Color copy printing uses yellow, magenta, cyan, and black four-color dots at different angles for plate printing. The four-color dot pattern that is transferred to the white paper is: in the bright part of the picture. Each color dot is always a combination of side-by-side combinations; each color dot of the intermediate tone portion is formed by a combination of a large number of overlapping small portions in parallel; each color dot of a dark tone portion is almost a completely superimposed combination of dots or dots. In principle, no matter whether it is the overlap of dots or the appearance of dots, the principle of color rendering is the color rendering method.
In terms of multi-color overprinting sequence, no matter what color sequence is used, the tonal reduction of the image's bright-toned part will not be affected at all, and the midtones and shadows will be affected. This is because the midtones and shadows are based on overlapping dots. The ink has different degrees of hiding, that is, transparent yellow. For example, transparent yellow is printed on silver-white aluminum foil. It will turn silver-white aluminum foil into all-yellow aluminum foil. Similarly, the color of the ink film that was first printed on the white paper is covered by the ink film that is printed on it. Ink can not be fully presented, and the ink of the post-printing can be fully presented. This is the coverage of the ink.
Another factor that affects the tone reduction of a color image is that, in a wet-press printing state, the first color ink film printed on the paper will be successively overprinted when the second color, the third color, and the fourth color are overprinted. The rubber roller sticks a part of the ink, and this phenomenon can be on the fourth color rubber roller. Only the third color ink is the least sticky, except that the fourth color ink film is 100% retained on the paper. It can be seen that the third color sequence and the fourth color sequence constitute two extremely important color sequences in the printing sequence. Practice has proved that with the same set of plates, the same paper, the same series of inks, the same type of offset press, the same operator, the same temperature and humidity, all other conditions are the same, due to the different printing sequence, India The print color effect will not be the same. For four-color printing, printing color sequences can be combined into 24 types. If you add a light or brick color, the combination of overprinting color sequences is even more. There are three kinds of overprinting color sequences that are commonly used in actual production. From these three kinds of overprinting color sequence charts, all follow the following principles:
1. For the convenience of color change;
2. The paper has poor smoothness, coarse ink pigment particles, poor transparency, strong hiding power, placed in the first color sequence;
3. Putting black in the first color order is for overprinting;
4. The ink with a small amount of ink is printed first, and the ink with a large amount of ink is overprinted;
5. The ink transparency is good after overprinting.
The above principles are all taken into consideration from factors such as paper, ink, and color change convenience, but less consideration is given to the advantages of tone reduction. There are three major standards for measuring the quality of offset color prints: first, tone reduction; second, tone reduction; and third, overlay accuracy (ie, high image resolution). The reduction of hue is related to the overprinting sequence of the printing in addition to the close relationship with the plate making.