Interlaced Video

[Katie Boundary]

Infinite minus one

Ah, you finally see things my way :)

You say nothing about pixel width nor framerate nor physical sizes... it all is inter dependent upon other parts of spec.

So in other words, you can make a CRT with whatever number of scanlines you want as long as you're willing to sacrifice other specifications? That sounds a lot like exactly what I've been saying this whole time.

So I would say that your question 1) amounts to "How long is a piece of string ?".

No, I'm asking for the maximum possible length of a piece of string, regardless of what it's made of or any other practical considerations, because you all claimed that such a limit existed, and now you're yammering on about how there's only a finite number of yaks in the world and you refuse to make string out of anything but yak fur even though I already told you I don't give a shit what the string is made of.

[StainlessS]

I've tried my best, it was lacking, I give up.

[hello_hello]

So in other words, you can make a CRT with whatever number of scanlines you want as long as you're willing to sacrifice other specifications? That sounds a lot like exactly what I've been saying this whole time.

Sounds more like a funny attempt at backpeddling to me. You said "nothing about CRT technology inherently prevented us from making a TV standard with 100,000,000 scanlines or any other number we wanted". Are you really trying to claim that wasn't based on the assumption the picture needs to be watchable?

No, I'm asking for the maximum possible length of a piece of string, regardless of what it's made of or any other practical considerations, because you all claimed that such a limit existed, and now you're yammering on about how there's only a finite number of yaks in the world and you refuse to make string out of anything but yak fur even though I already told you I don't give a shit what the string is made of.

As you've been shown, although you continue to ignore it, when the BBC began broadcasting, a little over 200 lines per 1/50th second was the limit of CRT technology, so that was the maximum length for a piece of string at the time (resulting in 405 line). Please explain how they could have implemented a 100,000,000 line system as you've claimed.

Here's some more information for you to ignore:
NTSC Lines_and_refresh_rate (https://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate)
The actual figure of 525 lines was chosen as a consequence of the limitations of the vacuum-tube-based technologies of the day. In early TV systems, a master voltage-controlled oscillator was run at twice the horizontal line frequency, and this frequency was divided down by the number of lines used (in this case 525) to give the field frequency (60 Hz in this case). This frequency was then compared with the 60 Hz power-line frequency and any discrepancy corrected by adjusting the frequency of the master oscillator. For interlaced scanning, an odd number of lines per frame was required in order to make the vertical retrace distance identical for the odd and even fields, which meant the master oscillator frequency had to be divided down by an odd number. At the time, the only practical method of frequency division was the use of a chain of vacuum tube multivibrators, the overall division ratio being the mathematical product of the division ratios of the chain. Since all the factors of an odd number also have to be odd numbers, it follows that all the dividers in the chain also had to divide by odd numbers, and these had to be relatively small due to the problems of thermal drift with vacuum tube devices. The closest practical sequence to 500 that meets these criteria was 3×5×5×7=525. (For the same reason, 625-line PAL-B/G and SECAM uses 5×5×5×5, the old British 405-line system used 3×3×3×3×5, the French 819-line system used 3×3×7×13 etc.)

100,000,000 is an even number of scanlines, isn't it. :)

[hello_hello]

The "vertical retrace distance" in the info above had me a little perplexed in respect to the requirement of an odd number of lines for interlaced scanning. I think I understand it a little better now, and those half lines at the top and bottom of the picture.... the "vertical retrace distance" seems to be what they're about. Ahhhh.....

back to reading this and trying to get my brain to absorb it.
Interlaced Scanning (http://www.infocellar.com/television/scanning.htm)

[johnmeyer]

There are too many designs elements that interact to answer the questions. Perhaps another way to approach it, assuming we are talking about what can actually be achieved in this real world, and within the constraints of the laws of physics, is to look at what was actually achieved before the CRT gave way to LCDs and digital technology.

Runco (and Barco) were at the top of the high-end CRT manufacturers. In order to get the most out of an SD signal, they would first double or quadruple the number of lines using a Faroudja line quadrupler. This was then fed to a CRT that was capable of 2x the normal number of scan lines, and was also displaying at 60 frames per second, progressive (i.e., 60p). Here is the description of one such product:

Runco DTV-991 CRT Projector (http://www.avrev.com/home-theater-front-projectors/crt-projectors/runco-dtv-991-crt-projector.html)

The price of the line doubler and CRT projector together was $50,000 (1999 dollars).

This represented the most that any engineer could design and build. It was designed for a crowd that would pay anything to get better quality. If 2,000 lines or 4,000 lines could have been built, it would have, but this was pretty much as far as they could go with CRT technology.

So, rather than argue theoretical points, as an engineer I look to what was actually built and claim that, like the old Oklahoma song, it "was about as fer as they could go."

[Katie Boundary]

If 2,000 lines or 4,000 lines could have been built, it would have, but this was pretty much as far as they could go with CRT technology.

Errr, no, that was just the fanciest hardware that anyone wanted to build for the purpose of displaying standard-definition (480i) content. CRT computer monitors with resolutions of 2048x1536 used to be quite common, and a hell of a lot less expensive than $50k. The main reason why we never went higher was because, for resolutions that high to mean anything, the screens had to be quite big, and while a 4-foot-wide CRT might be suitable for a home theater (which would only be displaying 480i content anyway), it's definitely not something to put on your desk.

Sometimes, the real reason why things don't get built is because they're stupidly impractical, not impossible (https://www.youtube.com/watch?v=bvYUq6Ox0Hc).

[hello_hello]

Errr, no, that was just the fanciest hardware that anyone wanted to build for the purpose of displaying standard-definition (480i) content. CRT computer monitors with resolutions of 2048x1536 used to be quite common, and a hell of a lot less expensive than $50k. The main reason why we never went higher was because, for resolutions that high to mean anything, the screens had to be quite big, and while a 4-foot-wide CRT might be suitable for a home theater (which would only be displaying 480i content anyway), it's definitely not something to put on your desk.

It's no different to claiming there's nothing about aviation technology that inherently prevented the first flight by the Wright brothers from being in a supersonic jet aircraft. Well maybe that wouldn't be quite as silly as your 100,000,000 scan line claim, given we do have supersonic jet aircraft now.

You haven't tried to explain how it'd be possible, leading to the obvious conclusion you have no idea, and you're vainly trying to defend a claim you simply made up.

[johnmeyer]

This conversation is so pointless ...

[nussman]

We had an interessing conversation but then you all decided to argue with this Katie troll.

Imho for pal (ntsc as well) interlaced content via DVB is still very important.
We need 50 or 60 fields/frames per second for video content (quick sport etc.) and for original 24p/25p content a 50i/60i broadcast is lossless.
Using 50p for original 24/25p content doesnt make it "better". Its just need more satellite bandwith.

My question: Is switching between 25p and 50i/p covered by DVB broadcast standards (DVB-S2 etc.)?

[kolak]

Not sure, but BBC transmits movies as 25p and other programmes mostly as 50i, so this works.
50p may not be in DVB-S2 spec.
TV stations are also not so happy to invest money into bits which won't translate directly into bigger profits. People would not even notice that they watch 50p not 50i :) Stations are more interested in capping bandwidth, so they can start another channels which in 50% transmits adverts :)

[nussman]

Ah ok. That's cool. :)
25p/50p would be even better.
We get 720p50 here in germany, so its possible via DVB-S2 but I dont think 720p50 makes sense for the most content.

[wonkey_monkey]

Not sure, but BBC transmits movies as 25p and other programmes mostly as 50i

Not mostly - entirely.

Edit: sorry, I misread your post. What I meant to say is that, to the best of my recollection, all BBC HD output is only ever 1080i50, doing the same kind of "wrapping" as happens on what would otherwise be 1080p25 Blu-ray, for example.

That's broadcast output. iPlayer uses 720p25/50.

[nevcairiel]

50 fields are 50 fields, the only difference is from which point in time you take them. Both from the same time and its progressive. Technically they call this "progressive segmented frames" (PsF). Add some signaling to tell the receiver not to deinterlace, and you're done.

Or as an alternative, use 2:2 pull-down (ie. telecine), which is strictly speaking not the same thing as PsF, but thats probably just because different organizations standardized those.

[kolak]

Not mostly - entirely.

Edit: sorry, I misread your post. What I meant to say is that, to the best of my recollection, all BBC HD output is only ever 1080i50, doing the same kind of "wrapping" as happens on what would otherwise be 1080p25 Blu-ray, for example.

That's broadcast output. iPlayer uses 720p25/50.

Possibly, but my TV is showing me 1080p for movies and 1080i for most other things. There is something different in how they send movies which allows for TV to switch to 25p mode.

[kolak]

This is some hint:
https://ukfree.tv/article/1107051635/Freeview_HD_will_be_1080p25_and_1080i25_

And this even better:
http://www.bbc.co.uk/faqs/help-receiving/bbchd_channels_schedule

I'm using Freeview.

[kuchikirukia]

Does anyone even broadcast in 50/60p? Because anything under 50fps is garbage.

[manono]

Does anyone even broadcast in 50/60p?
There are US channels that broadcast 720p60. Earlier posters mentioned 720p50 in Europe.

Because anything under 50fps is garbage.
So, virtually every movie you've ever seen in a movie theater is 'garbage'?

[nevcairiel]

Some german stations broadcast in 720p50 instead of 1080i50 like many others.

[sneaker_ger]

Plus 1080p50 on German DVB-T2.

I believe 720p50 was kinda recommended by the European Broadcasting Union (EBU) so there ought to be other countries using it as well.

[Sharc]

I remember that 1080i vs 720p created a lot of emotions when HDTV broadcasting was introduced. Eventually we got both.

Just an example from the "pro 720p" campus:
http://www.bluesky-web.com/numbers-mean-little.htm