HDTV resolutions

[smtkr]

We have a 1080i projection and both 1080i and 720p look beautiful on it.

[5lab]

I have some questions:

720p = 720 horizontal lines, so why the hell do we get 768 lines? Is it cheaper because pc monitors have 768 lines so they can use these? When looking at HDTV's, there are no black bars at the top or bottom, so I am assuming that the picture is being stretched to fill all 768 lines. Wouldn't this cause fuzzyness and reduced picture quality? (this is also the case for the number of vertical lines - there are always more than the actual 720p HD resolution)

basically yes. however

lots of films/tv etc atually have artifacts round the edge of the picture - as a result of which you *do* want to overscan the picture (ie not see the very edges) - so even on a 720 screen you would want to stretch the picture - as a result of which, 768 doesnt matter..

720 panels are arriving - i think all 27" panels are 1280x720

[nvening]

WHy do films have artifacts on the ebge? Because of camera work, compression or what? If whats you are saying about allowing extra space so the artifacts are hidde/covered up then would the signal not have black lines on its edge (which you seems to suggest would be covered up) and so the image would not be stretched? (i fhave a strong feeling that was nothing to do with what you were saying, im a bit confused.

What do you mean but there beinging artifacts on the edge of the screen? Just like little white dots at the edge and again whats that caused by?

[directhex]

http://www.mastersofcinema.org/revie...kingbeyond.htm

[nvening]

Wow thanks, that explains it lol. However:

The overscan problem is presumably somewhat less severe with the newer higher quality progressive scan and HDTV monitors. We welcome comments on this from our readers. Of course, viewing DVDs on a PC monitor or an RGB computer-grade projector is most likely 100% overscan-free.

Im thinking that is talking about non flat pannel monitors however i would have thought it raised a good point. Surely LCD and Plasma TVs do not suffer the image "bending" problems at the edge and therefore why sould they be overscanned at all?

[G4Z]

Well I have the Samsung HDTV with laptop plugged in via VGA at 1360 x 768 res, I have zero HD content apart from stuff I download, As far as I can the HDTV rips you get are not ful res and are upscaled. I have noticed that the quality does tend to be better than sky even though there is a fair bit of upscaling going on. Also playing DVD is far sharper than my old CRT was and it upscales nicely. Just looking at that I dont think there will be a marked improvment at 1080i/p over 720p and to be honest Id sooner have the higher fps (whoever said the human eye cant see any diff between 25 and 50fps should try playing counter strike source on crap PC and then a good one).

I dont think its worth waiting for 1080 as the standard in the UK will be 720p for many years to come, all of the HD broadcast services will be in that res. Weather its worth getting an HDTV now is debateable, I had to get a new telly as my old one died but it is great to be able to plug my laptop in and be able to read it perfectly. Looking at my desktop in the full res is pretty jaw dropping after using S-video on CRT - *Shudder*.

[G4Z]

Sorry double post.

[kojak71]

So assuming that you have two 42" screens, one that supports natively 720p, the other a 1080p resolution and you fed both of them a high-def 720p signal, which one would be better? The screen that natively supports 720p, or the one that has to upscale the image to fill up the 1080p screen.

The reason why I ask this, is because it could end up being rather academic which standard of HD to go for. Not so much on the content side of things, but broadcasting bandwidth. Broadcasting 1080p contains over twice as much information as 720p. For Sky and Cable, this might not be too much of a problem, but let's not kid ourselves, the vast majority of people rely on Freeview for digital content. The BBC will no doubt be lobbying the government to allow them to reuse the frequencies that are used by analogue terrestial) to allow them to broadcast in HD. It's not a given that this will happen, but let's assume it does the available spectrum is far too precious to use up on 1080p. I hope that I'm wrong.

The only challenge to this is going to be the changing face of how we get our broadcasts and pre-recorded movies, i.e. super high broadband speeds. You've only got to look to see what's possible in Korea to realise that their ADSL makes our broadband speeds the equivalent of a 33.6 modem!

[5lab]

the former tv, with 720p native res, would look better. ANY SCALING has detrimental effect on picture quality.

something to note is that 1080p is not on the cards - 1080i *is*. however 1080i still takes a large chunk more bandwidth than 720p (i think i've read something like 50% more, dependant on the codec).. additionally the equipment is more expensive. i think the vast majoity of the general public would rather have 50% more channels than a little bit more quality - particularly if thier sets can not display it..

[kojak71]

the former tv, with 720p native res, would look better. ANY SCALING has detrimental effect on picture quality.

Just as I suspected

something to note is that 1080p is not on the cards - 1080i *is*. however 1080i still takes a large chunk more bandwidth than 720p (i think i've read something like 50% more, dependant on the codec).. additionally the equipment is more expensive. i think the vast majoity of the general public would rather have 50% more channels than a little bit more quality - particularly if thier sets can not display it..

On a pixel by pixel basis:
Currently standard definition is 720x576 which is 414,720, but because it's interlaced this drops to 207,360 pixels every frame
720p 921,600 pixels every frame which is 345% more than standard interlaced definition
1080p 2,073,600 pixels every frame, which is 125% more than 720p
1080i 1,036,800 pixels every frame, which is 12.5% more than 720p

This doesn't neccessarily mean that going from standard def to 720p will require 3.45 more data, as you've rightly pointed out it can depend on the codec used by the broadcaster. Standard def is an mpeg2 stream, and I think that Sky are using mpeg4 for their high-def service which uses heavier compression. However there is a trade off, mpeg4 can have more artifacts in the image, and has fairly hefty decoding requirements. Sony actually said that their decision to stick with mpeg2 on blu-ray was because currently mpeg2 has better quality than mpeg4.

[5lab]

hmm if you've seen life feeds over sky or cable of football on a top-end telly, you'll see that mpeg2 has quite severe artifacting at times too..

the reason that interlacing cant be encoded as well as prog-scan is because theres no frame-frame consistancy - you'd have to (i think) have 2 'streams' of frames, then encode the difference between every other frame, but then the jump between those frames would be twice as big as on progressive and..

arrrrgh!