Anamorphic widescreen

Anamorphic widescreen is a process by which a comparatively wide widescreen image is vertically expanded to fit into a storage medium (photographic film, for example) with a narrower aspect ratio. Compatible play-back equipment (a projector with modified lens) can then recompress the vertical dimension to show the original widescreen image. This is typically used to allow one to store widescreen images on a medium that was originally intended for a narrower ratio, while using as much of the frame - and therefore recording as much detail - as possible.

The technique originally comes from cinema. A film would be framed and recorded as widescreen, but the picture would be "squashed together" using a specially crafted concave lens to fit into non-widescreen 1.37:1 aspect ratio film. This film can then be printed and manipulated like any other 1.37:1 film stock, although the images on it will appear to be squashed horizontally (elongated vertically) as in a fun-house mirror. An anamorphic lens on the projector in the cinema (a convex lens) corrects the picture by performing exactly the opposite distortion, returning it to its original width and its widescreen aspect ratio.