Overlapping Colors in Flexographic Printing (Part 3)

Evaluation of characterization and color conversion (figure after the article) These data include the L*a*b* values ​​of these printed patches (color blocks in the IT8.7/3 color scale), increasing in L* value. In order. Based on the color gamut range formed by the conventional CMYK color data, the color reproduction ranges of various ink systems are compared. Figure 11 shows the color gamut of the CMGK ink system. Figure 11-13 shows an overall composition of the entire Munsell brightness value plane. It includes the color gamut of green (G), orange (O), and purple (V) in addition to the traditional CMYK color gamut. range. The study of these color gamuts can also be divided into three data segments of 20-30, 50-60, and 70-80 according to the size of the L* value, and constitute the corresponding color space portion. This was achieved by measuring IT8.7/3 color scales (IT8.7/3 color scales include not only the traditional CMYK color gamut, but also the complementary color instead of the ink color gamut.). Because it contains non-traditional inks (inks other than CMYK), it can reflect the size of the actual ultra-color gamut color space after printing. The next task is to find a color management software that can handle the hyperchromatic ink system in a color lookup table. A problem often encountered by color management software when describing colors outside the CMYK ink system is the inability to achieve gray balance. This is because the printer profile is created based on the color data of the ink system used, and the color information creates a corresponding brightness value from the color lookup table. In order to effectively position the data at an a*, b* zero point, it is assumed here that the neutral gray color blocks are also in the measurement system. After replacing the ink system with the complementary color of the IT8.7/3 color standard, the neutral gray component will change. Finally, according to the settings listed in Table 3, scan 5G (green) and 2.5YR (orange) in the Munsell Color Atlas. When scanning, in addition to the CMYK, CGYK, or OMYK ink system feature descriptors, the Fuji REFLIT IT8.7/2 color input device profile is also applied. See Table 4 for the feature description software settings. Table 3 Scan Settings for Munsell 5G and 2.5YR Monitor Settings Display Apple Apple Mac 13" RGB Gamma 1.6 White Point 5000°K Phosphorescent Trinitron Environmental Light Medium Printing Ink Set Custom ink color Dot Gain 20% Gray Balance C(1.0), M(1.0), Y(1.0), K(1.0) Separation setting parameters GCR Black Limit 80% Total Ink 320% UCA 0% Table 4 Used to calibrate the Munsell gamut space Software Settings Printer Description Software Settings Reference IT8.7/3 Reference Sample Spectral Scan Color Patch Description File Large Color Paper Gray Scale Axis Color Set GCR2 Black Limit 80% CMY Maximum Total Ink 320% Consider The purpose of this system is to provide viewers with what they consider to be "real" color reproduction, influenced by factors such as substrate materials and color characteristics. Visual results are immediately apparent when these profiles are applied. The orange (O) color system uses the OMYK character description file, which replaces cyan (C) with orange (O), and actually becomes cyan (C) because most of the color information is converted into the blue channel. When printing, the color information of the blue channel is printed by the orange (O) (2.5YR is printed by OMYK), so it will be color cast. But this is only suitable for on-screen display, and the XyY of the ink is replaced with the XyY value of the orange (O) ink in the printing ink setting dialog of Adobe Photoshop 5.0. Complementary color substitution results To evaluate the color gamut of the CMYK IT8.7/3 color scale and compare it with the color gamut range of the CMYK IT8.7/3 color scale, it is necessary to discuss the purple (V) complementary color substitution. Printed 2.5YR (orange) and 5G (green), and the printed results were analyzed and evaluated. Using CMYK inks with CMYK feature descriptors is not available in these colors. Complementary colors replace the ink system with complementary color profiles, and these colors can be obtained after printing, but no neutral grey is obtained. Based on the L*a*b* value of 2.5YR in the Munsell Color Atlas, we found that the brightness values ​​of the printed high-saturation patches are even lower than those of the corresponding patches in the Munsell Color Atlas. The brightness value is even higher. Since the use of complementary colors replaces a certain color ink in a conventional CMYK system, it is very difficult to maintain a neutral gray balance. Taking the orange ink system (OMYK) as an example, since there is no cyan ink, it is impossible to obtain neutral gray from the OMYK system. The Essence of the Problem So far, we have established that the Munsell color space and the CIELab color space can be compared, both of which are color system models suitable for flexographic color printing. We studied the role of color management systems and tested various transformation settings and their role in the workflow. Once the hyperchromatic space has been quantified, the focus of the problem has shifted to the interior of the gamut space, that is, how to accurately replicate neutral ash. This requires printing more IT8 color patches, this time with different adjacent colors to replace the ink in the traditional CMYK system. Table 5 lists these alternatives. Table 5 Adjacent Ink Alternative Ink Type Ink System Adjacent Color Substitution VMYK Adjacent Color Substitution CVYK Adjacent Color Substitution COYK Adjacent Color Substitution CMOK Adjacent Color Substitution GMYK Adjacent Color Substitution CMGK