King arthur
Trevor Hogg talks to CG supervisor Stuart Penn about making slow-motion battles and monstrous creatures for King Arthur
We discover the VFX secrets behind the epic movie scenes
The elephants were 300 feet Tall, so we had To Take That into account with The dynamics and The speed They move Stuart Penn, CG supervisor, Framestore
The story of a man who would be king, with the ability to pull a special sword from a stone, gets reimagined in the kinetic filmmaking style of Guy Ritchie with the release of King Arthur: Legend of the Sword. Dealing with all of the speed ramps and slow-motion action was no easy matter for Framestore, with facilities in London and Montreal looking after 437 shots involving elephants, serpents, eagles and a menacing adversary known as Nemesis. “The fight between Arthur [Charlie Hunnam] and Nemesis for us was the biggest thing. Most of that sequence was shot at high speed and re-sped or vari-timed,” states Framestore CG supervisor Stuart Penn. “All of the simulations around it had to be vari-speed as well. If you’re doing explosions, cloth simulations or a big splash you have to retime them so your physics are correct for the varispeed, not for real time.”
Massive animals are summoned by Mordred to attack Camelot as he attempts to lay claim to the English throne. “The elephants ended up being 300 feet tall, so we had to take that into account with all of the dynamics and the speed that they move,” remarks Stuart. “You need to put in an additional level of detail for things like hair and dirt to avoid them just looking like scaled up versions of normal elephants.” Texture variations on the skin were produced at multiple levels, which could be read either far away or with a foot filling an entire frame.
The overcast and misty environment was modelled on a real place in Wales called Nant Gwynant, near Mount Snowdon. “We did extensive photogrammetry [surveying and mapping with photography] with helicopter plates, but largely what you see in the film is fully recreated CG.”
“We built a detailed model for what Camelot castle was to look like, where it would sit in the terrain, and worked out which parts of the real valley we were using and what needed to be modified to fit the castle in,” states Stuart. “The structure and
shape of the castle and the courtyards all came from the production art department.”
Practical sets, including interior courtyards, a gatehouse and a section of viaduct were built at Leavesden Studios. “If you’ve got something real to match to, it’s always preferable. There were LIDAR and photo scans of sets. There were a lot of shots where we had to do fully CG versions of the same area because they were wider or more complicated than what was practically shot. The destruction of Camelot was CG as it all had to be choreographed to the action.”
making giant Creatures
New tools were developed to produce good scale interaction for the giant and baby serpent as the creatures would be seen in close-up shots. “We weren’t going to be able to get away with just putting a scale texture map on,” notes Stuart. “We laid out individual scales along the snake’s body and created a system called Snake oil that allows the scales to slide around the skin and over each other. The serpent was rigged to deform when it came into contact with the ground.”
The size of the giant serpent caused some creative problems. “It could easily wrap around the inside of the throne room twice. There was a little bit of cheating going on in there just to keep the serpent moving but not getting in its own way,” Stuart says. “The serpent also covered the lights in the set so we had to do some creative thinking for how it was lit and relight the environment.” The baby serpent was not a scaled-down version, but was given baby features, says Stuart. “Alterations were made to get a different proportional ratio between the eyes and head so that the baby serpent had slightly bigger eyes.”
An eagle that carries the baby serpent into Camelot was groomed and colour matched feather by feather to a real eagle that was photoscanned. There was also a stuffed eagle on set for lighting reference. “When it is in flight you get the wind rippling through the feathers so we had a dynamic system to simulate that interaction,” says Stuart.
The bird was not much bigger than a normal one, as a real eagle appears in some other sequences. “We stitched together helicopter plates and used photogrammetry to recreate geometry for that part of the valley. In that particular scene, we were matching the lighting to another plate that had been shot at a slightly different section of the valley, but we liked the sunset so used the sky from the other plate. It’s based on a real look of a real location even though we moved the location around, moved and modified the valley, and added a castle with an island around it,” explains Stuart.
Animating A BATTLE
Arthur battles his evil uncle King Vortigern (Jude Law) who has been transformed into a huge and vicious being named Nemesis. “It’s the final act of the movie so had to be epic,” notes Stuart. “Charlie Hunnam was up against a stunt guy on stilts pretending to be Nemesis so that we had the right eye line
and height. Charlie was very physical in his performance and that helped us when we came in to replace the stunt guy.” Nemesis was inspired by a dummy cadaver used by forensic scientists that has grey, mottled flesh. “We also brought a body builder in to run through poses and to see how muscles of that actual size move and work.”
“The environment [where the fight between Arthur and Nemesis takes place] was fully CG because there isn’t anywhere on this planet that looks like it,” states Stuart. “It’s a rocky island surrounded by a raging ocean surrounded by a mountain range. At one point, there was lots of lava and volcanoes exploding but it was getting to be too busy, when combined with Nemesis’s fiery cloak. FX simulations were art directed on a per shot basis. We have a massive library
The environment [where The fight between arthur and nemesis Takes place] was fully cg because There isn’t anywhere on This planet That looks like it Stuart Penn, CG supervisor, Framestore
of CG pyroclastic smoke, splashes and ocean elements that we could dress into shots and render to fit into the lighting.”
In regards to what shot or sequence he is looking forward to seeing on the big screen, Stuart remarks: “There’s the big final battle between Arthur and Nemesis, but my favourite still is going to be the snake. I just like the snake!” Find out more about the film at www.kingarthurmovie.com