XYZ LUT + Matrix profile not applied correctly?

[Andrea3000]

Hi all,

I made a XYZ LUT + Matrix calibration for my external monitor with DisplayCAL. I’m on a 2020 13″ MacBook Pro running Mac OS Catalina 10.15.5.

When I run the measurement report via DisplayCAL, I obtain good results for both color accuracy and stability of the gamma curve (see attached report).

I then exported each patch of the above test chart as 16bit tif files via Testchart Editor , imported them into Lightroom and run an untethered measurement report, manually scrolling through the test patched in Lightroom while in the Develop module.

I use very surprised to find out that the results of this measurement report are way off, for both colors and gamma. (see 2nd attachment).

I am aware of the ColorSync bugs when using an XYZ LUT profile in Mac OS, but Lightroom in the Develop module uses Adobe’s CMM and shouldn’t therefore be affected.

I have then decided to run a 3rd measurement report, again untethered, but this time I’ve used Apple Preview to display the test patches.
This time I obtain results which were even worse than what I got with Lightroom (this was somewhat expected).
See 3rd attachment for the measurement results.

While the results of Apple Preview don’t bother me at all and where expected, the results of Lightroom are totally unexpected to me.

Do you have any idea why the results are so poor? Have I done something incorrectly?

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[Vincent]

Calibration/profiling test patches are encoded in display colorspace, not sRGB, adobe, eciRGB or other one. RAW RGB data numbers that will look different on every display.
If you want to do this kind of test you should open TIFF with patches in Photoshop and assign your display profile as image’s colorspace (assigning a reference so RGB values have CIE XYZ coordinates) , then measure.

Another alternative is to do not use LR (colormanaged, it expects images to have a colorspace, even a default one), use MS paint (win) or another non color managed viewer on MacOS (whcih IDNK if it exists).
If you use Photoshop softproof to monitor “raw monitor RGB numbers” (I do not remember exact words) then color management is disabled and you can do those test even in a mac

Also remember that HTML report values are PCS translated if you wish to compare them to raw readings from other tools. Change coordinates to xyY or XYZ and check abs values to get measured values for each patch.

• This reply was modified 5 years, 2 months ago by Vincent.
• This reply was modified 5 years, 2 months ago by Vincent.
• This reply was modified 5 years, 2 months ago by Vincent.

[Andrea3000]

Thank you Vincent.

I have assigned my display profile to the test chart images and repeated the measurements with both Lightroom (in Develop module) and Apple Preview.

The results with Lightroom are now good, roughly comparable with what I get with the standard measurement report.

With Apple Preview (as expected) some of the colors are way off and the gamma spikes in the shadows. (crushed blacks)

Thank you
Andrea

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