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Old 4th August 2020, 19:08   #21  |  Link
wswartzendruber
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I believe due to not all players (devices like TVsets etc) support HLG as well as SDR but in nearest future HLG must becomes standard de facto because declared backward compatibility with SDR.
I've concluded that HLG was never intended to be viewed on SDR devices unprocessed. The compatibility that has been mentioned refers to the production environment. Specifically, the BBC states that HLG can be viewed on existing devices for "non-critical monitoring."

From my experimentation, HLG can look really good on SDR (with 709 color) as long as:

1. The player is HLG-aware and tone maps accordingly.
2. The reference white level for the picture is at 75% signal strength.

The Avengers came out looking really good after using the "MARVEL" text at the beginning to set reference white. I'll post an Imgur link when I'm off work.

Screenshots: https://imgur.com/a/9nEZhlR

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Old 9th August 2020, 16:58   #22  |  Link
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I've concluded that HLG was never intended to be viewed on SDR devices unprocessed.
Seems you're right.
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Screenshots
Great colors.
Can you upload some PQ video and therefore HLG video after your PQ to HLG Converter?

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Old 9th August 2020, 22:21   #23  |  Link
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I find it interesting that such a significant technical decision (PQ vs HLG) appears to have been made solely based on concern for such a small group of 4K early adopters with UHD SDR BT2020 displays.

If you are okay with giving that small cohort FHD SDR 709 along with all the other people with legacy HDTVs, then you can just have that legacy feed and a pure HDR feed.

You could make it HLG, sure, but there's a lot of very good HDR TVs that don't support HLG. That seems like a much more important cohort than the tiny number of UHD SDR TVs. Understood that production and acquisition must be done in LOG or HLG, fine, but what you COULD do is distribute in PQ that's compatible with Dolby Vision Profile 8.1, HDR10+, and HDR10.

This is compatible with every single HDR TV ever manufactured.

This is all doable today for VOD, and I think soon for live (tho not sure live HDR10+ is even a thing? Doesn't seem possible to me). Even if it's just HDR10, that works literally everywhere AFAIK. Show me a single HDR TV without support for HDR10.

For live via traditional satellite distribution where transponder capacity is so expensive, this seems like the ideal HDR WCG solution to me.

I guess, it comes down to -- who do you screw over? Someone with an old UHD SDR display, or someone with an earlier UHD HDR display that is excellent other than its lack of support for HLG? For example, I bought an LG B6 a few years ago. It's a great TV still to this day, but it only supports HDR10 and Dolby Vision. Do you screw me over, or the guy with a super expensive first generation UHD TV who, let's face it, has probably already upgraded because he wants HDR!

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Old 9th August 2020, 23:47   #24  |  Link
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Originally Posted by Blue_MiSfit View Post
Understood that production and acquisition must be done in LOG or HLG, fine, but what you COULD do is distribute in PQ that's compatible with Dolby Vision Profile 8.1, HDR10+, and HDR10.
Technically yes, but that would require testing from scratch the whole playout ports behavior in all different scenarios and most importantly metadata... Yeah... metadata, which should change according to the content and would have to be included and aired as well and that could create issues as the whole thing would have to be tested again. Just think about ads in between, you would have a movie at a certain amount of nits with a reference display and then an ad with a totally different amount of nits and reference, with its own metadata... It's not exactly easy to do and test, while in HLG almost everybody actually don't air metadata other than the fact that it's HLG and BT2020nc and leave the TV to deal with the incoming feed, but that shouldn't really happen with PQ, which brings yet one added nag.



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This is all doable today for VOD
Yep, 'cause VOD is a completely different thing, but who would ever encode the same movie or TV Series twice once it has been encoded in HLG already? No one (just like no one would do it in PQ only as playout channels are still in HLG). In other words, it can be done, but no TV Studio does it 'cause it would require two encodes, two mezzanine files and two QCs unfortunately... (but services that are VOD-only and not owned by a TV Company could potentially do it and are doing it already I think). Derek, I don't know if I can ask you directly out of curiosity, but you work for big D, is your + offer in PQ with HDR10? HDR10+? Dolby Vision? HLG? SDR only? Are you dragged behind by linear channels as well?


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and I think soon for live (tho not sure live HDR10+ is even a thing? Doesn't seem possible to me). Even if it's just HDR10, that works literally everywhere AFAIK.
Well, HLG is not here to last in the very long run, but I think we'll have to live with it for quite some time...

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I guess, it comes down to -- who do you screw over? Do you screw me over, or the guy with a super expensive first generation UHD TV who, let's face it, has probably already upgraded because he wants HDR!
lol your TV would still recognize the feed as BT2020nc SDR and you would see the same "just barely watchable" feed someone with an old BT2020 SDR UHD TV would see, so none is screwed (or both of you are, depending of the point of view hahahahahaha)

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Old 10th August 2020, 00:26   #25  |  Link
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Originally Posted by Blue_MiSfit View Post
I find it interesting that such a significant technical decision (PQ vs HLG) appears to have been made solely based on concern for such a small group of 4K early adopters with UHD SDR BT2020 displays.
The BBC and NHK wanted a scene-referred HDR system that did not depend on metadata.

https://www.bbc.co.uk/rd/projects/high-dynamic-range

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Old 10th August 2020, 21:06   #26  |  Link
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Technically yes, but that would require testing from scratch the whole playout ports behavior in all different scenarios and most importantly metadata... Yeah... metadata, which should change according to the content and would have to be included and aired as well and that could create issues as the whole thing would have to be tested again.
It's pretty interesting to see how many displays totally ignore the ST2086 metadata and just do their own thing

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Yep, 'cause VOD is a completely different thing, but who would ever encode the same movie or TV Series twice once it has been encoded in HLG already? No one (just like no one would do it in PQ only as playout channels are still in HLG). In other words, it can be done, but no TV Studio does it 'cause it would require two encodes, two mezzanine files and two QCs unfortunately
This is always required. If you deliver both 2020 and 709 you've got two files to QC. If your 2020 file happens to use HLG or PQ that doesn't change this.

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Derek, I don't know if I can ask you directly out of curiosity, but you work for big D, is your + offer in PQ with HDR10? HDR10+? Dolby Vision? HLG? SDR only? Are you dragged behind by linear channels as well?
I'll take a moment here to clearly state for the record that anything I have ever said or will say here on doom9 is NOT as a representative of Disney, but is from me as an individual

I don't work on D+, but I know the service offers SDR, HDR10, and Dolby Vision. There's not currently any HLG or HDR10+ support.

I DO work on Movies Anywhere, which supports the same formats.

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Old 10th August 2020, 21:09   #27  |  Link
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Originally Posted by wswartzendruber View Post
The BBC and NHK wanted a scene-referred HDR system that did not depend on metadata.

https://www.bbc.co.uk/rd/projects/high-dynamic-range
Interesting. These seem directly coupled. Is the desire to be scene referenced specifically because of the FUD surrounding the impact of metadata?

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Old 11th August 2020, 16:06   #28  |  Link
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Interesting. These seem directly coupled. Is the desire to be scene referenced specifically because of the FUD surrounding the impact of metadata?
FUD? You mean Fear, Unbelief, and Doubt?

My background is that I didn't get into HDR at all until HDR10+ was already a thing. So I'm very late to the game. Research and study (various docs from the ITU and BBC) revealed that for some reason, the industry had chosen to begin distributing content in a system that used absolute brightness coupled with metadata. Distribution to end users inherently entails differing viewing environments, which metadata doesn't address at all.

If you are going to point at HLG and call its rationale FUD, then I want you to defend distributing content in PQ instead. What advantages do you receive?
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Old 12th August 2020, 00:08   #29  |  Link
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I'll take a moment here to clearly state for the record that anything I have ever said or will say here on doom9 is NOT as a representative of Disney, but is from me as an individual
Yeah, just like mine represent my own point of view and have nothing to do with the company I work for as they're my personal thoughts.

(Since you specified it, I specified it as well; better safe than sorry xD)

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I don't work on D+, but I know the service offers SDR, HDR10, and Dolby Vision. There's not currently any HLG or HDR10+ support.

I DO work on Movies Anywhere, which supports the same formats.
Oh, ok, I see.

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Interesting. These seem directly coupled. Is the desire to be scene referenced specifically because of the FUD surrounding the impact of metadata?
As long as nobody brings up the joke about broadcast guys screaming when they hear the word "metadata", I'm gonna keep posting in the thread xD
Jokes aside, non-static metadata on a linear channels with contents played by a playout port, encoded live and aired can be a pain in the... *forbidden word :P * so I understand why some decision were taken in the past (along with all the other reasons I stated before).
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Old 12th August 2020, 01:47   #30  |  Link
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FUD? You mean Fear, Unbelief, and Doubt?

My background is that I didn't get into HDR at all until HDR10+ was already a thing. So I'm very late to the game. Research and study (various docs from the ITU and BBC) revealed that for some reason, the industry had chosen to begin distributing content in a system that used absolute brightness coupled with metadata. Distribution to end users inherently entails differing viewing environments, which metadata doesn't address at all.

If you are going to point at HLG and call its rationale FUD, then I want you to defend distributing content in PQ instead. What advantages do you receive?
FUD = fear, uncertainty, and doubt

To be honest, I was just trolling a little I don't have any hard evidence whatsoever that HLG is inferior to PQ, or that using PQ offers some advantage over HLG --- aside from my unchallenged point that PQ offers wider device compatibility in the rec2020 case, especially on early HDR TVs.

Thankfully, almost everyone seems to support HLG on modern devices now from what I can tell. The notable exception is Roku set-top boxes (distinct from TVs with Roku's software like TCL). This is a ___HUGE___ market in the US, actually, and is the single biggest cohort for 10 foot viewing here, so that's a major factor.

Does anyone know of any other new devices that support a PQ format but not HLG?

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.

However, I absolutely do feel the pain of needing to worry about a 1000 nit grade or a 2000 nit grade, and worrying about how mapping these to a 4000 nit display is not defined, even if there are a lot of pretty good solutions to map either of those examples to a 600 nit display, for example. I can see the draw of sticking to a relative, scene-referenced signal, and having a reasonable degree of faith that it will display nicely on a broad swath of HDR WCG displays without needing to futz with metadata.

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

Personally I still prefer Dolby Vision Profile 5 for a number of reasons, but that's getting OT pretty fast!

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Old 12th August 2020, 07:22   #31  |  Link
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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.

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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...

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Old 13th August 2020, 19:53   #32  |  Link
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Theoretically, if they were present and accurate wouldn't the MaxCLL / MaxFALL values in the ST2086 metadata be helpful here?
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Old 13th August 2020, 21:04   #33  |  Link
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Theoretically, if they were present and accurate wouldn't the MaxCLL / MaxFALL values in the ST2086 metadata be helpful here?
Half of my 4K discs don't even seem to have HDR10 metadata, and I'm not sure why not. Only one of them (so far), Rogue One, goes above 1,000 nits.

In any event, I can compute this stuff myself. And that's what I'm already doing with pqstat. I could have it compute MaxFALL as well, if I wanted.

But what I'm really after is reference white and I'm not seeing how MaxCLL and MaxFALL will help with that. By reference white, I mean the border between SDR and HDR brightness levels.
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Old 13th August 2020, 22:03   #34  |  Link
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Half of my 4K discs don't even seem to have HDR10 metadata, and I'm not sure why not. Only one of them (so far), Rogue One, goes above 1,000 nits.
Really?! O_o Leaving aside the 1000 nits, even if they're lower, they should all have metadata and it's actually very important in HDR10 PQ. I would understand HLG .ts files, but not UHD-BD disk with PQ... Are you ripping the original m2ts file? What does ffprobe say? Perhaps it's just MediaInfo not showing them for some reason? I mean, it would be weird for an HDR10 official disk not to have metadata.
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Old 13th August 2020, 22:47   #35  |  Link
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Half of my 4K discs don't even seem to have HDR10 metadata, and I'm not sure why not. Only one of them (so far), Rogue One, goes above 1,000 nits.

In any event, I can compute this stuff myself. And that's what I'm already doing with pqstat. I could have it compute MaxFALL as well, if I wanted.

But what I'm really after is reference white and I'm not seeing how MaxCLL and MaxFALL will help with that. By reference white, I mean the border between SDR and HDR brightness levels.
I see, yeah that's the real trick. I wonder how companies like Colorfront do this in real-time with a pleasing result...
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Old 16th August 2020, 05:28   #36  |  Link
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Can you upload some PQ video and therefore HLG video after your PQ to HLG Converter?
What you have asked for no doubt seems simple, but I do not know how to accurately do that. I suppose I could start by compressing the Rec.2020 colorspace into the Rec.709 triangle.

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Really?! O_o Leaving aside the 1000 nits, even if they're lower, they should all have metadata and it's actually very important in HDR10 PQ. I would understand HLG .ts files, but not UHD-BD disk with PQ... Are you ripping the original m2ts file? What does ffprobe say? Perhaps it's just MediaInfo not showing them for some reason? I mean, it would be weird for an HDR10 official disk not to have metadata.
VLC has a metadata display. It's probably just not working. I haven't tried ffprobe. I've actually been using the pqstat program just to be sure.

I use MakeMKV to remux whatever streams I pick from the disc into Matroska.

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I see, yeah that's the real trick. I wonder how companies like Colorfront do this in real-time with a pleasing result...
I have no idea, but the deeper I've gotten into this, the less it's become about math and the more it's become about eyeballing it. Which is what I did with Rogue One finally to put reference white at 180 nits. I'll link to screenshots of that when I'm off work. So maybe they have some fancy machine learning algorithm.

Speaking of which, my friend bought a HDR-capable phone and had no idea. So we sampled Rogue One (my latest attempt) on both our sets side-by-side. And while I didn't notice much difference in luminousity, the color on his was absolutely gorgeous compared to mine.

EDIT: Rogue One HLG Screenshots

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Old 16th August 2020, 22:01   #37  |  Link
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VLC has a metadata display. It's probably just not working. I haven't tried ffprobe. I've actually been using the pqstat program just to be sure.

I use MakeMKV to remux whatever streams I pick from the disc into Matroska.
Well, the remux shouldn't really get rid of the metadata as they're in the video essence itself, so if they put them there, they're still gonna be there after the remux. Anyway, VLC is probably one of the worst players for HDR contents, in fact my choice falls on MPV, especially if you have an SDR monitor. By the way, I actually found the MPV tone-mapping for PQ contents with metadata to be pretty much fine, while it's kinda sloppy for HLG materials without metadata...
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Old 16th August 2020, 22:38   #38  |  Link
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VLC is probably one of the worst players for HDR contents
You should provide evidence when making baseless claims that impugn others' work. And 'probably'? Is that only on random days or do you roll dice every day to decide?

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...while it's kinda sloppy for HLG materials ...
What does "kinda sloppy" mean here? Can you show it with screenshots?

When someone resorts to rhetoric we have to question their confidence in their technical arguments.

Don't mean to be harsh.

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Old 17th August 2020, 00:27   #39  |  Link
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You should provide evidence when making baseless claims that impugn others' work.
Well, when I tried it years ago it wasn't doing any kind of mapping, it was just wrongly displaying the data on SDR displays, outputting both BT2100 PQ and BT2020nc HLG without taking into account their color curve nor their color matrix (i.e grey-ish).

VLC: https://imgur.com/JktOMOt
MPV: https://imgur.com/ky2Kg6k

You can clearly see that VLC got it wrong and that it shouldn't really be displayed that way on SDR displays...
I gotta say that I don't have it installed anymore, so I don't know whether things improved or not, but I can say that MPV definitely applies the tone-mapping when it has to display HDR on an SDR monitor (and it did it years ago as well, while VLC didn't).

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What does "kinda sloppy" mean here? Can you show it with screenshots?
Well, it's kinda hard to do it with screenshots 'cause they would look ok. What I mean by "sloppy" is that when I try it with 1000 nits HLG files without metadata (other than the fact that they're HLG and BT2020nc 10bit) that have frequent transitions between a scene with high lights and low lights, it struggles. When I was watching Riviera, for instance, there was a fairly dark room with sharp lights every few meters. When Cherry was walking and was not under the light, the picture was going to dim while, as she walked under the light, the picture was going all the way up to the maximum brightness allowed by SDR. This is fine, however imagine a person walking with the monitor going bright, dark, bright, dark, bright, dark all the time in a matter of seconds with the whole scene (not just the main character) changing (including the background). I never noticed such a thing with PQ with metadata in which a compromise between being "under the light" and "not under the light" was chosen and it was much "easier" to watch and way less stroboscopic. The absence of scene-referred metadata might play a very big role in some contests, especially with SDR monitors watching an HDR content which is supposed to be viewed on an HDR display. This of course doesn't really mean that the HLG tone-mapping of MPV is bad nor that the developers didn't do a good job; heck, the tone-mapping it's good and I don't even know whether it can be improved much further given that HLG doesn't have metadata, but I just pointed out that in my personal experience MPV generally behaves better with PQ files with metadata than it does with HLG ones without metadata and with very high spikes in terms of nits on some scenes.


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When someone resorts to rhetoric we have to question their confidence in their technical arguments.

Don't mean to be harsh.
lol, no problem at all, when I say things they're always based on my own personal usage and on what I found out in my examples, not as "absolute statement" or "dogma". They're definitely open to discussion. So... even if I don't specify anything, always take them as my personal point of view

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Old 17th August 2020, 22:03   #40  |  Link
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I've noticed that VLC tone maps HLG differently depending on OS, which is strange.

Anyway, I also remember the release notes for 3.0.0 saying that they corrected HLG tone mapping.
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