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This topic comprises 2 pages: 1 2
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Author
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Topic: Technical Specs for UP Now Available
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 05-28-2009 09:12 AM
DCI specifications (I guess we can call it "standard") don't spec for 4K 3D (4K-48fps). If such thing existed, which is does not, wouldn't be officially supported by DCI.
DCI compatible equipment must support 2K-24fps, 2K-48fps (which can be used for 3D) and 4K (24fps).
John: what's HD-DCI? Never heard that one before. For the time being, Sony takes the 4K input through dual srlv inputs. The logical thing would be that they eventully implement a quad 3G-SDI input.
On top of all that (4K 3D not being a supported standard in DCI specifications, thus no servers support it, etc), CGI animated features would be substantially more expensive in 4K than in 2K, as 4 times as many pixels would have to be rendered. And, if it was to be in 3D, then 8 times as many pixels would have to be rendered compared to 2K, driving the cost way too high for little perceived improvement.
And Sony projectors could only do 4K 3D in up to 30fps-per-eye (single flash), meaning it is not really suitable for 4K 3D.
It can do fine 2K up to 60fps, 2K-3D up to 60fps-per-eye (others can't really do 3D properly at over 24fps-per-eye) or 4K up to 60fps. But 4K-3D, it's not really suitable for doing at all. I mean, it could do it at up to 30-fps-per-eye, but it would flicker a lot at 30hz (a regular film projector, with a two-blade shutter, does 48hz ... imagine a film projector with only 1 blade in the shutter and you get the approximate idea).
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 05-29-2009 09:54 PM
Well, the way I see it is: right now, DCI wants equipment to do (basically) and in order of MY perceived importance:
-Keep a very high security data path so that it is very difficult to pirate the film (digitally). Other than projecting it and videotaping it, of course. Even then, the security measures calls for (eventual) watermarking of the picture and audio with all the information leading to the theater and time/date the recording happened (again, even when video-taped/audio-taped/recompressed/etc).
-A minimun of on-screen quality for the projector. This is (roughly) defined as full on/off contrast of 2000:1 (around 400:1 ANSI), 14fl screen illumination, 2K minimun resolution. The way I see it, as long as a projector does at least 2K, I don't think they have any problems certifying a theoretical 3K or 8K projector or, of course, a 4K. For 3D, for the time being, although they WANT 14fl, they are allowing light levels way below that (between 3.5fl and 5.5fl) because, until recently, most setups weren't able of much more and you may get more ghosting with more light. I think they'll eventually demand 7fl+ for 3D as a minimun somewhere in their (updated) specs.
-That all servers (players) play back encrypted DCP (Digital Cinema Packages) of 2K-24fps, 2K-48fps (suitable for 3D as well as for improved motion) and 4K-24fps, with optional subtitles (captions) and uncompressed soundtracks (up to 250Mb/s).
Those, I think, are in "2 words" the goals of DCI. They don't define all the hardware details, such as how servers should communicate with projectors, other than it must meet their security requirements (FIPS-3 Level 3).
Since most projectors are based on Texas Instruments DLP projection "heads", most servers implement communication with the projector through an encryption scheme of sufficient security that TI calls "Cinelink II" and that they implemented over a slightly non-standard version of the widely used video transmission protocol in the a/v industry known as HD-SDI ( SMPTE_292M ).
What they do, is encrypt the signal travelling out of the server (which must also license and buy chips for cinelink II) and into the projector, similarly equipped.
HD-SDI was thought for the transmission of signals of HD resolution (1920x1080) digitally and uncompressed over a cheap single coaxial cable, like the ones used in cable TV at quite large distances. But, it was thought-out for signals with color subsampled 4:2:2 and at up to 10bits in quality.
Since DCINEMA specifies their signals slightly above this (2048x1080, 4:4:4, 12 bits), then the cheap way out was to use two of these serial interfaces HD-SDI together and carry "half" the information for the signal in one cable and the rest of the (additional color) information on the other.
Thus, most servers communicate with (TI) projectors using two non-standard, encrypted, variations of the HD-SDI standard outputs/coaxial cables/inputs. This has UNOFFICIALLY started to be known as dual DC-SDI (Digital Cinema Serial Digital Interface) instead of HD-SDI, since DCI is now sort-of a wide standard on itself. It would mean the usage of dual HD-SDI to transmit 2K-4:4:4-12bits-XYZ within the DCinema industry instead of the original intention of using it for HD-4:2:2-10bits-YCrCb signals within the Television industry.
But there are other standards, like the blooming 3G-SDI ( SMPTE_424M ), which, when used in a non-standard way, could allow the transmission of a DCI 2K signal over a single cable instead of having to use two, like it's being done today.
Eventually, 3G-SDI may lead the way to the future, since it's getting kind of messy to have to use two cables for a regular 2K projector, 4 cables for dual projectors (Imax), and 8 cables to a theoretical 4K projector.
Also, when you do 3D over a "regular system" (i.e. not-dual-projection), since the server only has a dual HD(DC)-SDI connection and current projectors only has a dual DC-SDI input, they must downgrade the quality of the image throwing away half of the color resolution (4:2:2) and using only 1/4 the amount of possible colors (10 bits instead of 12 bits), because the 3D signal doesn't fit at full quality through the only two cables the way it comes on the DCP package from the studio.
If you have a server with quad HD(DC)-SDI outputs, like some do (and is an option on others), then you can use the full quality of the signal when paired with a dual-projection setup (like Imax) for 3D as well.
Once again, DCI is closing their eyes at 3D being commonly shown at 4:2:2 10 bits for the sake of it being the cheap way to do it currently with a single projector, and giving the scheme their blessing in spite of such an image being hardly (at all) any better than a blu-ray disc, specially in Scope 3D movies shown on 2K projectors.
Sony has its own way from the server to the projector, so it can also preserve the full resolution and color depth when playing back 3D.
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Julio Roberto
Jedi Master Film Handler
Posts: 938
From: Madrid, Madrid, Spain
Registered: Oct 2008
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posted 06-01-2009 11:02 PM
I haven't started to work with DCI servers yet, but it looks fine to me.
If you have an older non-triple flash non-"Brilliant 3D" projector and the movie is 3D flat, you use your
-3D Flat 1920x1038 on Channel 15
If you have a newer projector, then you use:
-3D Flat 1998x1080 on Channel 13
...which seems to be misstagged in your server.
If it is Scope, same thing:
-3D Scope 1920x804 on Channel 16 for non-triple flash old projectors
-3D Scope 2048x858 on Channel 14 for newer ones
There is no (true) setting for 2048 flat, as DCI specifies 2K flat 2D-or-3D as 1998x1080 and 2K Scope 2D-or-3D as 2048x858.
The other smaller resolutions (1920x1038 and 1920x804) are, once again, compromises made for earlier projectors that couldn't support the whole resolution in 3D 48fps, and DCI turned a blind eye to in order to rush the adoption of digital, but that doesn't really meet their own specs ...
Worst case scenario: you have an older non-triple flash projector with a 3D Scope movie. You are actually probably putting on the screen a 1920x804, 4:2:2, 10bits picture, at 24fps. If you are watching Smallville or American Idol on your TV, you are watching a 1920x1080, 4:2:2, 8bits picture, probably at 30fps (or 25fps). ![[Roll Eyes]](rolleyes.gif)
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