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What are the shortcomings of traditional four-color printing technology?

People's recognition of natural scenery, always inseparable from the shape and color. Natural scenery can not be directly printed copies, must be converted with the help of the conditions, the shape and color recorded in the light-sensitive materials and other planar media, the formation of color analog, or recorded in the CCD and other optoelectronic conversion devices, directly generate the color of the digital quantity. Plane media generated on the color analog, and ultimately still need to use scanners and other equipment, which will be converted to digital quantities, in order to be accepted by the computer software for printing and reproduction processes.  In terms of color reproduction, what is reproduced, is broken down into two parts, the color component and the neutral gray component. Breaking down color in this way simulates the way the human eye visually perceives color, with the optic rod cells perceiving light and dark and the cone cells perceiving color. The color perceived by the external color that produces a stimulus to the human visual system is a combination of color lightness and darkness and the degree of color perception. In color, stereoscopic perception is mainly described by the neutral gray component.  The color displayed in a natural scene is perceived in the visible color gamut. When they are reproduced, the realism of the color suffers because of the limitations of the range of the color gamut of the light-sensitive material or the performance of the photoelectric conversion device. When the color digital quantity is printed and reproduced, the ink printing gamut range will make the color space compressed again, and the color separation algorithm will make the color tone characteristics change. Conventional four-color printing gamut area is less than half of the visible color gamut, so the printed color and the visible color gamut compared to the color, often appear gray, more loss of color gradation compression. Printing color gamut range can be determined in the CIE Yxy system, but also in the CIE Lab system.CIE Yxy spectral color map CIE Lab system schematic diagram Due to the limitations of the ink pigment and production process, four-color printing using the C, M, Y, K base color ink printing the spectral curve of the color rendering, and the ideal color spectral curve has a large gap. Ideal ink and the actual ink spectral reflectance curves are as follows: yellow ink magenta ink cyan ink ink ink overprinting of the secondary color CM, CY, MY color rendering effect, especially blue and green, and the ideal color gap is even greater. Magenta and cyan ink overprinting of blue yellow and cyan ink overprinting of green magenta and yellow ink overprinting of red with the existing ink production process, significantly improve the performance of ink, leaving little room. Therefore, four-color printing color gamut is difficult to have a great expansion.