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Discussion Starter · #1 ·
Assume for the moment that we had cameras capable of fully capturing either of these formats and displays capable of fully rendering them.

I have a mental model which breaks this into two separate debates:


1) 720p60 vs. 1080p30

This part seems easy to understand. Pixel rates are only about 10% different. The tradeoff is between temporal resolution and spatial resolution. 720p60 is better for sports, 1080p30 is better for travel documentaries, other material falls in between.


2) 1080p30 vs 1080i60

This is the comparison I don’t understand as well. Pixel rates are exactly the same. Interlacing is bad for compression, is hard to reverse, and yet it must be reversed if the display device is anything other than a CRT. So why do we do it? Wouldn’t it be better to just transmit 1080p30? A CRT display could easily interlace the 30p signal to display it as 60i while fixed pixel displays could just as easily do a 2:1 pulldown to display it as 60p (in addition to whatever conversion to native resolution is required).
 

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Quote:
Originally posted by oxothuk

Wouldn’t it be better to just transmit 1080p30? A CRT display could easily interlace the 30p signal to display it as 60i while fixed pixel displays could just as easily do a 2:1 pulldown to display it as 60p (in addition to whatever conversion to native resolution is required).
How would a 1080 image captured at 30p and doubled (or higher) by the display compare with the current 1080 captured at 60i, stored and transmitted at 60i, and converted by our eyes/brain to 30 frames per second? Does the current 1080 60i system (NBC's Leno, PBS, HDNet) deliver 'smoother' images since it's capturing 60 fields (540 lines/field) each second compared to only 30 frames per second, (or 24p with 2:3 pulldown to 1080 60i in practice)? Can't say because I haven't A/Bed them. But I look forward to the technology catching up and, hopefully, the adoption of 1080 60p--starting at the camera--to everything (sports, drama, news, DVDs, etc.) -- John
 

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1080p30 would work in most instances as well as 1080i60,

but for many CRT based TVs, the electronics make it much easier to show interlaces pictures....


It's true that they could do the p30 to i60 conversion themselves, but that's not how the standard fell out.

So, with appropriate electronics, it is close to the same, and if the source was originally progressive, it is the same.


But 1080i60 has the advantage of requiring less processing in the CRT based TVs.


Now, when it comes to source data that isn't progressive to begin with, it gets harder to compare the two.

If each interlace field is generated in real-time at the TV camera, there is no way to ever perfectly deinterlace it.

But, it does carry more temporal information than 30p would.


Interlace is definitely a holdover from an earlier era, but the truth is that most TVs built today aren't able to handle 60p (too expensive to make them that way, they say).
 

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Discussion Starter · #5 ·
Quote:
Originally posted by Chuck_McDevitt
1080p30 would work in most instances as well as 1080i60,

but for many CRT based TVs, the electronics make it much easier to show interlaces pictures....


It's true that they could do the p30 to i60 conversion themselves, but that's not how the standard fell out.

So, with appropriate electronics, it is close to the same, and if the source was originally progressive, it is the same.


But 1080i60 has the advantage of requiring less processing in the CRT based TVs.


Now, when it comes to source data that isn't progressive to begin with, it gets harder to compare the two.

If each interlace field is generated in real-time at the TV camera, there is no way to ever perfectly deinterlace it.

But, it does carry more temporal information than 30p would.


Interlace is definitely a holdover from an earlier era, but the truth is that most TVs built today aren't able to handle 60p (too expensive to make them that way, they say).
From what I've read it's not harder for a CRT to display 1080p30 than 1080i60, but rather it's harder on the viewer since we tend to notice flicker if the refresh rate is less than 50Hz.


1080p30 is one of the 18 DTV standards, so any ATSC-compliant tuner would be required to accept it. What it puts out to the display device is another matter; it's usually the job of STBs to make conversions to whatever format the display device prefers.


Overall, your comments just reinforce the impression I was trying to articulate:

a) 1080p30 gains spatial resolution over 720p60 at the expense of temporal resolution.

b) 1080i60 gains temporal resolution over 1080p30 at the expense of effective spatial resolution.

So in the end, going from 720p60 to 1080i60 leaves us no better off in terms of performance, and worse off from having added all the problems which result from interlacing. It seems like a high price to pay to slightly reduce the cost of CRT-based HDTVs.
 

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I do agree... I wish the ATSC standard had allowed only progressive.

720p60 is great for sports and live TV,

1080p24 is great for movies transfered from film.

1080p60 takes too much bandwidth for 6Mhz TV channels.


Would 1080p48 have fit in the 6Mhz ?? It might have been a good compromise....
 

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Quote:
Originally posted by oxothuk

So in the end, going from 720p60 to 1080i60 leaves us no better off in terms of performance, and worse off from having added all the problems which result from interlacing.
That reads like what I saw in a May Widescreen Review piece, by a well-known 720p advocate, and commented on. Why, if the ATSC approval committee measured the results shown in this table back in 1995 gives such an obvious edge in terms of resolution, are we no better off in terms of performance with current 1080 60i? The limitation seems to be current MPEG2 encoders maxing out at around 1400 lines for detailed full-motion video; also, widely used Sony HDCAMs filter recordings at 1440. But that doesn't pin down whether the 1780 lines dynamic resolution for a test pattern measured in 1995 would have been possible (as an equivallent) with full-motion video. Simple test patterns don't 'stress' MPEG2 encoders.


The resolution for a 720p dynamic test pattern was 1068 horizontal resolution. If it's achievable with today's (or next year's) gear, I'd always take ~1780 resolution over ~1068. Even if roughly 1440 is the current limit on OTA ATSC resolution, my several years of 1080i observations suggests some type of oversampling effect (not >1920) may be occurring with 1080i, making the overall resolution better than the 1280X720p I've seen. My system, like most, displays 720p sideconverted to 1080i, and probably can display ~1600-1700 horizontal-resolution lines as an upper limit. No doubt straight 720p would look better without sideconversion, but those capable of seeing it either way say 1080i sideconversion doesn't spoil 720p very much.


That includes sports for a 1080i preference here. Caught a part of a special NBA game last night as 1080i, which looked just fine in 1080i--even during rapid motion. Some viewers around the country complained about blurring, and some attributed it to poor camera focusing. Generally, with my cable HDTV viewing, I haven't encountered the serious 1080i problems seen by those viewing stations with Mbps-robbing subchannels. So, on my setup, sports and drama, etc. is excellent in 1080i. Programming in 720p I view has perceptibly less resolution when you 'average' all 720p/1080i versus all 1080i. Naturally, with the variations in recording and telecines, some sideconverted 720p looks similar to 1080i programming. -- John
 
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