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Old 20th June 2018, 16:05   #21  |  Link
hydra3333
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thank you, videoh.
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Old 20th June 2018, 16:23   #22  |  Link
videoh
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You're welcome, hydra3333. I am also adding HLG support to DGHDRtoSDR. Current version (no HLG yet) is here:

http://rationalqm.us/misc/DGHDRtoSDR_1.4.rar
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Old 20th June 2018, 21:55   #23  |  Link
SeeMoreDigital
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Originally Posted by Revan654 View Post
The sample you Uploaded is not HLG from what my editing software is reading out. Mediainfo been hit or miss when it comes to HDR content.
I can confirm the sample triggers the HLG HDR flag on my LG television

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...I tried this that i found on another site, but the color results are horrible...
Out of interest... Are you viewing HLG content on a screen that supports HLG decoding?
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Old 21st June 2018, 11:29   #24  |  Link
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Originally Posted by videoh View Post
That stream does contain the SEI message discussed. Next slipstream of DGDecNV will show it in the DGI file.
Are you sure, I think it does. If I make an encode with x265 with --atc-sei 18 --transfer bt2020 (it should be --transfer bt2020-10 though), I get the same readout in ffmpeg and mediainfo as OP:s ts file.
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Old 22nd June 2018, 07:10   #25  |  Link
hydra3333
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don't know if this is relevant, someone said
https://mrmc.tv/forum/viewtopic.php?t=3973#p16210
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The transfer characteristics for true HDR10 content cannot be BT.2020 ( # 14). It has to be PQ/ST.2084 ( #16). BT.2020 transfer characteristic is the same as for BT.709 (BT.1886/SDR)
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Old 26th June 2018, 04:39   #26  |  Link
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Interesting! Can you tell me the details on the SEI message, or point to a spec? Thank you.
You should hear broadcast guys FREAK OUT at the very mention of metadata! Because if you have it, that implies it could change with content, and broadcast infrastructure has no way to switch metadata when switching between sources, ads, etcetera. Nor do device specs really say what should happen when display metadata changes mid-stream. In the HDR-10 world, the assumption is that a piece of content has to have the same metadata during an entire playback session, and that changing it would only be honored if there is an HDMI reset or something.
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Old 26th June 2018, 04:44   #27  |  Link
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HLG uses a separate SEI element to indicate a secondary transfer function, which allows fallback to SDR with non-HLG aware players. So the main transfer function entry would be an SDR one, and the extra SEI element would indicate the HLG transfer. If your analyzer does not understand that separate SEI, then it would show as SDR.
Real-world, it's more that the HLG code values look okay when treated as SDR.

HLG is something that works in practice (decent HDR on supported devices, with decent SDR on legacy devices) but not in theory (same set of code values without metadata can deliver two different creative intents).

The challenge with HLG is that it gets optimized for SDR, HDR, or sort of in the middle. It's never going to be as accurate or "HDR" as well-graded HDR-10(+) or Dolby Vision.

But if you are a broadcaster limited by RF instead of IP, having one channel that can do SDR and HDR is very appealing.
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Old 3rd July 2018, 18:06   #28  |  Link
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Oh, another thing I just recalled - HLG is supposed to always be 10-bit. Weird things might happen using it in 8-bit instead due to lack of precision and/or hardware support.
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Old 3rd July 2018, 21:58   #29  |  Link
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Oh, another thing I just recalled - HLG is supposed to always be 10-bit. Weird things might happen using it in 8-bit instead due to lack of precision and/or hardware support.
Yeah as is all HDR except Dolby Vision which is a 12-bit mess. 8-bits would limit the dynamic range i.e. cause banding in frames with large range, loss of detail in highs and lows etc.

Last edited by Gser; 3rd July 2018 at 22:01.
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