James Cameron’s ‘Titanic’ sailed back onto theater screens last week sporting a fresh 3D makeover. This follows last year’s very successful run of ‘The Lion King 3D’. If similar projects continue to make money, we can no doubt expect to see more beloved classics subjected to the 3D treatment – not to mention that even many brand new movies are converted to 3D in post-production. But how exactly are these conversions actually done? The short answer, of course, is: “Computers!” The long answer is a little more complicated.
As you probably know, 3D images are created by viewing a scene from two viewpoints slightly offset from one another, one that goes directly to the viewer’s right eye and one that goes directly to the left. Movies that are natively produced in 3D use camera rigs that capture both viewpoints on set. (CG animated movies render the two views separately.) However, a movie that was originally shot (or animated) in 2D only has one viewpoint on the action. The second camera view must be created artificially using software that interpolates what that view would look like based on cues in the existing imagery.
Some of this can be automated based on generalized rules about how photographic depth usually works. For example: bright objects are typically closer than dark objects; large objects are often closer than small ones; objects with a hazy focus probably belong in the background, and so forth. Many 3D TVs, Blu-ray players and outboard video processors (like the recently-reviewed 3D-Bee) can do 2D-to-3D conversions in real time, but the results are erratic at best. While these devices will no doubt get better with time, a proper conversion job requires human interaction and guidance.
The technicians, called stereographers, will look at the movie on a frame-by-frame basis and create a “depth map” or “depth script” for each frame that determines which objects get pulled forward, which get pushed backward, and how much in each direction. To convert ‘The Lion King’, 60 artists worked on the movie for four months. ‘Titanic’ was an even bigger project. That one required 450 people and two years of labor, at a reported cost of $18 million.
As described in the ‘Titanic’ article:
Fortunately for those converting feature films, they already know how far away each object on the set was — or was supposed to be — when the movie was made. Productions stills also provide additional information. While this means they don’t have to guess or estimate depth, humans still need to painstakingly assist the software in adding depth information to hundreds of thousands of frames.
Many of the necessary decisions are more artistic in nature than technical. ‘Lion King’ stereographer Robert Neuman explains:
The way I approach depth on the movie is to create a depth score, which is a similar process to the way that a film composer creates a musical score. A film composer uses the rises and falls of the score to echo the emotional content of the film. I try to do the same thing with depth in the movie…
I equate stereoscopic depth to emotional depth. In other words, the shots in the depth script with a value of one get the minimum amount of depth. We’d pull out all the stops on shots with a value of ten by using as much depth as possible. Additionally, if there’s a scene where we’re supposed to feel detached from a character, then I put the character further back into the background. If we’re supposed to feel connected to a character, I bring them further forward. In this way, we’re not using 3D randomly. We’re using 3D as part of the narrative.
The amount of time, effort and skill expended on the project will mark the difference between a tasteful conversion like the above and some of the quick-and-dirty conversions that have plagued recent theatrical releases, such as the notorious ‘Clash of the Titans‘.
Back to that ‘Titanic’ article:
One reason [James] Cameron says that previous 3D conversion efforts have failed is that they were shoehorned into an already busy production schedule, meaning the filmmaker didn’t have the dedicated attention needed to ensure the conversion came out the way they wanted. He also credits his learnings from Avatar with helping him know how to work on this conversion — experience which most other filmmakers don’t have.
Yet when it comes to older films like these, even the best possible conversion will still remain limited by one unavoidable fact: These movies were not originally made with 3D in mind. When James Cameron directed ‘Titanic’, he chose his camera angles, lighting and staging based on the rules for 2D photography, which are not the same as those for 3D photography. Contrast this to a more recent movie that was converted to 3D in post-production, Tim Burton’s ‘Alice in Wonderland‘. Although Burton shot his film in 2D, he planned for 3D from the beginning, and had stereographers on set to advise him on the best camera angles and staging that would maximize the 3D impact. Neither ‘Titanic’ nor ‘The Lion King’ had that benefit. No matter how tastefully done, the conversions for those films were imposed after-the-fact and are, in a way, just the 21st Century’s version of colorizing black & white movies.