Cigarette Packaging Boxes print gray balance and three primary ink overprint

Cigarette Packaging Boxes print gray balance and three primary ink overprint

 

The color management system is controlled by printing, and in contrast, printing control can only be achieved when the substrate color, primary color ink color, ink overprint, and other printing variables are relatively stable and balanced.

 

There is no doubt that three-color ink printing has made great progress from original painting to scientific stamping, from photographic plate making to fully digital prepress. But printers must also perfect the variability of raw materials such as inks and substrates that are directly related to the composition of the final printed product. These variability, especially in the inclusion of multiple types of substrates, have a large impact on color balance.

 

The color imbalance will cause the printed copy to produce overall color bias, and the typical case is that the overall color of the print containing neutral gray areas is skewed, and the characteristics are very obvious. Color imbalances can occur at multiple stages of printing, regardless of when the image is transferred to another format. For example, when scanning, the conversion from RGB to CMYK, the output to the proof press and the press (or printer) will result in a change in color.

 

The digital color management system reduces the color imbalance in the prepress part to a large extent by adjusting the tone values of different devices. However, in printing as a whole, color imbalance is still prevalent, especially in paper prints. This paper describes the application of three-color color management to gray balance control in printing.

 

Color transmission

To understand how to control color bias, you must first look at the color delivery system. When characterizing the reproduction process and the printing process that follows, there are two important operators who determine the color balance of the entire range of tones in the three primary color printing. One is the printing operator, who decides the printing order of the ink, the printing value and the control of the three primary color density; The other is the prepress operator, who sets the percentage of ink in the half-tone area of the printing press color, such as high and middle tone Settings.

 

The overall color balance of printed reproductions is determined by the strength (density) and color (hue and saturation) of the three primary colors of the ink. Only when these printing factors remain stable can the mixing percentage of color dots in the printing be determined. In the printing and printing and pre-press color transmission and reproduction, if there is no strict control, only the parameter control of the color management system can not guarantee the printing quality. Practice shows that the control of ink density and gray balance through experience is one of the most important parts of color management in half-tone color printing.

 

Gray balance control is not a new concept, and standard SWOP (Offset Publishing Guide) densities were established before the computer age for photo-based color separation. But there are several things have changed, one is flexographic printing in the three primary color printing has occupied an important seat; Second, due to the emergence of new ink pigment technology, the basic ink primary color has also changed greatly. And digital art has emerged.

 

In the moment of transition to new technology, although the talk of gray balance control seems to have lost its significance, so to emphasize it, it must be made more effective color management efforts.

 

The color management system is controlled by printing, and in contrast, printing control can only be obtained when the substrate color, primary color ink color, ink overprint, and other printing variables are relatively stable and balanced. In fact, the balance of these important parameters will change as the printing changes, such as to match the changing base materials, inks and substrates. Prepress artists, taking advantage of all the control, color management, and measurement systems, are still not guaranteed a consistent, color-balanced half-tone product. The reason for this is that small changes in substrate color, ink opacity or overprint are not noticed by the printer.

 

Gray balance and three primary ink overprint

In printing, the three primary colors of the ink are mixed in different proportions to obtain the desired color spectrum hue value. The correct density and balance of the three primary colors of ink printed on the substrate are directly related to the printer. As a guide to obtaining the correct ink contrast, density balance is performed according to FIRST (Flexographic Image Reproduction Specifications and Tolerances Flexible Map Reproduction Guidelines).

 

Print operators can only measure and set ink density within a limited range, which is described in various publication guides such as FIRST and SWOP. However, these density ranges can obtain a large range of overprint ink colors, and regardless of whether the ink is pure and transparent, or whether the substrate is pure white. Generally speaking, the application of the existing prepress color management system is not ideal for the control of printing color.

 

The ink density range specified in the instructions can be used in any ink overprint order, i.e. YMC, YCM, CMY, CYM, MCY, or MYC. But does each order produce the same color? Not really.

 

Even when the field density is controlled to an absolute value, each overprint sequence will produce different overprints of red, green, and blue, because each printing ink formula has its own different properties, such as ink opacity, which affects the coverage. Therefore, the surface energy of the first printing ink drying film will affect the adhesion characteristics of the wet ink after printing.

 

The coverage of yellow pigments is poor, and the coverage of magenta and cyan pigments is good. But the surface energy of yellow pigment inks is high.

 

The first step in color management in printing is to determine the best ink overprint sequence and density balance that provides a high color range. The GATF Association developed a simple color hexagonal color map many years ago to visualize the matching of different colors. The density meter can show the advantages and disadvantages of colors by measuring hue deviation, gray scale and overprint color and compare with the three primary colors.

 

For example, the three corners of the hexagonal color diagram that are not adjacent to each other are the ideal ink three primary colors (YMC), the other three corners are overprinted composite colors (RGB), 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, the farther away from the neutral color.

 

When the actual printed and composite colors are distributed into the hexagonal color diagram, the density, color difference, and grayscale values of the three primary inks (CMY) and composite colors (RGB) are presented. Because the ink is not very ideal, the distributed hexagon (irregular) will not be the same size as the entire ideal hexagon color map, but it can be used for optimal printing.

 

Therefore, using the irregular hexagonal distribution of GAFT method to display the printed primary color and composite color information, you can get the best density and overprint order.

 

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