UHD BD to BD?

[X5gb]

Trying out ripbot264 tonemapping sdr conversion (bt 709) on Grease at the moment using crf 18 and the temp h264 file appears to be very good, better than madvr. Could be just what I'm looking for, Staxrip appears to be good as well.

[X5gb]

Here,s just a couple of screenshots from the beginning of the simple crf 18 encode, to me, much nicer than the 40th bluray, it also allows you to tweak the colour and brightness to your liking but I found the default is just fine. Once this encode is done, think I will do a two pass high bitrate variable encode using the perfect bluray compliant settings.

[CSchmidlapp]

Ive started to play around with converting UHD to BD.

From what Ive learned from talking on here and reading article's, is the 4k 10bit rec2020 video stream has 'HDR' metadata that crushes / adapts the video to the spec's of the playback monitor. (This is due to the majority of UHD screens being unable to produce all of the information contained in a 10bit rec2020 stream.) This is dictated on your screens ability to produce its peak brightness (Measured in nits), contrast ratio, color gamut and bitdepth.

When it comes to viewing a 10bit rec2020 video file on a 8bit rec709 screen (without any manipulation) results in a 'washed out' looking image due to the need to adapt/squash the information into a much smaller spectrum (kind of like what the HDR metadata is doing.) This can be done on the fly with hardware/software (Im viewing using the MADVR conversion in potplayer) or applying a LUT.

With this in mind I trans-coded a clip through TMPGenc 6 (10bit environment) from 'The Dark Knight' UHD.
I encoded to a 10bit RGB .avi using the UT lossless Codec (The 'UtVideo RGB VCM (ULRG)' option in the codec is 10bit according to the documentation) I went with this because the other 10bit options kept giving me errors!
I also down-scaled to 1080p during this process.

Ive imported it into Premiere (10bit environment) and just appled a 'rec2020 to 709' LUT.
Rendering out to a 8bit 4:2:0 Rec 709 lossless clip I get these results.

[Synnove]

Important to note that the washed out look of HDR data displayed on a sRGB screen results from the use of different electro optical transfer functions (HDR using Dolby's PQ or Perceptual Quantizer and SDR using 2.4 gamma) and has nothing to do with the differing color spaces (in fact, a larger gamut such as P3 being displayed on a smaller gamut like REC709 would result in over-saturated colors).

What are the details of the LUT you're using? There is a much faster and more flexible way to do this via the non-commercial edition of Nuke if you're willing to download that and use FFMPEG to trans-code the UHD footage to ProRes 4444.

[CSchmidlapp]

I literally typed in rec2020 to rec709 LUT into the interwebs and my first hit was this video on you tube with a LUT file link.
https://www.youtube.com/watch?v=wxkNSbL8Veo
It's certainly not been made for this application but I was having a quick play

EDIT: Im really only playing and learning at this point. Thanks for the information.

[X5gb]

Does this method improve on the relatively simple ripbot264 method I've found as it appears quite long winded, are the results alot better. That youtube video link also suggests having to do further colour correction in whatever editor you use.

[CSchmidlapp]

Does this method improve on the relatively simple ripbot264 method I've found as it appears quite long winded, are the results alot better. That youtube video link also suggests having to do further colour correction in whatever editor you use.

Ive not really tried the ripbot264 way. It's probably much more exact and not the same method at all.
I'm just showing where im playing around with a UHD to BD method. The youtube clip does indeed suggest further CC and its a LUT not designed for what we are doing.

[CSchmidlapp]

Could anybody list all the variables that need to be adapted / converted to get an accurate UHD to BD conversion?

[Synnove]

You need to convert the EOTF from PQ to bt1886 (2.4 gamma), and you need to convert the (usually) P3 gamut to REC709 primaries. However, since PQ was designed for 10,000 nit max and bt1886 was designed with a 100 nit max, you'll need to decide where to clip or roll off the EOTF conversion.

Try experimenting with this: https://cameramanben.github.io/LUTCalc/L...index.html

Camera: generic
Rec Gamma: HDR Display (PQ EOTF ONLY, 10k nits)
Rec Gamut: P3 D65
Out Gamma: Display, linear/gamma, 2.4
Out Gamut: Rec709, Rec709

Clip: white only

Experiment with the Knee customization to find the ideal roll off/clip point for the film you're working with.

If you can provide me with 16 bit PNG capture of a frame from TDK UHD (no tone mapping or anything applied) and a capture of the corresponding frame from the Blu-Ray, I can show you an example of this in action.

[Beber]

This RipBot264 is interesting. I just made a test with it. And this is what I came up with:

UHD using MadVR


Remastered Blu-ray


UHD to HD, HDR to SDR using RipBot264


I end up liking more the UHD RipBot conversion than the actual remastered blu-ray, which looks too bright in that scene.