Hello,
In the case of a Multi-Point Volumetric Matching (MPVM) between two probes that have different Minimum Luminance Range/sensitivities (lets call it MLR).
If we want to match an active fast more sensitive probe (Probe A, Colorimeter) to a reference, slower, and more accurate probe (Probe B, Spectroradiometer) that has a higher MLR (Minimum Luminance Range/sensitivity)
Then the probe match will basically bottleneck (lift up) all the measurements from Probe A that are under the Probe B MLR.
So, is there any easy way to configure the probe matching to avoid bottlenecking (lifting up) probe A measurements under a certain level of luminance?

I mean, at the end of the day, If the goal is to create an accurate display profile, I could use profile concatenation, I guess :

1st profile will be for over 0.02 nits value patches, using MPVM probe matching between CR-100 and CR-300.
2nd profile will be for under 0.02 nits value patches, using FCMM probe matching between CR-100 and CR-300.

But that would take a dreadful amount of time if multiple displays have to be calibrated this way. And we always have a lot of display to calibrate during camera prep.
What I'm looking for is an option to make MPVM aware of the active and reference probe MLR and get the best of the lower MLR probe mersurments. That would be a must.
But maybe MPVM is what it is and what I'm looking for is more of a new kind of probe matching, like a luminance threshold dual probe matching.

This seems like a very hypothetical case scenario, but I recently ran into that problem calibrating SmallHD monitors for a film set using CR-100 (colorimeter) and CR-300 (spectroradiometer) probes.
The CR-300 has a MLR of 0.02 nits
The CR-100 has a MLR of 0.0007 nits

Point is : Some of the monitors have black levels that goes bellow the CR-300 MLR of 0.02 nits.
Using the traditional FCMM will not alter the CR-100 under 0.02 nits measurement (as there is no black reference in this kind of probe match), but the literature from Small HD recommended using MPVM : https://guide.smallhd.com/a/1813803 for better results over FCMM or FCVM probe matchs.

So here we are, how could I accurately use a Multi-Point Volumetric Matching (MPVM) if the active probe has a lower MLR than the reference probe without going through a dual profile concatenation workflow that is very time-consuming and can also be a source of mistakes?

The last shot I gave to try to solve this problem was creating a new CR-300 matching profile using a luminance filtered cube-based set of patches (filter: L > 0.02).
Then I extracted a .BPD probe matching file from this new profile and used it in as a MPVM probe match.
But even if there are no measurements under 0.02 nits in the new CR-300 .BPD, it seems that it takes the next lower measurement in the profile as reference, and the CR-100 measurements under 0.02 nits were even more lifted up by the probe matching.
So, not an option.

NB: In the end, I went with traditional FCMM for the SmallHD displays, and the results were totally acceptable for set conditions.
But still, what if we want to do better?

Looking forward to reading about your experiences.

What you are attempting to do does not make sense. MPVM is supposed to produce a better profile for your colorimeter compared to FCMM. However, there is no logical reason why you would ever make both for one colorimeter. Pick one and only one profile methodology for your CR-100.

It does not make sense to concatenate CR-300 measurements with CR-100 measurements with any large characterization. You can "Hint" your CR-100 characterization with a small CR-30o characterization for extra accuracy if you so choose.

If and when you do choose to create a MPVM for your CR-100, focus on making sure the patches you use do not go below the +/- 0.0015 Chromaticity Accuracy luminance of the CR-300. That luminance value is 1.7 nits... or simply 2 nits as an additional accuracy buffer. Chromaticity Accuracy along with Chromaticity Repeatability is far more important than simple minimum luminance capability.

Make sure you are aware of the +/-0.0015 Chromaticity Accuracy luminance of the CR-100. It is 0.34 nits with 0.4 exposure time and 0.069 nits with a 20 second exposure time. Consider anything below those thresholds as questionable results when you are doing your work.

Thanks a lot for your prompt answer DNice,

It greatly helps in my understanding of probe capabilities and MPVM workflows (which need to take probe capabilities into consideration for the patch sequence).

Still, I can't wrap my mind around the translation of CIE xy coordonate to nits values.
How do you calculate the 1.7 nits value limit from the Chromaticity Accuracy luminance of the CR-300 probe (± 0.0015 x, y)?

If I virtually try to mimic a worst-case scenario measurement with the CR-300: Using the virtual probe to measure the luminance difference between two measurements that have exactly -0.0015 difference in CIE xy coordinates, the luminance difference I get between the two patches is 0.015 nits. (See screenshots 1 and 2).

Patch 1 : 1 Y 0.9999 x 0.3127 y 0.3290
Patch 2 : 2 Y 0.9849 x 0.0312 y 0.3275

I must be missing some parameters in this equation.

1 Y 0.9999 x 0.3127 y 0.3290

2 Y 0.9849 x 0.0312 y 0.3275

Forget my last question about the Chromaticity Accuracy min luminance of the CR-300,
I just found the answer in your Guides under the CR-300 probe specifications...

(I was first looking in the official Colorimetry Research specifications for the CR-300 Chromaticity Accuracy, but for some reason they didn't mention it clearly, as they do with the CR-100.
For the CR-300, the PDF specification on the Colorimetry Research website says:
Chromaticity Accuracy: ± 0.0015 x, y Ω
--> then you have to go to the note at the end of the PDF for "Ω" which says: Ω Measured with a luminance level of 1.7 Nits (0.5 fL)

For the CR-100, the PDF specification on the Colorimetry Research website says:
Chromaticity Accuracy: ± 0.0015 x, y @ 0.34 Nits (0.1 fL), 0.4 second exposure // ± 0.0015 x, y @ 0.069 Nits (0.02 fL), 20 seconds exposure
Which is more straightforward. )

Anyway, some more relevant questions about MPVM:
1) Could you validate that when doing MPVM, both probe profiles need to be made with the exact same patch sequence?
2) Does the patch sequence need to contain primaries patchs?
3) Does the patch sequence need to have pure white and/or pure black patches (I guess black is not needed) ?

Thank you for your time and help!

Yes the same patchset is needed. You cannot make any profile with using the exact same patches with each meter.


Yes


White is needed but not black. Make sure the same stimuli is used with both white and primaries.... even though Steve will say it does not matter with the primaries

The User Guide info for MPVM probe matching does state that it is better to use a Cube based profile, so that will indeed include primary colour patches.
But, you can also delete low-light patches from the patch set if either of the probes struggle with low-light values.
(I'll add that info to the User Guide.)
It is also best to maintain a Cube based patch set, so better to delete patches equally throughout the cube volume.

Steve