Within the following article the Color Management System will be described with each profiling-step and possible settings therein.
1. Transition
In 6-color printing systems, light inks are used in addition to CMYK, light cyan, light magenta and light black. In order to use these additional colors in a way that matches the primary process colors, they are also measured using a defined measurement chart. Thereby, light-color-curves are created. Correct use of the light-colors can bring many advantages for production and must therefore be precisely coordinated. For example, it is possible to set the color value to a value for which light-colors are always to be added. Furthermore, it is possible to set the percentage from which light-colors are no longer to be used. This makes it possible to produce skin tones and lighter colors better and to prevent banding and graininess problems.
For example, if a customer mixes Light colors with 100% “dark” Magenta, the ink consumption will be high, which also effects the color gamut volume. To reduce ink consumption for Light colors, the use of these inks should amount to approx. 60%. Thereby, ink can be saved and the usual ink consumption problems are reduced.
2. Linearization
In the digital printing industry, it is common to bring printers into a linearized (calibrated) state to perform profiling. Unless light-colors are used, linearization is the first step in profiling. For that, a measurement chart is printed, which contains the primary process colors of the printer, e.g. CMYK. The measurement chart is subsequently measured - thereby, the compensation calculation for the linearization curve is acquired and the printer is brought into an absolutely linear state. The linearization curves are calculated and smoothed automatically by an algorithm in the background. This is advantageous to users, as they do not need to have any previous knowledge about the algorithm to smooth out the linearization curve.
Furthermore, it is possible to crop the linearization which results in are a smaller gamut volume. This could be used to e.g. achieve a smaller color space like ISO Coated v2, PSO Coated v3 or SWOP2013C5 and depends of course on the specified values for the constraint. In this case, only certain color channels can be clipped - CMY and K remains at 100% - so a bit of economization may be achieved.
3. Ink Limit
The total ink coverage, also called TAC, describes the sum of all overlapping ink values in the printing industry. If no ink limit is entered, 400% ink will be applied in a maximum state. This can lead to problems such as unsecured drying or breaking of the ink at edges. Therefore, the TAC is reduced to a certain percentage value depending on the used substrate and ink (UV or water-based) and the printing configuration.
To ascertain the appropriate percentage value, the operator must print out a chart and examine the print result. Therein, the focus lies e.g. on the questions such as "on what point does ink run", or "on what point the ink can be smudged due to insufficient drying".
In addition, a strong reduction of the TAC inevitably leads to higher ∆E values for spot colors.
4. Black Point
The black point is the darkest point in a profile. This point can be achieved by blending the primary process colors together, which is usually done automatically and does not need to be defined by the operator.
Note: the manual reduction of the black point to a higher L value can have a big impact on the ink consumption.
5. UCR – Under Color Removal
The so called Under Color Removal is the process of eliminating overlapping Cyan, Magenta and Yellow that would have added to a dark neutral black and replacing them with K ink only. This happens during the ripping process when color management is done. The biggest advantage of UCR is that it solves problems of sticking ink.
This function is automatically applied in the Workflow in the background. The user does not have to set the function manually.
Figure 1: Color structure without and with UCR
6. GCR – Gray Component Replacement
In Gray Component Replacement the CMY values that add up to gray throughout the tone scale are replaced with black ink. The advantages of GCR are less ink consumption and consequently better drying, especially when post-printing-processes have to be carried out.
This function is also applied automatically and the user does not have to change it manually.
The use of Light Black ink supports the GCR approach additionally, as the reduced contrast of Light Black results in best possible smoothness by replacing CMY.
Figure 2: Color structure without and with GCR
7. Save Ink Feature
The Save Ink function will be applied on top of the rendered image.
7.1. What is the real difference in Color Management?
The Save Ink algorithm from Color Logic uses color analysis to replace parts of the image intelligently. The color combinations contained in the original image are changed so that gamut-enhancing colors such as orange, green, violet, light magenta, etc. are used. When adding additional colors, the same colors can be achieved with less ink, thus saving some percentages on ink. Still, the savings for ink costs might be lower, as gamut-extending colors are usually more expensive. The mixture of process and gamut-extending colors always results from the used print item. The algorithm doesn‘t change the visual appearance of the image.
7.2. What are the potential savings when using Ink Saving Profiles?
The amount of Ink Saving depends on various criteria, note that e.g. identical ink saving cannot be achieved for every print image. Furthermore, the ink saving may be much higher than the overall cost savings. The reason for such a result could be the use of relatively expensive gamut expanding colors, such as orange, green, violet. Another big factor in ink saving is the way that the Substrate Profiles are created. When creating a Substrate Profile with settings that use already reduced costs, it is more difficult for the algorithm to reduce additional ink savings.
7.3. What effects does it have to apply an Ink Save Profile on images?
The appearance of the print image will depend on the image quality itself and the Ink Saving Profile that is selected. Each of the available Profiles has different algorithm settings, which in turn can create different results. The available Ink Save Profiles (Low, Medium, and Extreme) will be explained below. Note that even when using the „extreme“ Ink Save Profile, there are no visible streaks in shapes and/or gradients. If, for example, a comparison is made between a Profile without the activated Ink Save feature and a Profile with the activated „Extreme“ Save Ink feature, a visible streaking in shapes and/or gradients may occur. If the "Low" Ink Save feature is used, a slight desaturation of the colors may be possible.
7.4. Available Ink Save Profiles
As already mentioned three Save Ink profiles are provided in Durst Workflow and will be more closely examined below:
Low
This profile saves ink by increasing the amount of black that is used by replacing CMY.
With this Profile the savings are little but it is possible to save some percentages of ink. Due to the 0 ∆E difference there is no visual difference to a print without save ink.
Medium
With this profile the black ink amount compared to the CMY usage is increased, this means the color combination is changed and more black is used if possible. The use of this profile leads to a greater ink reduction, especially with CMY. One of the main goals of this profile is to get skin tones and lighter colors despite savings. At a maximum value of 0.5 ∆E, there should be no visual difference.
Extreme
With this Profile, the maximum setting is achieved by replacing Rich Black (CMY) with Pure Black (K). This results in high amounts of Ink Savings. Thereby a maximum ΔE tolerance of 4 has been stored.