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Advanced : Interlacing Guide

Posted: Thu, 28th Aug 2003, 3:56pm

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TAP2

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For those of you who are more serious and pro about your films... I reccomend you read this interlacing guide, It explains everything you need to know. Great tutorial... hope you find it useful

http://www.lukesvideo.com/interlacing.html
Posted: Thu, 28th Aug 2003, 4:07pm

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padawanNick

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That link is, by far, THE BEST explanation and discussion of interlacing I've ever seen. (and I've seen a lot.)
The graphical images and animations really make everything crystal clear.
Thanks for the link !!!!

Have fun.

[EDIT:
P.S. How do I rate a post ??? I'd love to rate this one with positives but I can't find any "rate" link or button anywhere. Maybe I need to have earned more force points first ???
/EDIT]
Posted: Thu, 28th Aug 2003, 4:15pm

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TAP2

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It's a great guide - I fully understand everything now...

I believe that since the release of fxhome.com you can't rate posts unless you're a gold member. Don't worry about it .. I'm not trying to earn myself as much force as possible i'm just trying to share some great links with everyone.
Posted: Thu, 28th Aug 2003, 4:24pm

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Kid

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www.100fps.com is anoth handy guide to interlacing
Posted: Thu, 28th Aug 2003, 5:34pm

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anonymous

Considering that I shoot with a Canon GL1 on 30P "Frame" mode, and all my videos are going to be viewed on standard interlaced NTSC displays, I haven't really delved into this topic.
Posted: Thu, 28th Aug 2003, 5:36pm

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sidewinder

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off topic, but that's a great sig, kid.
Posted: Thu, 28th Aug 2003, 6:15pm

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Kid

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Anonymous wrote:

Considering that I shoot with a Canon GL1 on 30P "Frame" mode, and all my videos are going to be viewed on standard interlaced NTSC displays, I haven't really delved into this topic.
Well its still something to delve into because it will explain why all your footage looks stuttery when you do that. Knowledge gives you the flexibility to make the effect what you want it to be rather than go with something just cos 'it looks a bit like film'.

Sidey: thanks
Posted: Thu, 28th Aug 2003, 6:51pm

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Sollthar

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I must say I always wondered why so many people have problems understanding that interlace thing... I mean, when you look at your video closely, you can see what's going on. It's not something that needs years of study or an IQ of Einstein... smile
Posted: Thu, 28th Aug 2003, 6:57pm

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TAP2

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Indeed... but it explains it in more detail.
Posted: Thu, 28th Aug 2003, 7:26pm

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Sollthar

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That's true. Good tutorial indeed...

Actually I'm impressed they can write so much about it. smile
Posted: Thu, 28th Aug 2003, 7:29pm

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padawanNick

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Sollthar wrote:

I mean, when you look at your video closely, you can see what's going on.
That's just it though. You really do have to look at it closely, and for many people just getting into this sort of thing, it's a totally new concept.

Most people are very comfortable with the concept of movie film frames and just assume TV is the same. Everything looks fine on TV. Many modern VCR's, DVD Players and cam corders even include an automatic deinterlacing feature that kicks in when you pause, so people typicaly never actually SEE an interlaced frame.

Then you get your video into a computer and suddenly, what looked perfectly clear in the viewfinder and on TV now looks like some one dragged a rake through it! Then you try to explain... "A frame is not really a frame, but two fields (fields? what's a field?) and those are .... oh, never mind. "
For someone totally new to all this, it can be quite daunting.

The same goes for TV safe / Title Safe zones.
Most newcomers to all this have no idea that a good 10% of your frame is "displayed" BEYOND the edges of a TV.
Just explore in any DVD software forum, where you've got all these people converting their snapshots to DVD slide shows with titles.
These forums get the same question on a monthly (almost weekly) basis. "Where did the edges of my picture go!?!?! It looks fine on the computer!!"
I help host the Media Studio Pro forum over at the CreativeCOW site, and the same thing comes up.

Basically, the underlying tech (even the old tech) that drives this hobby is very new and alien to most people. Sites like this that attact and cater to amateurs and hobbiests are bound to be loaded with these questions and it's just really cool that there is such a good base of friendly, helpful members around to share and translate all this new data.

It's helpful links like TAP's that make this a great place to be for new comers.

Have fun!
Posted: Thu, 28th Aug 2003, 7:53pm

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Sollthar

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Of course you are right, and I always answer people who need help too (even if for example in my own forums have to answer the same question a 100 times and this even though it is already answered in the tutorials)


I just sometime think, people rather ask away then sitting a couple of seconds down and actually use their common sense.



But hey, you are totally right! biggrin
Posted: Thu, 28th Aug 2003, 8:03pm

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padawanNick

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Yeah, I agree with you as well.
I can't even begin to count the number of times I've posted links to your site, over-and-over-and-over again in the same forums.
Still, next week I know some one's gonna ask...
"How can I do that effect they do in the Matrix...." wink

BTW: Thanks for all the great info on your site.
It's definitely one of the THE key internet stops for anyone interested in doing their own special effects. It's pretty much always on the Most Popular list at the Amateur Movie Portal.
You're helping a LOT of people.

Have fun!
Posted: Thu, 28th Aug 2003, 9:40pm

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anonymous

Well yeah, as far as "knowledge" goes, I've known what interlaced / deinterlaced meant from the very beginning -- my point was that I wouldn't need to bother going into After Effects and de-interlacing my footage (because it would be interlaced once viewed on a normal TV anyhow).

As far as "stuttery video" on the GL1, I don't know why people always say that. I don't find it stuttery, I find it just right -- normal 60i video to me seems too fluid.
Posted: Thu, 28th Aug 2003, 10:12pm

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Sollthar

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Thank you very much PadawanNick! It is great to hear that my tutorials are helpful to people!


I hope you will like the site, when the redesign goes online. We'll have a better and faster Forum and will improve our tutorial section by making the already existing tutorials more clear and making many new tutorials.

(I plan to make some tutorials in videoformat, so that you can actually see the steps)
Posted: Fri, 29th Aug 2003, 12:24pm

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Ben

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Here's something I don't quite get. Aren't dvd's progressive images (correct me if i'm wrong), and if that's the case, how come they look fine on tv's? If you could either correct me or answer me i'd be grateful.
Posted: Fri, 29th Aug 2003, 12:31pm

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TAP2

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Good Question...
Kid might now the answer to that.

Many televisions have a Progressive Scan (I use it when watching dvd's... but It seems to make it flicker a bit more)
Posted: Fri, 29th Aug 2003, 12:53pm

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Sollthar

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You can encode a DVD progressive or interlaced. It's depending on the footage.

And a TV can display progressive as fine as interelaced. Real problems you'll just get on TV if your field dominance is reversed or on Computer if you forget to deinterlace.
Posted: Fri, 29th Aug 2003, 1:02pm

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Ben

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I was thinking, if you want to deinterlace, but not loose the vertical resolution, could you use a stretchy lense, and then squash your video into widescreen? Would that make sense? Would it? eh?
Posted: Fri, 29th Aug 2003, 1:50pm

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otteypm

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A stretchy lens eh...most of the ones I use are made of glass biggrin

de-interlacing doesn't loose any resolution, it's moving things sideways, not vertically...
Posted: Fri, 29th Aug 2003, 2:19pm

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Joshua Davies

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Most NTSC DVDs are interlaced although more and more are being released in progressive format. All PAL DVDs are interlaced until the standard has been set (which they keep saying has already happened but all the progressive PAL DVD players on the market seem to follow different standards and cost loads).

The hardware you use can change this a bit. When you play DVDs on your computer most software deinterlaces the footage so that it looks better on a monitor, the same can be true of some DVD players made for linking to progressive devices.

As for 25P or 30P on a normal TV, this won't be exactly stuttery but it will appear less fluid than interlaced video. A 25P camera is about as close to "film look" as you can get on a TV - film projectors show every frame of a film twice which is basically what your TV does with progressive footage. Unlike a projected film, a film running at 25P on a TV can cause headaches dued to the way the TV displays the image and the eyes natural persistance of vision.

All this stuff is down to apparent motion - the eyes ability to perceive movement from sequences of still images. Basically anything running below 14fps and your eyes can detect every single image, and therefore it will look really jerky. This is because there is actually a moment between frames where the screen is actually black. To counteract this films are projected at 48fps, but with each frame being shown twice. At 24fps the persistance of vision isn't enough to eliminate the flicker totally. Even at 30fps this flicker is not eliminated, hence why interlaced video was created. By displaying 50 or 60 fields per second the eye sees no flicker.

So there ya go.

NOTE: I've just read that cinemas actually show each frame 3 times so 72fps but everything else I've read says 48fps. Anyone know?

Last edited Fri, 29th Aug 2003, 2:29pm; edited 1 times in total.

Posted: Fri, 29th Aug 2003, 2:20pm

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Sollthar

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Heh, the oracle has spoken biggrin
Posted: Fri, 29th Aug 2003, 3:05pm

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Ben

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otteypm wrote:


de-interlacing doesn't loose any resolution, it's moving things sideways, not vertically...
Hmmm, it's probably me not knowing enough again, but from everything i've read on deinterlacing (the kind where you discard one field) they say that means you loose half of the vertical resolution, as by removing the field the image is only half the vertical height, so it needs to be stretched up to make it a normal size, therefore loosing vertical resolution.
Could someone please clear this up for me? I think I just spilt something.
Posted: Fri, 29th Aug 2003, 3:28pm

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padawanNick

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I think you've got it Ben. ( though the whole stretchy lens thing is ... well ... a stretch. wink )

The effect of interlacing/de-interlacing LOOKS horizontal because data is grouped into horizontal rows. The comb effect that results from shooting a moving object, capturing odd rows at one moment and even rows a split second later, looks horzontal.

When you use the discard method to deinterlace one set of rows (even or odd) is tossed out the window, and the remaining set is copied (verticaly) into the gap. The result LOOKS like you slid the combed rows into their proper position horizontally, but what you really did was loose the data out of a set of rows.

The image of the person in that article in the first post show this with more clarity, because not only did the person move, but he also opened his mouth between fields. As a result, if one set of rows is discarded, you see an image of him with his mouth closed, but if the other set is tossed, you see an image with his mouth open. (Man I love that article.)

Anyway, the picture stays the same size. You still have the same number of pixels, so you don't SEE that you've lost any resoltion, and technically you haven't, because the information wasn't there to begin with. It's not lost, just filtered.

Still, what you've done is copy one set of rows down one pixel vertically. Compared to a progressive shot, you've lost half you're verticle resolution.

Clear as mud for ya??
Best thing to do is read every word of that article, look at every picture, and if you end up with a specific question about a particular statement, image, or animation in there, ask that. It's all really in that article.

Have fun!
Posted: Fri, 29th Aug 2003, 3:32pm

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otteypm

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De-interlacing should be done using the blend fields method, I don't know all the techy details, but I can't beleive any proffesional video gear would delete half the frames.

Reading the two guides listed would probably make it clearer, I scanned one and it mentioned removing the frames and stretching, but why do that when the two fields can be blended and the resolution kept???


My method is don't bugger about unless you need to, I have only deinterlaced my films for the internet versions, anything else stays how it was recorded.
Posted: Fri, 29th Aug 2003, 3:53pm

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Kid

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Ok well to answer those questions in reverse order.

1. You don't want to blend because you get ghosting on each frame. This makes it hard to combine footage or effects and footage because the stuff you are adding should be ghosted to match. What you really want to do (if you are going back to tv) is to split fields. This gives you 50 or 60fps footage which looks squished. You add your effects to it and then combine the fields again to get 25 or 30fps interlaced footage. A lot of professional editing and effects programs do this automatically when they adds effects.

2. Yes if you drop even or odd fields then you half the vertical resolution. You cannot use a lens to squish the image because you still throw away half the data.

3. DVDs are very odd. They can be interlaced or progressive. As Schwar said previously it is mainly NTSC commercial discs which are interlaced however it is only a small amount of films, most are progressive (it is notoriously porn vids that are interlaced razz )

What the progressive ones do is store the film as 24fps progressive with a flag saying that its PAL or NTSC. The player then interlaces it on the fly for your tv. There are common ways to get from 24fps progressive to 30 or 25fps interlaced. You can choose to ignore this however and thats how people rip DVDs or play them on progressive players. (although you are getting 24fps progressive not 25 or 30 so it has to deal with that somehow)

The interlaced ones are hard to deinterlace because the picture on dvds by design always get resized. So its like interlace footage that has been risized and a nightmare to deal with.

Addn: when you are outputting for the intenet you are gonna resize it down anyway so you may as well use the drop field method.
Posted: Fri, 29th Aug 2003, 4:42pm

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TAP2

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This gives you 50 or 60fps footage which looks squished. You add your effects to it and then combine the fields again to get 25 or 30fps interlaced footage. A lot of professional editing and effects programs do this automatically when they adds effects.
Is there a programme which will do this all automatically....
Does alamdv2 drop any fields or leave the video as it was imported, because ParticleIllusion 2 drops a field which really annoys me.
Posted: Fri, 29th Aug 2003, 4:43pm

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Ben

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Here's a question which i think the answer will help me out (and hopefully others) alot. When I make videos almost every shot is edited in someway, adding more layers or elements. For this to work properly I usually have to deinterlace (by dropping one field). Now does anyone know the best way to add effects like this, but be able to reinterlace afterwards for output to tv?

I understand alamdv3 will have an option to do this automatically, but we don't always use alamdv for our effects (like 3d objects).
Posted: Fri, 29th Aug 2003, 4:52pm

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otteypm

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Most packages have a render to fields option, where you choose either odd or even first.

I think PAL is odd first and NTSC is even first, but I'm sure someone can correct me if I am wrong.

You should also be able to do this from your editing package, when all your effects are assembled.

Just check the output options for whatever package you are using....
Posted: Fri, 29th Aug 2003, 5:36pm

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Joshua Davies

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Most people with interlaced cameras find that they need to deinterlace their footage to add effects or warped composites. If they don't they either have strange interlace artifacts (try distorting an interlaced image) or if the background is interlaced the effect doesn't appear to really be part of the movie.

If you deinterlace a film you will always lose data and unless you can reinterlace the image again it will never look correct on a TV as it will be running progressive.

All our new programs have several modes to help you. You can work on your footage with the automatic deinterlace feature or you can use the professional spilt field mode.

Split Field Mode basically switches your movie from 25/30fps to 50/60 field frames per second. Every frame is created from a field of your movie therefore doubling the frame rate - the fields are stretched (just double lined) to create full resolution images. This does mean twice the amount of frames to animate but our new tweening engine should help there. Once you have finished applying your effects your can reinterlace the footage with zero loss of the original video data and flawless broadcast output. Sure it'll take a little longer to animate, but the quality on a TV should speak for itself.

Not many programs make it that simple for you smile

Ben - as for your 3D objects. The best bet would be to animate and render them at 60fps then use AlamDV3 or Chromanator to composite them. That way you'll get flawless TV output.
Posted: Fri, 29th Aug 2003, 6:52pm

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padawanNick

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Ben wrote:

Here's a question which i think the answer will help me out (and hopefully others) alot. When I make videos almost every shot is edited in someway, adding more layers or elements. For this to work properly I usually have to deinterlace (by dropping one field). Now does anyone know the best way to add effects like this, but be able to reinterlace afterwards for output to tv?

I understand alamdv3 will have an option to do this automatically, but we don't always use alamdv for our effects (like 3d objects).
Most of today's pro-grade editors will handle this for you automatically.

In Media Studio Pro for example, you can specify that the final output video should be 30i/30p/25i/50p etc. It uses this data when processing every frame, transition and effect.
If for example, you specify that a project is to be 30fps interlaced, then add an interlaced video as a source clip, the video will pass through clean and interlaced. If you then also add a 60fps full frame (progressive) animation to the project, MSP will automatically interlace this to the 30i output. I would suspect that the same abilities would be present in Premiere, Vegas, Avid, etc.

This is good stuff to keep in mind when using something like AlamDV, that uses pre-rendered animations, for a video that will be displayed on a TV. If you have a 30 frame explosion plugin, it will only last half-a-second if you want it interlaced.

Hope this helps.
Have fun.
Posted: Mon, 9th Jun 2008, 2:49pm

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Elijah

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TAP2 wrote:

For those of you who are more serious and pro about your films... I reccomend you read this interlacing guide, It explains everything you need to know. Great tutorial... hope you find it useful

http://www.lukesvideo.com/interlacing.html
Archive of this guide anywhere?
Posted: Mon, 9th Jun 2008, 3:17pm

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pdrg

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Blimey, that's one serious necro!

As it's not there, I'd try the http://100fps.com one, it's pretty excellent, and sadly Lukesvideo.com used a robots.txt to stop spiders indexing and archiving the article sad
Posted: Mon, 9th Jun 2008, 5:24pm

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EvilDonut

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Videosyncrasies DVD

d
Posted: Mon, 9th Jun 2008, 7:26pm

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SilverDragon7

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pdrg wrote:

Blimey, that's one serious necro!
I can only think of one way this statement was to mean.

lol.
Posted: Mon, 9th Jun 2008, 10:18pm

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pdrg

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SilverDragon7 wrote:

pdrg wrote:

Blimey, that's one serious necro!
I can only think of one way this statement was to mean.

lol.
in the sense that it was showing love for a long-dead thread, yep smile