Compensation Curves (CTV Export Mode)

Compensation curves can be used as correction curves for print form production (printing plate, cylinder, screen, etc.). They serve as the target curves for the tone values to be achieved on the printing form.

In GMG Measure, you can calculate compensation curves according to CTV (as defined in ISO 20645:2017) and save them in CTV Export Mode as CSV file or MXN profile. Though the ISO standard describes the procedure for spot colours, it can in principle be applied to all printing inks, including CMYK, and will yield correspondingly harmonic gradation curves.

A separate compensation curve is generated for each printing ink. The values of the correction curve can be exported either as a CSV file (one file per printing ink) or as an MXN profile (all printing inks in one profile).

The number of fulcrums for the CSV export of the correction curve can be set before export:

This setting is not relevant for MXN profiles, as the profile always uses a curve with maximum resolution and precision.

Data quality

Before calculating and exporting a correction curve according to CTV, verify that the measurement data form a monotonically increasing curve. If the measured values are not monotonically increasing, the calculated compensation curve may be incorrect.

To check this, first switch the value and curve calculation mode to CTV. Then review the displayed curve and ensure that it increases continuously without any drops. If the curve contains non-monotonic sections, identify and correct the underlying measurement issues (for example, by removing isolated outliers or repeating the affected measurements) before calculating and exporting the correction curve.

Example of non-monotonic values → leads to an incorrect compensation curve:

Such a compensation curve requires smoothing or manual adjustments which should result in the following:

How to correct compensation curves (Chart Mode)

1. Switch to the Chart view.
   Perform smoothing with at least level 1 by pressing the Smooth button.
   
2. Check whether the extreme values have been corrected.
   
3. If necessary, repeat the Smoothing with a higher strength level.

How to correct compensation curves (Color Mode)

• Remove all measurements manually in the Colors list that strongly distort the curve,
  OR
• Re-measure the corresponding tone values if a measurement error is suspected.

Alternatively, export the spot color(s) as a CGATS file to use the Smooth function in Chart mode:

1. Export the colors as CGATS.
   
2. Load the CGATS file in Chart mode.
3. Apply the Smooth function.
4. Then export the CTV compensation curve directly from Chart mode, without having to switch back to Colors mode.