4K UHD Blu-ray to DCP for playback on 2K commercial projector?

[ivankjt]

Hi folks,

I've been renting space at a local theater chain just to screen my favorite films on their setup (has always been a dream of mine, besides having my own personal dedicated theater of course).

What I've been doing is converting my own Blu-rays to DCP via DCP-o-matic. The DCP's are then ingested by the theater's server for native playback on their projectors. The theater uses 2K Christie projectors (unsure of the exact model).

My question is, should I even bother using 4K UHD Blu-rays as the source when creating my DCPs, since the projectors are 2K?

Would using 4K UHD Blu-rays rather than standard 1080p Blu-ray as the source for my DCPs result in better quality in the details, grain, etc because of the higher bitrate? I understand there are also things like HDR > SDR conversion which come into play and that may introduce more problems instead.

If anyone has experience converting 4K HDR Blu-rays into DCP - I would really appreciate tips and/or guidance.

[Carsten]

It would be interesting to compare a standard BD with an UHD conversion of the same title. I am not exactly sure if all UHD are color coded the same. I would assume that the conversion from BT.2020 incl. dynamic metadata to EDR is the weakest point currently. Digital Cinema is not SDR, but 'EDR'

I have recently watched a Netflix HDR production in it's SDR playout version. It was watchable, but sucked once I noticed what was going on.

[Squidmaster7]

I think theoretically yes using the UHD version would be better but Im not sure how well DOM handles converting REC. 2020 to P3 (I think thats whats going on). I think youre more likely to introduce errors and would just stick the regular HD files for now until someone more knowledgeable can chime in.

[Carsten]

I'd be interested in doing some tests, as we do have a high contrast projector, but, I would first need to get an UHD capable disc reader.

[Antti N]

Would using 4K UHD Blu-rays rather than standard 1080p Blu-ray as the source for my DCPs result in better quality in the details, grain, etc because of the higher bitrate? I understand there are also things like HDR > SDR conversion which come into play and that may introduce more problems instead.

After doing some rather extensive testing with HDR UHD Blu-Rays recently, this was exactly the conclusion that I came to... The reason being that:

the conversion from BT.2020 incl. dynamic metadata to EDR is the weakest point currently.

I guess that to do the color space downconversion properly, you'd have to play the disc on a UHD Blu-Ray player, have its hardware handle the SDR conversion in real-time according to the HDR metadata, hook the player up to some kind of a HDMI capture device (bypassing HDCP first of course) and then record the downconverted SDR video, ideally to something like ProRes 4444. Even with such a setup you'd still probably only get Rec. 709, not P3, but at least you'd get the "official" SDR image as intended by the color grader.

That being said, apparently there are some UHD Blu-Ray releases that are not HDR. I suppose that those would be plain old Rec. 709 then, so converting them to DCP would be no different than from traditional Blu-Rays.

[Carsten]

I am in the happy position now that I received a Steel Box of the same title with both a BluRay and UHD disc. And I assume both have been created from the same master.
So, I*m going to dig into UHD disc ripping and will convert both discs to DCP and see what happens.

[IoannisSyrogiannis]

Depending on your BD-drive, you might be able to get away with UHD reading with just a firmware upgrade.
It depends on whether it is what is called "UHD Blu-Ray 'friendly'".
A few of them do not play directly from the disc though, only rip.

[jamiegau]

Technically, the best way to handle this is..
Extract the HDR 4K stream from the BR, however you like..

Import into Resolve, ensuring Resolve understand EXACTLY the type of format the source material is in. Probably need to override what's going on.

Then you have it in a tool that understand whats going on in terms of colour space and peak brightness issues.

The problem I see here is that BR content it typically targeting 1000nits peak luminance utilising PQ (SMPTE ST 2084_
A cinema projector is only 48nits.... Effective tone mapping is required to make this look "right" when you render out to a DCP targeting a very different peak brightness. Typically there is a totally different grading pass when creating these two different deliverables.

Would be interesting to see what it looks like , if done right, and just stuffing a HDR1000nots source into a DCP/EDR/48nits container for presentation, using defaults, do nothing but convert path..
Is it severely compromised???

NOTE, SDR is 100nits peak based on ITU-R BT.1886

James

[Carsten]

The question is wether DCP-o-matic could be able to implement a suitable mapping. This particular title is a classic 35mm title. It is indicated as HDR, but I'm wondering what they actually did to it. I will probably see this weekend. Wondering how far beyond classic rec.709 we can go from UHD to DCI-P3.

Whatever, work in progress.

[Carsten]

Okay, it's a bit complicated, but...bought a drive that has been reported to work nicely, drive has been reflashed with the necessary firmware. Thousands of people in threads about methods, firmware version, and drives, but no guide that has all the necessary information. Or some that simply have too much information.
Anyway, after third attempt, drive has the necessary firmware, is recognised as suitable. First try to analyse the disc fails - after some reading, I learn that the software has to be on an internet-connected computer in order to download some necessary disc specific hash files. Now, the MKV is pouring onto my hard disc - 55GBytes, almost as large as a DCP. I'm already excited what it is and how it looks like in VLC...

Now, do I stay at the cinema and wait another 40min for it to finish, or do I go to sleep and come back tomorrow?

...we'll see...