Print Image Information Processing - Color Reproduction (2)

(b) Three primary colors of pigments and subtractive colorants

The color material includes a pigment material, and the color material in the ink is mainly a pigment. Pigments are insoluble in water, oil or other organic solvents.

If yellow, magenta, and cyan materials are mixed in "proper" proportions for each of the two colors, the color of the three primary colors of shades (see color image 3) can be obtained.

Yellow + Magenta = Red Yellow + Blue = Green Magenta + Blue = Blue Magenta + Blue + Yellow = Black (BK)

By changing the mixing ratio of the three colorants yellow, magenta, and cyan, various colors can be obtained by selectively absorbing and reflecting color light. However, any two or more kinds of color mixing can not be obtained yellow, magenta, and blue, so the three primary colors of the color material are yellow, magenta, and cyan.

According to the relationship of the color light complementary colors, the hue exhibited by the three primary colors of the coloring material is the effect obtained by subtracting one kind of monochromatic light from the white light and obtaining another kind of color light. By subtracting (absorbing) the three primary colors red, green, and blue light from the white light, the complementary color light, magenta, and yellow that are subtracted from the light are called minus blue, and the magenta is called minus green. Green is called reducing red, that is, yellow, magenta, and blue can also be called three subtraction.

Since the color obtained by the addition (mixing) of the color materials is reduced in brightness, the mixing of the color materials is called a subtractive method.

The color rendering principle of the color subtracting method can also be expressed by the following formula.

Y+M=W-B-G=R
Y+C=W-B-R=G
C+M=W-R-G=B
Y+M+C=W-B-G-R=O (black)
The yellow, magenta, and cyan pigments are mixed together. Blue, green, and magenta light are absorbed by yellow, magenta, and cyan materials, respectively, and they appear black.

As seen in the color image 3, the yellow material and the blue material are mixed to obtain black, and the magenta material and the green material are mixed to obtain black, and the color cyan material and the red material are mixed to obtain black color. When a certain color material is mixed with another color material and appears black, the two color materials complement each other. Therefore, yellow and blue are color complementary colors, magenta and green are color complementary colors, and cyan and red color complementary colors. The complementary color of the colorant appears black, and the complementary color of the color light shows white light. The two are the opposite. However, the three primary colors of the complementary primary color of the three primary colors of light, and the complementary colors of the three primary colors of the colorant are the primary colors of light, and therefore, the light and the color are There is a mutual connection, which has been cleverly applied in the color decomposition of color manuscripts.

(III) Non-color

The colors are divided into non-color and color categories. Achromatic colors are black, white, and various shades of gray from darkest to brightest. They can be arranged in a series, as shown in Figure 3-10. They are called black and white series. Changes from black to white in the series can be used. A gray band indicates that one end is pure black and the other end is pure white. The material reflects all visible light, and the reflectance equals 100% pure white; the material absorbs all visible light, and the reflectance equals 0% is pure black. There are no pure white and pure black substances in actual life. The magnesium oxide can only be approximated as pure white, and the black velvet is close to pure black.

Figure 3-10 Black and White Series

The achromatic color of the black and white series can only reflect the change in the light reflectance of the substance, and the visual sensation is a bright change.

When the surface of the print has a reflectance of 80% to 90% of the radiation of all wavelengths in the visible spectrum, the visual sensation is white. If the reflectance is less than 4%, it is black. White, black, and gray objects are not selective for reflections at various wavelengths of the spectrum and are called neutral features.

(four) color

Colors other than black and white series are called color. Any color is represented by three quantities: hue, brightness, and saturation.

1. Hue

Hue is the most basic feature of color. People call colors such as red, yellow, and green according to hue. Hue is determined by the color of light reflected from the surface of the object to the optic nerve of the human eye. The monochromatic light can be determined by the wavelength of its light. If the color of the light composition is mixed, the hue is determined by the ratio of the light amounts of the various wavelengths of the mixed light. For example, in sunlight, the printed surface reflects colored light having a wavelength of 500 to 550 nm, while the light that absorbs other wavelengths is visually green.

Hue can be represented by the shape of the spectral reflectance curve, as shown in Figure 3-11. Curve A indicates that the hue of the object is green, and curve B indicates that the hue of the object is greenish blue.

Figure 3-11 Hue and hue differences