can bring a lot of benefits to the printing and copying, but there are also deficiencies: Table 1 Separation parameter settings for a typical printing type 1 Dark print density is slightly reduced, gloss is low; 2 Brightness transparency is decreased , Slightly dark; 3 color areas, color and gray level transition area registration deviation occurs when hard or white edge 4 dark tone area color saturation and details are reduced. Therefore, when the GCR process is used, the background color gain (UCA) technology can be used to increase the dark tone of the CMY component of the image and increase the image density, thereby overcoming the defects of the GCR process.
The amount of UCA gain depends on the amount of GCR replacement. For color-originated manuscripts, the UCA gain setting is higher; for neutral-gray images, the UCA gain can be zero; for night-time and dark-dominated images, the inter-tone color is rich and vivid. Fine tune and color, suitable for UCA. The amount of GCR replacement is large, and the UCA gain increases accordingly; otherwise, it decreases accordingly.
4. Black Edition ink limit (Black, nk Limit)
The default value of the black ink limit is 100%. This value is generally reset. The black ink volume setting should be determined based on the combination of factors such as the change in the black level of the image, the limit value of the total ink amount, and the printing conditions.
(1) Color-based manuscripts, with a neutral gray component, and mainly CMY three-color when copied, the black version is only used for stable dark tone color, emphasizing the outline of the image, which is a short tone black version, black ink volume Can be set to 5596-65%.
(2) Manuscripts with moderate light and darkness, when copying, the CMY version has a longer tone, and the black version not only stabilizes the dark tone, but also contributes to the reproduction of the gray balance in midtones. The setting is 65% to 85:6.
(3) Manuscripts with color-dominated and color-aided manuscripts, such as traditional Chinese paintings and mechanical manuscripts, have a neutral gray component of more than 7,096, and have a small color component. When copying, CMY tricolor is used as an auxiliary short-distance, black version. In the light, medium and dark tone all play a role in the black version of the Governor, the black version of the ink can be set at 85% to 100%.
(4) For the same type of image, if the limit value of the total ink limit value is to be decreased, otherwise, the set value must be increased.
(5) Different printing materials, the black ink volume setting is also different The printing setting value is smaller than the offset paper.
5. Total Ink Limit (Tota, Ink Limint, black ink volume such as coated paper total ink represents the sum of CMYK four-color ink dot percentages in the darkest part of the printed image. The total ink volume limit default value is 400%, which is too large Produce printing troubles, dark tone and leveling, image clarity decline; printing process is easy to produce pulling hair, powder removal, and even stripping phenomenon, printing ink drying is bad, easy to produce the back of the dirty phenomenon is not conducive to the form of high pressure wet wet printing Therefore, in order to obtain prints rich in darkness, the total amount of ink must be limited in order to ensure the best reproduction.
The total amount of ink is set to limit, in general, that is, the sum of CMYI<four percentage of dots at normal black point calibration points. The same image is printed using different printing methods, and the total amount of ink is limited. The total amount of offset ink is limited by factors such as printing machine type, paper, ink, and blanket, etc. Generally, the number of dots in the dark tone area is determined. If the dot gain value is large, the total ink volume setting value should be decreased; conversely, if the dot dot volume increase value is small, the total ink volume setting value is increased accordingly.
(1) Printing using imported equipment, due to the high precision of the equipment, the increased value of the printing dots is small, and the total ink amount can be set larger.
(2) Using air-cushioned rubber blankets, the liners are stiff, the printing dot gains are small, and the total ink set value should be too large; if ordinary blankets are used and the liners are soft, the dot gain value is larger, the total ink The volume setting should be small.
(3) The coated paper has good ink absorption, high surface smoothness, low printing pressure, and small dot gain. The total ink volume setting is generally 320:6-340%.
(4) The surface of offset paper is rough and ink absorption is poor, and the printing pressure is relatively large, then the total ink volume setting value is about 300:6.
(5) The newsprint paper has a large amount of ink absorbed and the surface is rough, and a high-speed "wet-press-wet" overprint is required. The dot gain value is large, and the total ink amount setting value is 250% to 280%.
In short, when setting color separation parameters, the image itself and the printing process conditions must be taken into account. Each parameter is related to each other and restricted to each other. The characteristics of the image determine the color separation type, the black version of the tone, black ink limit and UCA value need to be set, and the printing process conditions (printing equipment, ink, paper, blankets and other factors) affect the dot gain value And the total amount of ink restrictions. Table 1 is the color separation parameter settings for typical printing types, for reference.
In addition, the set parameters can be saved and can be directly called when dealing with similar documents.
Qufu Normal University Zhang Jianqing Henan Textile College
Source: Print Technology 2005, 10 (Publishing and Commercial Printing)
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