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Old 3rd December 2017, 02:07   #1  |  Link
shag00
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How to check if a BD is really HDR

OK, I have my first 4K BD labelled HDR so I disassembled it and was looking at it with Media Tab to determine what some of the technical differences are between non HDR and HDR video, as compared to my existing library.

The first one was that the new video is 10 bit instead of 8 bit but further investigation has led me to believe that you can have 4k, non HDR video at 10 bit also.

Further comparison discovered that my HDR video has these attributes that appear to denote that it is HDR:
1/ Chroma subsampling : 4:2:0 (Type 2)
2/ Color range : Limited
3/ Color primaries : BT.2020
4/ Matrix coefficients : BT.2020 non-constant
5/ Mastering display luminance : min: 0.0050 cd/m2, max: 4000.0000 cd/m2
6/ Maximum Content Light Level : 500 cd/m2
7/ Maximum Frame-Average Light : 200 cd/m2

Does anyone have the technical expertise to confirm that these attributes mean the video is HDR? Also, do these attributes give any indication if WCG is enabled in the video?
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Old 3rd December 2017, 07:59   #2  |  Link
Asmodian
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Your 1 - 3 do not indicate HDR. 4:2:0 and limited range are standard for everything back to DVDs. Video with BT.2020 color primaries is usually HDR, but not always.

4 being non-constant and the presence of 5 - 7 all indicate it is encoded as HDR video. 5 - 7 is the "HDR metadata" you may have seen discussed.

Edit: I got confused on this point again.
BT.2020 non-constant would also be used for SDR BT.2020, it is BT.2020 constant that would most likely be HDR. I believe most HDR material out today is BT.2020 non-constant anyway. The constant or non-constant refers to linear or gamma like transfer functions, constant is linear.
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Old 31st January 2018, 12:34   #3  |  Link
von Suppé
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This "HDR metadata", how does the size of this metadata compare to the SDR video itself?

Or is it "just extra info" (by no means this is meant diminishing) so HDR compatible players/tv's can handle it?
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Old 31st January 2018, 13:41   #4  |  Link
sneaker_ger
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Depends. HDR10 metadata is basically just some flags, size is negligible. The stored data is HDR, not SDR.

Dolby Vision is different.
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Old 31st January 2018, 14:03   #5  |  Link
von Suppé
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Thanks sneaker_ger.
I always imagined HDR video would be SDR video with extra HDR videodata for compatible hardware. So, like something as a "SDR core" + extra HDR videoinformation.
Quote:
Originally Posted by sneaker_ger View Post
The stored data is HDR, not SDR.
This does raise a question:
How does a non-HDR device play it back then as SDR?
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Old 31st January 2018, 14:05   #6  |  Link
sneaker_ger
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An UltraHD Blu-Ray player will convert the video to SDR on-the-fly if a non-HDR display is detected.
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Old 31st January 2018, 14:12   #7  |  Link
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Okay, clear.

Do I then understand correctly, that HDR (whether it is or isn't there on a UHD BD) is a part of the official UHD BD specs?
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Old 31st January 2018, 14:15   #8  |  Link
sneaker_ger
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Yes, it is.
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Old 31st January 2018, 14:25   #9  |  Link
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Thanks sneaker_ger

My apologies to shag00 for this interruption.
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