Naked Science Forum
Non Life Sciences => Technology => Topic started by: Geezer on 27/11/2009 20:30:38
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I don't know what it's like in other parts of the world, but here, the TV signals that we receive via cable come in all sorts of different formats. Even if you only watch one channel, the format can change frequently.
As soon as you adjust the TV to match the transmission, it changes. I like to see the entire picture on the screen, but the only way to guarantee that is to shrink the image which means I'm only able to use a fraction of the screen.
Now, you'd think in this time of technological ingenuity the TV stations could embed some information in the transmission that described the format so that TVs could automatically optimize the image. Does anybody know of such a thing?
Perhaps this is all part of a grand conspiracy to wear us down so we have to pay for high definition channels.
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As soon as you adjust the TV to match the transmission, it changes. I like to see the entire picture on the screen, but the only way to guarantee that is to shrink the image which means I'm only able to use a fraction of the screen.
Now, you'd think in this time of technological ingenuity the TV stations could embed some information in the transmission that described the format so that TVs could automatically optimize the image. Does anybody know of such a thing?
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I'd turn your question upside down, and suggest that the reason why the picture format changes is precise because there is a format-descriptor (which specifies the picture size and shape) being transmitted along with the picture.
I'm not familiar with the situation in the US, but here in the UK I think that although the satellite/cable or digital terrestrial receiver knows the format information, this is not always successfully communicated to the TV set. In the European family of 625-line standard-definition television we have a 'line-23' signalling standard (sometimes known as WSS -wide screen switching), where one of the scan-lines just above/outside the visible picture area codes a pattern which flags the aspect ratio of the picture.
This gets complicated because
1) broadcasters have been known to put the wrong flag alongside the picture
2) older TV sets may not understand the convention
3) the receiver/set-top-box may itself be transforming the picture content, e.g. putting a 16:9 aspect ratio picture into a 4:3 'container' which it would (might) then flag as 4:3 aspect ratio to the TV...
In any case, faced with a picture which is a different shape (aspect ratio) to your screen, what do you wish to do about it? For example, you receive a 4:3 picture and have a 16:9 screen. Your options are:
0) show the complete picture in the original shape, with black bars down the left and right sides of the screen
1) stretch the picture to fill the width of the screen (everyone looks short and dumpy)
2) expand the picture to fill the width of the screen, loosing a sizable chunk off the top and bottom of the picture (loosing tops of heads, feet, and some captions, and loosing resolution so the picture looks rough)
3) do a non-linear stretch so the central portion is roughly the correct width (so people standing in the centre have an appropriate figure) but increasingly stretch the edges of the picture to fill the otherwise black bars (people standing at the edges get asymetrically stretched, and horizontally-scrolling ticker-bars stretch and shrink disconcertingly as they cross the screen)
4) some partial-permutation/mixture of the above
The purists maintain that they want to see the whole picture "as the director intended" - so will choose black bars at top+bottom or left+right as required.
Joe public apparently feel short-changed by having black bars on the screen, hence the abomination of stretch-modes normally provided.
You have to admit though, that a cinemascope (2.35:1) ratio picture is miniscule when presented showing its full width as a "deep letterbox" on a 4:3 TV screen, so some sort of partial-zoom/enlarge is often preferable for all but the most die-hard purists.
This can then get even more complicated if the broadcasters transmit something in a non-native frame with black bars. Then what's your kit supposed to do? The broadcasters have notations for communicating all such permutations, e.g. 4:3 material in a 16:9 container (implies bacl bars at left+right edges) - but how far this goes into consumer equipment I'm not sure.
Certainly a few years ago some of the British broadcasters had a policy of transmitting everything in a 16:9 widescreen frame, including old or news material as 4:3 with the black bars. But then if you watched this on a 4:3 set, configured to display 16:9 material letterboxed, then the 4:3 inserts appeared as a small picture with a black frame on all sides!
It's a mess!
If you're really unlucky it could be that your TV and receiver just can't communicate (especially if one is rather old). It's probable however that there's menus on the TV and/or receiver which will give you many more permutations to try, of which some may be closer to your ideal behaviour.
In an ideal world, you'd probably want the receiver/STB to output the picture in its native format, and let the TV make the most of it. Every time a piece of equipment reformats the picture you loose definition and may create artifacts such as jaggy kinks in the lines on sports pitches.
It might be worth working out what your preferred behaviour under different scenarios actually is, though.
BTW: Modern cinema films are made in either 1.85:1 "widescreen" or 2.35:1 "scope" aspect ratios, and the 16:9 TV format is a compromise between these.
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A mess indeed!
The telly is brand new, 16:9 LCD by Sharp. It's plugged directly into the cable - no cable box or anything. I don't think the TV has any ability to detect format information, but I will investigate that.
A lot of the "machinations" seemed to coincide with the recent switch from analog to digital "over the air" transmission in the US. Of course, the signal supplied by the cable company is still analog for most of the channels. It may be digital for premium HD, but I don't subscribe to any, and I can't receive any over the air transmissions at this location.