Calculate gray balance using ICC Profile
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Gray balance is a commonly used concept in printing. It represents the percentage relationship of dot colors (Y), magenta (M), and cyan (C) of a series of neutral gray colors. Some people also use a density relationship of yellow, magenta, and cyan, which produce a series of neutral gray colors, to measure the gray balance. In practical applications, most places still use the CMY dot percentage relationship to represent the gray balance. Gray balance control is the most basic control factor in printing, achieving gray balance, and it does not cause color shift when printing. CMY's gray balance relationship is also a data relationship often used in prepress processing and process control. For example, in the pre-press separation setting, the black version is generated, the gray component substitution (GCR) is calculated using the gray balance data relationship; the gray control bar on the printing plate is actually used to check whether the gray balance is achieved or not. It is also a form of application of gray balance relations.
Gray balance is actually a feature of equipment. The meaning is the relationship between the amount of CMY representing the neutral gray color in the case of normal operation of the device. So it should be part of the ICC Profile in Color Management, or the ICC Profile contains information on gray balance. The concept of equipment here is a generalized concept. It refers not only to printing machines, but also to color output devices such as printers and proofing machines. The characteristics of the equipment here actually refer to the comprehensive state of the machine's operating state plus its ink characteristics.
We have a variety of ways to get the gray balance of the device. The usual method is to see which combination of dots is closest to gray by a combination of different dots. Here is a method for calculating the gray balance relationship of a device using a color profile.
Step 1 ‧ Debug the device so that it is in normal working condition.
Step 2 ‧ Print a color code for creating an ICC Profile. For example, the IT8.4 color standard.
Step 3 ‧ Measure the color value of the color code (either spectral value or LAB value) on the color measurement equipment.
Step 4 ‧ Create a black version of the ICC Profile file in ProfileMaker or other software that creates the ICC Profile. Figure 1 shows the settings for creating a black-free ICC profile file in ProfileMaker. Here, select "NoK" at "Separation", the total ink CMYKMax is set to 290, and then a black version of the ICC Profile file can be generated. In the experiment we calculated the gray balance for the EPSON Stylus Pro 4000 color printer, the file is 0301-3.icc.
Step 5 ‧ Create a table file in Excel that defines a set of neutral gray color values, L is 0, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, 65, 70, 75, 80, 85, 90, 95, 100, a, b values are all 0, see Figure 2. In fact, this is a gray ladder. Note that the header data format here should meet the requirements of the ColorThink Pro software to be applied below, so that it can be read in the ColorThink Pro software.
Step 6: Open the table file in ColorThink Pro software, simulate the color space conversion in the software, select the ICC file of B to A space conversion to 0301-3.icc, you can see that the Lab value is converted to CMYK color. The color value of the space, and the K value is 0, as shown in Figure 3. This is because 0301-3.icc is a black version of the ICC file. The CMY value corresponding to each brightness value L in the figure is the gray balance relationship we are looking for. Figure 4 shows the gray balance of the final calculated EPSON Stylus Pro 4000 color printer. Fig. 5 is a gray balance relationship curve based on C. ColorThink Pro software is a color management software developed by Chromix.