Pretty as it is, 70mm film has been deemed too expensive for shooting Hollywood productions. So this is how IMAX preps finished movies for the up close and personal demands of IMAX.
(Left, 35mm reel. Right, IMAX reel.)
Before we move on, let's explain IMAX film. Technically, it's a 70mm standard that—unlike the 70mm that was popular back in the day with big movies like Lawrence of Arabia —has been turned sideways on the celluloid. So while typical 70mm motion picture film runs vertically and takes up 5 perforations on the film strip, IMAX runs horizontally and takes up 15 perforations. Yes, that means that the IMAX 70mm standard is three times bigger than normal 70mm and nine times bigger than 35mm.
Now do you know why we've been making such a big deal about it?
Kodak estimates their 35mm film stock to run at an equivalent of 6K digital resolution—that's 2K better than the famous 4K Red One camera. As Kodak makes IMAX film out of the same ink/material that they make 35mm film, to scale, you can argue that IMAX reaches a theoretical equivalent of 18K digital, or 252 megapixels. In real application, even an expert we talked to within IMAX doubted if the viewer can see 18K projected, estimating that 12K might be a more accurate guess.
IMAX film is—unquestionably—far more impressive than any other standard on the block, analogue or digital. So how the heck can IMAX claim they can take a normal 35mm film, like Star Trek, and play it on IMAX screens?
(Left, 35mm reel. Right, IMAX reel.)
To be fair, this insanely high resolution 70mm film format is only used in the huge free-standing IMAX theatres found in museums and parks throughout the world. As you might recall from our previous story on IMAX "retrofitting" in multiplexes, IMAX's digital projection system used in those theatres is a mere 3K or 4K in resolution. There's definitely a double standard, and though it's still an impressive theatre experience, it's not the same and you have the right to feel a bit ripped off if you're expecting a 70mm print.
But regardless of the film's destination, it is carried through roughly the same process known as DMR (which, enigmatically, stands for "digital re-mastering"), which starts with a digital encoding of a standard 35mm Hollywood film, and ends with a remastered, (usually) higher-resolution digital format for multiplexes, and a bunch of reels of remastered crazy-high-resolution 70mm film for the true IMAX theaters.
During my day at IMAX HQ, I kept referring to the process as "uprezzing"—the same mundane miracle that allows DVDs to play on HDTVs. But every time I used this term, it was met with a shiver from production personnel. After seeing their process, I still think "uprezzing" fits, but blowing up a film's resolution requires a lot of tweaking and artistry, so I can appreciate their reaction a bit more.
When IMAX converted Apollo 13, the first 35mm movie to be converted to IMAX, the whole process took three months. Now, a team of about 20 digital artists can convert a movie in three weeks with the help of a powerful render farm.
Source film generally arrives at IMAX pre-digitised in either 2K (2048×1080) or 4K (4096×2160) resolution. In the case of the Dark Knight, some footage reached 5.6K and even 8K. It leaves IMAX at anywhere from 4K to 8K resolution, sharpened with film grain reduced.
The staff views the movie while analysing general trends like lighting and colouring in a film. Each movie has a certain overall look, and then each scene (exterior night, interior day, spaceship orbiting planet, etc.) has a certain particular lighting and coloring of its own, so they note all of the overarching trends—the keys to each scene type—and then they tailor uprezzing (or just polishing) algorithms to take them into account. The algorithms are unique to the film but the result, after all the painstaking customisation, is a fairly automated hit-the-render-button-get-an-IMAX-movie video-scaling process.
Well, almost. About 80% of the film's frames come out of the automated process looking great. It's the remaining 20% that's the real bitch. Sometimes the process arranges pixels in ways that bring forth unforeseen oddities in the image. These tainted frames are either sent back through the render farm again with tweaked settings, or they are fixed by hand.
I watched a member of the IMAX team screen a clip from Night at the Museum 2 in which Owen Wilson is green screened in front of a pile of sand. He had just a few frames of the film looped on his monitor, less than a second of real material, and they looked fine by my account. (Our apologies for a lack of pictures, but acquiring studio rights to images has proven difficult.)
Of course, this was a 20-inch display, and the film would play on a screen...a bit larger than that.
So the film analyst urged me to look closer, at which point I noticed an aura of softness around Wilson's figure, killing the texture of the sand. With a keypress, the screen snapped to the same frames in the 35mm, which looked fine. The automated uprez process had highlighted some of the intentionally hidden seams of the special effects.
That footage was sent back to the artists to fix by hand, as are a lot of the 10,000 to 20,000 frames of film IMAX processes during a day of DMR work.
That's just the artistic side, which happens for both the multiplex digital IMAX and the 70mm film IMAX —there's also the delicate matter of assembling all this film properly back into one big strip for the the true IMAX theatres and their film projectors.
IMAX reels and 35mm reels don't line up in a convenient 1-to-1 ratio. Because the film is physically bigger, there are almost five IMAX reels for every reel of 35mm. Not only do they have to make sure every single cut from one reel to the next is smooth, they have to make sure everything stays in the right order, a huge pain, especially when just a few frames are being fixed at a time.
The film part of the process culminates in a scene-by-scene analysis of the 70mm dailies—172,800 frames for a 2-hour movie—viewed on a lightbox with the 35mm film right beside the IMAX uprez. If the in-and-out points are the same, things are generally fine. If not...it's gonna be a long night.
But even with all this earnest work of artists and video wizards, will that original 35mm content look better when either upscaled or just cleaned? I'm going to say yes, not because I've had the opportunity to analyse a pre- and post-DMR film with my own eyes, but because a staggering amount of the staff's efforts are simply to eliminate film grain. And while, to me, that's a sin to do for archival film restoration or 1080p Blu-ray transfers, I can understand the necessary evil when a movie is expanded to epic proportions and the audience is forced to sit in ridiculously close proximity to the screen. Nobody pays to see blackheads the size of a house, especially on Ben Stiller.
Besides, regular IMAX movies shot on IMAX 70mm film are always going to look better. Anyone who's ever used Photoshop knows there's no way that digitally enlarging an image will ever look as good as an already-large image in its native resolution. Parts of The Dark Knight were shot for IMAX, and I've seen that footage on true 70mm IMAX projection. I've also seen plenty of 35mm movies (like Star Trek) up on the IMAX screen, projected from a 70mm film print, after DMR. There is absolutely no comparison. Star Trek is fun to watch on a big screen. The Dark Knight is so ridiculously detailed that your brain can barely process it.
As much as I can admire IMAX's DMR process and the truly staggering amount of effort going into digital enhancement, this does beg one question of Hollywood: You've got hundreds of mil lions for talent and marketing, but you don't have enough cash to buy a truckload of 70mm film and deal with tricky cameras? I find that hard to believe.
Read more from Gizmodo Goes to IMAX