Calling all gurus: to de-interlace or not to de-interlace

[muddyshooz]

Okay, I've read at least a dozen posts and several "guides" (not just on this site) and some questions still remain for me with regard to the whole de-interlacing question. (I'm pretty sure the answer is 42, but ...)

What would be -really nice- on this site (for relative newbies & non-video-engineers like myself) is some kind of matrix where one could find a definitive "de-interlace this" check-mark in a box where along the vertical left-side of the table were video format types (e.g. interlaced DV @ 720x480, progressive DV @ 720x480, progressive DVD source @ xres, anime-cartoon DVD source @ xres, captured tv @ xres, etc.) and along the horizontal top line of the table were the desired outputs (e.g. SVCD 480x480, VCD 352x240, DivX 720x480, DVD 720x480 ... and several other possible permutations). I don't know if the whole "bottom-field-first" vs. "top-field-first" stuff even comes into play in this type of table, but certainly the "view on tv" vs. "view on computer" question does. Maybe the "answer" in the checkbox could just be a number indicating the percentage of people who think it should or should-not be de-interlaced. And then there's the whole question of the -type- of de-interlacing and then whether the thing needs to be inverse-telecined and then 3:2 pulldown added and all that. Right? Ugh. Maybe a 5-dimensional matrix is in order. A little hard to visualize, but thorough to a "T".

I've heard people say "season to taste" meaning, "try it 'til you like it" and I've heard other people say (definitively) for VCD, always de-interlace; for SVCD, never de-interlace, for DivX, always de-interlace, and so forth. The latter is about the only one I -think- I understand.

There -has- to be a real answer to all of this. I know that opinions will differ, but there should at least be a majority consensus. No? I'm guessing it would cut the number of posts down (or incite a riot?). Personally, I'm only dealing with DV footage from a Sony camcorder and making VCDs and SVCDs and computer-viewable DivX files, so you can surmise what I really want to know, but ... for the GOOD of MANKIND can't we come up with something?

Baldrick? Adam? Sefy? ShiZZZon? Virtualis? Death-by-bitrate? Bueller?

Maybe a "Video Encoding For Dummies" book is in order. I'd buy it.

[Stisse1]

Hi,

I agree... Can some pro on this make some kind of matrix on this.. ( Hi will be "the choicen one" ). )


/Stisse...

[muddyshooz]

Hey Stisse,

I assume from the lack of responses that all the video gods are busy busting out Excel and making their matrices even as we speak! (Let's hope!)

Shooz.

[Sefy]

I'm not a professional, although some people think I am for some reason, I consider myself a newbie just like most of the newbies, as for Deinterlace, don't Interlace, i'll tell you this, TV uses Interlace, and a PC uses Non-Interlaced, so if you are creating your movies for viewing on a TV (like me) i'd prefer keeping it at Interlaced.
If you are making your movies playback on the PC, then I think Non-Interlaced would be proven to be more sufficent.

But i'm not busting my butt on Excel or any Matrices, well, for one, I don't even have Office, secondly, i'm working on the 1.9 of the guide for you guys

[KoalaBear]

far be it from me to steal anyone's thunder, particularly Baldrick's, Adam's, ShiZZon's, or especially Vitualis', but it seems to me that this is a legitimate theoreticsl as well as practical question.

Who's going to field it?

[kinneera]

It seems to me like it isn't a terribly complicated concept/issue. The short rundown:

If source is film (DVD) - It is progressive, but generally telecined to an interlaced format to work on NTSC TVs. Never deinterlace this, but rather perform an inverse-telecine (or forcefilm where applicable). This goes for TV and computer playback. If your target format is SVCD or DVD, make sure to apply the 2:3 pulldown-on-playback flag, so your DVD-player will telecine on the fly.

If the source is any type of tape (VHS, SVHS, Hi-8, etc) - it is interlaced. You must deinterlace it for VCD, since MPEG1 does not support interlacing. For SVCD/DVD, the choice is yours. Most find it preferable to retain the interlacing in these cases because a progressive frame can not be properly (perfectly) reconstructed from two time-displaced fields.

Unfortunately I don't know the details on DV. You should be able to determine whether it is interlaced by observing the resultant artifacts when displayed on a progressive screen (computer monitor). If it is interlaced, again it is probably best to preserve it, unless you're converting to VCD. If it is progressive, you may as well keep that, too (especially if it is 23.976 fps), unless your DVD player doesn't seem to like it. Don't ask me the details of how, but my DVD player (Pioneer DV-343) is able to play progressive 29.97 video to my NTSC TV.

[KoalaBear]

Perfect! (well, almost.)

DV is interlaced. And one should always produce progressive video if the source was progressive, unless one desires to achieve higher quality as a result of converting one's interlaced materials to progressive format prior to encoding.

But how does one encapsulate all that knowledge in the form of a truth table? That's what I want to know.

[kinneera]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR size=1 color=black></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
unless one desires to achieve higher quality as a result of converting one's interlaced materials to progressive format prior to encoding.
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

Careful here...as I mentioned, converting natively interlaced video to progressive is really a quality loss, not gain, albeit usually a fairly minor one.

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR size=1 color=black></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
But how does one encapsulate all that knowledge in the form of a truth table? That's what I want to know.
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

I can give this a shot...although the table will likely need a lot of "but if" sidenotes.

[bbb]

When backing up DVDs, always deinterlace using Blend! To avoid de-synced audio and video problems, never inverse telecine, always use 29.97 (NTSC).

It will look great on computers and TVs, plus it smooths out jaggies and minor blocks. Don't limit your viewing options by using interlace. Don't waste time pondering whether to interlace or not (unless it's a pure digital clip such as a QT video or DV capture then you don't need to deinterlace).

<font size=-1>[ This Message was edited by: bbb on 2001-12-28 19:36:05 ]</font>

[kinneera]

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When backing up DVDs, always deinterlace using Blend!
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

No no no, inverse telecine (IVTC) it and recover the original progressive frames! Better quality all around!

[Xesdeeni]

Please listen to kinneera:

(For NTSC)

Film: Inverse telecine

Typical video: Deinterlace for single-field destination (typically 352x240 MPEG1 for VCD):
The question of what kind of deinterlacing is probably something you'll have to experiment with yourself. IMHO, removing one field is preferable to averaging them, because you don't get those annoying ghost trails on motion. The smart deinterlacers are OK, but I still haven't been blown away by one yet.
For interlaced destination:
This is where I think it gets tricky. There is NO QUESTION that, given infinite bandwidth, the video will look better left deinterlaced. HOWEVER, my experiments have shown me that the two best MPEG2 encoders (IMHO), TMPGExe and CinemaCraft produce streams with (in some cases significantly) less MPEG artifacting if the source is deinterlaced before encoding. I strongly suspect that this is a case where even though the number of pixels is the same (480x240x60 == 480x480x30), the non-interlaced stream, which has fewer frames/fields (instants of time), requires fewer bits for encoding motion vectors and the like. So as always, YMMV, so experiment and see what you like.

DV: Not all DV is interlaced. My Cannon Optura Pi, and many other models, have a "Progressive Scan" mode. It actually captures 30 frames instead of 60 fields. This is not good for high motion video, but it is good for low motion stuff like the wedding I shot. The MPEG2 encoders like it much better, and even converting to a single-field format like VCD looks better.

BTW, DVD players play progressive video (through a progressive monitor), because almost all
DVDs came from film (see above) and are not interlaced by nature.

Xesdeeni

[Beavis]

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On 2001-12-28 20:23:35, Xesdeeni wrote:
Please listen to kinneera:

(For NTSC)

Film: Inverse telecine
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

...but not if your stand-alone can't play 24 fps VCD's.

The reason there's no chart is that you just need to take the time to actually understand the basics of what you're doing, what you want to accomplish, and what works best with your particular set of equipment.

[muddyshooz]

Thanks for all the replies! Let's keep 'em coming! You've given me more than enough to consider while I don't sleep tonight. (Does anyone else debug software in their dreams besides me??!?) Hopefully some more of you can shed even more light.

-Shooz.

[bbb]

When all goes well, IVTC produces cleaner results during the mpeg encoding process. However, the sound has a much much much greater tendency to go out of sync. This is the reason to avoid IVTC until perfect sync is available (manual syncing is a migrane and not worth the time). IVTCers know about this prevalent desyncing problem but will they admit it?

It's all about getting the best quality under a reasonable amount of time. Blending gets rid of the interlacing lines and some blocks.

If it has to take several weeks to 1 month to get a perfect IVTC encoded movie with zero blocks, and perfect sync, then you have too much time on your hands.

Besides, you can't go wrong with sticking closer towards VCD/SVCD specs at 29.97 for NTSC.

[Xesdeeni]

Beevis,
If you have a VCD player that doesn't support 24fps, I'd say you don't have a standard compliant player. The spec supports it, so the players have to do the 3:2 pulldown (talking NTSC here). What kind of stand-alone player do you have that doesn't support 24fps?

Xesdeeni

[kinneera]

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IVTCers know about this prevalent desyncing problem but will they admit it?
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>

Not if it isn't a problem. I've never had an audio sync problem with any movie I inverse telecined. However, I do make SVCDs with the 2:3 pulldown on playback flag enabled.