1080i signal to 1080P display question

BamaPanda

Is there any documentation or a study that shows what a 1080P display does with a 1080i signal?

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BobY

There are only two things a 1080p display should do with 1080i content:

If the display detects the content is film-sourced (i.e. 24 Frames-per-second), it should simply weave together the two fields of the interlaced frame. This will perfectly reconstruct the original progressive frame that was interlaced for transmission. To detect film content, the display must examine multiple fields and determine if they match the 3/2 repetition cadence which is produced when 24 Frames-per-second film content is pulled-down to 60 fields-per-second video.

If the display determines the content is not film-based (no 3/2 repetition), then it is 60 fields-per-second video captured in interlaced form (i.e. no progressive source frame). The proper thing for it to do is to examine multiple frames and weave together the portions of the frame that are not moving or moving slowly, while line-doubling/interpolating (bobbing) the portions of the frame that are moving quickly. This preserves full vertical resolution on static or slow moving images, where weaving won't cause any artifacts, while preventing motion artifacts and degraded motion response which weaving would cause on fast moving images.

Not all displays do it properly. A lot of displays don't reliably detect film content or stay in film mode, so they don't always weave the fields and therefore do not properly recreate the original progressive frame. Some displays simply line-double/interpolate each field, yielding an effective resolution of 540p and essentially throwing out half of the vertical resolution for each frame.

Neither of these errors are obvious except in direct comparison to a display that does it properly.

If you want to know which displays do it properly, you have to seek out the Home Theater Magazine tests and, it appears this is now a standard part of C-Nets reviews. It's very easy to test with an HD test pattern generator or appropriate HD test disc.

BamaPanda

I have read (I think) that a 1080i signal on a 1080P panel will be close/closer to 1080P as far as resolution, but I have never seen anything from a test in print that actually confirms this.

There are lot of opinions on this forum (mine included) that are easily based on what we have been told, or presented out of an excellent working knowledge of the technology.

This is not to undermine anyones opinion, no matter how much fact it may carry within. I was just hoping for some tests. I will stroll through C-net, and perhaps I will find one if one is not mentioned here.

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BamaPanda

??
With all the talk about the superiority of 1080P I would have thought there would be a plethora of documented info out there.
Don't get me wrong. 1080P is great. I sell it. The main thing I am wondering if the hype of 1080P - other than the ability to play HD DVD's through a Blu Ray - is overstated, and mostly a marketing ploy.
Here is something I found, but it is not a full test - from what I can see, and it does not seem to really boost 1080P to it's celebrated levels, other than with Blu Ray.
http://www.hometheatermag.com/gearworks/1106gear/

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BobY

You have to keep the concepts of 1080p signal transmission and 1080p display separate in your mind.

First, there is no, zero, nada difference in resolution between a 1080i signal and a 1080p signal, they both have 1920 x 1080 pixels per frame. If you start with a 1080p source frame (as with HD DVD and Blu-Ray), there is absolutely no difference in the data itself transmitted between 1080i and 1080p, the only difference is the 1080i signal is transmitted as all the odd lines first then all the even lines, while the 1080p signal is transmitted as all lines in sequential order.

As far as displays are concerned, any progressive display with 1920 x 1080 pixels is a 1080p display and will show any image it receives as 1080p. It will de-interlace 480i and upscale it to 1080p, it will upscale 480p to 1080p, it will upscale 720p to 1080p and it will de-interlace 1080i to 1080p. If you weave together the odd and even lines of a 1080p image that has been interlaced for transmission, you will perfectly recreate the original 1080p frame. Whether the de-interlacer works properly has nothing to do with the concepts involved.

The current confusion (aside from Sony muddying the waters with their "only 1080p is Full HD" marketing campaign) is that not all 1080p displays accept a 1080p signal, although more and more are coming on the market.

The advantage of a 1080p display receiving a 1080p signal is that it bypasses the internal processing so it doesn't matter whether the de-interlacer works properly or not, although, as I said, if the de-interlacer works properly, there is no difference in the final image whether it's a 1080p frame transmitted and received as 1080p or a 1080p frame interlaced, transmitted and received as 1080i and de-interlaced to 1080p.

If the original frames are not progressive, but were captured in interlaced form (such as live 1080i HD video), then there is no choice but to de-interlace it, either for display at 1080p or transmission at 1080p, so in that case there is no advantage to a 1080p input, the signal has to be de-interlaced somewhere along the line.

It's important to note that there really aren't many sources of 1080p signals. There is no OTA/cable/satellite content at 1080p. The only sources of 1080p are Hi-Def discs (HD DVD, Blu-Ray), some high-end video game consoles (PS3, XBOX 360 over VGA) and some computer graphics cards (and possibly a 1080p camcorder for home video if you have the bucks). There is a *lot* of 1080p content (i.e. frames were captured at 1080p), but most of it is then interlaced and transmitted as 1080i.

The final issue is frame rate. Movies are captured at 24 Frames-per-second. There is no 1080i/24 ATSC standard, all 1080i is 1080i/30. That means 1080p/24 film content must be pulled-down from 24 Fps to 30 Fps/60 fields-per-second. This adds a jerkiness to movement called judder, which can be avoided by transmitting a 1080p/24 signal as 1080p/24, but *only* if the display accepts a 1080p/24 input (not just 1080p/60) AND the display switches it's refresh rate from 60 Hz to 72 Hz (or the display has a 120 Hz refresh rate).

Transmitting 1080p/24 at 1080p/60 requires pull-down and causes judder. Transmitting and receiving 1080p/24 at 1080p/24 will still have judder if the display refreshes at some rate that isn't a multiple of 24 Hz.

I don't believe there are any true sources of 1080p/60 except possibly some really high-end computers. AFAIK, neither the PS3 or XBOX 360 generate new 1080p frames every 60th of a second. They may transmit frames at 1080p/60, but they are not drawing new frames every 60th second, so they are repeating frames, which effectively reduces the frame rate.

In the not too distant future, most displays will be 1080p, will accept a 1080p/24 input and will refresh at 120Hz. Right now we are in a transitional phase with some displays offering various combinations of these features and only a very few offering all of them.

That pretty much sums up the objective concepts--they are not my opinions. Whether a particular display does what you want is something only testing will show. All displays *should* work properly, but CE is a cut-throat, narrow-margin business and every manufacturer cuts every corner they think they can get away with.

BamaPanda

Good response. Good info. Still no documented tests.
One thing I did get was that as we progress forward to the day when most sets will be 1080P, certain broadcasters should really start advertising that they have a real advantage over others. After all, the national broadcasters that put in equipment for 720p broadcast are at a real disadvantage to 1080i camp. I am surprised they are not already shouting it from the rooftops "My 1080i OTA signal will give you the closest thing you can get to Blu Ray resolution, and it is free"!
Seriously, why are they not doing that?

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rbinck

There are documented test run by Gary Merson of Home Theater Magazine. I have collected links to them on my blog. See: The 1080p HDTVs for starters.

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BamaPanda

Read the 'Are You Getting All the HDTV Resolution You Expected?' article, first installment, anyway.
Interesting how Gary and Geoff Morrison had different results by a large margin using two different forms of testing.
I guess I am just a skeptic at heart. I just can't help but wonder if 26 of those 54 sets failed as miserably as stated, that people would not come out of the woodwork continually the first time they viewed say - a fast NASCAR race with motion problems. Personally I have not seen it. Maybe it is something that can be measured, but not seen. If that is so, it is immaterial.
Also, I again bring the question (and Gary alluded to this in his first sentence .."The current top HDTV broadcast resolution is 1080i") ..IF 1080i is so superior to 720p, why are not all the broadcasters that use 1080i really flaunting this factor to thier favor?

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rbinck

Just go back to what was said, "The current top HDTV broadcast resolution is 1080i" it seems like a true enough statement if you use the meaning of top to be the higest resolution (in pixels) as opposed to the top meaning the best. Since he refered to broadcast resolution rather than broadcast format, I assumed the former.

The question was were there any documented tests and those fit that description in my mind.

The argument as to the better format between 720p and 1080i is a whole 'nother subject.

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nmlobo

Where did you see any testing conducted by Geoff Morrison? I must have missed it in the article link you provided. From what I read, Geoff's and Gary's conclusion appeared to be the same. Geoff wrote " If the TV correctly deinterlaces 1080i, then there should be no visible difference between deinterlaced 1080i and direct 1080p " http://www.hometheatermag.com/gearworks/1106gear/ Gary wrote "So, regardless of what you may have read elsewhere-or what your local TV-store sales clerk has told you-if a 1080p display's processor is capable of content based on HD 3:2 inverse telecine (and properly deinterlaces, as well), you can see all of the content in full 1080p resolution."

BTW Gary also conducted a third test on different sets: http://hdguru.com/?p=17

BamaPanda

Bottom of this page. It was the 1st installment of the article.
http://hometheatermag.com/hookmeup/0506halfrez/
Thanks for the other info.

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BamaPanda

I relent.
Looks like the testing is there after all. Whether it can be easily seen by the consumer might be another issue.
Thanks for the links. Now to do some study.

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BobY

I'm not sure what kind of tests you're looking for. If you're looking for tests that verify what I'm saying, you won't find them, just like you won't find tests to prove 2+2=4. These are just facts.

If you want to know whether a specifc display does what it *should* do, like I said, Merson's articles for Home Theater Magazine and current C-Net reviews.

It's really true, there are a lot of displays that don't do what they *should* do, but like I said, unless you see them in direct comparison to a good display you may never know. Absent a real 1080p reference, are you really going to notice that the display is showing 540 real lines of information plus 540 interpolated lines (or even just 540 lines doubled to 1080) instead of 1080 real lines?

You aren't going to notice motion problems, that's one of the reasons they use the 540p cheat--each 540-line field is upscaled to a 1080-line frame at 60 Frames-per-second, so it doesn't harm the temporal resolution, only the spatial resolution.

1080i broadcasts that were captured at 1080i can't claim they will produce the same result as Blu-Ray or HD DVD because they never started with a progressive frame, so there is no progressive frame to recover by de-interlacing. More significantly, OTA uses much more severe compression and MPEG2 encoding which isn't nearly as good as either HD DVD or Blu-Ray at this point, with far more artifacts.