High-fidelity color printing finished product quality inspection

In the 1970s, CIE recommended two approximately uniform color spaces and corresponding color difference formulas, namely CIE Lab and CIELuv. L, a, and b in the CIE Lab color space are transformed from the X, Y, and Z in the CIE XYZ color space by a nonlinear cubic root function. The CIE Lab color space belongs to the psychological color space and can be explained by the principle of the Herlin four-color opposition theory. In the a and b two-dimensional coordinates of the CIE Lab color space, +a indicates red, -a indicates green, +b indicates yellow, and -b indicates blue. The lightness of the color is represented by the percentage of L. The foreign experts used 555 pairs of color samples to evaluate the correlation between the ΔE of the Lab color space and the visual inspection results. It was found that the CIE Lab system was 0.72, which is the closest color difference and visual perception in all color spaces, and the Munsell color card The constant hue trajectory and the constant chroma track in the two-dimensional coordinate system of a and b are also very similar. At present, the color industrial sectors such as dyes, pigments, and inks are the first to use the CIE Lab color space. The printing technology research and production departments at home and abroad have also adopted this space successively as color matching and evaluation methods for printing colors.

China has developed relevant technical standards on the application of colorimetric measurement methods. The purpose of the chroma measurement described in the standard is to provide as much as possible the instrument response of the analog standard observer. In printing, colorimetry is mainly used to establish color matching and color standards. The standard specifies the technical requirements for the use of colorimeter measurements and measurement data calculations for CMYK four-color printing substrates, ink colors, tone values, and chromatic aberrations. At present, the standard has not directly specified the related technical requirements for the high-fidelity color printing of the basic color ink beyond the CMYK, nor has it specified the control parameters of the amplitude modulation network above 250 lpi and the modulation value of the FM network.

The domestic high-definition high-fidelity color printing complete set of process technology research unit Beijing Jiaji Tianshi Electronic Technology Co., Ltd. cooperated with experts and users to establish high-definition and high-fidelity color printing process control and finished product quality inspection based on CIE Lab system. Related technical methods. The brief introduction is as follows:

The technology has been successfully applied to the printing industry—Hangzhou Zhongliang Meite Container Co., Ltd., which has obviously improved the product quality, expanded the application range of the products, increased the added value of products and market competitiveness, and has good economic benefits and promotion value. Compared with the conventional four-color 175lpi printed product, the product produced by this technology has distinctly improved image sharpness and improved fine details, and the visual roughness of the overprinted color caused by rose spots is significantly reduced. The color gamut of printing is obviously increased, the printing color is brighter and more saturated, the layers are more abundant, and the three-dimensional feeling is stronger. Under certain conditions, reducing the use of spot color inks, in the printing iron industry technical level, has a certain degree of anti-counterfeiting effect. ”

High-fidelity color printing process control and product quality inspection technology methods, mainly in the CIE Lab color space evaluation of the characteristics of the basic color ink, measuring and displaying high fidelity ink printing color gamut range, color separation printing color gamut range, printing color gradation characteristics, Gray balance characteristics, etc., and the use of simulated Lab three-dimensional coordinate effects, a comprehensive analysis of the hue angle, color saturation and color brightness of the printed color. Through the application of the above-mentioned technical methods, the understanding of high-fidelity printing principles is further deepened, the key control indicators are grasped, and the ability of independently designing color separation models is gradually improved, in particular, the setting and use level of the security color code for the color security model. Printing companies can choose the most cost-effective technology solutions based on the original or user's needs to produce new products. Thanks to the use of colorimetric measurement and control technology, technicians can further enhance the understanding of the nature of color printing and replication, and will have a lasting impact on improving the technology management level and R&D capabilities of companies.