When I worked at Framestore I was hanging with one of the digital matte painters while he was working on a scene from Harry Potter 3. The scene consisted of Harry walking down an open air corridor. The corridor (floor, walls, bricks, etc) were real and the actor was really walking down it. The artist then painted a digital night sky and moon (BTW, he still used real photographic elements, but they were enhanced to look nicer, and there was some paintwork too). The finished scene looked great.
When I worked at Framestore I was hanging with one of the digital matte painters while he was working on a scene from Harry Potter 3. The scene consisted of Harry walking down an open air corridor. The corridor (floor, walls, bricks, etc) were real and the actor was really walking down it. The artist then painted a digital night sky and moon (BTW, he still used real photographic elements, but they were enhanced to look nicer, and there was some paintwork too). The finished scene looked great.