How did working on this film compare to The Fifth Element? We've been waiting for a while to see you handling a big sci-fi world again.

I'm back! Honestly, The Fifth Element was a nightmare to do, because, at the time, special effects were old-fashioned, it was before we went digital. Every time I wanted to use a green screen, it took like six hours. It was really painful. This one ... because we prepped a lot, it was easier. Longer, but easier. The Fifth Element has 188 shots with special effects; Valerian has 2,734. It was less painful, but technology has made it easier for a director. You just have to specifically be very precise about what you want, and you need to have a good time to do it.

I was also very lucky because I worked with WETA, who did Avatar, and ILM, who did Star Wars. So I've already got the best two companies in the world. Usually, you have one or the other. But for the first time, they accepted working together. The film was actually too big to handle by themselves. And it was just a pure pleasure to work with those guys because they were trying to be the best, each of them. I was on the postproduction for the last year, and I was amazed every day by the level of what they had.

There's a third company who worked on [Valerian] called Rodeo; they did all the spaceships and Alpha station. They were also very good.

Now that you can do so much more with digital effects, when do you go practical instead? The practical costumes in The Fifth Element still look very realistic today.

I'm going to give you an example: You have something to build, so you open your toolbox and take what is most appropriate to do it. If it's a hammer, or a screwdriver or a saw, it's the same. So if I have a shot to do, my first question with my team is to say, "What is the best way of doing this?" It's not automatically CGI or props. And for me, that's the best approach.