Technical question about HD progressive/interlaced

[Jedi2016]

I saw something the other day that got me thinking... I was browsing through HDTVs on some website (Best Buy or something, I don't recall), and I saw this description of a television's resolutions: (it was a direct-view CRT, incidentally)

720 progressive (interlaced), 1080i, etc.

Now, at first, I'm thinking "interlaced-progressive-what?", but then I got to thinking... What's the actual refresh rates of HDTVs these days?

I was thinking that, if TVs were no longer "locked" into the old-school 60Hz, that it could be possible for an interlaced display to project a true progressive image. So I figured I'd ask the gurus here, see if anybody knows.

Let's say a modern HD CRT has a much higher refresh rate than before.. say, 120Hz. It would then be possible to display a 720p image, at 60fps, by drawing the frame in two interlaced passes, twice as fast as was possible on older SDTVs (like the one I have downstairs).

Is such a thing possible? That a modern CRT can draw an entire frame (two interlaced passes), in 1/60th of a second?

This also fits in with the overall resolutions.. 480i, 480p, 720p, yet only 1080i.. because it's not quite fast enough or powerful enough to draw a 1080 frame in 1/60th of a second (hence the "limit" of 1080i), but it can draw a 720 frame or smaller in that time.

Am I making stuff up, or do TVs these days actually work like this?

If so, would it not be possible to display video, up to 720i, at 120fps by interlacing it?

 

[MacManNM]

I saw something the other day that got me thinking... I was browsing through HDTVs on some website (Best Buy or something, I don't recall), and I saw this description of a television's resolutions: (it was a direct-view CRT, incidentally)

720 progressive (interlaced), 1080i, etc.

Now, at first, I'm thinking "interlaced-progressive-what?", but then I got to thinking... What's the actual refresh rates of HDTVs these days?

I was thinking that, if TVs were no longer "locked" into the old-school 60Hz, that it could be possible for an interlaced display to project a true progressive image. So I figured I'd ask the gurus here, see if anybody knows.

Let's say a modern HD CRT has a much higher refresh rate than before.. say, 120Hz. It would then be possible to display a 720p image, at 60fps, by drawing the frame in two interlaced passes, twice as fast as was possible on older SDTVs (like the one I have downstairs).

Is such a thing possible? That a modern CRT can draw an entire frame (two interlaced passes), in 1/60th of a second?

This also fits in with the overall resolutions.. 480i, 480p, 720p, yet only 1080i.. because it's not quite fast enough or powerful enough to draw a 1080 frame in 1/60th of a second (hence the "limit" of 1080i), but it can draw a 720 frame or smaller in that time.

Am I making stuff up, or do TVs these days actually work like this?

If so, would it not be possible to display video, up to 720i, at 120fps by interlacing it?

The limitations here are not in the CRT or display projection system. The limitation here is in the camera or recording device. Standard CCD arrays have a hard time getting enough light to record images with an integration time less than 1/30th of a second. So what is done is interlacing. The price of equipment skyrockets when you start talking about low noise high gain cameras. A lot of cameras have gain, but the problem is that they also amplify the noise. Photometrics has come out with an on chip amplifier, but that is a long way away from commercial use (one camera is about 75k). As things get better and better (low noise digitizers and better TE cooling) the ability to get better broadcast quality will increase. The display electronics can handle much more than they are doing now, until you get into phosphor decay times and the like. There is a lot more to this but this is the simple explanation.

 

[Hanse18]

Good question, and it actually has a somewhat more useful purpose. Preferrably, TV's and dvd's and all other video apparatuses (apparati?) will be able to display an image at 72 fps. As you know, 3:2 pulldown is one of the major issues with tv and movies, and a tv or dvd player that doesn't do 3:2 pulldown is basically useless, unless you enjoy a choppy picture. 24 x 3 = 72, and since we are currently at 60, it doesn't make much sense to go down to 48, so people are hoping for 72 fps tv's some day.

 

[BMXTRIX]

If it's two interlaced passes, then it is interlaced. It may be 720i/120 instead of 720p/60 but it is still interlaced.

CRT does not have a current limitation that forces it into displaying in an interlaced format and PC CRT monitors are an example of this as they are constantly used for 1024x768 and well beyond those resolutions at refresh rates that go a good bit higher than 60hz.

The reason you don't typically see it with home CRTs is that there is some fine tuning and tweaking that must go on for sets to change from 480i to 720p to 1080i. Nothing that couldn't be dealt with, but manufacturers seem to not want to deal with this. I know my old projector (3 gun CRT) could handle resolutions right up to 1080p with almost no problem at all.

Digital displays are an entirely different story. 72 fps means nothing on a digital display unless it is fed 72 fps. If the source is 24 fps then a digital display has no benefit to operating at 72 fps... repeating the same frame three times. It makes no sense. Digital displays will maintain the 1st frame for EXACTLY 1/24th of a second, then go to the second frame - all perfect, all very similar to film.

But, yes, 720p + CRT is very possible.

 

[Jedi2016]

Yeah, I know 720 is possible, I'm just wondering how the specifics of it work inside the television itself.

Another aspect that occurred to me after thinking about it a while is these new game systems coming along. Ken Kutaragi hinted at the possibility of the PS3 being able to play games at 120fps. If a CRT's "progressive" 720 is, in fact, interlaced at double-speed, then a 720i signal exported from a game system (which is generating everything in real-time, unlike pre-recorded stuff like movies), then it should be theoretically possible for already-released televisions to display games at 120fps interlaced. Interesting thought.

That wasn't the heart of the question, though, I was merely curious when I read that statement on the website. The game thing didn't occur to me until just a day or two ago.

 

[BMXTRIX]

No, 720p is 720p. Period.

A CRT doesn't make 720p interlaced.

A CRT may have processors that convert 720p into 1080i - but that isn't the same thing.

CRT is not the technology for any of this really - it's all about digital displays. LCD, DLP, LCoS, Plasma, SED, OLED, etc., etc.

Inside the television, if a TV is capable of true 720p display then it scans all 720 lines in one swoop at 60 frames per second. Most CRTs don't do this, they convert it internally to 1080i and then do two 540 line passes to create the interpolated 720p image at 1080i.

 

[MacManNM]

No, 720p is 720p. Period.

A CRT doesn't make 720p interlaced.

A CRT may have processors that convert 720p into 1080i - but that isn't the same thing.

CRT is not the technology for any of this really - it's all about digital displays. LCD, DLP, LCoS, Plasma, SED, OLED, etc., etc.

Inside the television, if a TV is capable of true 720p display then it scans all 720 lines in one swoop at 60 frames per second. Most CRTs don't do this, they convert it internally to 1080i and then do two 540 line passes to create the interpolated 720p image at 1080i.

This is true, but the limitation is not the CRT, it is a limitation of the vertical and horizontal electronics which drive the CRT.