Thursday, March 24, 2011

Anamorphic widescreen 3

Television
Major digital television channels in Europe (for example, the five major UK terrestrial TV channels of BBC One, BBC Two, ITV, Channel 4 and Channel Five), as well as Australia, carry anamorphic widescreen programming in standard definition. In almost all cases, 4:3 programming is also transmitted on the same channel. The SCART switching signal can be used by a set-top-box to signal the television which kind of programming (4:3 or anamorphic) is currently being received, so that the television can change modes appropriately. The user can often elect to display widescreen programming in a 4:3 letterbox format instead of pan and scan if they do not have a widescreen television.

TV stations and TV networks can also include Active Format Description (AFD) just as DVDs can. Many ATSC tuners (integrated or set-top box) can be set to respond to this, or to apply a user setting. This can sometimes be set on a per-channel basis, and often on a per-input basis, and usually easily with a button on the remote control. Unfortunately, tuners often fail to allow this on SDTV (480i-mode) channels, so that viewers are forced to view a small picture instead of cropping the unnecessary sides (which are outside of the safe area anyhow), or zooming to eliminate the windowboxing that may be causing a very tiny picture, or stretching/compressing to eliminate other format-conversion errors. The shrunken pictures are especially troublesome for smaller TV sets
Many modern HDTV sets have the capability to detect black areas in any video signal, and to smoothly re-scale the picture independently in both directions (horizontal and vertical) so that it fills the screen. However, some sets are 16:10 (1.6:1) like a computer monitor, and will not crop the left and right edges of the picture, meaning that all programming looks slightly (though usually imperceptibly) tall and thin.

ATSC allows two anamorphic widescreen SDTV formats (interlaced and progressive scan) which are 704×480 (10% wider than 640×480); this is narrower than the 720×480 of DVD due to 16 pixels being consumed by overscan (nominal analogue blanking) – see overscan: analog to digital resolution issues. The format can also be used for fullscreen programming, and in this case it is anamorphic with pixels slightly taller (10:11, or 0.91:1) than their width.


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