Aspect ratio and conversion
4:3 This is the term used for the traditional a square shaped Television picture that we have all been used to watching and grew up with. The somewhat newer term of 12:9 may also be used since the mathematical equation of X-Y is the same. An original 16:9 widescreen picture would have to be Pan & Scanned in order to make it fit the traditional 4:3 / 12:9 picture, resulting in considerable loss of picture information at the sides.
16:9LBX (Letterbox) As the term implies, the widescreen picture is recorded with black horizontal bars top and bottom of the screen when viewed on a 4:3 shaped Television set. Although the picture does not fill the entire screen vertically, no picture information is lost horizontally at either side and the correct proportions are maintained. This is the only ratio which allows the viewer to see the entire original 16:9 shaped picture on a 4:3 shaped Television set. The disadvantages with this ratio are that the picture is often considered to be quite small when viewed on small size 4:3 Television sets.
14:9LBX This is the current compromise ratio which has been agreed by all of the UK broadcasters for terrestrial analogue transmission. The picture looks similar to 16:9 Letterbox, but with lesser amount of horizontal black bars top and bottom. Additionally, a smaller amount of often incidental picture information has also been lost at the sides.
16:9FHA (Full Height Anamorphic) This is a true 16:9 widescreen image which has been electronically squeezed in order to make it fit into a normal 4:3 TV ratio. This ratio can only be viewed with the correct geometry on a 16:9 shaped Television set. However, when viewed on a traditional square shaped Television set, the images will appear to be tall and thin, circles will become elliptical and people will have long heads because it’s been squeezed horizontally. Some of the more modern square shaped domestic Television sets now feature a 16:9 button which will collapse the scan in order to produce a 16:9 Letterbox image which can then be viewed with the correct image geometry.
Any letterbox ratio of say, 16:9, 15:9, 14:9, 13:9 etc. are all intended to be viewed on a 4:3 shaped television set with varying amounts of black bars top and bottom. For this reason, it may also be referred to as 4:3 Letterbox but not Full Frame 4:3 since it does not fill the entire 4:3 frame. The newer term of 12:9 has since been adopted in order to describe a 4:3 image as being full screen and not letterbox.
This summary is provided by Intervideo as a guide to the technical subject covered. Clients should read the relevant EBU / SMPTE Technical Specification relating to the subject before placing reliance upon these notes and no responsibility can be accepted by Intervideo for errors or omissions.
