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Old 19th January 2020, 12:03   #1  |  Link
Jamaika
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How the sample range and HDR functions should be set?

I have doubts about the new VVC codecs. Should the default sample range limited be entered for HDR HLG?
HDR HLG is 300-1000 cd/m2 isn't the same as range limited 100 cd/m2 or full for 10000 cd/m2. Should the codec disable sample range for HDR?

Last edited by Jamaika; 19th January 2020 at 12:05.
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Old 20th January 2020, 06:03   #2  |  Link
FranceBB
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I think that it should actually offer the option to include all the metadata that x265 already offers.
The thing is that HLG doesn't have to be 1000 nits; it can be up to 1000 nits but there's nothing stopping you from mastering at let's say 400 nits.
As a matter of fact I did it for a documentary where I had mixed contents (archive footages and new interviews) in order not to show much difference between the old archive SDR footages and the new HDR interviews.
And... yes, you can argue that in official HLG streams there's no metadata whatsoever other than --colorprim bt2020 --transfer arib-std-b67 --colormatrix bt2020nc --atc-sei 18 so no master display or max-cll and the decoder (a TV) has to guess the values and it generally does it by finding the brightest pixel in the frame and adjusting accordingly. Some other TVs instead assume that it's going to peak at 1000 nits anyway since it's HLG (even if it doesn't) and they decode it accordingly, which is one of the reason why some people prefer to bump everything up to 1000 nits and master it that way even if the camera doesn't have enough stops.


In a nutshell: I do think that the option should be kept for HLG as well; it's not mandatory but if people insert it, the hope is that the decoder will read it and scale accordingly rather than just ignoring it.
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Old 21st January 2020, 18:03   #3  |  Link
Jamaika
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Indeed the metadata applies to HEVC but I get the impression that X265 has more header data than the rest of the concurrency.
I don't think about metadata but about the fact of options in VVC that specify import / export in HLG. VVC hasn't import full range and export HLG. It's troublesome.
This means that I should import YUV into HLG.
Interestingly the range of colors is limited by default. I'm starting to worry how is it? Is this function turned off automatically?

Apparently there are more options for metadata in mpeg5
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Old 21st January 2020, 23:09   #4  |  Link
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Quote:
Originally Posted by Jamaika View Post
Indeed the metadata applies to HEVC but I get the impression that X265 has more header data than the rest of the concurrency.
I don't think about metadata but about the fact of options in VVC that specify import / export in HLG. VVC hasn't import full range and export HLG. It's troublesome.
This means that I should import YUV into HLG.
Interestingly the range of colors is limited by default. I'm starting to worry how is it? Is this function turned off automatically?

Apparently there are more options for metadata in mpeg5
I can't think of any scenario where HLG wouldn't be used in limited range. The whole point of it is backwards compatibility for broadcasters.
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Old 22nd January 2020, 17:12   #5  |  Link
FranceBB
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Interestingly the range of colors is limited by default. I'm starting to worry how is it? Is this function turned off automatically?
It makes sense actually.
Whenever you work in HLG, the idea is that you're going to air it at some point in time so you wanna have it Limited TV Range 64-940 as per 10bit standard. People may argue that what I said it's true for a mastering process and for a final encode, but there are cameras that actually let you record directly in HLG.
Well, my reply would be that although it's true that some cameras allow you to record directly in HLG, that is only to speed up the editing and encoding process OR to connect them straight to a video mixer and go on air live, so, again, in limited TV Range.

I'm not saying that Full Range HLG shouldn't be done, I mean, it's worth having it if you want to support it, but I don't see any reasonable use of it and I do understand why it's set to limited TV Range by default.
And to those who may say that HLG Full Range would be more efficient than limited if you have to retain more details and nits to then go to something else like PQ, I would say that pretty much any cameras that can shoot in HLG can almost definitely shoot Log and any sane person would choose Log over a (hypothetical) full range HLG to go to PQ.

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Originally Posted by benwaggoner View Post
I can't think of any scenario where HLG wouldn't be used in limited range. The whole point of it is backwards compatibility for broadcasters.
That's exactly right.







Side note:
As a brief side note I gotta say that there are some cameras that DO NOT output a complaint HLG stream and just don't care about standard (I'm looking at you Sony!). Some Sony cameras try to squeeze HLG in an 8bit yv12 H.264 100 Mbit/s 4K stream, trying to make use of all the 255 bits, which should not be allowed and it's not supported by pretty much anything. Thank you, Sony. -.-

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Old 22nd January 2020, 20:25   #6  |  Link
benwaggoner
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Side note:
As a brief side note I gotta say that there are some cameras that DO NOT output a complaint HLG stream and just don't care about standard (I'm looking at you Sony!). Some Sony cameras try to squeeze HLG in an 8bit yv12 H.264 100 Mbit/s 4K stream, trying to make use of all the 255 bits, which should not be allowed and it's not supported by pretty much anything. Thank you, Sony. -.-
Yeah, but 16-235 can increase banding. Doing 8-bit with HDR is just full of making less-bad choices to hopefully reach mediocrity.

I believe the future is doing everything in half-float, including in displays. So many great panels still have panel controllers that treat everything as 8-bit RGB with gamma, and so tons of dithering and tricks get done on the nice internal 10-bit HDR image to get it to the screen. Going straight to the native panel color volume would be simpler and improve quality. But that's now how the supply chain factors the components.
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