You’ve got the DVD. Let’s just say that you have all the rights to the film, too. This is how you would turn Titanic, filmed in 2D in 1997, into the 3D version released this week. True, James Cameron did it better: he took a painstaking year to do the job and he spent £11.3m on it.
But in principle, this is how he did it – and not only will it show you why it cost so much, it’ll demonstrate exactly why so many previous 2D to 3D conversions have been done poorly.
Take a frame from the original 2D Titanic.
This is, of course, from when Jack (Leonardo DiCaprio) and Rose (Kate Winslet) are standing at the very front of Titanic. It’s a famous shot to start with but we’ve also picked it because it’s comparatively simple: there are only two people and the background is uninterrupted sea and sky.
Separate the foreground and background parts of the picture.
We used Photoshop to mask out Jack, Rose and the bits of the Titanic. Even for such a simple shot, this is harder than you think: Kate Winslet’s hair, for instance, is blowing in the wind and you’d have to be pixel-perfect to get it all. We weren’t.
Fill in the background.
Real 3D works by filming a scene from two very similar but different angles. Depth is achieved by each angle showing a slightly different part of the background. When you fake that by converting 2D to 3D you hit the snag that there isn’t any more of the background: you can’t see behind Jack and Rose because whatever was really there at the time was not filmed.
Some 15 years on, you can’t go back to shoot more material, either. So instead you have to digitally paint in what ought to be there. In this case, we know there was sky and sea behind them – and we know what that looked like, because we can see such a lot of it. You fill in the rest by copying the parts you can see and digitally filling in that black hole where our characters were.
Recombine all the elements. We’ve done this especially roughly here so that you can see a little bit of depth in the image. It looks like they’re standing in front of a painted backdrop – but it does look like they’re in front of it.
When you’re happy with that, move on to the next frame and repeat. At 24 frames per second and a running time of 194 minutes, that means you’ve got just 279,359 frames to go.
That’s not really how they did it
Oh, yes it is. With unimaginably more precision, patience and artistry, but yes. That’s how it was done.
Using the same techniques, though, they did go further with Titanic than we have, or than some other 2D to 3D converted films have. Look again at our example image: in Titanic 3D, they moved Jack slightly further back from Rose. They did it the same way: separating his image and then drawing in the bits that a real 3D camera would’ve caught.
Then, of course, Jack’s coat is moving in the wind so sometimes that’s further away than others.
Similarly, parts of the Titanic rope work and hull rails you can see would be closer to us than the characters, some further away. So it’s as much a job of determining where things ought to be as it is then doing this layering trick.
It gets harder
In theory, you just do this over and over and better and better until you’ve done every shot. But you know there are scenes with thousands of extras and maybe it’s even harder with ones like those on the bridge, where there are just a few characters.
If you follow this method precisely for every person and every single thing in shot, you end up with absolutely everything popping out of the screen. James Cameron explains that it’s all a matter of choices: “You have to be judicious,” he said to US press. “There is a shot where Leonardo is leaning over and he hands Kate a note to meet him later. Right in the foreground there’s an out of focus lamp.
“If I was doing that shot in 3D, I’d have moved that lamp. When we did the 3D conversion at first, it became a shot about a lamp. You weren’t even looking at him because there was this lamp right in your face. And this is where the film-maker has to step in and say ‘this isn’t a shot about a lamp’ and collapse the stereo space. That shot’s now barely in 3D.”
What we’ve ignored
Lighting. If we’d moved Jack back a smidgen behind Rose, we would also have had to change the lighting on him because from one angle he’d be a touch more in shadow.
Also, myriad shots in Titanic were entirely computer generated: not just images of the ship at sea but often background characters on the deck were CGI. All of those could be redone by re-rendering them from the computer originals.
But apart from that, so long as you have patience and a steady hand, you could now make your own 3D Titanic.
Titanic 3D is released Friday 6 April 2012