There is no doubt that three primary color ink printing has made great progress from original painting to scientific embossing, from photographic plate making to complete digital prepress. However, the printer must also improve the variability of raw materials directly related to the final printing products, such as ink and substrate. These variability, especially in the variability of substrates containing many types, has a great impact on color balance. 

       Color imbalance will cause overall color deviation of printed copies. Typically, when the overall color of printed products with neutral gray areas is biased, the characteristics are very obvious. Color imbalance can occur at multiple stages in printing, regardless of when the image is transferred to another format. For example, during scanning, conversion from RGB to CMYK and output to proofing machine and printer (or printer) will lead to color change.Prepress Color Management Connection

      The digital color management system reduces the occurrence of color imbalance in prepress to a great extent by adjusting the hue values of different equipment. However, on the whole, color imbalance is still common, especially in paper printing. This paper describes the application of three color management in gray balance control in printing.

Color transfer

      To understand how to control color bias, you must first look at the color transfer system. During the characteristic reproduction process and the subsequent printing process, two important operators determine the color balance of the whole tone range of three primary color printing. Prepress Color Management Connection

     One is the printing operator, who decides the control of ink embossing sequence, embossing value and three primary color density; The other is the prepress operator, who sets the ink percentage of the embossed color in the halftone area of printing, such as the setting of high tone and middle tone.Prepress Color Management Connection

     The overall color balance of printed copies is determined by the intensity (density) and color (hue and saturation) of the three primary color inks. Only when these printing factors remain stable can the mixing percentage of color dots in printing be determined. In printing and color transmission and reproduction between printing and prepress, if there is no strict control, the printing quality can not be guaranteed only by the parameter control of color management system.Prepress Color Management Connection

      Practice shows that controlling ink density and gray balance through experience is the most important part in color management of halftone color printing.Prepress Color Management Connection

      Gray balance control is not a new concept. Before the computer age, when color separation was based on photography, the standard swop (offset publishing Guide) density had been established. However, several things have changed. One is that flexographic printing has occupied an important position in three primary color printing; Second, due to the emergence of new ink and pigment technology, the basic ink primary color has also changed greatly. Moreover, digital art has emerged.Prepress Color Management Connection

     At the moment of transition to new technology, although the discussion on grey balance control seems to have lost its meaning, if you want to emphasize it, you must work hard to make color management more effective.Prepress Color Management Connection

      The color management system is controlled by printing. On the contrary, printing control can be obtained only when the substrate color, three primary ink color, ink overprint, and other printing variables are relatively stable and balanced. In fact, the balance of these important parameters will change with the change of printing, such as to match the changing basic materials, inks and substrates.Prepress Color Management Connection

       Prepress artists use all control, color management and measurement systems, but they still can’t guarantee to obtain halftone products with consistent color and balanced color. The reason is that small changes in substrate color, ink opacity or overprint have not been found by the printer.Prepress Color Management Connection

Gray balance and three primary ink overprint

      In printing, the three primary colors of ink are mixed in different proportions to obtain the desired color spectral hue value. Whether the density of the three primary color ink printed on the substrate is correct and balanced is directly related to the printer. As a guide to obtain correct ink contrast, density balance should be operated in accordance with first (flexographic image reproduction specifications and tolerances).Prepress Color Management Connection

      The printing operator can only measure and set the ink density within a limited range, which is described in various publishing instructions such as first and swop. However, these density ranges can obtain a wide range of overprint ink colors, regardless of whether the ink is pure and transparent or whether the substrate is pure white. Generally speaking, the application of prepress color management system is not ideal for printing color control.Prepress Color Management Connection

       According to the ink density range on the instructions, it can be used for any ink overprint sequence, i.e. YMC, YCM, CMY, CYM, mcy or myc. But does each order produce the same color? noPrepress Color Management Connection

      Even if the field density is controlled at an absolute value, each overprint sequence will produce different overprint colors of red, green and blue, because each printing ink formula has its own different properties, such as ink opacity that affects the coverage. Therefore, the surface energy of the first printed ink drying film will affect the adhesion characteristics of the later printed wet ink.Prepress Color Management Connection

      The covering rate of yellow pigment is poor, and that of magenta and cyan pigment is good. However, the surface energy of yellow pigment ink is high.Prepress Color Management Connection

      The first step of color management in printing is to determine the best ink overprint sequence and the density balance that can provide a high color range. GATF developed a simple color hexagonal color map many years ago to visualize the proportion of different colors. The densitometer can display the advantages and disadvantages of colors by measuring hue deviation, gray scale and overlay color, and compare them with the three primary colors.Prepress Color Management Connection

      For example, in the hexagonal color map, the ideal ink tricolor (YMC) is on the three corners that are not adjacent to each other, the overprint composite color (RGB) is on the other three corners, and the center of the hexagonal is a neutral color (white to gray to black). The stronger the ink color, the closer it is to each corner and the farther it is from the neutral color.Prepress Color Management Connection

       When the actual printing color and composite color are distributed in the hexagonal color map, the density, color difference and gray value of three primary color ink (CMY) and composite color (RGB) are presented. Because the ink is not ideal, the distributed hexagon (irregular) will not be the same size as the whole ideal hexagon color map, but it can be used for optimal printing. Prepress Color Management Connection

     Therefore, the best density and overprint order can be obtained by using the Gaft method to display the printing trichromatic and composite color information. By measuring the size of the color coverage area, the contrast strength of the whole ink color performance and printing color is determined. Of course, the larger the area, the better.Prepress Color Management Connection

      Other density values can also be distributed as part of the measurement sequence, such as 25% dot, 505 dot and 755 dot density values of color. If the distribution of these other tone values is concentrated, it means that the printing is under control. On the contrary, if the distribution is not concentrated, it means that the printing is out of control and necessary adjustments should be made.Prepress Color Management Connection