Generally refers to the use of 16:9 aspect ratio pictures in a 4:3 standard definition TV system. For example, anamorphic supplementary lenses are used to change the proportions of the captured image to 16:9. These horizontally squashed images can then fit onto the surface of a 4:3 sensor. Outputs from 16:9 cameras and telecines produce an ‘anamorphic’ signal which is electrically the same as when working with 4:3 images, but will appear horizontally squashed if displayed at 4:3 aspect ratio.
The alternative way of carrying 16:9 pictures within 4:3 systems is letterbox. Letterbox has the advantage of showing the correct 16:9 aspect ratio on 4:3 displays, however the vertical resolution is then less than when using 16:9 anamorphic.
Cinema film is sometimes printed with anamorphic frames, allowing widescreen presentations from, typically, 4:3 images projected via a suitable anamorphic lens.
See also: Aspect ratio – of pictures