# HDTV and Interlaced video



## wado1942 (May 14, 2006)

Hello all. I've just started looking into a replacement for my 26" HD CRT and had what's hopefully a quick question. I hear flat panels are natively progressive only. I assume when playing a 24p Blu-Ray or whatever, it just displays the same frame 5x in a row (for 120Hz) then moves to the next frame. What actually happens to interlaced video when displayed on say, an LCD TV? Is the image field-interpolated or what? Considering all 1080 TV is interlaced, this would make a huge difference in clarity.


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## RBTO (Jan 27, 2010)

Who watches 1080i anymore???

Just Kidding!!

You're quite correct that 1080i is prevalent from a number of sources, including satellite TV. Thing is though, if that 1080i came from a film source (24 fps), it should have exactly the same information that a 1080p24 signal has, plus a little redundant information. The most common way 24 fps material is transformed to 1080i is with 3:2 pull down in which some frames of the 24 fps film are scanned more than once. If done _correctly_, this 1080i signal can be converted back to a 1080p24 signal (for use with a progressive type display) with no change in information. 

To make a long story short, if you look at _24 fps source material_ (movies and most TV shows) on a flat screen (progressive scan) display, even though it was converted to and sent in 1080i format, you should be seeing exactly the same thing as you would with a 1080p24 signal. All this assumes your display locks onto the 1080i signal and gets the cadence correct.

You're also right in assuming that interpolation is needed for non-film material such as live action (sports) and has the potential for introducing conversion artifacts. Depending on how good your set is, you may see artifacts or not. However, much live action seen on the air (again, sports) is shot in 720p so there is no interpolation (other than fitting 720 format to your 1080 pixel screen). When interpolation is needed, it can be quite good with the latest engines that do interpolation. Chances are, you wouldn't notice, unless you look at some fairly specific test patterns which are designed to reveal aliasing.


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## wado1942 (May 14, 2006)

Yeah, I'm familiar with 3:2 pull-down. You're saying if a Blu-Ray or whatever just sends out a 60i signal of a film, the TV should remove the pull-down?
I was more concerned with traditional video signals such as on-air broadcasts, not that I watch much TV. Most TV is 60i, either 480 or 1080, so I'm just wondering how both the clarity and motion might be degraded by such a signal and if there's any insight on how to chose a display that will minimize any such problems. BTW, I haven't quite decided on whether I should go with projection or LCD flat panel (LED backlit most likely).

Thanks for the quick reply.


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## RBTO (Jan 27, 2010)

wado1942 said:


> Yeah, I'm familiar with 3:2 pull-down. You're saying if a Blu-Ray or whatever just sends out a 60i signal of a film, the TV should remove the pull-down?............... BTW, I haven't quite decided on whether I should go with projection or LCD flat panel (LED backlit most likely).
> 
> Thanks for the quick reply.


The TV will reverse the steps that were used to convert the 1080p24 to 1080i (which effectively "removes" what the 3:2 pull down did).

I have a projection system that I really like, but what you get depends on your theater room environment. For projection, you need well controlled lighting and a good screen (also a good projector that will set you back upwards of $1k or more), but for the real theater experience, projection is the way to go.

If you don't go projector, a good plasma flat panel display will give you an excellent picture. Second to that is LCD/LED. I can't decide for you, but there is a wealth of knowledge that you can research on the web which can help you make up your mind.


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## wado1942 (May 14, 2006)

I personally like the quality/price of the LED back-lit screens, so that's the direction I was originally leaning. We don't spend a lot of time in the theater and it's only a 14' wide room any way, so no need for extreme viewing angles. What has me interested in projection is the fact that there's a stupid fireplace where the screen belongs (due to the shape of the room). I thought I could put a pull-down screen in front of the fireplace and avoid completely blocking it like we have now. It's a pretty dark room even in broad daylight (I've screened 16mm films in there with a 500W projector lamp) and we may wall-in the one window we have there before long.

Any way, resolution, brightness etc. is all easily researched, but is there any way to find out how well a given display device handles things like 60i video and 24p converted to 60i? Oh, and I noticed a lot of newer displays do some really freaky, ugly, motion smoothing that I definitely DON'T want. I hope that's something that can be bypassed on all systems if it comes standard. I guess what I'm saying is, I want the image output to be as much like the original source medium as possible, be it 70mm film or a $300 MiniDV camera. And yeah, I'm expecting to pay about $1,000 +-$200 or so.


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## RBTO (Jan 27, 2010)

I think what you're describing would work well for you.

I have a DaLite High Power pull-down screen with a Panasonic AE2000 projector, and I couldn't be happier. The projector will take almost any video format you can throw at it, and has inputs for composite, component, S-video, computer, and HDMI. With the High Power screen, it produces brightness that will "knock your socks off", and the color rendering is fantastic.

A High Power screen will help with your lighting issues since it is directional. It has an ultra-fine bead surface that doesn't show any texture as some beaded screens do.

With such a projector, you get image resolution just short of theater 2k digital quality (maybe _better_ overall quality than some theaters) when the source material is up to it. With Blu-Ray source material, the images are really stunning! Rango is one of my demo Blu-Rays, and you can see every hair and the smallest details in the image.

There are a lot of projectors available, some DLP, but most all accept any HD or SD video format so that shouldn't be an issue. Don't expect a theater experience unless your source is BD (or a good HD source like satellite) however, because the larger the image, the more you see defects in it. Using a VHS source for my projector is downright depressing!

My projector doesn't have motion smoothing although the newer models do, but in all the cases I've seen, it can be turned off.

Sorry, but you won't quite get _70mm film_ quality from any present day video system. In any case, you wouldn't be able to see that kind of resolution except on the really big screen, and up close to the screen. To see if you would benefit from 4k (which I'm sure you're not ready to get into right now), check out the attached chart. If you're above the red line with a 1080 projector, and your screen size & viewing distance, you're in good shape.


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## wado1942 (May 14, 2006)

Yeah, I'm all too familiar with the forced obsolescence of film capture & projection. Even our IMAX theater gets their movies on thumb drives now. There's literally no reason for me to go to a theater anymore because I can get similar quality at home for a fraction of the price.

So, no way of knowing exactly what a given display will do to the image huh? S-VIDEO is important to me since I have an S-VHS deck and Laserdisc player. I have a couple of glass bead screens already, one of which is much better than the other, but they're both smallish, free standing jobs and I haven't found any really good ones to hang from the ceiling. I have also just started my search, though.

Thanks again.


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## RBTO (Jan 27, 2010)

Here's a link to a company where I've bought several screens. The DaLite model B is a lower cost pull-down (though you can get it with their High Power fabric which is somewhat more costly). This link is for a 45x80 inch, 16:9 screen but they have a good selection of others (including other brands).

http://www.projectorzone.com/Da-Lite-Model-B-Manual-45x80-HDTV

This might give you some starting point for screens.


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## wado1942 (May 14, 2006)

That's not bad at all. Thanks!


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## Sevenfeet (Feb 2, 2009)

RBTO said:


> Who watches 1080i anymore???
> 
> Just Kidding!!


Sadly, some of us are still clinging to old school CRT RPTV which has always been 1080i, which still matches nicely to network TV. Most of you with LCD/Plasma flat panels have forgotten what 1080i actually looks like.


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