Why not use RGB for printing?

RGB is the three primary colors, red, green and blue. The color used for printing is CMYK (cyan, red, yellow and black), and printing is printed by the percentage of these four colors.

Colors can be divided into shades and pigments. Shades are light and pigments are pigments. Color is an inherent property of an object. Color is an inherent spectral expression of an object. Color light is divided into visible light and invisible light. Visible light is red, orange, yellow, green, blue, blue, purple, and white. Invisible light such as infrared rays, ultraviolet rays, gamma rays, radio wavelengths, etc. The color of the object is affected by the ambient light and the physiological characteristics of the person, but its essence is unchanged. The three elements of color are hue, lightness, and saturation. Hue is the characteristic of color, lightness is brightness and saturation is purity. The three elements of color can be represented by a symmetrical cone (please refer to chromatology), the brightest and darkest part The less obvious the color. The three primary colors of shade are red (R), green (G), and blue (B) (used in Photoshop, TV, etc.), the three primary colors of color materials are cyan (C), red (M), and yellow (Y); the three primary colors of shade The mixing of the three primary colors of the color material is the principle of the additive color method; the mixing of the three primary colors of the color material is the principle of the subtractive color method; CMY is superimposed to be black. No matter the color light and the color material can be mixed with other colors through the superposition of the three primary colors, the range of the color light is much larger than the range of the color material, that is, the display range of RGB is larger than the range of CMY, which is why the image of the display looks better than the printed matter. The reason why the color looks good.

Color printing is based on the principle of the three primary colors of the color material to turn color originals into color prints, but it is usually done in four colors: blue, red, yellow, and black. Black was added because it was too difficult to print black and gray (ie neutral gray) with the purity and precise amount of color, so black was added. Color printing in printing refers to four-color printing, namely blue, red, yellow, and black.
Printed matter printing can be divided into four-color, single-color, two-color, spot-color, etc. printing