As of 2012, around 60% of all cinema screens worldwide have been converted from film to digital projectors. Over half of those digital screens are outfitted with stereoscopic (3D) projectors. By 2015, it is expected that almost every cinema screen will be digital and that film projection will all but die out.
Digital cinema is a lot more than just a digital projector, however — the film industry, as I’m sure you’re aware, is a multi-billion-dollar behemoth, and digital cinema is probably the biggest shake-up since the advent of 35mm film itself. There’s a whole framework behind digital cinema, from filming, to digitization, to distribution and projection, with some seriously cool tech along the way — which, of course, we’re going to dig into.
For the most part, movies are still predominantly shot using 35mm film stock. Cinematography is certainly moving towards digital cameras, but the legacy of film is so great — the equipment, the process, the human expertise — that it won’t disappear for a long time. With the rest of the movie making process being almost entirely digital — from editing, to distribution, to exhibition — digital footage is a lot easier and quicker to work with. Just as digital photography usurped film photography, digital video cameras are destined to replace film video cameras, with digital cameras from the likes of Canon and Red leading the way.
The irony of using film cameras, though, is that they’re all scanned into a digital intermediateanyway. Almost every big film of the 2000s was converted from film to a 2K (~2048×1080) digital intermediate — so even if you think that film has a higher resolution than 2K, or if the grain is somehow more attractive than pixels, tough luck. If the film is shot with a digital camera, then this scanning stage (which is quite expensive) can be skipped.
Once you have a digital intermediate, talented artists take care of the editing, color grading, and CGI (computer generated imagery).
In 40% of cases (conventional projection cinema screens), the digital intermediate is then transferred back onto film, and copies are made (at a cost of thousands of dollars each) for each cinema that will be screening the movie. For digital screening, the digital intermediate is exported as adigital master, which includes all of the video, sound, and data required to project the movie correctly.
Now we get onto the techie bit of digital cinema. Before distribution to cinemas, the digital master is encrypted and compressed into a Digital Cinema Package (DCP), which is a standard format defined by Digital Cinema Initiatives (a joint venture by the major movie studios).
A DCP contains a bunch of multi-gigabyte MXF (Material eXchange Format) files and playlist/index XML files (very similar to the way a DVD contains VOB and IFO files). MXF stores video in JPEG 2000 format (an updated version of JPEG), at 2K resolution up to 60 fps, 4K resolution up to 30 fps, and 2K 3D at 48 fps. XYZ color space is used, with 12 bits per pixel precision (36-bit color). The max bitrate of MXF video files is 250Mbps, or around 30MB/sec. This means a single movie in DCP format is around 200GB. (By comparison, Blu-ray movies generally have a bitrate of around 30Mbps, or 3.8MB/sec.)
The audio MXF files use a standard WAV container with a 24-bit sampling rate of 48 or 96KHz. Up to 12 separate, concurrent audio channels can be used.
Most importantly, these MXF files are encrypted using 128-bit AES — if they fall into the wrong hands (those of a pirate, say) it is virtually impossible to decrypt them.
Finally, the DCP is copied onto a hard drive, which is protected by a rugged enclosure (usually a CRU DX115). These hard drives are then distributed to cinemas via courier. It is also possible to deliver the DCP directly to the cinema via high-speed internet connections, though this isn’t usually done.
Digital cinema servers
Once The Avengers DCP hard drive arrives at the cinema, it’s slotted into a digital cinema server (DCS). A DCS is basically a proprietary, rack-mounted computer that has a hot-swappable hard drive bay on the front, and a bunch of video/audio outputs on the back. There are many companies that produce DCSes, but Dolby (pictured below) and Sony are two of the frontrunners (and their systems run Linux!)
When a new hard drive is slotted into the DCS, the movie is “ingested” onto local storage (usually a big, multi-terabyte RAID). This is where the encryption kicks in: Every DCP hard drive is encrypted with a key that is only known by the target DCS. In other words, whoever originally encoded the DCP has the cinema’s public key — and then when the movie is ingested, the private key is used to decrypt it for playback. The certificate that accompanies every DCP also defines how long the movie is valid for (i.e. the studio can force The Avengers to expire within a month, if it wants). This ensures that DCP copies don’t go walkabout, and explains why the pirate movie scene still has to rely on cam, telesync, and telecine releases (though I wonder why no one has managed to extract that private key from a DCS yet…)
It is possible for a cinema to have just one central DCS that outputs to every screen. I’m told that a single copy of a movie sitting on a DCS can be streamed to more than five screens at the same time (though with each stream requiring 30MB/sec, it’s more likely that we’re talking about a cluster of DCSes all slotted into the same rack, each with a mirrored copy of the film). Generally, a cinema’s DCS is controlled using a Theater Management System, which could be a discrete computer or just a web-based interface running on the DCS. The TMS allows employees to set up a playlist for each of the movies currently showing at the cinema.
And finally we arrive at the bit that most consumers actually care about: digital projection. Because most digital intermediates over the last decade have been at 2K (2048×1080) resolution, a lot of cinemas are still outfitted with 2K projectors. With the emergence of 4K digital cameras from companies such as Red, and 4K projectors from the likes of Christie and Sony, 4K digital cinema is making inroads.
Digital projectors are beastly machines, with huge, 4-kilowatt xenon lamps that produce tens of thousands of lumens. Price-wise, these projectors — such as the Sony SRX R320, pictured right — are usually around 50,000 to $100,000, with replacement lamps costing more than $1,000 each. Fortunately, for that price you do get 3D projection thrown in for free. At the core of nearly all digital projectors are Digital Light Processing (DLP) chips made by Texas Instruments.
In case you’re wondering, these cinema projectors are worlds apart from the Sony and Red 4Kprojectors that we’ve written about recently (and they’re significantly cheaper, too). The Sony and Red models are home theater projectors, with lumen ratings of a few thousand — about a tenth of the Sony SRX R320, which needs tens of thousands of lumens to illuminate 20+ meter screens.
The future of digital cinema
There is no doubt that cinema is moving away from film and towards digital — but is that a good thing? Digital distribution is undoubtedly more flexible than moving around bulky, costly film reels — but on the flip side, what about archiving? Properly-stored film stock can be archived for a hundred years, and unlike hard drives and other digital storage mediums, there’s no risk of film playback ever being antiquated (all you need is a lamp).
Driving down the cost of distribution has also significantly empowered student and independent film makers, and as the cost of digital cameras and storage continues to drop, this trend will only accelerate. Much in the same way that we’re drowning in digital photos, we will soon drown in digital videos and movies (if we’re not already).
Looking forward, the resolution of digital cinema will eventually hit 8K (which should finally quiet any digital image quality naysayers), and we should begin to see a lot more movies played back at higher frame rates like 48 and 60 fps. The Hobbit will be the first worldwide release of a 48 fps film, shot entirely with digital Red 4K cameras — and I’m sure it won’t be the last.