Overprint color sequence affecting color image tonal reproduction
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Color copy printing is to use four colors of yellow, magenta, cyan and black to make plate-making at different angles, so that the four-color dot combination transferred to the white paper is: in the bright part of the picture. The dots of each color are always a combination of juxtaposition; the dots of the color of the middle tune portion are combined with the majority of the superimposed small portions; the dots of the color of the dark tune portion are almost completely combined, from the dots or colors In principle, whether the dot is superimposed or the color of the dot is juxtaposed is the principle of color reduction.
In terms of multi-color printing overprinting, no matter what kind of printing color sequence is used, the tone reproduction of the bright part of the image will not be affected, and the affected parts are the middle and the dark. This is because the middle and dark adjustments are superimposed with dots. The inks have varying degrees of opacity, as are clear yellow. For example, a transparent yellow is printed on the silver-white aluminum foil. The silver-white aluminum foil is turned into a full yellow aluminum foil. Similarly, the color of the ink film first printed on the white paper is covered by the ink film after printing. The ink color can not be fully presented, and the ink color of the post-printing can be fully presented, which is the hiding power of the ink.
Another factor affecting the color tone reduction of a color image is that in the wet-pressed printing state, the first color ink film printed on the paper will be sequentially printed when the second color, the third color, and the fourth color are overprinted. The blanket cylinder sticks a portion of the ink, which can be on the fourth color blanket cylinder. Only the third color ink is adhered to the least, but 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 color sequences which are extremely critical in the printing color sequence. Practice has proved that with the same set of printing plates, the same paper, the same series of inks, the same type of offset printing machine, the same operator, the same temperature and humidity, under all other conditions, due to the difference in printing color sequence, printing The printed color effects will not be the same. For four-color printing, the printing color sequence can be combined into 24 types. If you add light or brick color, the combination of overprinting and color sequence is more. Generally, there are three types of overprinting color sequences that are most commonly used in actual production. From the analysis of these three types of overprinting color sequence tables, all of the following principles are followed:
1. Convenient for color change;
2. The paper has poor smoothness, and the ink pigment has coarse material, poor transparency and strong hiding power, and is placed in the first color sequence;
3. Put the black in the first color order for accurate overprinting;
4. The color with a small amount of ink is printed first, and the color with a large amount of ink is overprinted;
5. After the ink transparency is good, the overprint is printed.
All of the above principles are considered from the factors of paper, ink and color change, and the advantages of color reproduction are less considered. There are three criteria for measuring the quality of offset printed color prints: one is tone reproduction; the other is tone reproduction; the third is overprint accuracy (ie, high image clarity). In addition to the close relationship with the plate making, the reduction of the hue is also related to the printed overprinting sequence.