Filming green screens can be so frustrating it actually made Sir Ian McKellen cry during production on The Hobbit, but what is it about the lack of real location that makes giving an authentic performance so difficult?
We asked cast members of Game of Thrones, a show which has to use it a fair amount in order to realise its medieval fantasy world.
Maisie Williams (who plays Arya Stark) told us she was “really, really grateful” that the Hall of Faces was actually a meticulously created physical set in season 5, as “standing with a green screen I find so tricky.
“Particularly when you’re trying to work with someone else, as you’re both imagining something totally different - neither of you are imagining exactly what they’re going to put there."
Asked what exact element of an actor’s performance green screen can disrupt, she said: “Your eye line.
“They’re like ‘look out to the castle’ and you just think ‘well, how far away is it? Is it right here?’ and although you can ask all of those questions it never looks right.
“You watch it back and you think ‘I can tell I’m looking at a green screen’, even though for an audience member it may not register.”
Williams, Carice van Houten (Melisandre) and Liam Cunningham (Ser Davos) were quick to praise the HBO show’s crew though for going above and beyond when it comes to elements that are tangible.
“It’s really small, the use of green screen,” Cunningham said. “We’re still making a very expensive TV series but it’s not, you know, Lord of the Rings, with two or three million dollar budgets - our use of CGI is very little though.
“The boat that we travel on to Braavos is actually in a car park - they’ve obviously got to use [VFX] to get the sea right - but there is such beautiful attention to detail from the costumes, from the sets, from the props - they’re magnificent.
“This goes right down to when I handed over money to Salladhor Saan in the brothel. They brought out this coin that was so intricately made even though there was never going to be a close up of it. The money was minted with two different forms of metal with the Braavos bank seal.
“That morale is right through the crew, everything they make they want people to look at and ‘ooh’ and ‘aah' over, they want it to be real as possible.”
Cunningham also enthused about one of Melisandre’s dresses, which, though it might not be picked up by the cameras, “the material is made of very faint skulls, just millions of tiny skulls.”
Last week, some major cinematographers called for a new cinematography award category at the Oscars that distinguishes between VFX (as seen in this year's Best Picture nominees Mad Max: Fury Road, The Revenant and more) and actual photography.
Game of Thrones returns for its sixth season on HBO and Sky Atlantic on 24 April. Season 5 is out on DVD and blu-ray 15 March.