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Posted by Jukka Aho on 11/30/05 03:42
Keeper of the Purple Twilight wrote:
>> I had wondered about how widescreen TVs handled
>> 1.33:1 aspect ratios--I hadn't realized they auto-switched.
> What TVs do that? I've never heard of such a thing.
Most all of them? At least here in Europe, where widescreen SDTV sets
are the current norm - and have been for a number of years, at least
as far as shopping for a new tv set goes.
There are three wide-screen signalling methods which allow a video
player (or a set-top-box) to notify the tv set about a change in the
image aspect ratio:
- Wide screen signalling embedded in the analog video signal itself,
just above the visible picture, as defined in ETSI EN 300 294 (see
<http://pda.etsi.org/pda/AQuery.asp?qSEARCH_STRING=EN%20300%20
294&qSEARCH_Type=EXACT>)
- Wide screen signalling based on the voltage level of the pin
number 8 in the Scart AV connector (which is ubiquitous in European
tv sets, VCRs, set-top-boxes and the like - practically all consumer
video devices, except for camcorders, have one or several Scart
connectors instead of the RCA jacks used in the North American
equipment): <http://utopia.knoware.nl/users/eprebel/SoundAnd
Vision/Engineering/SCART.html>.
- Wide screen signalling based on a DC component in Y/C (S-video)
signal. (I do not have the details, I just know that there's this
kind of standard, too. I think the two above-mentioned WSS methods
are more widely used than this one, though.)
* * *
In addition to the above-mentioned methods (which are all based
on relaying the WSS information between devices that use analog
connections), there are also aspect ratio flags embedded into
the digital tv broadcasts (which in Europe means DVB.) TV sets
with an integrated DVB tuner/decoder can read these flags
directly and act accordingly.
Moreover, in the absence of real WSS signalling, some wide screen
tv sets have a "smart" mode in which they're trying to guess the
correct aspect ratio and/or the zoom level from the image content
(especially from the presence or the absence of the black bars
which are taken to be an indication of letterboxed content.) These
systems usually don't work all that well, but fortunately you can
switch the feature off.
--
znark
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