Color prints differ from monochrome prints in color reproduction. The color on the original is reproduced on the printed sheet by using the relationship between light and color. Color classification and characteristics Color comes from light, and light is accompanied by coloring, and color has a close relationship with light. (1) The three primary colors of colored light and the additive method of colored light Let a beam of sunlight enter the dark room, illuminate the prism through the slit, and then project it onto the white screen through the prism, and then display a light composed of red, orange, yellow, green, blue, blue and purple Band, this band of light is called the spectrum. If the prism is insufficient for the dispersion of white light, you can find that the red, green, and blue colors each account for 1/3 of the spectrum. If we do a series of color light synthesis experiments and find that selecting the "appropriate" combination of red, green, and blue light can simulate various colors in nature, we call red, green, and blue light the three primary colors of color light. In order to unify the chromaticity data, the International Lighting Commission in 1931 stipulated that the wavelengths of the three primary colors of red, green, and blue are: 700.2nm, 546.1nm, and 534.8nm (1nm = 1 × 10-7cm). If the three primary colors of light are added to every two or three, the following colored lights can be obtained. Red (R) + Green (G) = Yellow (Y) Red (R) + Blue (B) = Magenta (M) Blue (B) + Green (G) = Green (C) Red (R) + Green (G) + Blue (B) = White (W) The above formulas show that the brightness of the new colored light obtained by the addition (mixing) of colored light increases, so the mixing of colored light is called the additive color method. By changing the mixing ratio of any two or three colored lights among the three primary colored lights, various colored lights can be obtained. Light is electromagnetic radiation that acts on the human eye and causes bright vision. It has energy. The more the color light is mixed, the greater the light energy and value, and the brighter the formed color light. If the three primary colors of red, green and blue are mixed with cyan, magenta and yellow in equal amounts, white light can be obtained, that is Red light + Cyan light = White light Green light + magenta light = white light Blue light + yellow light = white light When the two colored lights are added to obtain white light, the two colored lights are complementary to each other. Therefore, red light and cyan light are complementary colors, green light and magenta light are complementary colors, and blue light and yellow light are complementary colors. (2) The three primary colors of the colorant and the subtractive coloring method of the colorant If the three colors of yellow, magenta and cyan are mixed in an appropriate ratio, each of the three primary colors can be obtained, namely Yellow + magenta = red Yellow + green = green Magenta + Cyan = Blue Magenta + Cyan + Yellow = Black (K) By changing the mixing ratio of the three colors of yellow, magenta, and cyan, various colors can be obtained by selectively absorbing and reflecting colored light. However, if any two or more colors are mixed, yellow, magenta, and cyan cannot be obtained, so the three primary colors of the colorant are yellow, magenta, and cyan. It can be seen from the relationship of complementary colors of colored light that the hue of the three primary colors of the color material is the effect of another colored light obtained by subtracting a certain monochromatic light from the white light. The three primary colors of red light, green light and blue light are subtracted (absorbed) from the white light, and the complementary colors cyan, magenta, and yellow of the subtracted light are obtained. Therefore, yellow is called blue reduction, and magenta is called green reduction. Cyan is called red reduction, that is, yellow, magenta, and cyan can also be called three subtractive colors. The addition (mixing) of the colorants reduces the brightness of the color, so the mixing of the colorants is called the subtractive color method. The color rendering principle of the color subtractive color method can also be expressed by the following formula. Y ＋ M ï¼ Wï¼Bï¼G ï¼ R Y ＋ C ï¼ Wï¼Bï¼R ï¼ G C ＋ M ï¼ Wï¼Rï¼G ï¼ B Y ＋ M ＋ C ï¼ Wï¼Bï¼Gï¼R ï¼ k （black） The three colors of yellow, magenta, and cyan are mixed together. The blue, green, and magenta colors are absorbed by the yellow, magenta, and cyan materials, respectively, so they appear black. The yellow material and the blue material are mixed to obtain black, the magenta material and the green material are mixed to obtain black, and the cyan material and the red material are mixed to obtain black. When a certain color material is mixed with another color material to appear black, these two color materials are complementary colors to each other. Therefore, yellow and blue complement each other, magenta and green complement each other, and cyan and red complement each other. The complementary colors of the colorants appear black after mixing, and the complementary colors of the light colors appear white after being mixed. The two are exactly the opposite. There is a mutual connection, which has been cleverly applied to the color decomposition of color manuscripts. (3) Non-color Color is divided into two categories: achromatic and color. Achromatic is black, white and various grays from dark to brightest. They can be arranged into a series, called black and white series. The change from black to white in this series can be represented by a gray band, one end is pure Black, the other end is pure white. The substance reflects all visible light, and the reflectivity equals 100% is pure white; the substance absorbs all visible light, and the reflectivity equals 0%, pure black. In actual life, there are no pure white and pure black substances. Magnesium oxide can only approximate pure white, and black velvet is close to pure black. The achromatic color of the black and white series can only reflect the change of the light reflectance of the substance, and the visual perception is a bright change. When the reflectivity of the surface of the printed matter to the radiation of all wavelengths of the visible spectrum is above 80% to 90%, the visual perception is white. If the reflectance is below 4%, it is black. White, black, and gray objects are not selective for the reflection of each wavelength of the spectrum, and they are called neutral features. (4) Color The colors other than the black and white series are called colors. Any color is represented by three quantities: hue, brightness, and saturation. 1. Hue Hue is the most basic characteristic of color. People call colors such as red, yellow, green, etc. according to hue. The hue is determined by the color light reflected from the surface of the object to the optic nerve of the human eye. For monochromatic light, the wavelength of the light can be used. If the color is composed of mixed light, the hue is determined by the ratio of the various wavelengths of the mixed light. For example, under sunlight, the surface of a printed product reflects colored light with a wavelength of 500 to 550 nm, and relatively absorbs colored light of other wavelengths, the printed product has a visual perception of green. The hue can be expressed by the shape of the spectral reflectance curve, curve A indicates that the hue of the object is green, and curve B indicates that the hue of the object is green and blue. 2. brightness Photometrically describe the brightness of a color as the value of light (ie, the energy of light). Can be measured with a photometer. It is generally believed that the reflectivity of the surface of colored objects is high, and their brightness is large. The hue of the two colors of A and B is the same, but the brightness of A is greater than B, so the two colors of A and B are different visually . 3. saturation Saturation (also called saturation) refers to the purity of colors, and the various monochromatic lights that are visible are the most saturated colors. The more white light components doped into the spectral color, the more unsaturated it becomes. The saturation of an object ’s color depends on the selectivity of the surface ’s reflected spectral radiation. The object ’s reflectivity to a narrow band of the spectrum is high, while the reflectivity to other wavelengths is low or no reflection, the saturation of this color high.
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Basic principles of color reproduction in screen printing