Elementary: Will Cohen talks about Sherlock

Trevor Hogg chats with Will Cohen about bringing the right elements together when creating the visual effects for Sherlock…


78560“The Milk team have been involved with Sherlock since it first started,” states Milk VFX CEO Will Cohen. “We are proud to be part of one of the UK’s most popular TV drama series.” Creative freedom was not a problem when bringing the iconic sleuth created by Sir Arthur Conan Doyle to small screen. “Television is a medium that often allows for true collaborative production partnership. The budgets and schedules create a situation where the VFX team is able to have a lot of creative ownership over what they are doing. As teams are smaller all the way up the chain, you get greater access to the client and so internal and external communication is a lot more streamlined. With an established franchise, everybody always respects what has come before but they also have the desire to push things further with new ideas or embellishments.” Cohen notes, “Although TV and film have converged over recent years in terms of technical pipeline, shooting methodology and ambition, they are very different with different sets of disciplines. Time and budget constraints and also the greater level of detail and polish required for film to stand up to scrutiny on a 90 foot screen in the dark, mean that generally a movie’s trailer shots are the equivalent to the finished article on TV, creating a different set of rules.”


“In order to create maximum impact Milk created the explosion of the Houses of Parliament in slow-motion, revealing full detail,” explains Will Cohen. “We decided to create the explosion in slow motion having considered a number of other ways to depict it. An accurate model of Parliament was built in Maya and pre-fractured. Explosive forces were selectively applied to imply structural collapse from deep below the building and then fire and gas explosive elements added afterwards. Milk used reference photos taken at night to accurately place over 100 CG lights to replicate the same lighting as in the original plate. When the explosion is triggered Milk animated the CG lights to flicker and go out. At this point the team imported Arnold ASS sequences of the explosions from Houdini and used them to further illuminate the walls of Parliament. As the building begins to crumble we triggered further animated lights of varying intensity within random rooms to give the explosion more depth. Milk replaced the live action water in the Thames entirely in CG in order to create a secondary aftershock ripple in the water. Rendering over 100 lights in the water reflection was a challenge from a time perspective so we put the rendered CG onto a stand-in card, which gave us fast reflection renders, as there were far fewer ray calculations to be made. Everything was rendered using Arnold. Houdini was used to create the explosions and billowing dust clouds. The compositing was done in Nuke.”


“We planned, prevised and blocked out timing very early on for our Houses of Parliament explosion shot so that the editor could cut it into the edit for sign off / changes from the director,” explains Will Cohen. “This kind of shot is a big one to achieve on a TV budget and so in order to fully maximise time, pre-planning was/is absolutely essential. Obviously, you can’t shoot fire and an actor in the same shot. For example, we deliberately slowed down the timings of the post explosion components in our Houses of Parliament Explosion sequences, so the full-scale destruction could be fully appreciated.”


Interaction between the CG and practical elements is critical. “A lot of effects CG were used for our Houses of Parliament shot: smoke, fire, explosions, air distortions, water simulations and exploding building simulations,” notes Will Cohen. “We had to build a model of Parliament so we could add our interaction to the building. Explosions bursting through windows had to illuminates the surrounding surfaces. The interior was also built so that when it breaks apart you would get a sense of the guts inside Parliament. CG element/s and practical effect/s worked side by side. Effects such as the water in the Thames required a simulation to create a ripple on the water surface once the explosion goes off. The bridge and other buildings surrounding parliament all had their own interactive elements created to ensure the realism. There were some finer details added such as debris, library sourced explosion elements, lens artifacts such as glow/ flares, dirt on the lens and finally some camera shake to magnify the impact of the explosion.”


Devastation also happens on the subway. “Fortunately, for this sequence we were allowed to shoot part of the actual London Underground tunnel system which was perfect as we had the real thing as a basis for all the work we did,” remarks Will Cohen. “However we then faced the challenge of how we would show a fireball travelling through the tube carriage as part of Sherlock’s mind palace. Unsurprisingly Transport For London weren’t keen on letting us use one of their tube carriages in which to shoot fireball elements but we were able to use a set built replica carriage and shoot several practical fire elements within that. The final challenge was blending together the multiple practical fire, newspaper debris and interactive lighting/reflections so that it felt real.” All the elements had to have the right scale in order to appear realistic. It is very important that the shot matches the plate lighting because without good lighting the shot doesn’t work.” In order to cinematically show his phenomenal deductive abilities at work, a Mind Palace was created for Sherlock Holmes. “We needed to make sure that the work we generated was consistent with Sherlock’s ‘mind palace’ style that occurs throughout the series. We needed to make sure we gave a sense of visual intelligence, a sense of inviting the viewer into the mind of a genius.”

Milk VFX was responsible for CG augmentation, background replacements and digital doubles. “That is why Sherlock is a great project to work on!” observes Will Cohen. “Sherlock harnesses all the tools in the effects toolbox to make Sherlock so visceral and exciting and real! There are always elements of ‘invisible effects’ such as the graphic inserts onto TV screens, the digital enhancement of practical bloodstains or green screen background replacement of Sherlock smashing through a glass window for example, in this series.” The amount of green screen required was not a major issue. “It was used as and when necessary and appropriate. We knew that we would need to use green screens in order for us to create the VFX for certain sequences. On TV work generally it is usually avoided where possible, especially on location, but as ever it’s about pre-planning and using good judgement.”


“Overall things ran very smoothly,” states Will Cohen. “But one challenge was the Underground Train Carriage Sequence, in which a fireball travelling through the carriage with Sherlock in the foreground. To maximize budget, we decided to shoot and blend together two separate plates [one with the carriage and the other with Sherlock in the foreground] then combine them together and add in the a practical fireball elements. This involved a complex technique of blending and reconstruction of the plates so that everything lined up perfectly.” Cohen adds, “The biggest challenge was the explosion of the Houses of Parliament. This was the very first thing we discussed the director Jeremy Lovering, producer Sue Virtue and production designer Arwel Wyn Jones. We looked at a number of solutions and decided that a slow motion explosion would have greatest impact.”


“Milk worked on all the core VFX elements for Sherlock,” remarks Will Cohen. “It is always exciting when you start with a concept and then see it develop into something that feels like it was part of the original material that was shot.This year we were particularly excited about the Mind Palace Sequence that lead up to explosion of the Houses of Parliament.” Cohen concludes, “Sherlock is an extremely visually innovative television series that pushes the boundaries in the way it tells its story. In terms of visual effects everything has to look real. It is very much a job of supporting the narrative and we at Milk are proud to be part of the team!”


VFX images courtesy of Milk VFX.

Many thanks to Will Cohen for taking the time for this interview.

To learn more visit the official websites for Sherlock and Milk VFX.

Trevor Hogg is a freelance video editor and writer who currently resides in Canada.

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