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Old 12th August 2020, 07:22   #31  |  Link
wswartzendruber
hlg-tools Maintainer
 
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Quote:
Originally Posted by Blue_MiSfit View Post
The creatives I've spoken with with prefer PQ, and are in general fans of having an absolute signal that is display referenced. Their standpoint is that with relative luminance, for example, HLG can misrepresent contrast.
Compliant HLG displays are supposed to have an EOTF modifier that adjusts the gamma curve depending on ambient light, if that is what you are referring to. With that said, I've never actually gotten my grubby paws on a HLG set. My workflow has been:

1. Study spec sheets.
2. Write code.
3. Write tests for code (checking math values).
4. How does it look on SDR through a HLG-aware (tone mapping) player?

Nailing #4 is all about figuring out a good reference white value (in nits) for the PQ source material. That's everything. It'll look too dim if that's set too high and it'll look completely clipped if it's set too low. I think I've said this before, but I am going to say it again and again because of how important it is.

Nailing #4 is a massive step in having HLG content that can play back on 709 devices. Assuming of course, you have a competent color+tone mapping player, which even the open source community has access to.

Quote:
Originally Posted by Blue_MiSfit View Post
My point was that, to be totally pragmatic, many displays totally ignore metadata and just do their own thing. So like, I wouldn't be surprised if everything would mostly be fine if we just had no metadata at all (other than the transfer, primaries, and differencing flags to identify content as PQ or HLG, and 709 or 2020, of course!) hence the "metadata FUD" troll
BT.2408 makes an attempt at this, which puts reference white at 203 nits. Notice how we're taking something relative (reference white) and pinning it to something absolute (203 nits). This, of course, depends on movie studios following these conventions. And I can tell you with absolute certainty that this is not the case.

FOR FUN: Here's an attempt at Rogue One on VLC (SDR/709 tone mapping) with reference white set too low. https://imgur.com/gallery/AyQW7Pg

EDIT: I need to watch Rogue One again just to pick out a good reference white scene. That movie is really throwing me around.

Alita: easy
Avengers: easy
Age of Ultron: slightly difficult
Rogue One: "Ohhhhhhh no! You are NOT converting me to HLG!!!"

EDIT: I wonder if I could build a sort of predictive model that analyzes every pixel of every frame and then computes an approximation for where reference white should be...

Last edited by wswartzendruber; 12th August 2020 at 07:45.
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