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Display Calibration Light Illusion Forums / Display Calibration /  
 

Is this the proper use of sub-space?

 
Author ChadN
ZRO
#1 | Posted: 12 Feb 2024 16:53 
I have a Vizio that does not properly display CMS primaries and there is no way I can find to adjust them and fix this issue.
For example, here are the measured coordinates for RGB:
R - 0.631, 0.334
G - 0.291, 0.598
B - 0.157, 0.056
Incorrect primaries = incorrect secondaries, luminance, saturation, etc.
Is this an example of when I'd use a "sub-space" and create a custom Rec709 with the custom RGB coordinates above and enable that when doing my manual calibration of primaries/secondaries/saturation?

To make matters worse, the coordinates above are what I measure for Rec709, P3 D65, AND Rec2020. If the above answer is yes, would I use the same process and use a customized "ST2084 Rec709" subspace for HDR calibration?

I'm trying to understand when and why to use sub-space. I "think" this is a valid use case for this feature, but wanted to check and make sure I'm not wrong.

Also, with a ZRO license and manual calibration, do I use the "Sub-Space Calibration" checkbox on the Graph Options tab or is that mainly for LUTs?

Author Steve

INF
Male
#2 | Posted: 12 Feb 2024 18:35 
If the display just has limited gamut capabilities, but that is the actual native colour space of the display, then no, you would not use Sub Space.
You can verify this easily by profiling the display with a decent size patch set, and then comparing the profile to a user generated colour space extracted from the profile itself.
If the profile maps well to itself, then that is the native colour space of the displays.
You would then use the normal calibration workflows - targeting whatever colour space standard you want.

For manual calibration, you would likely not need to use Sub Space at all.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author ChadN
ZRO
#3 | Posted: 12 Feb 2024 18:53 
If I should not use a sub-space in this example, should I instead input the native RGB coordinates and create a custom color space to calculate secondaries/saturations like below?


In other words, how do I compensate for a limited/inaccurate gamut when calibrating Rec709 and Rec2020?

Author Steve

INF
Male
#4 | Posted: 12 Feb 2024 19:20 
Just use 'Modify/Extract' to extract the colour space from the profile.
https://www.lightillusion.com/colourspace_manual.html#modify

This is just for assessment of the display.
You always calibrate to the correct colour space standard - Rec709 for example.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author ChadN
ZRO
#5 | Posted: 12 Feb 2024 19:44 
Modify is what I used to get the above example. I took the Rec709 profile and changed the RGB coordinates to match the RGB coordinates measured. My assumption was this would accurately produce the correct secondary coordinates CMY since those are always based on the RGB coordinates.

Are you saying that even if my primaries are incorrect, I should map the secondaries to Rec709 standards?

FYI, I only have a ZRO license currently. I cannot extract spaces due to license limitations. I was hoping that manually specifying the correct RGB coordinates would mimic that functionality.

Author Steve

INF
Male
#6 | Posted: 12 Feb 2024 19:54 
Sorry - the Modify/Extract function extracts the native colour space from the profile.
You can copy the values manually too.

The new colour space should ten be used to assess the profile, to see if its maps to itself well.
It if does, it just means the display has a low gamut.

If that is the case, you still calibrate to Rec709.
But, you may need to use something like 75% target colours.

You do not calibrate to the extracted colour space, as that would cause the calibration to not follow the required standard - Rec709.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author ChadN
ZRO
#7 | Posted: 12 Feb 2024 21:01 
Just to be clear, even if my primaries are:
R - 0.631, 0.334
G - 0.291, 0.598
B - 0.157, 0.056

I still need to calibrate CMY to:
C - 0.224, 0.328
M - 0.320, 0.154
Y - 0.419, 0.505

In the past I've used the AccuPel Display Calibration Calculator to calculate the xyY coordinates of the secondaries based on the primaries and calibrated accordingly. See below...



I understand you ALWAYS want to get the primaries as close to standard as possible, however, I've always calibrated the secondaries based on the calibrated primaries. Is that not correct?

Author Steve

INF
Male
#8 | Posted: 12 Feb 2024 21:37 
It is not the primaries or secondaries that we are talking about here.
If the display cannot make the full gamut of the target colour space - Rec709 - all colours it can make must be calibrated to their Rec709 coordinates.

So if 100% Red - 255,0,0 - cannot be made by the display, but it can make 75% Red, - 255,64,64 - that needs to correctly map to its coordinates of x0..907, y0.3298.

Does that make more sense?

Steve
Steve Shaw
Mob Boss at Light Illusion

Author Steve

INF
Male
#9 | Posted: 12 Feb 2024 21:45 
Now... you have made me think of something.
If you invert Sub Space use - so the main colour space was your actual display's native colour space, and the Sub Space was Rec709, that could/should be the correct workflow.
It's been a while since I played with Sub Space, but the theory says that should work.

Steve
Steve Shaw
Mob Boss at Light Illusion

Author ChadN
ZRO
#10 | Posted: 12 Feb 2024 21:51 
If I did that, would I use the custom color space I showed in an earlier post to define the target space and then use 709 as the sub space?

Do I also use the sub space calibration checkbox or no?

Author Steve

INF
Male
#11 | Posted: 12 Feb 2024 22:14 
Yes - that is correct.
The extracted colour space as the Target colour space.
And Rec709 as the Sub Space.

And the 'Sub Space calibration' option is only applied when a Profile is Saved.
https://www.lightillusion.com/colourspace_manual.html#graph-options

Steve
Steve Shaw
Mob Boss at Light Illusion

Author ChadN
ZRO
#12 | Posted: 12 Feb 2024 22:43 
Awesome! Thanks for your help! It's nice to find out I'm not completely crazy, just needing to know the proper method.

Luckily my other TVs don't have this issue. I'm thinking Vizio released a FW update that broke CMS.

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 Is this the proper use of sub-space?

 

 
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