Hal Hickel was Animation Supervisor at ILM for Rogue One. The film provided a lot of work for the character animation team at ILM. Lead amongst these characters was rebel droid K-2SO.
K2 had the greatest amount of screen time of the full animated characters in the film. We will cover the various Digital Humans in the film in Part 3 of our special fxguide coverage.
In addition to these characters the team animated Bor gullet, the large, octopus-like creatures with the ability to read thought. This was brought to life with a combination of a practical creature from Creature and Special Makeup Effects Supervisor Neil Scanlans, and CG tentacles from ILM.
The team also animated the space battle and the AT-ACTs (All Terrain Armored Cargo Transports) at Scarif and the AT STs (the two legged versions: All Terrain Scout Transport) seen at Jedda. For more on these see part 1 of our coverage.
K-2SO is a reprogrammed Imperial security droid now loyal to the Rebel Alliance, K-2SO is a fully digital character voiced by Alan Tudyk (Firefly/ Serenity, Transformers: Dark of the Moon ). The brutally honest droid is an effective rebel agent, as he can blend in perfectly at Imperial installations as a strategy droid.
The interesting animation aspect for the ILM character animators was the right level of expressiveness and range of motion. Not only was K2 fully digital unlike most on screen appearances of C3PO, but in the timeline of Star Wars this film was of the same era of tech as the 1977 original.
"We had a whole discussion up front as to how expressive to make K2 - Gareth was very keen to explore that," comments Hickel. "Anyone who knows the design aesthetic of Star Wars knows that it does not have droids with expressive faces, they don't have mouths that move, they don't smile or have eyebrows that move up and down - and that is one of the things that has always been so massively appealing about the Star Wars Universe."
Hickel likes the industrial feel of the series and that many of the droids such as BB-8 are not even anthropomorphically in shape. "And yet they are very expressive from their pantomime and vocal expressions," says Hickel. "whether that's Anthony Daniels (C3PO) or Ben Burtt (Master Sound Designer for R2D2) - they are super expressive."
Edwards wants to have a period of experimentation on what could be done, which meant mainly working with the eyes of K2. "We tried up to and including eye blinks with little metal shutters, which had a quasi utilitarian use, but mainly we were just using them for expressiveness," explained Hickel, "but it ended up feeling a step too far into the world of 'cartoony' expression - so we dialed it back but we did keep the ability to rotate the eyes which is not something we have seen before."
This allowed the animators to have K2 look around and do little eye scans and in particular it helped with comic timing. "Alan is brilliant and be brought so much to the role and we were always focused on preserving his acting choices and comic timing," says Hickel. The little eye tarts that one sees K2 do are direct references to Alan's eye movements on set. "That was our one nod to doing things beyond the established Star Wars aesthetic."
From a performance point of view, the animators cast the K2 to be "a little anti-C3PO," comments Hickel. While K2 does have some C3PO style lines especially about the chances of success, "C3PO is more nervous, more flappable, - K2 just never is - he just doesn't care. He is tough and he is strong... he speaks his mind, he is not eager to be liked, with the one exception of Cassian, who reprogrammed him, who he does seems to have a special bond with". While C3PO has a very upright posture and he seems almost perpetually surprised, the design of K2 has him hunched over "he is kind of slouched - his head sits lower, his long arms tend to just hang at his sides, his whole demeanor is quite different which is quite fun to deal with."
Design and animation can often be a two way street, a design can be adjusted or different traits amplified as the animators or the voice actor explore the character. In the case of K2 Alan Tudyk came to ILM about a week before principle photography and the ILM team fitted him with the stilts that Neal Scanlan's practical team had built for the actor. These two foot leg extensions put the actor at the correct 7ft tall height that matched K2 and this would provide Alan the chance to act on set and be at the correct eye line for the other actors.
Down on the ILM motion capture, stage Alan was able to move while seeing a digital version of K2 moving on giant screens placed around the stage. This real time retargeting allowed Alan to explore K2. "That was like letting an actor wear a costume and just walk around for the first time, to find their performance in the mirror". He walked, moved and jogged around for a whole day at ILM "he explored things and found out - 'maybe I shouldn't swing my arms so much'," recalls Hickel.
Interestingly, the result of wearing stilts is that the knee joint is pushed disproportionately up the leg. For a walk or run cycle this means a very different gait than if the knee is more mid way down the leg. Ironically, this happened before on Jar Jar Binks. Rob Coleman, who animated and supervised character animation on Episode 1 at ILM, pointed out to fxguide previously that while many people did not like the walk cycle of Jar Jar, it was how a character would need to walk if their lower tibia leg bone was so much longer than their thigh Femur.
The femur is the longest bone in the human body. Its length on average is 26.74% of a person's height. The tibia is normally the second longest bone in humans. For Jar Jar Binks the lower leg was over twice the length of the upper thigh. This lead to the unusual walk style of Jar Jar.
Actor Alan Tudyk is 1.83m tall, but K2 needed to be 2.1m tall. Stilts means adding 27cm to his height but this once again extended his lower leg length disproportionately. This would be fine if the actual K2 character allowed his knee position to be digitally retargeted to a more natural mid point on the leg, but no... "K2's lower leg is longer than his upper leg, and his lower arms are longer than his upper arms(!)" laughingly points out Hickel. "It's funny but it is something that the we animators keep asking the designers not to do. It is like designing three legged animals or robots - we keep saying 'please don't do that!' There is a good reason why there aren't any three legged animals on earth,.. but then I guess we do always figure it out".
On set, Alan's stilts did align his leg joints accurately to K2's joints, so his gait and stride were accurate and the motion capture data matched K2's design. It is perhaps the skill of the animators that they managed to tweak the walk cycle so that K2 walks without the comic bounce or hip swing motion that stilts can introduce, and we see a much more purposeful and deliberate walk cycle on screen for K2.
As with any character such as this, there were many other small key animation problems to solve. In the gap between the upper legs and the pelvis there are a set of little pistons which are all connected. "Those all had to work,.. and there were shots we'd play with to lend him extra weight, and there are some shots you can see that a bit more,"says Hickel. Giving a rigid body robot weight is very hard as secondary body mass does not exist to flop and swing and thus denote a heavy solid build.
On set and in post
While ILM could adjust many things in post-production, Tudyk would not be able to see himself on set, so this one day was key to "pushing the character along before principle photograph," commented Hickel. "It was a huge win." Most of the takes ILM "used were ones with Alan in shot, and we just digitally removed him," commented VFX Supervisor Mohen Leo.
For some scenes acting on stilts was too restrictive an option and for those times Alan wore a back pack rig that supported a K2 head at the right height above his head, for the other actors to have an eyeline reference.
ILM used a traditional HDR IBL lighting approach for K2, taking standard HDR measurements on set. Alan's performance on set was captured using single camera iMocap with Alan wearing a gray tracking suit. The primary solver uses the main camera, but the team also had two secondary witness cameras for reference.
While the iMocap is not as clear and precise as traditional capture volumes, the easy of capture and location freedom it offers outweighs the downside for ILM. 90% of K2's performance was estimated to be either directly or very nearly based exactly on Alan's performance on set, but still all the animation is hand polished and tweaked to the betterment of the story. "There is clean up - but also in the end you are looking at K2 not Alan and what might look good on Alan does not look as good on K2, so it all needs adjustment," explains Hickel.
The other key aspect of the real craft and skill of the animation team at ILM was finding ways to provide a performance that the director liked, but that came strongly from Alan's facial expression. "Clearly the facial expression does not translate so we have to find ways to deliver that performance but in other ways, and that usually means amplifying his pantomime - to increase that part of the signal to make up for the fact that we were not getting whatever funny expression Alan might be being making," says Hickel.
The team discovered that much of the comic communication could be achieved from the looks between characters. It was not the dialogue but the timing of a glance by K2 to Cassian, that communicated the subtext of the moment. Unlike BB8 or many other characters there was no secondary animation (antennas, cables etc) or other traditional devices the animators could fall back on.
For Edwards, the ILM team decided to initially only show a fully final rendered version of K2 during rushes or reviews. While the animators can review their work with hardware renders that include motion blur, Hickel decided to only show their animation work on K2 to Director Gareth Edwards initially as full final renders. "That was not for technical reasons of motion blur or whatever it was more for reasons of vibe and mood," he says. "So we could all see him fully rendered and in the scene get a sense of how real he felt". Hickel here is not referring to real in a render sense but more in terms of "real as a character, in an empathetic sense - his he a real living character."
For the interior of the ships, background extensions were often required. Instead of building just the immediate set and having green screen behind the foreground actors, the production took a very different approach. The ship sets were built with practical completed foreground sets, but in the background they built very simple stand-in solid forms but in roughly the right colours. This allowed the actors in that part of the shot to know approximately where walls and controls were rather than having to estimate from video splits.
But this approach served a more important function for the comp team, compared to traditional green screen keying. The white or grey rough plywood shapes that near any background actor produced the correct bounce light, and avoided green spill or fringing. The entire set could be lit, and the actors would be rotoscoped off the correct coloured backgrounds. While roto is a mainstay activity, it is still complex to roto blur out of focus background characters off one tonal plate and comp them into a different tonal CG background without either affecting the quality of the key edge.
The character department had to do various digital doubles and stunt double replacements, but not an enormous amount from Hickel's point of view. One key stormtrooper replacement was when K2 fights the attacking stormtroopers while our heroes try to steal the data. While there were stuntmen as stormtroopers rigged with wires for the shot where K2 actually throws a stormtrooper across set, in the end it was easier and more effective to have both Alan Tudyk and the Stunt man digitally replaced with a digital K2 and digital stormtrooper.
While the Digital Humans in the film, which we will discuss in Part 3 of our Rogue One coverage, had very specific animators cast to bring to life, Grand Moff Tarkin and Princess Leia, K2 was a team effort. The character animation team is so strong at ILM that Hal Hickel proudly points out that "any of the animators on the crew could do those shots and do them well, so they were spread out across all four of our ILM studios (San Francisco, Singapore, Vancouver and London)."
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