Scratch cards are printed in three primary colors (yellow, magenta, cyan) and black by subtractive method. If the printing process of copying the original color with ink other than yellow, magenta, cyan and black ink is used, it should not be called "four color printing", but should be called "spot color printing" or "spot color printing".
A lithography method in which red, green and blue primary colors and black pigments (ink or dye) are used to realize full color reproduction according to the principle of subtractive mixing.
It also refers to the lithographic printing method which uses black, medium blue, brown and green ink to copy maps. It is a common printing method for large scale topographic maps in China, and has a unified color code. The color of each element is specified as follows: black for surface features, outline finishing and annotation; blue for water line, single line River and its annotation; medium blue dot of 100 line / inch for common dyeing part of water; brown for contour line, special geomorphic symbol and its annotation, common dyeing for highway interior; green net line or dot with 100 line / inch for general dyeing of forest.
Defects of four color printing technology
Due to the limitation of pigment and production process, there is a big gap between the spectral curve of C, m, y, K base color inks used in four-color printing and the ideal color spectral curve. The secondary color cm, cy, my color rendering effect of ink overprint, especially blue and green, has a greater gap with the ideal color. With the existing ink production technology, greatly improve the ink performance, leaving some space is not big. Therefore, it is difficult to expand the gamut of four color printing. For a long time, four color printing matches the original density with the printing color density. To measure the printing color density is to measure the amount of printing ink. As mentioned above, the printing color is composed of color component and neutral gray component. Under the condition of limiting the amount of printing ink, if there are too many neutral gray components, not only will the brightness characteristics of the printed image be greatly distorted, but also the amount of color components will be relatively reduced, resulting in the decrease of color saturation. The visual lightness of four-color printing color is close to straight line, which shows that there are too many neutral gray components in printing color. Four color printing emphasizes on enhancing the saturation of copied colors at the expense of color brightness, which is another important defect of four-color printing technology. Compared with the color of natural scenery, due to the above defects, the color reproduction of four-color printing is heavy, the gradient distortion is large, the sense of hierarchy is not real, and the three-dimensional sense is not strong. Therefore, customers often complain that the printing quality is not high. After upgrading to five color printing.
