All of the vfx sequences were prevised by Persistence of Vision, including some in stereo.

"As we photographed the entire film in stereo, using specially designed rigs holding two cameras, ensuring that the two 'eyes' matched was another challenge. Lenses are physical things which, even though they are built to pretty tight tolerances, are never identical. The two images created can be off in scale, rotation, vertically misaligned, have a focus or depth of field mismatch, have a different exposure. All these things need to be adjusted so that the images are normalized with the only variation between the two being a horizontal offset, like your eyes. Otherwise, viewers will have a hard time resolving the two images. Even if they can, eyestrain and headaches will ensue. Not good for a full-length feature film!"

All of the vfx sequences were prevised by Persistence of Vision. "One sequence, the floating rocks, was also prevised in stereo, which allowed us to test out some of our thoughts on the interocular distances (how far apart the lenses should be) and convergence plains. We did an early test of an actress in a cave environment, shooting with the stereo cameras, to put everything through a dry run, to test out stereo pipelines in some of the facilities and to do some (image) development in stereo."

As for the software being used on the production, since there were multiple vfx firms involved, each used their own platforms.

"Each had to be enhanced to create compatibility with stereo. Some were tuned with proprietary GUIs to try to simplify working with two corresponding eyes. For others it was just a matter of designing a stereo workflow.

Frantic Films VFX's main contribution was the CG ocean for the raft storm sequence, which included rain, fully articulated creatures, water surface simulation, water spray dynamics and blowing mist. Courtesy of Frantic Films.

"On the set we used hollow cubes and grided markers to help the camera tracking in post, but rig and lens metadata was also encoded into the DPX frames. This information was then used by most vendors to further simplify the camera tracking process."

Townsend also credits FrameCycler as a viewing tool of major importance.

"Being able to view shots in stereo was key. Initially I reviewed work on a monitor, using Iridas' FrameCycler using active shutter glasses. The ability to analyze full resolution shots in realtime, in stereo, in my own time, without the constraints of having to book a theater, was incredibly important. Discerning what is right and wrong about a stereo image is complex. There are so many aspects, which can cause an image to be wrong. Is an element within the image flipped, misaligned, out of synch, in the wrong stereo space? Are the left and right eyes of different exposure? Are there photographic anomalies (lens flares, blur, dust, etc) that appear in one eye but not the other? All these things have to be studied in order to move the shot along, from a stereo point of view. And that doesn't even take into account the aesthetics of the shot itself; that was a whole other ball game."

Another viewing tool that Townsend used was Acuity's QuVis software.

"Having viewed the work on a monitor, I then reviewed the work on a 23-foot screen, using dual projectors, passive circular polarized glasses and Acuity's QuVis software. This allowed me to look at the work from an audience's perspective and to examine the stereo space more accurately."

Townsend admits that working in stereo is working in a whole other dimension. "It relies on techniques that we, as an industry, are only just learning, but that future promises to be richer and far more immersive, from an audience's point of view."

Frantic Films VFX, a division of Prime Focus Group, served as a lead visual effects provider on the film. The filmmakers came to Frantic because of the studio's expertise in creating believable digital water effects using its proprietary fluid simulation suite, Flood.