How special effects artists created a magical world in the 'Harry Potter' films
No "Harry Potter" movie is complete without a good flying scene, and most of those happened on broomsticks.
To shoot the scenes for Quidditch - a sport where people fly around on broomsticks and try to score goals against the opposing team by throwing, catching, and blocking various types of balls - the production team for the Harry Potter movies had a few tricks up their sleeve.
The filming methods were different depending on the scene. One of them involves jumping up and down on a trampoline in front of a green screen.
You can see Rupert Grint (AKA Ron Weasley) showing us how to do it in this old behind-the-scenes special for "Harry Potter and the Half Blood Prince" at 14:10.
"You go about 30 foot in the air," Grint said. "I was holding a broom and they were throwing balls at me. It's quite scary."
Another way they got actors to look like they're zooming around on brooms is with a really tall rig. There's a broom on top of a robot that moves around. Along with some artificial wind and a green screen, they could be made to look like they're flying.
It's really complicated. Every actor is filmed seperately, so even if they appear to be talking to each other in the scene, they're probably not in real life. A computer program determines where the broom rig moves, so even though it looks like the actors are steering it, they're acually just trying to hold on. The actors are up there for hours, and the brooms, as you can imagine, get uncomfortable.
And because the shots are made to look like they're thousands of feet in the air, the lighting gets complicated. Everyone is shot at multiple angles for the scenes. So when they're stitched together, they need to be controlled for various lighting angles that work for each person in the frame. Plus, the special effects artists need to create a digital environment and atmosphere that all looks cohesive.
Warner Bros made a video where the special effects team explains how it's done. It's worth a look:
Green screen special effects methods can be fun. Take this scene, for example, where Hermione holds up books to the Hogwarts library bookshelves and they float back into place:
In reality, there were people on the other side of the shelves wearing green gloves: