Quote:
Originally Posted by tp4tissue
If you take a gamut map to HDR content, you will see that it pushes some coordinates outside the DCI-p3 spectrum.
It's not the file that's causing problems, it's how argyll cms compresses the gamuts into whatever gamut the tv has. It does a different operation between P3 / Rec2020 as the source colorspace.
Depending on the movie, this may or may not work well. It's at the whim of Argyll, and its algorithm's interplay with the primaries of the TV.
You need both.
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Honestly I don't think anyone should be making a 3DLUT where the source color space is BT.2020 since no display comes close to reaching BT.2020.
I have tried making dozens of 3DLUTS for BT.2020 and every single one ends up with posterization near the gamut limits.
And for rendering intent, if you are trying to make a 3DLUT for a gamut that is wider than your display, the only ones that yield good results are the default "Absolute colorimetric with white point scaling" or maybe "Luminance matched appearance"
All the others are bad and lead to shrinking the native gamut even more and colors being much farther off.
Here is a measurement I took of what the 3DLUT does with 6 of the rendering intents for a display that cannot reach P3. Clearly the "Absolute colorimetric with white point scaling" is the best.
https://slow.pics/c/mldFlPW3
But unless your display can come within 10% of the native gamut you are targeting I would't target that gamut and would drop down to the lower one. Like if you are above 90% P3 then with enough patches you can get a result that's largely posterization free, otherwise if you are less than 90% then I wouldn't bother with P3 and would just stick to rec709.
And again I don't think anyone should be trying to target BT.2020 as that always leads to a lot of posterization no matter which rendering intent I used and for which display I tried making the 3DLUT for.