Computer ink color matching system I

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Computer ink color matching system (I)

the hue of ink is one of the key indicators affecting the quality of printed matter. Therefore, the allocation of ink has become an essential process before printing. The basic principle of color matching is based on the theory of color synthesis and color mixing, and the effect of the same color but different spectrum can be obtained by the way of pigment blending. With the development of computer technology, computers can store a large amount of data and have high-speed computing ability. With the help of colorimetric theory, they can process a large number of ink basic data and color values. Color matching through man-machine dialogue is fast and high-precision. Introducing it into the printing field can modernize color management and quality detection

I. ink color matching method

1 Experiential color matching method

experiential color matching method refers to color matching only based on the experience and feeling of the colorist without color measuring instrument. In the early stage, it is based on the experience accumulated by the colorist from practice, and in the middle and later stages, it is based on 10 basic color maps or printing chromatograms as the reference standard for visual color measurement. The empirical color matching method is often affected by the physiological and psychological factors of the colorist and other objective conditions, and the product quality is difficult to maintain stability. In addition, relying on experience and feeling, color matching can only be qualitative, not quantitative, and it is difficult to spread and exchange technology

2. Mechanical color matching method

mechanical color matching method is an advanced color matching method that has gradually become popular in modern times. In each link of color matching, certain machinery and instruments are used as configuration and measurement tools, and curves and charts are drawn as the reference basis for color matching, so that the color matching work can be carried out within a relatively accurate range. This method changes some blindness of previous experience color matching, and improves the speed and quality of color matching, but the accuracy of color matching is low and the error is large

3. Computer color matching method

computer color matching has a history of about 30 years abroad, and has been applied in many color departments at home and abroad. People use the connection between the color database stored in the computer and the relevant color matching software to analyze and process the color data on the sample. Through calculation, correction and color matching, they can select the color formula suitable for the sample that sometimes exceeds the limit requirements, and then complete the automatic color matching of the ink. Computer color matching requires that the colors of standard color samples and matched ink samples are expressed in numbers, which ensures the accuracy and unity of each color matching, and greatly saves the color matching time. Convenience, quickness, rapidity and accuracy are the advantages of computer color matching. However, the color matching software developed by different enterprises and companies is developed on the basis of considering their actual production and application conditions. There is no unified standard, which is one of the reasons why computer color matching cannot be popularized

II. Development and characteristics of computer color matching

1 Development of computer color matching

in industrialized countries, computer color matching system is widely used as a powerful tool for product development, production, quality control and sales in coloring related industries, such as textile printing and dyeing, dye, pigment, coating manufacturing, plastic coloring processing and ink, with a high penetration rate. For example, in recent years, foreign optical instrument companies have developed greinda Macbeth ink formulation software inkformulation 4.0, which can prepare accurate formulations for offset printing, flexo printing, plate printing and rotary gravure printing industries. It has the characteristics of automatic formulation generation and fast multi-channel calculation speed, and can quickly prepare low-cost formulations. The software window interface is friendly, ensuring the accuracy of formulations and the success rate of one-time formulation

in recent 10 years, China has successively introduced various types of color matching systems, but few have achieved significant benefits. The software developed abroad is based on the characteristics of European and American processing industry, and the color quality is relatively stable; Although the domestic processing industry has its own characteristics, the stability of color material quality is relatively poor. In addition, the varieties of color materials are constantly updated, and a large number of new base materials are emerging. However, the existing color matching systems at home and abroad lack flexible adjustment ability, so the practical application of color matching systems has encountered difficulties

Shenyang Research Institute of chemical industry began to study color matching system in 1984. Among them, the thinking color matching Chinese software is the earliest Chinese color matching software in China. With this software system, the total price for matching with domestic machine is 1/3 of the whole system. If matching with imported machine, the total price is 1/2 of imported machine. The system has been used in more than 70 manufacturers, covering many industries related to coloring, such as dye, printing and dyeing, wool spinning, knitting, paint, ink, rubber, wallpaper, etc. In addition, Xi'an University of technology has developed a density computer color matching system using color densitometer and computer online, which is convenient and extensive for popularization and application. From the current development trend, computer color matching has become an important part of ink color matching in the future

2. Characteristics of computer color matching

(1) it can reduce color matching time, reduce cost and improve color matching efficiency

(2) the modified formula can be calculated in a short time

(3) store all the previously prepared ink colors in the database and call them up immediately when necessary

(4) easy operation

(5) the color modification formula and the calculation of color difference are digitally displayed or printed out by the computer, and the final color matching results are also stored in the memory in digital form

(6) other functional systems can be connected. For example, the weighing system can be connected to minimize the weighing error; The reproducibility is improved. If the process flow is continuous, the print quality monitoring system can be set on the print. In case of any abnormal situation, the machine will be shut down immediately to reduce unnecessary waste

III. computer color matching principle and system

belka Munk theory and its limitations

k-m theory was put forward as early as 1931, but it was not successfully used in the textile printing and dyeing industry until 1958. The application of this theory in the printing industry resulted in the shortage of lithium salt began in the 1970s. Computer color matching systems developed by the United States, Japan and other countries basically still use this theory

through a series of derivation of K-M theory, the simplest form of function and its derivative form suitable for color matching calculation are given:

k/s= (1-r) 2/2r


where R represents reflectivity at wavelength; K is the absorption coefficient, which represents the light absorption rate of the medium layer with micro element thickness in the infinite thickness plane medium after the diffusion illumination light is incident; S is the scattering coefficient, representing the scattering rate of light by the micro element thickness

up to now, the basic principle of computer color matching (CCM) still follows the K-M theory. For example, spectral visual matching method, computer reflection spectral color matching, computer color matching approximation algorithm and so on are all based on K-M theory. However, in the practical application of K-M theory, there are often differences between its theoretical calculation and specific practice. The reasons can be summarized as two factors

① K-M theory is derived under certain assumptions

first, if the color layer thickness is x and the light falls on any micro element layer DX, the reflection caused by the interface will not be considered. As a result, the color layer using this theory will be immersed in the medium with the same refractive index. This algorithm that ignores different refractive indexes on the interface in order to simplify the problem may cause errors

second, DX is any micro element layer within the color layer thickness X. the absorption coefficient and scattering coefficient thus obtained are considered to be the same and uniform throughout the color layer when used. However, this assumption is difficult to apply to matting or semi matting oily materials

third, the colorant particles in the color layer are disorderly arranged, which makes the illumination in the color layer a diffuse diffusion form. The particles are completely immersed in the diffusion effect, resulting in two channels. However, in practical application, when the particles exist in the thin oil film and most of them are arranged horizontally, the assumption of the luminous flux of the two channels will be destroyed

fourth, on the thin color layer, the light has entered the color layer before scattering. In the dark color modulation, a considerable number of light has been absorbed before scattering, so these light beams entering the color layer do not show a diffusion state, resulting in great differences in the experimental results

② the printing industry must consider the interaction between light and pigment particles and the physical properties of the ink when describing the ink superposition effect. In practical application, it should be said that the K-M theory contains two constants, namely, the absorption coefficient K and the scattering coefficient S. compared with the scattering ability of the substrate, the scattering ability of the ink to light can be neglected. Therefore, the color rendering principle of the ink is mainly the selective absorption of the ink to light, and the absorption ability of the ink to incident light is affected by the thickness of the ink layer and the ink concentration. K-M theory is based on the premise of opaque media, and the ink used in printing is transparent or translucent. Therefore, K-M theory has great shortcomings

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