The Pmax, (or percentage) of an individual ink channel is dynamically set when the Dmax (or Density) has achieved 99%, thus setting the ink limit or Ink Restriction for that particular color.
In most cases using default values will yield satisfactory results, however objectively modifying the values can result in an optimized calibration and ICC profile, often more stable and using less ink.
Linearization with EasyMedia
In EasyMedia, you can choose to create a new linearization curve from scratch, relinearize, or edit an existing curve.
If you decide to create a linearization from scratch, you will have to print it and measure it with your spectrophotometer. The process is similar to the one you probably followed in the previous step (Transitions).
When the wizard prompts you to print the target, you will see an interface that allows you to edit the print settings as well as Ink Clipping values (for each ink and global).
Good to know
The "Ink Clipping" option helps prevent unwanted bleed before printing a test pattern, functioning similarly in transitions, linear applications, and ink limits.
This option is particularly useful if you know that you cannot deposit a large amount of ink on your media. By setting a smaller global ink limit, you can effectively avoid dirtying your printer.
After printing the target, the wizard will display the following screen:
- Data displayed in a spider graph Hue (ab) will display the hue of the primary colors such as CMY or additional colors such as Orange, Green, Violet, etc… Note, light inks such as Light Cyan or Light Magenta are part of the Cyan or Magenta channels respectively.
- Evaluating Spectral Density, Chroma & Hue values are an effective method to select the Pmax, as such establish Ink Restrictions.
- Use L* in Lab to find optimal Pmax for Black or K (generally the lowest value L*)
- Visually inspect the printed linearization chart to verify the selected Pmax agrees with the printed output.
Good to know
Starting with CalderaRIP V17, the Auto-Smoothing button described below is available to all users.
Starting with CalderaRIP V16.2, CalderaCare subscribers can use a new Auto-Smoothing button to improve the linearization curve and eliminate color measurement inaccuracies:
This color management feature comes in handy when you’re working on a printer with large variability, with difficult media such as textile or corrugated— or if the spectrophotometer has not been handled properly.
When you have finished checking and/or modifying the curve values, click Next. The wizard will then ask you if you want to test (print) the new settings. By choosing "Yes", you will proceed to Ink limit.
Example of use
In this example, Chroma is used to select optimal Ink Restrictions or Pmax.
Select Lch from EasyMedia, then observe measured values for c on the left side of the interface as you hover the mouse over the measurement data. EasyMedia pre-determines a Pmax value based on a calculated Dmax at 99%. With this pre-determined value, Chroma is at 66.8 with a Pmax of 85.8%, however, peak Chroma is 66.9 at a Pmax of 69.4%. By reducing the Ink Restriction less ink will be consumed without losing color, or Chroma.
Also note the Spectral Density value values (the small d under Measure on the left side of EasyMedia), ensuring there is not a significant loss of density based on the selected Ink Restrictions.
Using the same example as the prior page, notice the effect of the Ink Restrictions on the Hue angle for the color Cyan.
Note both the swing in hue from cyan to blue and how close the data points are together beyond 69.4% Pmax.
Restricting inks based on Hue, in addition to Chroma can result in a more accurate ICC profile. In the example of Cyan, as this color tends to show a more pronounced effect than other colors at 100% Cyan will print with a blue hue when ICC charts are printed and thus measured. This then results in color mapping that is not optimal since the color management thinks Cyan has a blue Hue to it.
The correction curves result in linear output for a given color thus changing the behavior of the printer when the correction is applied. In the illustration to the left, the results of the linearization target (A) are mapped to the corresponding correction curve (B) in order to achieve the linear behavior of the device (C).
Represented in the illustration above and to the left is the Pmax now becomes the maximum or 100% Ink Restriction for a given color.