DeviceLink Linearization

Optimizing tone values of primary gradation ramps

The Linearization tool optimizes the tone values of primary gradation ramps for any printer and color combination including Multicolor. The goal of Linearization is for adequate differences from white to 100% of primary inks, to smooth gradation curves and to bring primary colors to a defined and reproducible state.

Note: The Linearization tool is included with CoPrA 5 L and higher.

The linearization methods of this tool are based on ISO 20654, ColorLogic’s proven default calibration method or G7 calibration. It also provides a setting to protect the highlights which is important for Flexo printers and G7 calibration of difficult media and printers. All settings can be used for CMYK and Multicolor measurement data and there is a setting which allows the use of G7 for the CYMK parts of Multicolor data and ISO 20654 for the additional colors as G7 is only intended for CMYK.

Detailed Procedure

Load or Measure Data

The creation of a Linearization DeviceLink starts with printing a linearization test chart on the uncalibrated printer without any color management.

There are two ways to get the necessary measurement data for the creation of a Linearization DeviceLink profile:

1. Measure the test chart and optimize the measurement data using appropriate software, such as ColorAnt (using the tools Custom Chart and Export Chart) and open the measurement data in CoPrA’s Linearization module.
2. M
easure the linearization test chart by using CoPrA’s own Measure Tool.

Load: Opens and displays existing measurement data files. Alternatively, drag and drop the data into the window, to extract and view the data.

Measure: Opens the Measure Tool to measure the linearization test chart with a supported device.

Setting: Select the linearization method. CoPrA contains three [PREDEFINED] settings (Default, Flexo Linearization, G7 Linearization). These settings can be [EDITED] and [SAVED].

Customize: Allows fine tuning of the linearization setting by selecting the Calculation Mode and adjusting the Protect Lights (%).

Fit to Width: Fits the color patches of a row to the window width. Especially for large test charts with very many color patches and many rows the color patches will be displayed larger.

Show reference data: The device values such as CMYK or RGB and measurement data (i.e. Lab or spectral values) are shown on a split color patch. The data can be quickly compared for incorrect or faulty data.

Linearization Options

Calculation Mode: This setting defines the method to calculate the colorimetric linearity. Four standard methods are available which can be customized and saved.

ColorLogic Default (colorimetric linearization): Linearizes the curves based on Lab/dE-76 which means that a 50% value of a primary has the same distance to the left (white) as to the right (full tone) and is therefore located at the midpoint of the graphic.

Linearization according to ISO 20654: Linearizes the tone values of primary gradation ramps based on linearity according to ISO 20654.
Note: The methods ColorLogic Default and Linearization according to ISO 20654 are very similar. However, in contrast to the ISO 20654 approach, ColorLogic Default takes the hue of primaries into consideration.

Linearization according to G7 (CMYK only): The CMYK tone value curves are linearized to match the gray balance requirements of the G7 calibration process. Additional Multicolor channels are not affected.

Linearization according to G7 (CMYK) and ISO 20654 (spot colors): G7 is defined to work with CMYK only. The additional Multicolor channels are not affected. Therefore, activating this setting applies the G7 procedure to the CMYK parts of a Multicolor measurement file and the ISO 20654-based method to the remaining Multicolor channels.

Protect Lights (%): Protects highlight areas. Values below the set percentage are protected and will not be linearized. Make sure to get a smooth transition from the protected – non-linearized – highlights to the linearized part of the measurement data.
Note: For linearization of the entire measurement data, set the slider to 0.

The curves graphic allows assessment of the linearization results based on the selected settings. Use the two radio buttons to compare the Calculated Curves – which will lead to a linear behaviour of the printer when applied – to the original CMYK and Multicolor curves (Curves from Data).

Calculated Curves: Represent the curves based on the selected settings that will be applied in the resulting Linearization DeviceLink profile.

Curves from Data: Shows the original non-linearized curves. The graph is a colorimetric representation of the curves according to ISO 20654. Linear curves indicate a printer in a perfectly calibrated state according to ISO 20654.

Click Next and define the profile settings. Generate a Profile Report to get all important details about the DeviceLink profile.

Note: The generated Linearization DeviceLink profile can be used in a workflow for any kind of printing process. For example, it should be used when printing a profiling test chart on an uncalibrated printer. ColorLogic ZePrA supports the use of Linearization DeviceLinks as gradation curves. This way the linearization can be applied to a workflow like curve corrections in a RIP. In this case, curve corrections must be disabled on RIP level to avoid double changes.

Profile Processing

Format, Size and Further Processing

Name: Type in a Name for the profile.

Format: Define the Format of your profile. An ICC format in accordance with specification v2 is recommended as basic setting however, the newer format ICC v4 can also be chosen. In this case, please ensure that your programs support this format correctly.

Note: ColorLogic products handle and use ICC v4 profiles consistently and correctly.

Size: The setting Large is recommended. The size specifies the number of grid points in the profile and determines the amount of disk space required for the generated profile. Small profiles should only be used for test purposes. Very Large profiles can slow down further processing in subsequent programs. Additionally, some programs are not able to handle very large profiles.

Further processing

Create Profile Report (PDF): Recommended to activate. The PDF report provides an overview of the quality of the profile based on statistics, diagrams of gray balances, gradients and gamut representations as well as color separations of converted test files.

Save: Creates the printer profile and saves it in the folder Profiles (macOS) or Color (Windows), (macOS: /Users/Username/Library/ColorSync/Profiles, Windows: C:\Windows\System32\spool\drivers\color). Demo and encrypted profiles will be saved in a different location only relevant for ColorLogic applications.

Note: CoPrA-SP profiles are stored in the ColorLogic subfolder Licensed-Profiles.

Profile Reports

Profile reports can be created for Printer or DeviceLink profiles. To do so, activate the checkbox Create Profile Report in the last step of the profiling or, when updating profiles, the checkbox Create Profile Comparison Report.

Depending on the type of profile the report contains various statistical data, such as statistics about profile precision (Integrity, Precision, Black Point, White Point etc.), graphic representations of curves and gamuts (Gray Balance, Gradients etc.), conversions of test images, separations and color patches to evaluate the smoothness or the purity of colors. All this facilitates the detection of artifacts that may be present.

Profile reports can be created at any time in Batch Overview or in Profile Manager which, by the way, is not restricted to ColorLogic profiles.

Under Preferences specify whether to create a PDF report with sample images or an XML report with pure data.

Note: If a profile comparison report is created when updating a profile, the measurement data obtained from the update test chart will be compared to the data of the original profile (reference profile).

If the checkboxes Brightener Compensation or Measurement Correction have been activated, the data of the original profile will not be compared to the measurement data from the update test chart but to the data modified by these options.