HD Formats - Major Networks

[Craig Terott]

So after reading up a bit about which HD formats the major networks are using (ESPN, ABC, & Fox are using 720p and everyone else 1080i)... I decided to watch some primetime broadcasts last night to see how much I was able to see the difference... and this lead me to more questions and I hoping someone who has a better understanding than me will chime in.

I first tuned to the TNTHD channel which was broadcasting an NBA game. It clearly looked 1080i to my eyes. It looked to me to have been shot in 1080i & boradcast in 1080i.

Another network that supposedly broadcasts 1080i is CBS. So I turned to that channel -CSI was on and it looks to my eyes to be progressive scan. My question is this- is a program like CSI actually shot in 1080i or is it shot in some other format like 720p24 then broadcast at 1080i? It definately doesn't look interlaced to my eyes. It definately doesn't look like it was shot in 1080i. I realize I could wrong about this because I'm a bit confused as to what I'm seeing. My goal really is to have a better understanding of what I'm seeing in order to make a decision on my first HD camera purchase. -thanx

[Dylan Pank]

CSI is shot on 35mm film (probably 3 perf Super35), which is to all intents and purposes progressive scan.

If it is broadcast in HD it is probably TK'ed at 1080i.

[Craig Terott]

Thanks, then that leads me to another general question... if CSI is indeed shot in film (progressive) wouldn't the network better serve the viewers with a 720p broadcast of programs like this? ...because what I see on my TVs (LCD & Rear Projection) looks a bit confused ...like it has charateristics of progressive & interlaced at the same time? It seems defeating to me to take something progressive and dumb it down to interlaced. If the majority of programs are shot in some sort of progressive format - why are most of the networks choosing 1080i over 720p?

[Dylan Pank]

It would make sense - it would be great if HD broadcasts could be switchable, say 1080 24p (or 25p in PAL regions) for dramatic programmes and 720 50/60p for news/sports.*

Unfortunately, resolution for broadcast seems to be fixed, so we get 1080i as a way of broadcasting 1080p material, and as the stuff is shot at 24p and then broadcast at 60i, it has the 2:3 pulldown - urgh.

(* yes I know there's a million billion technical reasons why this can't be done, I'm just saying in a closer to ideal world...)

[Barry Green]

why are most of the networks choosing 1080i over 720p?

Because "bigger" sounds better.

If you look at the ATSC television specifications, there are six approved HD broadcast standards. Five are progressive, only one (1080/60i) is interlaced.

In fact, if you go further and look at all EDTV and HDTV standards approved by the ATSC, there are 15. Fourteen are progressive, and only 1080/60i is interlaced.

If you look at Europe, the EBU said "forget interlaced, it's dead technology, we endorse 1080/50P but it doesn't exist yet, so until it does, we recommend 720/50p". The EBU acknowledged that interlaced origination (1080i) is still likely going to happen, and they said they wouldn't take steps to prevent it, but they sure wouldn't endorse it.

But "1080" sounds better than "720", doesn't it? It's basically all about perception rather than reality. Both systems deliver approximately 60 million pixels per second to the viewer, but 1080 sounds "bigger" so some people think it therefore must be "better".

If you want a real test, watch football or basketball broadcasts. They just look much better on progressive, which is why the major sports networks (Fox, ESPN, ABC) chose 720p. The interlace aliasing drove me batty during the NCAA tournament broadcasts (CBS), vs. the pristine progressive of the Super Bowl (ABC).

Now, where 1080 is better is when you're comparing same frame rates -- obviously 1080/24p is better than 720/24p, and 1080/30p is better than 720/30p. The debate is 1080/60i vs. 720/60p.

if CSI is indeed shot in film (progressive) wouldn't the network better serve the viewers with a 720p broadcast of programs like this?

Actually, no, what they would do best would be to broadcast 1080/24p for those shows. Nobody does, AFAIK, I think all 1080 broadcasts in the US are done at 60i. But 1080/24P is included in the ATSC format table, and they could theoretically broadcast it if they chose to.

[Graham Hickling]

An additional complication is that your TV and/or (for DVD and forthcoming HD-DVD) your player may be re-rezzing and/or deinterlacing - say from 720 to 1080. Pondering all the possible permutations kinda makes my brain hurt, to be honest.

With regard to camera purchase, keep in mind that many of the "720P" cameras are 720P30. For material with plenty of action, the P30 is problematic and 1080i30 does have some advantages.

One possibility to consider is shooting in 1080i30 footage and then deinterlacing in post to a 720p60 end product. The Sony HDV cameras are only 1440x1080 resolution anyway, so you give away very little resolution while gaining smooooth-motion 60P!

More on this here: http://www.dvinfo.net/conf/showthread.php?t=63568

[Craig Terott]

Originally Posted by Graham Hickling

An additional complication is that your TV and/or (for DVD and forthcoming HD-DVD) your player may be re-rezzing and/or deinterlacing - say from 720 to 1080. Pondering all the possible permutations kinda makes my brain hurt, to be honest.

With regard to camera purchase, keep in mind that many of the "720P" cameras are 720P30. For material with plenty of action, the P30 is problematic and 1080i30 does have some advantages.

One possibility to consider is shooting in 1080i30 footage and then deinterlacing in post to a 720p60 end product. The Sony HDV cameras are only 1440x1080 resolution anyway, so you give away very little resolution while gaining smooooth-motion 60P!

More on this here: http://www.dvinfo.net/conf/showthread.php?t=63568

Yes, It's definately a "permutation" of HD I'm seeing.

Iteresting suggestion about the 1080i to 720p conversion. I'd have to see it to be sold. Anyone out there have samples??

From what I've read motion is more problematic for the 1080i format primarily because of the 15 frame GOP. It has less I-frames than the 720p format which has a 6 frame GOP. (I think) the effects of compression are more evident with a 15 frame GOP than with the 6 frame GOP 720p uses.

[Dylan Pank]

From what I've read motion is more problematic for the 1080i format primarily because of the 15 frame GOP. It has less I-frames than the 720p format which has a 6 frame GOP. (I think) the effects of compression are more evident with a 15 frame GOP than with the 6 frame GOP 720p uses

I think that's only for HDV cameras, I think the GOP structure is different for broadcast HD mpeg2, the 720 is 60p, twice as many frames per second. However the lack of interlacing comb edges should give any progressive format an advantage in terms of avoiding certain artefacts.

In 1080i, there's almost always interlace artefacts, unless the footage was aquired at 30p (which is rare because it's so hard to satisfactorily convert to PAL and SECAM) becuase 24p needs a 2:3 pulldown, that puts interlace artefacts in two frames out of every 5.

Barry my guess is that broadcasters have to transmit a consistent video stream, ie it's got to be all one thing, so once you start a 1080 60i stream, it ALL has to be like that, even if the receiver boxes and sets can decode any of the dozen or so formats out there. Is this a real problem or is it just laziness on the part of broadcasters?