A couple of questions. Maybe it is too general that the search couldn't help:

1. On a typical 768 lines display (LCD or Plasma), does 720p get upscaled into 768 lines?

2. I heard that many HDTVs only display half of the 1080i signals. i.e. treat the 1080i 30fps(?) as 540p 60fps and upscale 720p. Is it still true? How do I tell if the TV I wan t to buy does it or not?

Thanks for reading!

There is no such thing as an "interlaced" flat panel.

Flat panels are, by nature, progressive.

Every flat panel scales the input they receive to their native resolution.

A 1080i signal transmits the 1080 lines of resolution in two alternating parts.

A 720p signal transmits the 720 lines of resolution all at once.

You'll see many debates about which one looks better. Just by the math, 720p transmit more data per cycle.

That doesn't necessarly mean that you'll see a better picture with 720p.

As I said upfront, unless your source input exactly matches the native resolution of the panel and is progressive, your flat panel tv will be "scaling".

That's not necessarily a bad thing. The overall quality of the tv's scaler and picture technology are more important than the resolution of the source (assuming it's HD) and the better tvs will almost always look better scaling than a marginal panel receiving a native resolution source.

2. I heard that many HDTVs only display half of the 1080i signals. i.e. treat the 1080i 30fps(?) as 540p 60fps and upscale 720p. Is it still true? How do I tell if the TV I wan t to buy does it or not?For a short video tutorial on how this all works, see the "Film Cadence & Detection" and "De-interlacing" sections on the Silicon Optix HQV site (http://www.hqv.com/technology.cfm). Those two sections will answer your questions.

Only the better video displays can reconstruct full 1080p resolution, but even the cheapest of the cheap due better than 540p, except during fast movement.

1. On a typical 768 lines display (LCD or Plasma), does 720p get upscaled into 768 lines?Yes. The video processing circuitry in the display dictates how well this upscaling is done.

You'll see many debates about which one looks better. Just by the math, 720p transmit more data per cycle.

Actually:

1280x720 = 921600
1920x540 = 1036800

So 1080i signal contains slightly more data. This assuming same frame/field rate of course.

As I said upfront, unless your source input exactly matches the native resolution of the panel and is progressive, your flat panel tv will be "scaling".

And even then, most displays have 1-4% of overscan, so they'll be scaling no matter what the resolution of the signal.

Actually:

1280x720 = 921600
1920x540 = 1036800There is the stream on the cable to the TV, but the source bandwidth is typically much less.

Most content shown on the networks in primetime is sourced at 24p with repeat flags. This includes all movies and episodic programming. On a channel like ABC or FOX, the MPEG decoder in the STB/DVR reads 720p24 source and outputs 720p60 to the TV, but it's still 24 unique frames with flags telling it what frames to repeat. The only time you get "native" 720p60 with 60 unique frames is high-def video, such as sports.


And even then, most displays have 1-4% of overscan, so they'll be scaling no matter what the resolution of the signal.Scaling is only performed by those displays that create their overscan through interpolation (i.e., use video processing to 'zoom' in on the image). Many displays have optical overscan, with no interpolated overscan, and thus there is no scaling involved that could degrade the image.

There is the stream on the cable to the TV, but the source bandwidth is typically much less.

Most content shown on the networks in primetime is sourced at 24p with repeat flags. This includes all movies and episodic programming. On a channel like ABC or FOX, the MPEG decoder in the STB/DVR reads 720p24 source and outputs 720p60 to the TV, but it's still 24 unique frames with flags telling it what frames to repeat. The only time you get "native" 720p60 with 60 unique frames is high-def video, such as sports.

I appreciate the information but I must be honest - I have no idea how this applies to the point I made above? That is to say that, 1280x720x24 is still less than 1920x540x24.

Scaling is only performed by those displays that create their overscan through interpolation (i.e., use video processing to 'zoom' in on the image). Many displays have optical overscan, with no interpolated overscan, and thus there is no scaling involved that could degrade the image.

Now this is extremely interesting. Again you've said a lot here - but I don't really understand what you are getting at. Perhaps you can go into the math involved. Be as detailed as you wish - I truly want to know. From a purely laymen's point of view I can't easily come up with a way to think about overscan without scaling the source. It just doesn't make sense to me, since you are covering the same area of the screen with less pixels from the source.

Actually:

1280x720 = 921600
1920x540 = 1036800



Yeah, you're right, of course. My bad.

For some reason I was only thinking about the vertical scan lines which is, of course, rediculous.

I appreciate the information but I must be honest - I have no idea how this applies to the point I made above? That is to say that, 1280x720x24 is still less than 1920x540x24.I wasn't arguing your point, just pointing out that the differences, as they apply to channel transmission / broadcast, are even larger than you suggest, i.e:

1920x1080x24 = 49,766,400
1280x720x24 = 22,118,400

That's more than twice as much "data per cycle" for almost everything but video (sports).

It just doesn't make sense to me, since you are covering the same area of the screen with less pixels from the source.Well, some part of the fixed panel (be it LCD, plasma, etc) is covered with the frame, which means those pixels aren't available. This degree of overscan would be small. On the other hand, rear projection displays typically exhibit far more optical overscan, because the image projected is almost always larger than the screen. For example, Sony's SXRD XBR2 exhibits 4% total vertical overscan and 6-8% total horizontal overscan, such that the actual available resolution is closer to ~1800-1820 x 1010-1030 (varies from set to set). This is optical overscan, it doesn't involve any processing.

I wasn't arguing your point, just pointing out that the differences, as they apply to channel transmission / broadcast, are even larger than you suggest, i.e:

1920x1080x24 = 49,766,400
1280x720x24 = 22,118,400

That's more than twice as much "data per cycle" for almost everything but video (sports).

Aha, yes I see.

Interesting - I was not aware that most 720p content was recorded at 24 fps. For movies converted from film this of course makes sense. But I guess I had just assumed that most episodic content and other material that was shot specfically for television these days was 720p/60 or 1080i/60 video.

Well, some part of the fixed panel (be it LCD, plasma, etc) is covered with the frame, which means those pixels aren't available.
...
This is optical overscan, it doesn't involve any processing.

I see what you are saying now. I was thinking in terms of non-projected, flat panel displays only. I really don't have a whole lot knowledge in the front/rear projection area so I can't really comment there. I do know that for plasma and LCD though, in general, the entire pixel grid is available outside of the bezel. So, for example, on a 1920x1080 television, you can see the entire 1920x1080 grid. This can be demonstrated in that folks routinely display a computer desktop on these displays at native resolution, and verify with a test pattern that it is all there and scaled 1 to 1. I am one of these people, although my display is only 1366x768. Anyway, going back to the 1920x1080 display, this would mean that if ovescan is present, then there is indeed some bit of scaling going on even with a 1080i or 1080p source.