So does his or her voice. In comparison, film acting must be as subtle as possible. A film director has complete control over the images. Whereas a stage director conducts rehersals and suggests how to play the part, the film director controls the performance from day one to the end. Stage actors can change their performance from night to night, film actors can't.
Film is more closely akin to the novel.
The director infuses the script with his or her own viewpoint as the production progresses.