Color method and subtractive method

The colors in the image are ever-changing and varied. In the printing process, up to four colors are used to copy all the colors in the image. How is this achieved? This is a unique technology in our printing process. Before printing, the color in the image is decomposed and then synthesized in the printing process. In order to understand the color decomposition and synthesis in the image during the printing process, it is necessary to understand the three primary colors of the color light and the three primary colors of the color material.

Color light primary colors

According to Newton's dispersive experiment, when white light passes through a prism, chromatograms of red, orange, yellow, green, cyan, blue, and purple are formed, which indicates that white light is a kind of compound light and can be decomposed.

On the other hand, due to the formation of color and the human eye, according to anatomy, it is known that there are three kinds of optic nerves that respectively produce blue, green, and red sensations on the retina of the human eye. When the above three kinds of rays enter human eyes, the optic nerve is affected. The color is felt by stimuli, which means that the colors seen by human eyes are related to three types of light: blue, green and red.

Experiments have shown that all colors in the natural world can be reproduced according to different proportions of blue, green and red components. So in color science, we call blue, green, and red three-color primary colors.

Using these three wavelengths of light to synthesize all the colors in nature, that is to say, the different colors of objects only include the different combinations of blue, green, and red light. This is the color light addition method.

When two or more color lights are mixed with each other, another method of color light can be obtained, which is called a color light add method.

When the three primary colors, blue, green, and red, are mixed in equal amounts, they can be respectively obtained with higher luminance of blue (C), magenta (M), and yellow (Y) when the blue, green, and red phases are equal. When white is added, white (W) is obtained, and its color equation is as follows: B+G=C, B+R=M, G+R=Y, B+G+R=W.

In each of the above color synthesis equations, any color in the natural world can be obtained by changing the proportion of any one of the primary colors.

Printing is to make full use of the characteristics of the three primary colors of color light, using three kinds of color filters that can only pass blue, green, and red three-color light to achieve the decomposition of all the colors on the manuscript.

Color subtractive method

For printed matter, the human eye must be able to perceive the color of its surface and must be exposed to white light (blue, green, and red) to be seen on the surface of the print. That is to say, when we feel the color on the print, white light hits the surface of the print. Then, through the selective modulation of light on the surface of the printed matter, the modulated light is reflected back into the human eye to produce the impulse of the optic nerve into the brain, and the color is formed by the brain. In other words, the color of the print is the result of the absorption of a portion of the light in the white light. According to the color subtractive principle, we only need to use three types of substances that can absorb blue, green, and red respectively. By controlling the amount of these three substances, we can control the amount of blue, green, and red primary colors, respectively. Achieved object color reproduction. The substances that control the blue, green, and red primary colors are called colorants. It is because they can absorb blue, green, and red primary colors. Therefore, under the white light, these three kinds of colorants reflect or transmit green and red, blue, and red, blue, and green, respectively, and appear yellow to the human eye. Y), magenta (M), and cyan (C) are the complementary colors of the three primary colors of shades of light. Therefore, the three primary colors of coloring materials are called cyan (C), magenta (M), and yellow (Y). This method of synthesizing colors is called subtractive coloring.

Since white light can be simply seen as the result of the equal mixing of blue, green, and red primary light, if we subtract one, two, or three different proportions of primary light from white light, we can also obtain the natural world. In any color. The so-called subtractive color method is a method of subtracting one or two or more primary colors from white light to obtain another color, and we call such a method a color subtractive method. The color subtractive color forming equation can be expressed as follows: C+M=B, C+Y=G, M+Y=R, C+M+Y=K (black).

Printing is based on this principle to complete the color printing. The colorants used for printing are yellow (Y), magenta (M), and cyan (C), ie, Y ink, M ink, and C ink. Among them, Y ink absorbs B primary light, M ink absorbs G primary light, and C ink absorbs R primary light.

Color decomposition and synthesis

In color printing, the reproduction of colors is essentially the process of "decomposition" and "synthesis" of color. Any original, no matter how complex the color on the screen, and how rich the level, from the color science, the color of each point on the screen is a combination of three primary colors in a certain proportion. The color decomposition is to use R, G, and B color filters to separate the colors in each point of the screen from the mixed state, and form a monochromatic image in the distribution of the respective screens. The color synthesis is to use the three monochrome images obtained by decomposition to make a printing plate, and then printing the yellow, magenta, and cyan three-color inks onto the printing materials one after another by printing to reproduce the color images on the original. In these two processes, the function of light and color is indispensable from beginning to end. In lithography, in order to reproduce the colors on the original, the color on the color original is firstly decomposed by means of photographic color separation, electronic color separation, or scanner color separation. The color image on the manuscript passes through the R, G, and B color filters and is decomposed into three separate color pictures of cyan, magenta, and yellow. In the following, we will represent yellow (Y), magenta (M), cyan (C), red (R), green (G), blue (B), white (W), and black (K) eight color blocks to represent the original , and according to the offset printing process to illustrate the color decomposition and synthesis of the printing process.

Four-color printing

In the actual printing, due to the blackness of the yellow, magenta, and cyan three-color inks being superimposed, the darkness is not enough. In order to enhance the blackness of the dark areas of the image, a black plate is added to the printing to print. In color printing, it is not three-color printing but four-color printing. However, the color reproduction requires only three colors of Y, M, and C to be reproduced.