Photographer/director David LaChapelle thought he'd seen it all, but when his choreographer friends from South Central introduced him to krumping on the set of Christina Aguilera's 2002 video ''Dirrty'' (which he helmed), the 36-year-old found himself slack-jawed at the highly aggressive, herky-jerky flit that seems almost alien in its execution. ''I just flipped out,'' he says. ''I bought the best video camera I could find and [went] into that neighborhood day after day.'' Now he's emerged with the triumphant doc Rize. ''The energy when these kids dance is off the wall,'' says LaChapelle. ''I'd never seen anything like it. I saw an art form being created.''