1. Basic principles of color expression
All colors in nature are produced by light.Depending on the wavelength of light, the human eye perceives colors differently.The rainbow after the rain is the most peculiar natural phenomenon, the rainbow in the red orange yellow green blue purple is people can feel the color range.The sequential appearance of 7 colors in the rainbow and the transition color between each color is a typical way of color expression.
People often encounter examples of color expression in their daily life, such as color coordination in painting, color in the picture showing natural scenery in TV set, color reproduction in color printer, etc. All of these color expressions are based on color theory, namely, color combination of three primary colors.The tri primary method is the predetermination of three basic colors (primary colors) from which all other colors are mixed in different proportions.In this way, it is easier for people to get three basic colors when making various output devices, and all other colors to be expressed can be mixed by these three colors.
In color mixing, it can be divided into additive method and subtractive method.Such as the three basic colors of the television is red, green, blue (RGB), color expression through RGB these three basic colors (color light) to mix into its various colors, that is, the use of color light addition principle.Objects with selective absorption of color light are called colored objects. These objects absorb some color light in white light and reflect other color light at the same time. The color light reflected by this part stimulates the human eye to feel color color.In the printing industry, the pigment subtractive method is used
For the color of the object, people choose green, magenta (for short), yellow (CMY) pigment three primary colors, and through the mixing of CMY
Express other colors.When the light hits the print, the dye absorbs the red/green/blue colors and reflects them back to the eye, so that the corresponding complementary color is perceived as blue/green/yellow.When all three colors are present in the print, the red/green/blue reflected light is absorbed, giving the impression of black.Due to the presence of other chemical components in the pigment, it cannot be very pure. In the print, the black mixed by the three colors of CMY is not pure black. Therefore, a black (K) is added in the printing ink to express the black in the print works.The combination of CMYK four pigments enhances the color effect of prints.
The hue of the color can be achieved by color mixing, but the saturation of the color (color depth) is to use half-tone dot to express.The print is divided into small areas, each area as a dot, according to the color of this area to determine the percentage of ink in this area.When the saturation of the color l, the definition of the proportion of ink is 100%;When the saturation of the color is 0, the ink proportion is 0 %.Therefore, the smaller the dot, the more close to the quality of printed matter.However, the existing equipment is restricted by physical devices, so it is impossible to achieve the ideal goal.The current inkjet printing machine can achieve the accuracy of 70 ~ 100 dpi(7O ~ 100 points per inch).In print, the dot accuracy can reach 150-175 dpi.
2 ink jet printing machine color expression problems
Inkjet printing machine color expression is also extended by the printing industry four-color CMYK mixing principle and half-tone screening principle, that is, inkjet printing machine prints all patterns are composed of dots, dots can use different density, size and arrangement.If all four CMYK dyes are printed in the same area at different concentrations, they can display different colors and thus express thousands of colors.
Because ink-jet printing machine and printing is completely different, so direct printing industry color expression method to apply to ink-jet printing, there will be a lot of problems.At present, ink-jet printing machine mainly has the following problems:
One, color space problem
Color mixing can be divided into additive color mixing and subtractive color mixing.Additive colors are commonly used in various display devices, such as television and computer screens.Because this is the color of the light felt by the RGB primary color light source directly to the eye.
Subtractive color mixing is usually the way prints are presented.The light first shines on the print, and the CMY primary colors in the pigment selectively absorb part of the color light and then reflect it to the eyes of people. Therefore, the color people feel is the light after reflection, that is to say, some of the light is absorbed by the pigment and cannot be reflected.Therefore, additive mixing and subtractive mixing are complementary.As shown in figure 1, RGB adds mixed colors, and each additional color increases the brightness of the color.CMYK subtractive color mixing, each increase in a color will reduce the brightness of the color.