Instability/Artifacts in TRC Generation in ArgyllCMS V3.4.1

[Egor S.]

Hello everyone,

I use Palette Master Ultimate (BenQ software) to perform a hardware calibration  for my BenQ SW242Q Monitor with the following targets:
– Colour gamut: native
– White point: 6000K
– Gradation: L*,
followed by “Profiling Only” in DisplayCAL, skipping software calibration completely, using native white point. The LUT profile results are very good. I get a very smooth and neutral greyscale ramp and the colours look absolutely correct.

The issue:
In DisplayCal Profile Info I noticed a significant discrepancy between the TRC tags (rTRC, gTRC, bTRC) for the matrix part of the profile and the Tone Response Curves calculated from the 3D LUT, when the “LUT” Checkbox in DisplayCAL Profile Info is active.
3D LUT (Correct): The measurement data in the LUT shows a near-perfect linear progression following the hardware-calibrated state (refer to attached screenshot “LUT tone response curve”).
TRC Tags (Faulty): The generated 1D curves for the matrix part exhibit a massive “kink” at L*  ~30 and channel divergence that is not present in the physical measurements (refer to attached screenshot “TRC tags”).
The vcgt tag (graphics card V-LUT) is linear.
I have also attached the monitor ICC profile from DisplayCAL.

If I generate a matrix profile from the same measuring data as for the LUT profile and apply the matrix profile, the displayed colours get a significant colour shift (due to the wrong TRC ). White is not white and the greyscale is not neutral. In my opinion, this is a bug in the way that ArgyllCMS calculates the TRC tags. This is strange because it didn’t happen with my old PC system, which had an older version of ArgyllCMS and DisplayCAL 3.8.9.3 installed.
The issue persists regardless of the target gamma. Profiles created for both L* and pure Gamma 2.2 show the identical behaviour, confirming that the error is inherent to the TRC generation logic for this specific ArgyllCMS version and is not related to a specific transfer function. The LUT profile, on the other hand, is always very good.

Do you agree that this must be a bug in the current version of ArgyllCMS? Should I write a bug report?

My System:
Palette Master Ultimate 2.6.0.0 for hardware calibration of the BenQ SW242Q Monitor.
DisplayCAL 3.9.17
ArgyllCMS 3.4.1
Colorimeter: X-Rite i1 Display Pro
OS: Windows 11 (25H2)
Graphics card: NVIDIA GeForce RTX 5060 TI with studio driver
CPU: Intel Core Ultra 5 245K
Of course, HDR and Windows Auto Color Management (ACM) are deactivated.

Thanks!

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[DaniJ]

Contact ArgyllCMS via their mailing list.

[Kuba Trybowski]

DisplayCAL 3.9.17 is pretty buggy.

Try profiling your monitor using DisplayCAL 3.8.9.3 + Argyll 3.4.1. If the problem remains, contact Graeme Gill, the developer of ArgyllCMS.

[Egor S.]

Thank you guys for your assessment. I’ll do it the way you suggested.

Egor

[Author]

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