Aspect ratio

An aspect ratio describes the ratio used to broadcast television pictures. There are three popular types of aspect ratio:
 * 4:3 - standard "squared" appearance, with the horizontal width slightly greater than the vertical. Most older television sets and other visual equipment use this ratio, and therefore is seen as the "traditional" ratio method. Often certain 4:3 equipment will have an overscan where areas at the extreme top / bottom of a picture will be removed, most common in cathode ray tube devices. Equipment using 4:3 television sets should be set to "centre cutout" (removes extra left and right picture added for 16:9 broadcasting) or "letterbox" (placing a full 16:9 uncompressed picture into a 4:3 frame, by adding black horizontal bars at the top and bottom of the picture).
 * 14:9 - least common option. Analogue broadcasts in the United Kingdom are broadcast in 14:9, with narrow black bars at the top and bottom of the picture to fit a 4:3 frame. Certain digital channels also use this method, but is gradually being phased out, since there is little 14:9 equipment available. A 14:9 ratio option on equipment is useful for 4:3 television sets with an overscan.
 * 16:9 - "rectangle" appearance with the horizontal width significantly larger than the vertical, and is now the common format for most new TV equipment. All TV digital services in the United Kingdom have the potential to broadcast in 16:9, although certain broadcasters who do not wish to use this format can set preferences in broadcasting so that viewer's recieving equipment will automatically change the output aspect ratio to either 4:3 (commonly) or 14:9 (rarely). A 16:9 frame

Idealistically all new content produced will now be in 16:9 formats. 16:9 has been the preferred format in the UK since digital transmissions began in 1998. Most HDTV broadcasts are also in 16:9 as HDTV recieving equipment is almost all 16:9, and therefore many broadcasters take the opportunity to reduce the use of 4:3 and 14:9 safe areas as generally all viewers will be viewing the full 16:9 frame.