The aspect ratio of an image is its displayed width divided by its height (usually expressed as “x:y”.) For instance, the aspect ratio of a traditional television screen is four units wide to three units tall, often expressed as 4:3 or 1.33:1. 4:3 originated from silent film, which used the full 35 mm frame. It is the aspect ratio defined by the Academy of Motion Picture Arts and Sciences after the advent of optical sound-on-film.

Television came to market with a 4:3 screen to match the aspect ratio used for Hollywood films. When cinema attendance began to drop in response to the emergence of television, Hollywood created widescreen aspect ratios to immerse the viewer in a more realistic experience.