Traditional TV broadcasts have an almost square shape. Digital TV allows the ABC to broadcast a wide screen picture, similar in shape to most DVDs and many theatrically released films.
We refer to these two shapes - or aspect ratios - as 4:3 or 16:9 (four by three or sixteen by nine). These numbers describe the width and height ratio of the picture.
The diagram below illustrates the two aspect ratios:
A particular challenge of wide screen TV production is the need to produce a program that can be viewed on either 4:3 or 16:9 screens.
The program's producers usually decided the aspect ratio of a TV show. However, all broadcasters now require new material to be produced in 16:9.
The wide screen version is broadcast to digital viewers and a letterbox version is broadcast to analogue viewers. We aim to contain essential scene elements within a 14:9 safe area to ensure comfortable viewing for both groups of viewers.
Some programs, typically news and current affairs, may continue to show 4:3 library material - ie footage produced for TV before the introduction of widescreen. The diagrams below show techniques used to convert widescreen pictures for viewing on 4:3 TV sets.
This is a widescreen (16:9) image
This is a widescreen image that has been displayed in 4:3. While the entire image is visible, the image is distorted - people look tall and thin.
This is a 4:3 image created by cropping the original widescreen image. Part of the image is lost from either side.
This is a letterbox image, created by reducing the size of the image while retaining the correct proportions. This leaves a "gap" at the top and bottom of the image.
This is a partial letterbox image. This is a compromise between letterbox and cropped images. The black border at the top and bottom is smaller, less image is lost on either side.
