The basic principle of color reproduction in screen printing (center)

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=k(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.

It can be seen that the yellow material and the blue material are mixed to give a black color, the magenta material and the green material are mixed to obtain black, and the colored cyan material and the red material are mixed to obtain a 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 darkness to brightest. They can be arranged in a series called black and white series. The change from black to white in the series can be represented by a gray band. One end is pure. Black, 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.

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.

The hue can be represented by the shape of the spectral reflectance curve. The curve A indicates that the hue of the object is green, and the curve B indicates that the hue of the object is greenish blue. (To be continued)