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720p V 1080i: Whats Better For Fast-action Sport?

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Hi guys,

With the launch of Ch10s HD Broadcasts of the AFL this year, which i believe are 1080i, ive been wondering whether they would have been better of going with 720p given the bandwidth constraints.

But then i thought that dropping from 1080 to 720 is a significant drop to have to make up for by using less compression (thus fitting in the same bandwidth broadcast) so im not really sure which would be better?

1080 or 720 (assuming a constant bitrate)

Or is bitrate not the right consideration? Is it the progressive nature of 720p that may make it better than 1080i?

And how much can this be compensated for by using a HTPC which takes the 25fps interlaced signal and displays it at 50hz? Doesnt that effectively turn 1080i into 1080p?

I suppose that raises two arguments:

1080 v 720 (assuming you cant increase the bandwidth on 1080, and that its not enough to run 1080 properly...which it isnt)

interlaced v progressive (and can it be overcome with end-user equipment, i.e. htpc and progressive set)

EDIT: Oh btw, take it as given that the set in question is capable of displaying 1080p, and the viewer is at the right viewing distance to be capable of resolving the extra detail.

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Hi guys,

With the launch of Ch10s HD Broadcasts of the AFL this year, which i believe are 1080i, ive been wondering whether they would have been better of going with 720p given the bandwidth constraints.

But then i thought that dropping from 1080 to 720 is a significant drop to have to make up for by using less compression (thus fitting in the same bandwidth broadcast) so im not really sure which would be better?

1080 or 720 (assuming a constant bitrate)

Or is bitrate not the right consideration? Is it the progressive nature of 720p that may make it better than 1080i?

And how much can this be compensated for by using a HTPC which takes the 25fps interlaced signal and displays it at 50hz? Doesnt that effectively turn 1080i into 1080p?

I suppose that raises two arguments:

1080 v 720 (assuming you cant increase the bandwidth on 1080, and that its not enough to run 1080 properly...which it isnt)

interlaced v progressive (and can it be overcome with end-user equipment, i.e. htpc and progressive set)

EDIT: Oh btw, take it as given that the set in question is capable of displaying 1080p, and the viewer is at the right viewing distance to be capable of resolving the extra detail.

If both formats have enough bandwidth, they both should look great IF, and a big if.

In using 720p50, the whole signal path from the camera to your home is 720p50, not a conversion.

This is most likley the main hurdle to running AFL in 720. Yes they could run the OB in native 720, but what about SD inserts, adds etc which would go through convertors. The 2nd part to this is any native 1080i50 (or 25p) then has to be converted to 720p50, which is not ideal.

So in running 1080i50 for AFL, all other 1080 will fit in with least amount of degrading.

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It's a tough call. Some of the newer TVs have deinterlacers that are so good that 1080i can often look better than 720p for sport. That said, even with perfect deinterlacing, the vertical resolution of 1080i drops effectively to 540 (at least in parts of the screen which contain motion)...but 1920x540 is still more pixels than 1280x720. It could be argued that DTV bitrates are far too low for 1080 though.

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It's a tough call. Some of the newer TVs have deinterlacers that are so good that 1080i can often look better than 720p for sport. That said, even with perfect deinterlacing, the vertical resolution of 1080i drops effectively to 540 (at least in parts of the screen which contain motion)...but 1920x540 is still more pixels than 1280x720. It could be argued that DTV bitrates are far too low for 1080 though.

Yeah see this is what im getting at...the "big If" is the current DTV bitrates.

I dont think the bitrate is currently high enough to run 1080 properly....so the question is will lower level of compression required to fit a 720 broadcast into the same bandwidth stream make up for hte loss in pixels from 1920x1080 (or 540 in this case) to 1280x720?

And if not, does the fact that the 1080 signal (in this case) is interlaced, compared to a hypothetical broadcast at 720p.

Im not talking about running the current Ch10 1080i at 720p on my set, but rather would Ch10 have been better of choosing to do it in 720 rather than 1080 given that they knew their bandwidth would not be high enough?

To simplify it to an analogy, Is the 1080 a ferrari with no petrol in a race with say, a falcon with enough petrol?....the ferrari goes faster in theory, but the falcon has enough fuel and the ferrari doesnt, so its pointless.

Does that hold true in this instance of 720 v 1080?

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when sky uk was going into hd mode they also had this dilema.

they had found interlace not to be sufficent for sport,so they opted 720p for sky hd sports over 1080i.

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when sky uk was going into hd mode they also had this dilema.

they had found interlace not to be sufficent for sport,so they opted 720p for sky hd sports over 1080i.

hmmm, id love to see an example of each side by side. Too bad none of the other stations broadcast in 720p so we can compare.

Either way its a compromise, they should be trying to get 1080p happening in a decent bitrate.

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i don't know if you went up to 1080p in a 42" screen it would be a great diff.

compared to 720p,we are talking 2 diff formats,inter compared to prog,

for movies i don't think there would be a great diff 1080i to 720p,other wise sky hd would have opted for 1080i as there is no extra cost involved,

they must have picked 720p for a reason?

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i don't know if you went up to 1080p in a 42" screen it would be a great diff.

Yeah more than likely not, but thats why i said at the start to assume a set was being viewed from a distance that would allow proper resolution of the extra detail. I.e. a 70" from 3m

The whole argument becomes a bit pointless if your watching too small a screen or from too far away to notice anything.

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Interesting topic.

I wonder if part of the reason is because the networks here use 1080i/50 HD cameras. If they broadcast this out "as recorded" (ie. 1080i/50), and leave it to your TV's internal de-interlacer, screens that have better de-interlacing abilities may likely show a better resulting image.

If the networks de-interlace for us, to 1080p or 720p, will they use a standard bob method, which isn't as good as "motion-adaptive" (from what I have read).

I'm sure there is some argument for 720p/50 being better for fast-action video, however I'm sure there is a compromise in there somewhere, which is probably the reason why the networks use 1080i/50....

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1080p video is only 24/25 frames per second, and totally useless for sport.

A 1080i video stream can contain either 1080p 24/25 from film or 1080p video camera (the same as 1080p video) or it can contain genuine 1080i video from an interlaced video camera which deinterlaces to 50 frames per second and is much better then 1080p for sport.

Genuine 720p is 50 frames per second, and progressive video is more efficient to compress then interlaced, so for restricted bandwidth and fast motion 720p50 should be better overall then 1080i, however 1080i is not always 1920x1080.

If 1440x1080i is used in place of 1920x1080i the tables may be turned, as 1440x1080i requires LESS bandwidth then 1280x720p.

If we have to have only one HD format 1080i is definitely the way to go, as it is the best compromise. 1080p video can be carried without loss as 1080i, and true interlaced 1080i content has most of the motion advantages of 720p.

For low motion scenes, 1080i is noticeably more detailed then 720p can ever be on a 1080 display that is viewed up close.

The big limitation of 1080i has never been the video format it’s self, but how digital displays have dealt with it. The displays deinterlacing system is what makes or breaks the end result and until recently 1080i deinterlacing in digital displays has been poor at best.

With the much more advanced deinterlacing systems coming into use now, 1080i can begin to provide the performance it was always capable of.

The best deinterlacers are still only available in stand alone video processors or PC’s fitted with the best of the new video cards.

Cheap 1080p displays will no doubt have less then best deinterlacing, which significantly limits their potential performance with 1080i.

Having said all that, if you don’t sit close enough to the screen relative to its size, non of the above will be relevant, as you wont be able to see the difference anyway.

For 1080 to be visible on a 42” screen, you would need to view it from no more then about 1.7 meters, which for most people is impractical.

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Maybe it has a lot to do with the TV's resolution as well? The majority of HD sets are currently 768 pixel screens that lend themselves to 720 over 1080. I couldn't help but notice that when "Planet Earth" was being shown in 720p on ABC, most people raved about the PQ, but many of the criticisms of the PQ being ordinary seemed to come from the high-end "early adopter" users with their monster 1080 Panas, whatever.

Several screenshots were posted from a user showing how the BBC 1080i program looked and they were definitely better on his equipment.

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I was the one who posted the comparison of the ABC’s low bit rate Mpeg2 720p and the BBC’s high bit rate h.264 encoded 1080i version of The Planet Earth “Caves”.

My observation was that the 1080i version was rubbish by the standards of good 1080 content and that the 720p version was not much worse on a 1080 display.

I frankly could not understand why people where raving about the picture quality, as I rated it 5 out of 10 for HD.

It’s common for 720-768p displays to use simple bob deinterlacing with 1080i.

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when sky uk was going into hd mode they also had this dilema.

they had found interlace not to be sufficent for sport,so they opted 720p for sky hd sports over 1080i.

I googled around and found Sky Sports HD actually chose 1080i over 720p. See http://www.t3.co.uk/news/247/general/gener..._launch_line-up

It seems no one wants to use 720p for sports. I would have thought that 720p would have been the better format to use for fast action sports since there's more vertical resolution per 1/50th of a frame than the standard bob 1080i (1920x540).

Having said that even if bob is used for 1080i format and the TV is 768px in height with a good scaler, then the picture should still be pretty clear as long as they don't tamper with the bitrate. I'm not sure about those who have a very large 1080 panel whether they'll notice anything significant going up from 540 to 1080.

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It’s common for 720-768p displays to use simple bob deinterlacing with 1080i.

I believe that's the only method that can be used to deinterlace 1080i content where consecutive fields are significantly different from one another like in fast motion sport scenes. I have heard a combination of bob+weave is one of the best methods to use to deinterlace but I can't see where anything can be weaved when every 1/50 frame is totally different from the previous frame. Nobody cares about still scenes (where the weave method can be used to preserve the vertical resolution) in sport since nothing is happening here.

Having said that a very good scaler needs to be used to scale up any 540 fields to 768 or 1080 and I'm sure the expensive scalers do a better job than most TVs.

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I don't know if anyone else notices but when I watch the AFL in HD the grass sometimes pixelates badly. When I watch it in SD it doesn't happen.

Shouldn't it be more important to make sure that the signal can be transmitted consistently at a given resolution without pixelation then to worry about what res it is. I admit that close views of players is infinitely more detailed in HD then SD but if the overall quality of the transmission is compramised, why bother?

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I don't know if anyone else notices but when I watch the AFL in HD the grass sometimes pixelates badly. When I watch it in SD it doesn't happen.

Shouldn't it be more important to make sure that the signal can be transmitted consistently at a given resolution without pixelation then to worry about what res it is. I admit that close views of players is infinitely more detailed in HD then SD but if the overall quality of the transmission is compramised, why bother?

I can't say that I've really noticed pixelation in the grass on my TV (1366x768). From memory it looked pretty clear especially when the camera zooms in on players. The SD channel looks very soft and is probably why you don't see it. The other reasons could be the constrained bitrate ch10 uses or your signal quality is low.

Next time I watch AFL HD, I'll look out for it.

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I can't say that I've really noticed pixelation in the grass on my TV (1366x768). From memory it looked pretty clear especially when the camera zooms in on players. The SD channel looks very soft and is probably why you don't see it. The other reasons could be the constrained bitrate ch10 uses or your signal quality is low.

Next time I watch AFL HD, I'll look out for it.

It's only in high motion, when it is tracking quickly across the field.

The grass is more detailed when it zooms in in HD.

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The US Masters Golf looked spectacular in 1080. There were a few panning shots where it went a bit ugly but 90% of the time it was top notch and I could see the cut of the grass on the greens. Watching the replay later on Foxtel was almost unwatchable after seeing it in HD.

As for Planet Earth, I'm pretty sure it was shot on 720 cameras so it's not surprising that it didn't look much better in 1080.

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The US Masters Golf looked spectacular in 1080. There were a few panning shots where it went a bit ugly but 90% of the time it was top notch and I could see the cut of the grass on the greens. Watching the replay later on Foxtel was almost unwatchable after seeing it in HD.

That's what I mean - It's just the panning stuff and usually only in the background but I recon they should never transmitt at a resolution that is beyond that which allows it to be top notch 100% of the time.

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I believe that's the only method that can be used to deinterlace 1080i content where consecutive fields are significantly different from one another like in fast motion sport scenes. I have heard a combination of bob+weave is one of the best methods to use to deinterlace but I can't see where anything can be weaved when every 1/50 frame is totally different from the previous frame. Nobody cares about still scenes (where the weave method can be used to preserve the vertical resolution) in sport since nothing is happening here.

Having said that a very good scaler needs to be used to scale up any 540 fields to 768 or 1080 and I'm sure the expensive scalers do a better job than most TVs.

You have obviously never heard of pixel adaptive, vector adaptive or motion interpolated systems, these all blow bob away for quality.

Bob is THE most basic system of all, and should never be used on a 1080 display if want the best result.

The better PC video cards do an outstanding job, and so do the better stand alone scalers processors, much better then what you normally find in TV’s.

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The US Masters Golf looked spectacular in 1080. There were a few panning shots where it went a bit ugly but 90% of the time it was top notch and I could see the cut of the grass on the greens. Watching the replay later on Foxtel was almost unwatchable after seeing it in HD.

As for Planet Earth, I'm pretty sure it was shot on 720 cameras so it's not surprising that it didn't look much better in 1080.

Planet earth is very grainy and is almost certainly shot on film; however it may be only 16mm, which would explain the low resolution.

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You have obviously never heard of pixel adaptive, vector adaptive or motion interpolated systems, these all blow bob away for quality.

Bob is THE most basic system of all, and should never be used on a 1080 display if want the best result.

The better PC video cards do an outstanding job, and so do the better stand alone scalers processors, much better then what you normally find in TV’s.

I'm sure the expensive scalers that can detect the motion areas would produce better results than simply bob+weave. Whether it's better than 720p/50-60 remains to be seen (at least in my eyes). I'm sure someone or some company has compared the two (i.e filming the same action but using 720p and 1080i cameras).

As yet, I haven't found a website that has analysed the two formats:

1. 720p vs 1080i converted to 720p or

2. 720p converted to 1080p vs 1080i converted to 1080p

Some clip samples of each format to compare would be great to anyalyse.

Having the most expensive scalers just to convert 1080i into a high quality progressive format seems a lot. If only they could have stuck with some progressive formats (like 720p, 900p, 1080p), then the end user might not have to fork out as much to get a decent picture.

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1080p video is only 24/25 frames per second, and totally useless for sport.

A 1080i video stream can contain either 1080p 24/25 from film or 1080p video camera (the same as 1080p video) or it can contain genuine 1080i video from an interlaced video camera which deinterlaces to 50 frames per second and is much better then 1080p for sport.

If we have to have only one HD format 1080i is definitely the way to go, as it is the best compromise. 1080p video can be carried without loss as 1080i, and true interlaced 1080i content has most of the motion advantages of 720p.

For low motion scenes, 1080i is noticeably more detailed then 720p can ever be on a 1080 display that is viewed up close.

Owen, can you expand on this a bit further for the benefit of those of us...okay, me, hehe...who are still new to this.

specifically, i dont understand how a 1080i video stream can contain either 1080p 24/25 from film or 1080p video camera?

Isnt it the case that if 1080i is being broadcast, its being broadcast at 25fps? therefore you are going to need something at your end to convert this back to a 1080p signal (i.e. videocard)? If so, how can it "contain" the 1080p stream?

Also, i dont understand the part about the interlaced video camera being better for sport...why is this so? Is it because when you deinterlace a 1080i stream to 50fps, you are getting slight changes in each field, that are then being blended back together to make a 25fps 1080p stream, whereas if it was shot in 1080p in teh first place, it would only be capturing the 1 change every frame, rather than 1 change every half frame?

Or am i completely misunderstanding it?

Thanks,

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Owen, can you expand on this a bit further for the benefit of those of us...okay, me, hehe...who are still new to this.

specifically, i dont understand how a 1080i video stream can contain either 1080p 24/25 from film or 1080p video camera?

Isnt it the case that if 1080i is being broadcast, its being broadcast at 25fps? therefore you are going to need something at your end to convert this back to a 1080p signal (i.e. videocard)? If so, how can it "contain" the 1080p stream?

Also, i dont understand the part about the interlaced video camera being better for sport...why is this so? Is it because when you deinterlace a 1080i stream to 50fps, you are getting slight changes in each field, that are then being blended back together to make a 25fps 1080p stream, whereas if it was shot in 1080p in teh first place, it would only be capturing the 1 change every frame, rather than 1 change every half frame?

Or am i completely misunderstanding it?

Thanks,

Omega,

I am still learning myself about all this, though 1080i broadcasts are at 50Hz (in Oz), as 1080p/50 doesn't exist as yet (or is not mainstream).

Interlaced basically means each field (or frame) is either all the "odd numbered" or "even numbered" horizontal lines of the footage.

Scan number one down the screen shows all the odd numbered lines, scan two shows all the even ones. This happens so fast that the image looks like it's all being shown at the same time. Note there would be 25 frames of odd's and 25 frames of evens (using all 50 cycles, or 50 Hz).

Progressive is where all lines are shown at the one time (from line 01 to 1080), at this point in time, at 24 times per second (hence 1080p/24).

To convert the interlaced material into progressive, the scaler or de-interlacer (usually found within recent Plasma's or as standalone units) grab frame one and frame two (the first cycle of both odd & even lines), and merge them together (by using the methods of either BOB, WEAVE, MOTION ADAPTIVE, or other variations), to create a 1080p frame. Therefore, as two (i) frames are converted into one (p) frame, the Hz is halved accordingly (50/2=25).

Note: As many films etc are shot or converted into 1080p/24, some frames may need to be displayed more than once to achieve 25fps (instead of the 24fps).

I believe the reasoning that 1080i/50 is considered better for sport is that it records in 50Hz (wheras shooting in 1080p/24...which is the only other viable 1080 option at present is shooting at 24fps), which isn't as good for fast motion. However the potential downfall to the 1080i/50 is that some methods of converting back to 1080p often are not able to keep the full 1080 resolution in the fast areas of the footage.....though may still look on par (or better) than similar footage shot at 1080p/24Hz.

If I am not on the right track, somebody please jump in and say so....

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Ahh yeah i think the first and last lines basically cleared it up for me. I know what interlacing means, but what i didnt realise (probably stupidly) was that 1080i WAS broadcast in 50hz. For some reason i thought it was done at the end-user point.

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