Separation in cinematography describes a visual contrast between at least two elements in a scene for example between actor and set, between different actors or between foreground and background elements to name just a few. Good separation is a essential technique to get a clear read of the scene and help the audience to focus on what’s important.
The examples below show different approaches to achieve separation.
Citizen Kane, Cinematographer: Gregg Toland dark shadow on wall helps to separate the actor on the right side from the background
Transformers: Revenge of the Fallen, Cinematographer: Ben Seresin Separation through (complementary) colors
Using adobe color cc to to analyze the most common colors in this image. The unnatural orange skin color sits on the opposite site from the bluish background colors on the color wheel.
2046, Cinematographer: Christopher Doyle Separation through color as well as washed out background and contrasty foreground(actress Faye Wong). Additional separation through her dark hair left and right side of her face against the background.
Behind the Candelabra, Cinematographer: Steven_Soderbergh under his alias Peter Andrews Separation through dark foreground(actor Matt Damon) vs. bright background
Aliens, Cinematographer: Adrian Biddle Sigourney Weaver brightly lit vs. dark background as well as shallow depth of field
Inglourious Basterds, Cinematographer: Robert Richardson strong rim lights to separate the actors and guns froms background
Black Swan, Cinematographer: Matthew Libatique bright vs. dark and shallow depth of field
Manhunter, Cinematographer: Dante Spinotti Strong constrast between hazy athmosphere and actor William Petersen
The Big Combo, Cinematographer John Alton Shaft of light behind actors to separate them from background
Another shot from ‘The Big Combo’ heavy use of smoke to separate actors