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Old 17th May 2022, 16:19   #161  |  Link
wswartzendruber
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Originally Posted by ErazorTT View Post
So then you say that 90% of the SDR signal should map to 75% of the HLG signal?
That is my present philosophy until someone can argue why it shouldn't be.
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Old 17th May 2022, 23:33   #162  |  Link
ErazorTT
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That is my present philosophy until someone can argue why it shouldn't be.
I found a sentence in 2408-5 supporting your view. In section 7.7:
Quote:
The difference in perceived mid-tone contrast arises because of the difference in the diffuse white level of an SDR image (~100 cd/m2) and that of an HDR image (~200 cd/m2).
Thus in order to compare the pixel signal values of SDR and HLG, we have to carry out the comparison under the assumption that SDR and HLG have the same diffuse white level of ~200. Making the 100% signal of SDR going above 200 in that comparison.

PS: i found an even better quote from 2408-5. Table A8.2 states the following numbers:
90%SDR = 75%HLG = 203nits
100%SDR = 79%HLG = 260nits

Last edited by ErazorTT; 18th May 2022 at 00:03.
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Old 18th May 2022, 02:58   #163  |  Link
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Uh, wow. Appendix 8 is new for the fifth revision. And it's all about how the PRC does HDR/SDR simulcasting.

And...we independently came to similar conclusions about mapping HLG to SDR.
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Old 18th May 2022, 09:23   #164  |  Link
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You know, I had the impression that HLG not only has more headroom in the highlights but also in blacks ("bottomroom"..? ). At least when reading through the BBC documentations.
But now our HLG streams have basically the exact same pixel signal values in the darks and midtones as SDR. So how to reconcile this with the BBC statement?
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Old 18th May 2022, 21:57   #165  |  Link
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Wait, what does the BBC say that counters this?
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Old 19th May 2022, 01:25   #166  |  Link
ErazorTT
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this here for example at around minute 8:
https://www.smpte.org/webcast/dr-pq-...-presented-bbc
Granted, at this stage he talks about the camera curve (OETF) and not the display curve (EOTF), but I would have thought that there should have been also some repercussions in the display curve if the camera curve is different.

here are the slides for that talk:
https://www.dutchguild.nl/31jan2017/...0published.pdf
Especially slide 14, where it zooms into the curve, and one sees that the SDR curve does actually not match the HLG curve.

And then there is Figure 18 in 2390-10, again the OETF, the red HLG line is not exactly on top of the blue SDR line in the lower half, but slightly above it. Thus bringing home the same message as the plot on slide 14.

Or to put it differently: Section 5.1 and section 5.2 of 2408-5 do the SDR to HLG conversion differently. 5.1 produces an HLG signal that follows the same curve as SDR and can be matched exactly like we're doing, and 5.2 generates a HLG signal which looks more like the OETF plots I mention above.


I am aware however that the PQ to HLG conversion does not have any of these ambiguities and has only the luma-scale as a free parameter. So all this does not contradict your LUT generator, it's a question about the expectation of what curve the birghtness of the resulting HLG will follow. And this is not clear to me. Should I expect to get basically an SDR curve in the lower half, which would match the section 5.1 SDR to HLG conversion, or should I expect to get something looking like the OETF which does not match the SDR curve and would reproduce the section 5.2 SDR to HLG conversion.

Last edited by ErazorTT; 19th May 2022 at 02:13.
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Old 19th May 2022, 22:35   #167  |  Link
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The shape of the HLG curve isn't something I considered at all. Fundamentally, I view PQ with a reference white of 203 nits and MaxCLL of 1,000 nits as being logically equivalent to HLG. Once I realized that, I came to see most of the conversion process in the context of linear display light.

In any event, the HLG curve doesn't mean what it used to. Back when HLG was going to put reference white at 50%, the shadows and midtones were going be on a SDR response curve, while the specular detail above that would be on something closer to PQ. But now, reference white is at 75%. So 1/3 of the shadows+midtones are in the PQ-area of the curve.
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Old 10th June 2022, 16:54   #168  |  Link
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I didn't realize I could upload copyrighted HLG material to YouTube, but WB will apparently let me as long as I don't monetize it.

https://www.youtube.com/watch?v=D-F82b9m3Qo

Can anyone see this in HLG?
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Old 10th June 2022, 19:39   #169  |  Link
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Can anyone see this in HLG?
Yes I can:
when people are watching with SDR BT709 capable devices, it shows 1080p and google converts the colormatrix only from BT2020 to BT709, so the reference white will still be 75%.
When people are watching with SDR BT2020, google will serve the BT2020 HLG stream (although the monitor will ignore the transfer) and the reference white will still be 75%.
In my case, I'm watching this with an HDR HLG BT2020 capable device (and a 799 nits monitor) and it offers me the right HLG stream: Settings Image


I tried to make a few screenshots while the monitor and the OS are in HDR Mode, so hopefully they're gonna give you an idea of how it looks like in HDR HLG:

Img 1 - Img 2 - Img 3 - Img 4 - Img 5 - Img 6 - Img 7

On a real monitor it looked really good, though... except for the fact that YouTube bit-starved everything, but that ain't HLG Tools fault.
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Old 10th June 2022, 23:27   #170  |  Link
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Yeah the compression they applied is horrendous. I'm guess my small-time channel doesn't warrant any more bits than that. I would have paid them to do a better job.
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Old 11th June 2022, 03:10   #171  |  Link
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I wonder if Disney will let me get away with the same thing...
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Old 11th June 2022, 09:05   #172  |  Link
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I wonder if Disney will let me get away with the same thing...
I guess there's only a way to find out xD
Jokes aside, I wouldn't risk it.
When I upload samples they're generally stuff I recorded with my camera myself.
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Old 11th June 2022, 17:39   #173  |  Link
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I've also uploaded an Alita clip.

https://www.youtube.com/watch?v=XMdFweclflY

The BT.709 presentation here looks...kind of red...



YouTube's BT.709 mapping is on the left. Native BT.709 is on the right.
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Old 16th June 2022, 21:22   #174  |  Link
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Yep, looks quite saturated, but when I play YT and compare this to your grab then they don't match (maybe it's due my screen been P3 gamut and tags accuracy). YT is less saturated, but still more than the one on the right. It's hard to say which one is correct. Update: seeing HLG in native format actually one on the left looks more correct.
There can be HDR version and SDR version and HDR mapped to SDR doesn't really have to look as native SDR version.
If you want to compare you conversion to something else use Resolve which has Dolby mapping built in.
Dolby tools do best SDR from all tools I've seen. Maybe because they work per shot, so each seen is analysed for min/avg/max brightness and then mapped to SDR. This is way more optimal than global conversion.
From my tests Dolby tools preserve saturation better than eg Resolve's internal mapping filter. Overall they tend to create rather more saturated look.

I think YT now puts HDR over Dolby tools for SDR conversion, so it should be quite good. But not sure if they convert HLG to HDR10 and then use Dolby to map to SDR or do some direct HLG to SDR mappings.

Last edited by kolak; 17th June 2022 at 10:20.
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Old 16th June 2022, 23:03   #175  |  Link
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But not sure if they convert HLG to HDR10 and then use Dolby to map to SDR or do some direct HLG to SDR mappings.
They don't for HLG, no worries about that.

Quote:
Originally Posted by wswartzendruber View Post
The BT.709 presentation here looks...kind of red...


Speaking of the sample, I see it red-ish in HLG as well to be fair.

Those are the screenshots I grabbed while playing YouTube in HLG and with the OS being HLG aware and outputting in HLG BT 2020 like I did for Aquaman:

Img1 - Img2 - Img3 - Img4 - Img5 - Img6

Last edited by FranceBB; 16th June 2022 at 23:05.
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Old 16th June 2022, 23:13   #176  |  Link
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They don't for HLG, no worries about that.





Speaking of the sample, I see it red-ish in HLG as well to be fair.

Those are the screenshots I grabbed while playing YouTube in HLG and with the OS being HLG aware and outputting in HLG BT 2020 like I did for Aquaman:

Img1 - Img2 - Img3 - Img4 - Img5 - Img6
It can be tested if they use Dolby mapping for HLG input or not.

Your grabs are P3 gamut with sRGB gamma.
Are they really HLG just with sRGB tag or gamma is sRGB (then it's a conversion)?

Last edited by kolak; 16th June 2022 at 23:34.
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Old 17th June 2022, 18:47   #177  |  Link
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I don't know if they're gamma mapping or not...

However, I can generate a test signal for upload this weekend to find out.
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Old 17th June 2022, 19:23   #178  |  Link
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They're not mapping brightness. They're just interpreting HLG as BT.709.

https://www.youtube.com/watch?v=8g0NRk1afYk
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Old 17th June 2022, 20:39   #179  |  Link
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Alita is fake HDR, 203 nits everywhere. which is SDR level in 1000 nits. I would say any test with it is invalid. https://www.youtube.com/watch?v=JLmkRyhjzQ8

It mostly does not even exceed 709 primaries, which is ridiculous.

Of course it is still a cool example of blu-ray with both Dolby Vison MEL and HDR10+.

Last edited by Balling; 17th June 2022 at 20:48.
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Old 17th June 2022, 20:40   #180  |  Link
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Alita is fake HDR. I would say any test with it is invalid. https://www.youtube.com/watch?v=JLmkRyhjzQ8
It's not fake HDR, it's cinematic XYZ.

And the test in this case is in color gamut and how YouTube is mapping BT.2020 to BT.709.
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