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Old 12th July 2022, 17:08   #301  |  Link
wswartzendruber
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Quote:
Originally Posted by kolak View Post
7.7K- not a chance it's correct.
4K- may be fine if it was graded to 4K nits.
Rest sounds like 1K grades with MaxCLL measured on compressed masters.

I've read in different places that some HDR discs are disappointing, so 597 nits sounds like one of them (may be just such a grade).
Yeah, FranceBB threw the BS flag on Man of Steel last year.
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Old 12th July 2022, 20:06   #302  |  Link
FranceBB
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Quote:
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ProResXQ vs ProResHQ:


Ouch. And that's just from going from 4:4:4 to 4:2:2?! O_O
No wonder studios are sending IMF packages with MJPEG2000 in RGB or YUV 4:4:4 12bit...
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Old 12th July 2022, 20:11   #303  |  Link
kolak
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Even lossless Jpeg2000 4:2:2 shows same problems.
It may also depend how tool handles chroma down and upsampling, but errors are rather unavoidable.

Last edited by kolak; 12th July 2022 at 20:29.
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Old 12th July 2022, 20:48   #304  |  Link
wswartzendruber
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So should we not be using 4:2:0 to measure this? That's what the TV itself has to work with...

Last edited by wswartzendruber; 12th July 2022 at 20:50.
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Old 12th July 2022, 21:05   #305  |  Link
kolak
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And have eg. 5K nits value for title which was graded to 1K nits only because we have chroma subsampling messing with pixels ?
I don't think so. If anything I would say this is very wrong approach- way better to clip those "bad pixels", by using original MaxCLL value from uncompressed master.
I think industry needs to re-think whole MaxCLL value.

For your tool it's definitely pointless to use this bad MaxCLL in my opinion.

Last edited by kolak; 12th July 2022 at 21:07.
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Old 12th July 2022, 21:30   #306  |  Link
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Right, but if we filter the 1% extremes, will it not be more reasonable?
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Old 12th July 2022, 22:07   #307  |  Link
kolak
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Definitely more than using unfiltered.
I see it way simpler- if you know title was graded to (1K or 2K or 4K), you just use those values
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Old 13th July 2022, 00:31   #308  |  Link
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There must be also more precise math which would let you eliminate those "bad pixels".
How big is area in UHD which is visible from closer than typical viewing distance- 16 pixels, 36, 64? It's definitely not a single pixel or even 4.
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Old 18th July 2022, 15:35   #309  |  Link
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Quote:
Originally Posted by kolak View Post
There must be also more precise math which would let you eliminate those "bad pixels".
How big is area in UHD which is visible from closer than typical viewing distance- 16 pixels, 36, 64? It's definitely not a single pixel or even 4.
I would think that would be a function of how bright the disparity between that pixel and surrounding pixels is.

A solid white, 10,000 nit pixel will stick out against a black background.
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Old 18th July 2022, 15:40   #310  |  Link
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Quote:
Originally Posted by kolak View Post
And have eg. 5K nits value for title which was graded to 1K nits only because we have chroma subsampling messing with pixels ?
I don't think so. If anything I would say this is very wrong approach- way better to clip those "bad pixels", by using original MaxCLL value from uncompressed master.
I think industry needs to re-think whole MaxCLL value.

For your tool it's definitely pointless to use this bad MaxCLL in my opinion.
Wait a sec, how is even 4:2:0 going to throw off MaxCLL by 4,000 nits?
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Old 19th July 2022, 14:14   #311  |  Link
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Lossless 4:2:2 creates 4K MaxCLL instead of 1K, so heavily compressed 4:2:0 not going to be better I would think.
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Old 19th July 2022, 15:54   #312  |  Link
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Here's the same thing I did for HLG values, except now with PQ values:

https://wswartzendruber.net/uploads/pq-values.txt

1,000 nits sits at 723.
4,000 nits sits at 855.

That's a 15% jump. For chroma subsampling to do that seems...excessive.
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Old 19th July 2022, 16:20   #313  |  Link
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For such a jump to happen, whatever scaling algorithm you use to scale the chroma, its flawed (in either direction, up or down, since you can't directly measure it for the subsampled signal). Maybe its treating the image like gamma light for the process of scaling and thus this happens?
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Old 19th July 2022, 17:29   #314  |  Link
kolak
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Quote:
Originally Posted by wswartzendruber View Post
Here's the same thing I did for HLG values, except now with PQ values:

https://wswartzendruber.net/uploads/pq-values.txt

1,000 nits sits at 723.
4,000 nits sits at 855.

That's a 15% jump. For chroma subsampling to do that seems...excessive.
Not sure what exactly this is? Coded values to nits?
1K nits should be at 769 coded value, but for full range.
1K nits for limited is 723 as you said.
Should you not scale everything to full as whole HDR/DV is "designed" rather with full range in mind (I assume makes no real difference)?

This is nice calc for quick reference:
https://apps.apple.com/us/app/pq-calc/id1541419476

Last edited by kolak; 19th July 2022 at 17:34.
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Old 19th July 2022, 19:03   #315  |  Link
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DolbyVision as source to HLG conversion

In case it is of use to anybody, I have written an avisynth plugin which takes the HDR10 Base Layer and the DolbyVision RPU data together with the DolbyVision Enhancement Layer producing the result clip prior to the dynamic tonemapping. This clip could thus be used as input to the HLG conversion.

Not yet implemented is my idea to use the dynamic tonemapping data from the DolbyVision RPU data to steer the HLG conversion. I have yet to make up my mind how to actually do that.

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Old 19th July 2022, 19:15   #316  |  Link
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Idea sounds good and could work not only with RPU, but xml DV metadata which is equivalent of RPU, just in different format as far as I understand.

Other thing- do you know how to apply RPU on top of the main video, to get eg. SDR trim?

Last edited by kolak; 23rd July 2022 at 16:40.
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Old 25th July 2022, 20:55   #317  |  Link
ErazorTT
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DolbyVision to HLG

Ok so now I implemented the dynamic tonemapping as well. This makes it possible to convert Dolby Vision clips to HLG and dynamically change the LUT based on the signaled tonemapping from the Dolby Vision metadata.

Current releases are here:
https://github.com/erazortt/DoViBaker/releases
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Old 25th July 2022, 21:03   #318  |  Link
ErazorTT
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Idea sounds good and could work not only with RPU, but xml DV metadata which is equivalent of RPU, just in different format as far as I understand.
I just know the bin files, and I have only used theses until now.

Quote:
Originally Posted by kolak View Post
Other thing- do you know how to apply RPU on top of the main video, to get eg. SDR trim?
Well, I wished I knew how to perform the trim pass based on the signaled values, but I have not found any source which describes this technically. Does anybody have any idea how I could put my hands on that?
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Old 25th July 2022, 21:16   #319  |  Link
wswartzendruber
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Can Dolby Vision be used to determine reference white adjustment?
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Old 26th July 2022, 10:25   #320  |  Link
kolak
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Well, I wished I knew how to perform the trim pass based on the signaled values, but I have not found any source which describes this technically. Does anybody have any idea how I could put my hands on that?
This is Dolby secret I assume. Nothing public. Every tool does it using Dolby SDK.
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