Digital Effects Supervisor Gary Brozenich (inset) states that many of the film's effects were practical, but little tweaks like brooding skies were added to enhance the tone. 

TDB: Was Tim's goal to only have seamless, invisible vfx? If not, what were the key elements and sequences you had to plan and create?

GB: There are always moments, particularly in period films, where you know that a scene would not be possible without vfx content. But there are a lot of moments in Sweeney Todd that I hope the audience has no idea they are looking at a CG environment. In that sense, we were aiming for seamless work. The imagery is also very much about Tim's visual style, which can push some boundaries of reality, so seamless, also, meant not jarring with the visual style of the whole of the film. Our primarily concern was the creation of digital sets and environments. The whole production was shot on stages, which ranged from full on builds that only required a top up where the build hit the lights, to a set extension where the street required views beyond the limits of the stage. In some cases, the actors were shot on entirely green stages and we created the entirety of their surroundings. In one case, two of the principles walk down some stairs, through a gate, across a street and stop for a chat in front of a pub. The only practical element is the dressed floor that they're walking on, and the other performers on stage. They even brush up against the CG pub as they walk by.

TDB: Did you have to previs a lot of your settings?

GB: Yes, there was a small previs team in place from Nvizage throughout pre-production and on into the shoot. On certain shots, it was really instrumental and drove a lot of what was filmed. There was one shot, in particular, where we fly through the city at a real pace, which is essentially a full CG shot, with moco elements for the people. The previs drove this from the start. On others, it may have just allowed Tim to explore some ideas before rocking up on the day. It was rare that the previs was literally shot, as is the norm, but it's a very effective pre-production tool, as it can help raise issues creatively and technically that may have only come up too late when the cameras are about to roll. In that sense, a lot of the work was technical previs to inform the builds of the greenscreen stages.

TDB: What kind of vfx did you create for the film and what was the total shot count?

GB: We did a variety of work from some blood work as mentioned, a large number of digital sets and environments, some very small, but very funny CG creatures: roaches, rats, etc. We also did a few splendidly horrific human burning shots near the end. In total, we did over 300 shots of varying complexity for the film.

TDB: What was asked of MPC to grow or morph as production continued?

GB: As in any production, things will crop up as the shoot progresses. The main changes really occurred in terms of shot count in certain areas that shrank, but were usually very swiftly filled with requirements from other arenas that we didn't see coming. No great shocks, though.

TDB: Did the break in production [due to the illness of Johnny Depp's daughter] affect your team's work at all? Did you get breathing room or were you just asked to do more to fill the gap with productive time?

GB: The break was positive for us in the creative sense that it gave us more time to prep work for Tim. The shoot schedule was very full on and the original post period was very tight. This made access to TB's time hard to achieve. So, in a way, it did both things. It gave us some creative breathing room and made for very productive time as we headed into post as a result.