On Stranger Tides is the fourth film in the Pirates of the Caribbean series. This time around Jack Sparrow and Barbossa are searching for the fountain of youth, but so is their foe Blackbeard and his daughter. We talk to Cinesite about their visual effects contribution to the film, which was the studio's first full stereo 3D project, with the work spanning a carriage chase sequence through London, CG toads and the creation of Barbossa's peg leg.
Early in Tides, Sparrow eludes members of the English Royal Guards in a dramatic carriage chase through the streets of London. Production shot scenes at the Old Royal Naval College in Greenwich, which housed a collection a historic buildings dating back to the late 17th and mid 18th centuries, dressing the area with stand-in mud, period carriages and numerous horses and extras. Overall visual effects supervisor Charles Gibson also erected a series of 250-foot blue screens on location, with Cinesite tasked to create and populate CG streets, buildings, and set extensions and digital people for the 200 shot sequence.
Cinesite visual effects supervisor Simon Stanley-Clamp devised 19 different street environments for the chase sequence, presenting designs as concept art to Gibson. That way, the streets and buildings could be constructed as digital creations efficiently with the specific angles in mind. Buildings were realized using photographic reference from the Greenwich area and CsPhotoMesh, Cinesite’s proprietary photogrammetry and 3D scene reconstruction software solution for geometry capture.
"Given a set of digital images of a static scene, CsPhotoMesh produces a textured 3D mesh accurately representing the scene geometry and 3D cameras matching the original photos positions," explains Stanley-Clamp. “The tool is fully automatic. All it requires is to drop all the images in a directory and run the command. This kicks off a reconstruction process on our renderfarm resulting in a 3D mesh and camera positions ready for texturing."
"It's essentially a difference map that's generated as a vector analysis from three different views," adds Stanley-Clamp. "You get left and right and then height as well. The vector difference will generate a very basic geometry. It's like a low poly LIDAR scan, although we just take the stills with a camera on a tripod."
Buildings were then modeled in CG, and this geometry was cleaned up and refined in Maya, with reflections from other sides of the street, for example, added into windows. To match the period nature of the scenes, artists would also 'dirty' the initial renders. "I took our first render into Photoshop," says Stanley-Clamp, "then grunged it up and that was our base. We used isolated mattes more than anything. It was basically a question of giving it a little bit more shape, say the occlusion shadows, and adding reflections into the paving stones for example." Extras were also shot on bluescreen, extracted, and then placed on cards and added in true 3D space to the scenes in Nuke, ensuring that throughout the process full control was maintained over the stereo aspect of the production.
A broad issue Cinesite had to confront was just how dirty to make the buildings, including what would have at the time been a freshly re-built St Paul's Cathedral. "It's always a huge debate in period work because back then it would have been new and clean," notes Stanley-Clamp, "but that doesn't always fit into what movie audiences perceive. It was funny, actually - there were areas of Greenwich shortly before the shoot that were completely sandblasted and cleaned up. It was quite galling! From a photographic point of view, you can see more detail if it's dirtier."
For one scene in the chase sequence, Cinesite was called upon to add a late smoke addition for a shot in which Sparrow evades the Royal Guards by holding onto a sign above him. "The director thought that he had got away too easily from his pursuers," recalls Stanley-Clamp, "and that he should really be obscured by some fire and smoke. So literally the day before we delivered, we shot the smoke elements with a simple rig, eye-matching the move which was a tilt-up off into the distance. We did explore a CG route and there is some CG smoke underneath all this, but the practical approach made sense in terms of timing."
Suitably fit for a pirate, Captain Barbossa (Geoffrey Rush) sports a peg leg for On Stranger Tides. During filming, Rush wore a blue stocking covered with tracking markers. A CG leg modeled in Maya and rendered in RenderMan was then animated and composited into the shots by Cinesite, once painstaking plate preparation had been carried out. "This can be really tricky work," notes Stanley-Clamp, "because the real leg completely occludes other characters on some occasions. We had to re-build much of the scene from either side of the plate and other shoots. I did shoot clean plates, but the camera movement or actor’s action will never be an exact match, so we also ended up manipulating a lot of frames from within a take."
In addition to the carriage chase work and peg leg, the studio also contributed several CG toads, which Captain Barbossa collects to use for some poison. The toads were modeled in Maya and included sub-surface scattering for their skin. Artists also had to track the reptiles in a glass jar, with a CG version created for tracking and to create the appropriate refraction and displacement on the toads. Cinesite's total shot count was 248 finals for the film, and included included various wire removals, re-speeds, environment work and clean-ups, shots relating to the fountain of youth, ship water enhancement, plus shots inside St. James Palace for a scene of Sparrow escaping by clinging onto a chandelier, with Cinesite adding outside views to the windows, performing re-speeds, rig clean-up, Barbossa's peg leg, and, to top it all off, a digital cream puff.
Images © 2011 Disney Enterprises, Inc. All Rights Reserved.
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