Interlacing Questions

[maikii]

I have several questions about interlacing, that might fit in different forums. Not sure if this one is the best, but here goes.

For one thing, I believe I read that interlacing was created to deal with limitations of CRT tube TVs. True?

However, these days such TVs are rarely used. Most people have flatscreen TVs--LCD or plasma, and also watch video on flat screen computer monitors, tablets, etc.

If the second paragraph is true, why is video still interlaced at all, considering the preceding paragraph?

Modern DVDs are still interlaced, correct? Why?

Are blu-ray discs also interlaced? Why?

I have a new camcorder, quite good, the Canon Vizia HF M500. Setting it to the highest quality HD video setting (1920x1080, I think 24mbps), but all automatic, the video still comes out interlaced. (I don't know if there is a way to set it not to interlace. I can look into that.) Again one wonders why, in this world of flat screen video viewing.

I know that if one is to prepare the video to play on a computer, tablet, or phone, one has to deinterlace it first. But for putting on a blu-ray disc or DVD, should one keep the interlacing?

With the original reason for interlacing (so I thought, at least) being gone, an ancient relic (CRT-tube TVs), I really do not understand why interlacing still exists, why cameras shoot video interlaced, etc. Can anyone explain?

[jagabo]

For one thing, I believe I read that interlacing was created to deal with limitations of CRT tube TVs. True?

It was partly to keep the costs of TVs down. But more importantly, interlaced video used half as much bandwidth for transmission -- thereby retaining the smoothness of 60 pictures per second with the same bandwidth that would be required of 30 progressive frames per second. So more channels could be broadcast over the airwaves.

However, these days such TVs are rarely used. Most people have flatscreen TVs--LCD or plasma, and also watch video on flat screen computer monitors, tablets, etc.

If the second paragraph is true, why is video still interlaced at all, considering the preceding paragraph?

I think it was mostly because broadcasters wanted to stick with what they knew. They were worried that 1080p60 would have required too much bandwidth both in production and broadcast. As it turned out 1080p60 MPEG 2 doesn't require much more bandwidth than 1080i30 or 1080p30. Unfortunately, we're stuck with 1080i30 (or 720p60) for broadcast.

Modern DVDs are still interlaced, correct? Why?

Not really. Most DVDs are encoded progressive with pulldown flags that tell the player how to produce 60 fields per second (for the TV) from 24 frames per second. When the DVD spec was developed it was decided that players would be too stupid to figure that out for themselves. Interlaced encoding is available as an option when necessary. Some old TV shows shot on video are available on interlaced DVDs. Some less popular movies on DVDs are made from old interlaced video tapes.

Are blu-ray discs also interlaced? Why?

Same as above.

I have a new camcorder, quite good, the Canon Vizia HF M500. Setting it to the highest quality HD video setting (1920x1080, I think 24mbps), but all automatic, the video still comes out interlaced. (I don't know if there is a way to set it not to interlace. I can look into that.) Again one wonders why, in this world of flat screen video viewing.

Many camcorders can now shoot 1080p60. Canon is lagging in that area. But beware, there aren't a lot of devices that will play 1080p60. And some TVs won't accept it as input.

I know that if one is to prepare the video to play on a computer, tablet, or phone, one has to deinterlace it first. But for putting on a blu-ray disc or DVD, should one keep the interlacing?

Yes, leave it interlaced for Blu-ray.

With the original reason for interlacing (so I thought, at least) being gone, an ancient relic (CRT-tube TVs), I really do not understand why interlacing still exists, why cameras shoot video interlaced, etc. Can anyone explain?

I think the above answers that question.

[sanlyn]

Everyone in the whole world does not own an LCD (I own two, and three LCD monitors. They suck). Everyone does not buy a new BluRay player every 12 months and throw away every player, disc, tape, tv, vinyl record, and everything else they own. Many people in the world cannot afford the Latest and Greatest. Many people think the new stuff is not the latest and greatest. True, interlace will some day go the way of the dinosaur, and so will discs, video files, LCD's, and a lot more. Just not yet.

Perhaps you need an HDTV or player that handles interlace better than the one you own now? Not all digital devices are equal.

[sanlyn]

To add to jagabo's informative reply: anything that broadcasters can do to reduce costs and enlarge bonuses, including sending video over the cables and airways with insanely lowered bitrates and/or cheaper/older technology, is what they will almost always do. Then again, consider that the market for vinyl recordings and tube playback equipment -- no, it will never be the way it was 20 years ago -- has had a resurgence, along with classic films that have found new life going from old interlaced broadcast tapes to DVD and sometimes BD. Many pro video labs still make a lot of DVD and film restoration masters using CRT's, which are maintained at enormous cost. Telarc's music CD's, prized by many classic music fans and avid audiophiles, still make many of their masters on analog tape. Just a few examples of oldie stuff that still has its users use and its uses -- including gasoline-powered cars.

[maikii]

Well then, if it is best to use interlaced video for DVDs and BDs, I assume it is best to shoot video interlaced, in case one might wish to create such a disc with the video footage.

Then deinterlace it for showing on a computer, tablet, phone, or web.

Am I correct in my conclusions above?

[jagabo]

Whether it's "best" to shoot interlaced depends on what look you want (smooth TV motion or jerky film look) and your skills at resizing for DVD and deinterlacing when necessary. Best might be to shoot 60 fps progressive then interlace when necessary (making 30i from 60p is much cleaner than making 60p from 30i). But that's not an option for you.

[maikii]

No, don't have any interest in a "jerky film look". (Is that the interlaced one--jerky?)
I guess I still don't understand why video for DVDs and BD has to be interlaced, if one will not see it through a CRT..

[poisondeathray]

No, don't have any interest in a "jerky film look". (Is that the interlaced one--jerky?)

No, interlaced produces smoother motion because more motion samples per second 59.94 (or 50) vs. 24

I guess I still don't understand why video for DVDs and BD has to be interlaced, if one will not see it through a CRT..

Mostly for legacy and compatibility reasons .

It doesn't "have to be" for blu-ray . It supports 59.94p and 50p at 1280x720 resolution - 720p59.94 and 720p50 (PAL areas)

If you have a BD AVCHD 2.0 compliant player , it can play AVCHD discs authored with 1080p59.94 (1080p50 in PAL areas) .

[turk690]

I have a new camcorder, quite good, the Canon Vizia HF M500. Setting it to the highest quality HD video setting (1920x1080, I think 24mbps), but all automatic, the video still comes out interlaced. (I don't know if there is a way to set it not to interlace. I can look into that.) Again one wonders why, in this world of flat screen video viewing.

Blu-ray specs already currently allow 50p or 60p at 1080; only 720 was allowed at those frame rates before. Initially, 1080 can only be had at 50i, 60i (59.94i), or 24p. So if you really want progressive at 1080 with the best likelyhood of the disc playing in any blu-ray player, I'd author with 24p (23.976p) streams.
The HFM500 camcorder has a 24p mode (which, along with the 30p mode, is still the same 60i stream, just retagged; this is not the same as a genuine 24p mode on a professional camcorder such as the XA10, but will do for our purpose). I would shoot with this mode; the resulting *.mp4 or *.mts files will show up as 23.976p on your NLE, which you can author a true progressive-scan blu-ray with.
Some very specific scenarios are outlined at http://www.x264bluray.com/ if you use x264 to re-encode your streams with, with a view to creating a progressive-scan blu-ray disc.
It is true that interlaced scanning has twice the temporal resolution (60i, compared with 30p, for example). But as I have experienced with the people I create the discs for, none of them ever gave me any flak over 24p looking jerkier than 30i or whatnot. And either way, all recent hollywood crap on blu-ray is 24p without missing a beat. Everything in this chain (from the camcorder shot, to NLE, to authoring, to the blu-ray player, to the LCD TV) is just naturally geared for progressive scan, so i just start out 24p (genuine, or tagged initially as 60i for compatibility).

[jagabo]

Blu-ray specs already currently allow 50p or 60p at 1080;

Unfortunately, hardly anyone has a player that supports it yet.

[turk690]

Unfortunately, hardly anyone has a player that supports it yet.

Which was precisely my point. If 1080 and progressive are both essential in a to-be-authored blu-ray, with maximum compatibility across the multitudes of players out there, 24p is the way to go. That frame rate should as much as possible include the whole chain from shooting the video to watching it on a monitor.