Correct understanding and control of newspaper printing relative contrast

In the fourth national In the printing industry professional skills competition, For the first time, the newspaper printing quality score was evaluated by objective evaluation. The main printing parameters were solid density, gray balance, color difference, dot gain and printing contrast. Among them, the printing relative contrast (K value) is also called printing contrast, which is the ratio of the difference between the solid density and the dot integral density (usually the dot density of the dot area of ​​75% as the dot integral density) to the solid density. The higher the value of K, the more open the print layer is, the greater the visual impact is given. Conversely, the level of print is hierarchical and gives a poor visual effect.

In newspaper printing, there are many factors influencing the value of K. It is difficult for various newspaper printing houses to standardize these factors. Therefore, the K value is not given in the national standard GB/T 17934.3 and the international standard ISO 12647-3. Clear standard values. The author grasped the scoring data of this competition, summarized and summarized the printing data of this competition, and analyzed some K values ​​of newspaper printing in combination with actual cases.

Newspaper printing K value data analysis

1. The normal range of K values

Although the national standard for newspaper printing does not give a standard value for the K value of newspaper printing, there is a general range in the industry. Statistics of the printed data of this competition, the distribution of four-color K values ​​(expressed by probability) are shown in Table 1. From which we know that Under the condition that the number of screen lines is 100 lines/inch and the shape of the dot is circular, the normal range of the K value of the black plate is about 0.2 to 0.4, and the normal value of the K value of the green plate, the yellow plate and the magenta plate is about 0.1 to 0.3. Since the black ink has a large viscosity, when the ink is transferred onto the paper, the outward expansion is small, so that the dot gain is small, and the corresponding K value is large; and the viscosity of the cyan, yellow, and magenta inks is small. When the ink is transferred onto the paper, the outward expansion is large, so that the dot gain is large, and the corresponding K value is small.

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