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Old 28th March 2022, 04:11   #1  |  Link
wswartzendruber
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Alita: Battle Angel 4K - Help Me Understand the Grading

I have the US UHD release of Alita: Battle Angel. The color grading on this thing seems to be rather interesting. It's much different from my other 4K releases.

In particular:

1. I currently estimate reference white to be at 47 nits.
2. The brightest spot I can find in any frame with light directly into the camera comes in at 53.3% signal level.
3. The credits are the brightest thing in the whole picture at 55.7% signal level.

With an understanding of the PQ EOTF:

53.3% -> 128 nits
55.7% -> 162 nits

So at the mastered levels on disc:

Reference white: 47 nits
Direct light: 128 nits
Credits: 162 nits

Let's scale the linear display brightness to put reference white where SMTPE wants it:

Reference white: 100 nits
Direct light: 272 nits
Credits: 345 nits

Or if we bring things up to where the ITU wants them:

Reference white: 203 nits
Direct light: 553 nits
Credits: 700 nits

So I have two questions:

1. What is with the reference white level here? I saw in another thread that cinema XYZ masters have reference white at 48 nits. That's awfully close to my rough-eyeball estimate of 47 nits.

2. Why is the dynamic range so freaking poor for HDR10? I've read that cinema puts peak white at 2.7X reference white. That's awfully close to the ratio between my estimated reference white and the direct light going into the camera.

It's like this "HDR" grading is just a naive transfer from the cinema master.
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Old 28th March 2022, 14:55   #2  |  Link
FranceBB
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Quote:
Originally Posted by wswartzendruber View Post
It's like this "HDR" grading is just a naive transfer from the cinema master.
That's where my money goes, to be fair.
I wouldn't be surprised at all!
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Old 28th March 2022, 16:28   #3  |  Link
wswartzendruber
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You know, this disc has Dolby Vision on it. Could that possibly help anything? Will DV expand the dynamic range somehow?
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Old 28th March 2022, 17:26   #4  |  Link
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Quote:
Originally Posted by wswartzendruber View Post
You know, this disc has Dolby Vision on it. Could that possibly help anything? Will DV expand the dynamic range somehow?
Ah! Dolby Vision dual layer? I wish I had a Dolby Vision decoder, 'cause I have no idea what's in the metadata layer and what the resulting 12bit H.265 looks like, so I can't say how that it's gonna influence the result compared to just decoding the layer 1 which holds the HDR10 backwards compatible stream in 10bit.
I don't have much experience with Dolby Vision myself and I've always ignored the second layer due to the lack of open source decoding options. I wonder if Colorfront Transkoder is able to read it properly and output something...
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Old 29th March 2022, 15:59   #5  |  Link
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I don't know what kind of Dolby Vision it has. There's only one video stream in it, I think.

Although now I'm having thoughts of converting it back to XYZ just because I'm bored. And, well, maybe players will have a better idea of what to do with it.

Where's reference white? 0.68 signal level?
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Old 29th March 2022, 21:28   #6  |  Link
SeeMoreDigital
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I don't know what kind of Dolby Vision it has. There's only one video stream in it, I think.
The 4K UHD disc has been encoded with MEL Dolby Vision.

Also... When the disc was released (back in Jul 2019) it was one of the first to also include HDR10+
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Old 12th April 2022, 02:42   #7  |  Link
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mpv supports applying MMR of MEL, but not dynamic meta. Need to copy to profile 7 first.
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