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Old February 28th, 2005, 03:44 PM   #1
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difference between 720p and 1080i?

Why is there a choice between these two? Is one better looking than the other? What are the advantages to using one over the other?
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Old February 28th, 2005, 05:39 PM   #2
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Re: difference between 720p and 1080i?

<<<-- Originally posted by Brandon Murphy : Why is there a choice between these two? Is one better looking than the other? What are the advantages to using one over the other? -->>>

You really want to know?

Prepare for all sorts of personalised viewpoints on this one!!

Some would argue that 720p is better at handling movement. My take is that that might be true if the aperture and speed were incapable of adjustment on a 1080i camera to help counteract the mathematical advantage of 720p.

Same thing goes for resolution... Supposedly 720p has the same 'temporal' resolution as 1080i in the mathematical sense. However real world viewing on any decent WS HD large screen display - we are talking over 32" here - should immediately lay that one to rest!!!

Ultimately; despite what you may hear to the contrary, 720p was introduced as a level of broadcast that would give options to broadcasters who felt the expense of 1080i conversion was too great, while 720p could be implemented cheaper and marketed agressively as at least as good as 1080i, to less discerning customers.

Check any decent FTA (Free To Air) HD broadcast forum, and I'll guarantee you'll not find any endorsement of 720p over 1080i discussion whatsoever.... wonder why!! :)
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Old March 1st, 2005, 12:34 PM   #3
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1080i has better positional resolution.
720p has better temporal resolution.

The many who made the rules couldn't agree, so we have both!
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Old March 1st, 2005, 01:10 PM   #4
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thank you both for your replies!
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Old March 1st, 2005, 01:13 PM   #5
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The main difference resides on the what the 'i' and the 'p' stand for.

1080i provides a sharper, higher pixel resolution image, or at least the illusion of such. You get 2 interlaced fields, ie 2 images that were captured at 1/60th of a second, which are displayed at 30fps. So when you watch something on a standard TV, you are actually seeing 2 interleaved fields (even and odd) that are being displayed (one at a time) so fast that your brain thinks they're one.

720p is a progressive mode, ie, the frame is captured and displayed in full at the specified frame rate (30p, 60p, etc.), and as such there's no need to trick your brain with the technique mentioned above. Progressive mode is the way of the future, and once it's able to match the same resolution as interlaced (1080p) we won't have much need for the 'i' anymore.
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Old March 1st, 2005, 05:32 PM   #6
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Re: Re: difference between 720p and 1080i?

<<<Ultimately; despite what you may hear to the contrary, 720p was introduced as a level of broadcast that would give options to broadcasters who felt the expense of 1080i conversion was too great, while 720p could be implemented cheaper and marketed agressively as at least as good as 1080i, to less discerning customers.>>>

Hmmm, I guess that makes the United States military a "less discerning customer," since they decided some time ago that 720p is preferable to 1080i for purposes of surveillance videos. No matter what else you may say about tbe 1080i format, when you do a "freeze frame" it looks like crap compared to a decent progressive-scan format. And you can find plenty of discussion on the internet saying that Fox's 720p HD broadcasts look a whole lot better (in general) than other networks' 1080i broadcasts.

But the biggest practical problem for videographers is that we barely have enough computing power today to effectively edit and play back 1080i video, whereas we have a little bit more than we need to edit and play back 720p. If we'd gone straight to 720p cameras, editing and monitors we'd have a great end-to-end solution in place now, but instead we have to put up with a few years of pretending 1080i matters even though interlacing is a hack whose time is almost up.
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Old March 1st, 2005, 09:24 PM   #7
 
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<<<<but instead we have to put up with a few years of pretending 1080i matters even though interlacing is a hack whose time is almost up.>>>>

Gimme a break....you know something the ATSC and NAB don't know?
I'm not going to argue one way or another over which is better. Both have their advantages and disadvantages. But to
1. Suggest 1080i is a "hack"
2. Suggest 1080i is inferior

both imply that you aren't paying attention to the industry or who is controlling what. It's going to be a LONG, LONG, (repeat 5 times) time before 1080p rules the day. The bandwidth is expensive, the gear even moreso. It's not a recognized standard. If you think 720p or 1080i is difficult to edit/process....well....1080p is twice as hard. AND the acquisition of such simply isn't cost effective at all, not at this point in time.

I suggest you read the NAB Handbook and Peter Gloeggler's excellent treatise on this subject. He's a very well respected industry engineer with nearly 40 years in the can as a designer of lens/CCD integration. He predicted in the late 70's that we'd not see 1080p as an editing or delivery format for 50 years, and went on to explain why. He called it pretty well right, as far as the industry can see.
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Old March 1st, 2005, 09:48 PM   #8
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D.S.E - are you referring to 1080p @ 60 fps? I mean, practically it seems the only thing standing between us and 24p or 30p 1080p in the HDV format (with a pulldown of course) is a 1/3" 1080p CCD (i.e., a relatively small and cheap 1080p CCD - nothing magic about 1/3").
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Old March 1st, 2005, 10:04 PM   #9
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Re: Re: Re: difference between 720p and 1080i?

<<<-- Hmmm, I guess that makes the United States military a "less discerning customer," since they decided some time ago that 720p is preferable to 1080i for purposes of surveillance videos. -->>>

Actually, the military is a VERY discerning customer, but their application to justify your argument is naive. The military has a very narrowly defined requirement that has no counterpart in the commercial broadcast field. So the best method to attain the results needed AND not waste taxpayer money was to use the inferior of the two COTS solutions rather than spend a wad of money to build a unique 'military' format to suit their needs. The military would have much prefered the increased resolution of the 1080i format but other equally important factors tipped the scale to 720p. The decision all revolved around the use of the data and how it could best help the military, which amazingly does not always correspond with how commercial applications use a technology. So unless you have to be able to deconstruct every frame, apply Automatic Target Detection/Clasification algorithms against them, self-catalog, and then transmit single frame and short-clip extracts over the Global Command and Control System, you're requirements may lead you to a solution other than 720p.

But calling 1080i a 'hack' is as wrong as saying 720p is a 'hack'. Each format has strengths depending on the job, but don't think just because the 'military' chose it, it must automatically be better. And saying that "you can find plenty of discussion on the internet saying that [a network's] 720p HD broadcasts look a whole lot better (in general) than other networks' 1080i broadcasts" doesn't mean its true. Amazingly, much of what you read on the internet is half-truth, wishful thinking, bald-face lies or simple untruths (and wrestling isn't real either).

Define your job, seek the best tool to perform the job. And realize that "best" often requires trade-offs.
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Old March 1st, 2005, 11:00 PM   #10
 
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Yeah, I should have made that more clear. But that's where the change will come, when it comes. 30p is temporaly better, but spatially it's not.

I was a strong proponent of 30p and 24p acquisition until I saw a Thomson/IKE/Sony/Panasonic shootout in Burbank nearly a year ago. Once I saw in real world terms, on a real HD progressive scan display, what acquisition 30p looks like with high motion and saturated colors, it's no wonder it's not a chosen standard, even though we have the bandwidth and technology. Talk about a headache. On the other hand, 60i media offers a wonderful medium to deliver 30p.
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Old March 2nd, 2005, 07:10 AM   #11
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I don't want to stir the pot but I personally think the CBS broadcasts have the most 'visual appeal'. I first noticed it with their sports broadcasts, most notably the college football games. But now, with most of the prime time programming in HD, I see it there also. It maybe the fact that they use the Zenith HD system, I don't know. It just looks better on my tv.

As for the military's use of 720p over 1080i, IMHO it's because they want 'clean' frame grabs. Progressive frame acquisition holds the advantage in this regard whether you are talking HD or SD.

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Old March 2nd, 2005, 09:14 AM   #12
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I'll help you stir a little Greg. When the World Series was on my brother called me to ask why it looked so bad on his 32" HD tube. At the time we didn't know Fox was 720p...so after research we discovered it was 720p and not nearly as sharp as CBSs NFL Football or ABC's Monday Night Football.
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Old March 2nd, 2005, 09:34 AM   #13
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There seems little point in interlaced formats when CRTs (the only interlaced display technology) is effectively dead and all the plants that make them are closed or closing. The Phillips plant just down the road from where I was born just announced it's closure today, and Sony stopped making CRTs a while back, and have stockpiled tubes for their highest end customers.

1080i doesn't have much, if any, in the way of a real advantage in terms of vertical resolution over 720p due to interlaced formats needing vertical filtering to reduce interlace twitter, which is an objectionable artifact. 1080 formats do have a greater potential horizontal resolution, however.

The overall quality of de-interlaced 1080i for display on a modern display technology and 720p is pretty similar. 720p "up"converts to 1080i very well, and 1080i "down'converts to 720p nicely. Indeed as transmission bandwidth is an issue, 720p has an advantage in less potential artifacts as it's more temporily correlated and easier to compress with MPEG2 / MPEG4 (due to it being progressive) which about balances the higher horizontal resolution of 1080i.

So what's best?? 1080p60(50) of course!

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Old March 2nd, 2005, 10:27 AM   #14
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Re: Re: Re: Re: difference between 720p and 1080i?

<<<Define your job, seek the best tool to perform the job. And realize that "best" often requires trade-offs. >>>

Agreed. Right now the best camera for my purposes and budget appears to be the 1080i Sony, while the most practical distribution format for a while will be 720p. I'd just as soon shoot in 720p to start with and edit in 720p for efficiency, but I'll settle for working with 1080i for now. To me HDTVs with a 720p resolution look just fine, and as someone else pointed out the manufacturing of interlaced displays is rapidly coming to an end. What I really want is 720p/60 recording, which sounds like it may be available with the upcoming low-cost DVCProHD camera.
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Old March 2nd, 2005, 03:18 PM   #15
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Too bad Panasonic didn't see Grahame's post before they got committed to the HDX400. If 1080i has no reason for existence, they're going to be disappointed with this camera, I guess, since it shoots 1080i DVCPRO HD instead of 720p. Darn, what were they thinking, anyway...crazy engineers, you'd think they'd know better like we all do.
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