In fact, MPC generated 578 out of 800 total vfx shots under the supervision of Richard Stammers (in collaboration with sister company Technicolor India, which provided matchmoving and roto work). The remaining compositing, replacement and other enhancements were done by Lola Visual Effects, Hammerhead, Nvizible and The Senate.
"We always knew there was going to be a certain amount of CG work, taking on bigger sequences," Stammers suggests. "For example: the French invasion off the coast of England. When we were discussing this early on, Ridley talked about a large invasion fleet of maybe 400 boats and thousands of French troops, so obviously we knew there was never going to be a practical way to achieve all of that. Even with eight practical boats and 500 extras, we still had to add to that with a CG fleet of 200 ships and 6,000 soldiers. A lot of the time, Ridley's shooting style creates an amazing palette of great shots to work with to the point where sometimes you're not adding anything to the background, and other times it's just filling in some of the gaps. He was very pragmatic about what we had to do."
"We had one scenario that put us into a little bit of a technical challenge," Stammers adds. "Ridley needed the CG guys to come closer to camera because the practical stuff wasn't able to achieve that. So we were left in a position where we had to go back to our original assets and up res all the details in the models and the textures and additional post animation simulations on top of our motion capture library. We needed to create some additional nuances for the fact that we were using so many similar animations so close to camera. It worked out really well in the end and is a good hero shot."
MPC's digital environment work focused on two main locations: London and the beach setting for the French invasion and final battle. A combination of matte painting and CG projections was used to recreate the medieval city, which featured the Tower of London and included the original St. Paul's Cathedral and old London Bridge under construction, in the city beyond. The production's football field sized set provided the starting point for MPC to extend vertically and laterally, and in post alternate digital extensions were also created to reuse the set three times as different castle locations. Each extension was a montage of existing castles chosen by Scott and production designer Arthur Max. For the beach environment, MPC had to create cliffs that surround the location, and were added to 75 shots. Once approved in concept, the cliff geometry was modeled using Maya  and interchangeable cliff textures were projected depending on the lighting conditions.
MPC was also responsible for creating the crucial arrows. Practical blunt arrows were used in production where ever possible, but most shots presented safety issues so digital arrows were animated instead. Arrows were added to more than 200 shots, with 90% of these being handled by the compositing team using Shake and Nuke . MPC developed proprietary 2D and 3D arrow animation tools to assist with the volume of arrows required, which included automatically generating the correct trajectory and speed, and controls for oscillation on impact.
"Axel Bonami, a compositing lead, created a Shake macro that allowed the compositing artists to generate arrow animations almost automatically. He wrote some variations to this macro to specify where a number of arrows were fired from or landed and calculated trajectory and speed based on references that he worked from. The only input was a library of arrows they photographed under different lighting conditions.
"My biggest fear was that we had such a large compositing team and that there would be inconsistency in terms of the style of animation between one person and another and this allowed it to be a bit more consistent between everyone and save a lot of time. It was an incredibly effective tool and a good success."
Bill Desowitz is senior editor of AWN & VFXWorld.