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Old 3rd December 2019, 11:08   #1  |  Link
TomArrow
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How to analyze an HDR video for peak brightness level for the setting of metadata?

I wanna do an encode of a HDR video I made. I'd like to include the global peak brightness metric in the metadata, and maybe the average brightness too. How can I find the brightest pixel in a HDR video (PQ curve) and then calculate the brightness in nits from its value? And how could I go about calculating the average brightness?
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Old 4th December 2019, 02:28   #2  |  Link
Blue_MiSfit
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How did you master your HDR video?

Usually mastering tools output this info or can report on it.
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Old 4th December 2019, 12:57   #3  |  Link
TomArrow
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Well, I had a composition in After Effects in 32 bit floating point linear color space that had some clipped highlights. Basically came from a source with a high dynamic range already, I just adjusted exposure to look good in SDR and then decided to have the superbright details be HDR instead of tonemapping (curves or such) or clipping. Then exported into the Rec2100 PQ color space. Checked the result and the highlights weren't clipped, so it worked just fine. But ofc didn't tell me what metadata I need.
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Old 5th December 2019, 09:07   #4  |  Link
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I'm scratching my head a bit as to why you mastered content this way, but we can sidestep that.

I'll assume you want to encode your content into HDR10 using static metadata.

The key thing to remember here - the HDR10 metadata consists of a few things:

1 - Signaling the transfer function, differencing function / matrix, and primaries in the HEVC VUI (you'll likely use SMPTE ST 2084, BT 2020 nc, and BT 2020 respectively - since you say you used Rec.2100 / PQ to export from After Effects)

2 - Signaling the mastering display characteristics, both in terms of the CIE XYZ coordinates of the primaries / white point, and the min / max luminance of the display. This is also known as SMPTE ST 2086

Note that there's nothing here about the max light level of the content. There is an additional piece of metadata you can signal called Max Content Light Level (MaxCLL) which indicates the "hottest" pixel in the whole sequence, and Max Frame Average Light Level (MaxFALL) which indicates the brightest frame on average. However, these are optional fields and they do not need to be signaled. In fact, they have little to no effect in most cases.

So, the only real question is the ST 2086 metadata.

What type of HDR display did you master the content on? It seems like maybe you didn't master on an HDR display?

Last edited by Blue_MiSfit; 7th December 2019 at 02:30.
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Old 9th December 2019, 23:12   #5  |  Link
benwaggoner
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Quote:
Originally Posted by TomArrow View Post
I wanna do an encode of a HDR video I made. I'd like to include the global peak brightness metric in the metadata, and maybe the average brightness too. How can I find the brightest pixel in a HDR video (PQ curve) and then calculate the brightness in nits from its value? And how could I go about calculating the average brightness?
Colorfront Transkoder can do this very trivially.

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