Sky has confirmed to HEXUS that all eight of its own HD channels will initially be transmitted at 1080i and that the Sky HD receiver box can down-convert this to the lower-resolution 720p HD format needed by many current owners of HD TV sets.
The company had originally said that it would broadcast some programmes in 1080i and others in 720p. However, Sky's adoption of 1080i doesn't mean that the HD channels that Sky transmits for other broadcasters will follow suit. It's possible that BBC in HD, Discovery HD, National Geographic HD and Artsworld HD will use 720p for some or all of their programmes. We'll try to find out the score, though, and report back.
Sky's move is good news because 1080i's higher resolution - 1920x1080 (interlaced) - provides better detail than the 720p format's 1280x720 (progressive). And that's something likely to be particularly noticeable when watching high-definition movies and documentaries. The 1080i and 720p formats are just two of the three main options for high definition. The third and, potentially best of all, is 1080p, which is 1920x1080 (progressive).
Confused what interlaced and progressive mean and the implications?
Let us explain…
Progressive -
as used with 720p (that's what the 'p' stands for) - changes the
complete image you see on screen in one go, so each
new screenful is, in effect, like a single frame on a roll of
movie film. The refresh rate can vary from country to country but in
the UK and most of the EU it is 25 frames per
second. Progressive, theoretically, guarantees
smooth-looking pictures because it won't show any rolling lines, nor
artefacts caused by fast-moving objects.
Interlaced - as used with 1080i - refreshes the screen in two goes. It changes what's seen on every other picture line in one pass and the remaining lines in the next. Again, the refresh rate will vary from country to country. In the UK it's 25 frames per second and involves, in effect, 50 half-screens per second. The way in which an interlaced signal is handled means that, potentially, there can be problems with rolling lines but usually only in larger displays and even then, that shouldn't be noticeable if the set is working properly. In theory, 1080i may also show artefacts caused by fast-moving objects but until we'd had a lot more time in front of different types of HD footage, we're unwilling to be drawn into the progressive vs interlaced debate.
1080p - the the third main HD format contender. And, as you'll probably already have figured, it promises the best of both worlds - the highest resolution paired with the smoothest picture. Very few 1080p TV sets are currently available, even in the USA, but, in an ideal world, that's the format you would buy into when purchasing an HDTV set - assuming you could afford it and you knew that someone was going to start transmitting it or start making discs available in that format.
Interlaced - as used with 1080i - refreshes the screen in two goes. It changes what's seen on every other picture line in one pass and the remaining lines in the next. Again, the refresh rate will vary from country to country. In the UK it's 25 frames per second and involves, in effect, 50 half-screens per second. The way in which an interlaced signal is handled means that, potentially, there can be problems with rolling lines but usually only in larger displays and even then, that shouldn't be noticeable if the set is working properly. In theory, 1080i may also show artefacts caused by fast-moving objects but until we'd had a lot more time in front of different types of HD footage, we're unwilling to be drawn into the progressive vs interlaced debate.
1080p - the the third main HD format contender. And, as you'll probably already have figured, it promises the best of both worlds - the highest resolution paired with the smoothest picture. Very few 1080p TV sets are currently available, even in the USA, but, in an ideal world, that's the format you would buy into when purchasing an HDTV set - assuming you could afford it and you knew that someone was going to start transmitting it or start making discs available in that format.
One other interesting fact to emerge from Sky - at least we don't think it's been widely known - is that the Sky HD receiver box only allows you to access half the available space on its build-in hard disk. According to Sky, "It will have a 300GB hard disk with 160GB available for personal storage – the rest is reserved for future developments". Mysterious - and more than a little bit annoying if you're wanting to record the maximum number of programmes
Comments or questions? Let us hear 'em over in the HEXUS.community.
