Ultraviolet color copying in flexo printing (3)

Printing characterization and the role of color management systems

In the ANSI IT8.7/3 color standard, both the traditional CMYK four-color printing color blocks and the line color complementary printing ink blocks (CMYK, OMYK, and CGYK) are used to print color blocks. This is mainly for the purpose of using four color inks. Combine to achieve high-strength color printing and achieve the best printability. Due to the lack of corresponding ICC setup software in the past, that is to say, the software and hardware of the previous color management are few, and the phenomenon of color mismatch between the input device and the output device often occurs.

The density of the color patches printed in the same anilox roll test was matched to the solid density on the IT8.7/3 color scale. The printed color patches are measured and the spectral data is converted into the corresponding CIELab data, which can then be plotted against these data.

Evaluation of characterization and color conversion

These data include the L*a*b* values ​​of the printed color patches (color patches in the IT8.7/3 color standard) arranged in ascending order of L* values. 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 Mac 13", RGB
Gamma value 1.6
White point 5000°K
Phosphorescent Trinitron
Ambient light Medium (medium)
Printing ink settings
Custom ink colors
Dot gain 20%
Gray balance C (1.0), M (1.0), Y (1.0), K (1.0)
Separation setting parameters
GCR
Black Edition limit 80%
Total ink volume 320%
UCA amount 0%

Table 4 Software settings for calibrating the Munsell gamut space Printer description Software settings Reference IT8.7/3 References Spectra Spectral scanning Color block description file Large (Large)
Color Paper Grayscale Axial Separation Setting GCR2 Black Edition Limit 80% CMY Maximum Total Ink Volume 320%

Taking into account the effects of factors such as the substrate material and the color characteristics, the purpose of this system is to provide a visual representation that the viewer regards as "real".

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.