CTV Export Mode

Tone values (measured actual values) are calculated according to CTV (Spot Colour Tone Value) as defined in ISO 20645:2017 (Measurement and calculation of Spot Colour Tone Value "SCTV"). Based on this, a correction curve is generated which, when applied, produces a harmonic gradation aligned with human visual perception.

Note: The ISO standard describes the procedure for spot colours. However, it can in principle be applied to all printing inks, including CMYK, and will yield correspondingly harmonic gradation curves.

The calculated compensation curve can be used directly as a correction curve for print form production (printing plate, cylinder, screen, etc.). It serves as the target curve for the tone values to be achieved on the printing form.

A separate correction 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 support points 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.

Important note on data quality

If you want to calculate and export a correction curve according to CTV, you should first check that the measurement data form a monotonically increasing curve. Otherwise, the calculation of the compensation curve may be faulty. To do this, first switch the calculation of values and curve to CTV.

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

Correct extreme tone values as follows.

Correction in 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 Smooth process with a higher strength.

Correction in “Colors” mode

• Remove those measurements in the Colors list that strongly distort the curve,
  or
• re-measure the corresponding tone values if a measurement error is suspected.

Alternatively, you can export the spot colour as a CGATS file in order to use the Smooth function in Chart mode:

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