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Old 14-12-2006, 16:57
philnavigator
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I'm trying to get my head around the whole 720p/1080i business in preparation for Sky HD and a 50in Panasonic plasma screen.

With SD material on my old CRT tv, it was either 576i or 576p, and all was easy, but now things are a bit more complicated, so I was wondering if someone could help by answering a few questions for me?

1. Plasma and LCD panels are progressive by nature, do they have to convert all 576i/1080i to a progressive signal first?

2. With that in mind, the Sky box has a choice of setting to either 720p or 1080i, is it best to leave it on auto, select manually (how would I know which format a broadcast is in) or is it better to leave it always on one of the two settings?

3. If my screen only has 768 horizontal lines, will it be scaling any 1080 signal down anyway, meanig it will have to both scale AND deinterlace a 1080i signal? Would it then be less messing with a signal to always leave it on 720p on the Sky box?

4. Are these options best sorted on the Sky box totally, or can the tv just sort out whatever comes in? Which is better at it?
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Old 14-12-2006, 17:05
Jarrak
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A standard CRT will only accept interlaced content, even the recent HD CRT's were limited to 1080i in the early days before they could convert 720p internally.

1) Yep, flat panels can convert an interlaced input to progressive and of course scale if required. DVD players and STB's are appearing with their own scalers which can now supply a panel with a suitable signal which may or may not outperform the panels own internal processing.
2) All UK HD broadcasts are 1080i so if you don't have a 1080 panel then scaling is a fact of life, as to which piece of hardware does the job depends upon your own opinions of the results
I prefer the AUTO setting which sends the SD channels at 576p and my LCD scales to 1366*768 while all HD content is sent as 1080i and scaled/de-interlaced by my LCD.
3) Yes that's right. If you set the box to 720p then the STB scales the 1080i down to 720p and then the TV scales the 720p to 768p, less scaling the better
4) Depends, try all combinations and pick which looks best.
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Old 14-12-2006, 22:14
philnavigator
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Thanks for the info, it seems a bit of experimentation is called for, although if less scaling is generally better, it would seem logical to let the telly sort out an unaltered signal from the Sky box.

The Sky engineer told us that some, very few in fact, tv's make an unnervingly loud crack/bang when the Sky box is set to auto and the signal type changes. He said its not damaging, but just be prepared in case it happens! Has anyone experienced this?
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Old 14-12-2006, 22:21
Jarrak
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That sounds nasty

There shouldn't be a noise when the source resolution changes and the TV's internal processing has to adjust to 576p to 720p/1080i or back again and the HDCP handshake locks on, can't think what would cause that in either LCD, Plasma or DLP.
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Old 15-12-2006, 15:20
ALanJ
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Originally Posted by philnavigator
I'm trying to get my head around the whole 720p/1080i business in preparation for Sky HD and a 50in Panasonic plasma screen.

With SD material on my old CRT tv, it was either 576i or 576p, and all was easy, but now things are a bit more complicated
The reality of the situation is that in any issues trying the options and seeing what they look like is the only true anwer as to which is best.

Every TV does a different job in scaling and interlacing the image onto the plasma's native resolution.

Some units spend more than others on this function and you can sometimes tell the difference

This whole issue is one that people can spend lots of money on - there are standalone scalars that can cost thousands of pounds to do this properly so with any screen you have to play with all the options to find out what works best for your combination.

Good luck.
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