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De-interlace or Interlace? That is the question.

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Tom Laughlin
De-interlace or Interlace? That is the question.
on Mar 30, 2010 at 3:51:24 pm

Does anyone know what the interlacing is, what is does, if it is bad, how it is generated, how and why people de-interlace, and if you need to do it once on the FCP timeline, and the also de-interlace when you export, as some people de-interlace 2x. Is there a general industry rule on this and when or if you do it?

Thanks,

Tom

Tom Laughlin
Producer/Editor
Salt Lake City, UT
FCS3/Sony EX-3/Mac Intel


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Dennis Roliff
Re: De-interlace or Interlace? That is the question.
on Mar 30, 2010 at 4:28:56 pm

Tom,

I'm a new member at creativecow.net. This is a great question and one I have been wondering about as well. I will follow the thread for input from others.

Best,

Dennis

<a href="http://dennisroliff.com/folio">Dennis Roliff Photography</a>


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cowcowcowcowcow
Daniel Low
Re: De-interlace or Interlace? That is the question.
on Mar 30, 2010 at 4:32:52 pm

Tom, meet Wikipedia:

http://en.wikipedia.org/wiki/Interlace



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Daniel Low
Re: De-interlace or Interlace? That is the question.
on Mar 30, 2010 at 4:57:02 pm

Seriously guys, Google is your best friend here, there's such a huge about of great stuff to be found on Google, I'm really rather surprised the question has been asked here!

Anyhow, this is a great site that explains deinterlacing (and therefore interlace) simply.

http://www.100fps.com/


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Brian Alexander
Re: De-interlace or Interlace? That is the question.
on Mar 31, 2010 at 12:24:41 am

Long story short: only deinterlace upon output when your ready to go to the internet or distribute for computer use.

The long story...

The links Daniel provided are a great resource for learning about the science and practice of interlacing/deinterlacing. However, what you will not find in these resources, in plain English, are the practical instructions for when to de-interlace and when to leave well enough alone.

You typically would not want to deinterlace anywhere in your workflow until the last step: prepping your file for your intended medium.

Reasons to deinterlace:

1. Creating a distribution based format (h.264, wmv, On2VP6) for the internet or computer use.

2. Removing telecine frames.

Reasons not to deinterlace

1. DVD Creation (you can burn a 29.97 progressive sequence to your DVD. What you may not realize is that your DVD Player is most likely performing a scan line decimation only to have your TV perform a scan line interpolation. To much processing!)

2. Going to tape. I think some people still use tape machines? When you lay footage to tape, it's interlaced.

3. Providing the right codec for tapeless playback. A computer connected to a digital processor is not going to recognize a need for deinterlacing video, however, if you use the right codec and the right software, the file will deinterlace on the fly.

Interesting fact: 99 percent of the video you watch on TV is interlaced! Well, what's really going on is that most of the video has been shot at 24p (23.98) and has had telecine applied to it to conform to broadcast standards. These interlaced signals hit your TV and the first processor it comes to is the deinterlacer or deinterleaver.

Another interesting fact: Film DVDs are encoded a 23.98 (progressive, same as film) and your DVD player adds the telecined frames to create 29.97 fps for your TV. Of course, if your TV can accept a 480p signal, it can do it at 23.98 or 29.97.

--
Brian Alexander
Sr Video Engineer
Freeman AVS


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Dennis Roliff
Re: De-interlace or Interlace? That is the question.
on Mar 31, 2010 at 6:16:59 pm

Brian,

Thanks for providing this informative input regarding interlacing.
Great to know there are pros on this forum who are willing to share with open temperament toward neophytes :-).

Best,

Dennis

<a href="http://dennisroliff.com/folio">Dennis Roliff Photography</a>


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Daniel Low
Re: De-interlace or Interlace? That is the question.
on Mar 31, 2010 at 10:22:28 pm

[Brian Alexander] "1. DVD Creation (you can burn a 29.97 progressive sequence to your DVD. What you may not realize is that your DVD Player is most likely performing a scan line decimation only to have your TV perform a scan line interpolation. To much processing!) "

Only if the DVD player is connected to a CRT TV that does not support progressive scan. This does not apply to Plasma or LCD displays which are the norm these days. It's impossible to buy a new CRT TV (at least here in the UK) and that has been the case for a number of years.

[Brian Alexander] "2. Going to tape. I think some people still use tape machines? When you lay footage to tape, it's interlaced. "

So, what about all the HD tape formats?

[Brian Alexander] "Interesting fact: 99 percent of the video you watch on TV is interlaced!"

Certainly not the case in Europe. SD is interlaced but HD is a mixture of 720p and 1080i



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Brian Alexander
Re: De-interlace or Interlace? That is the question.
on Apr 1, 2010 at 5:37:59 pm

Daniel,
I don't disagree with your points, I'm just finding some end users who are still running CRTs and do not have progressive scan DVD players. Unless I know exactly where the content is going, I tend to play it safe so I do not double my work by having a client say, "this won't play on my tv".

[Daniel Low] "Only if the DVD player is connected to a CRT TV that does not support progressive scan."

Scan line decimation will also happen if your DVD player is not capable of outputting a progressive signal, i.e., 480i.

[Daniel Low] "So, what about all the HD tape formats? "

Fair enough, there are excellent SD and HD tape formats. I am fortunate enough that most of the workflows that I'm working with, from camera to display, are all tapeless. If I had my way, I'd have a fleet of HDCam SR decks!

[Daniel Low] "Certainly not the case in Europe. SD is interlaced but HD is a mixture of 720p and 1080i "

Isn't 1080i interlaced? There is a large mix of 720p and 1080i footage here in the states, it's predominately 1080i. My examples below are related to frame rates we have here in the states. 25 and 50 fps workflows and processing is probably a bit different.

I'm viewing this from the video processing side of the equipment and here's what I see:

1. 24p footage has added pulldown for 1080i 60 broadcast. This is deinterlaced by the cable receiver or the TV depending on what the output of the receiver is set to (720p, 1080i, 1080p).

2. 720p can get caught up in processing if your cable receiver is set to 1080i. If you receiver is set for 1080i and you look at 720p, the 720p is upscaled and turned into 1080i, the TV will take the 1080i and pass the signal through a deinterlacer to display a progressive signal.

Even if we're looking at 720p 60 material from a television station, wouldn't their feature films have a pulldown applied to it to get it from 24p to 30i to 60p? Deinterlacing is happening somewhere.

There is a lot of hardware processing going on. These processors are high quality so this thread is probably a moot point in today's world. Always deinterlacing may be a better way to go for 99% of applications but I'm a purist and I specify workflows based on the source media and what the media will be viewed on.


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Daniel Low
Re: De-interlace or Interlace? That is the question.
on Apr 2, 2010 at 9:29:46 am

[Brian Alexander] "Interesting fact: 99 percent of the video you watch on TV is interlaced!"

[Brian Alexander] "[Daniel Low] "Certainly not the case in Europe. SD is interlaced but HD is a mixture of 720p and 1080i "

Isn't 1080i interlaced? There is a large mix of 720p and 1080i footage here in the states, it's predominately 1080i. My examples below are related to frame rates we have here in the states. 25 and 50 fps workflows and processing is probably a bit different. "


I'm not following you.

You first said that 99% of what we see in on TV is interlaced. I pointed out that in Europe we have a mixture of Progressive and interlaced; 576i and 1080i, and then you go on to say that there's also a mix of 720p and 1080i int he States.

So what is it? 99% interlaced or.......





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Brian Alexander
Re: De-interlace or Interlace? That is the question.
on Apr 5, 2010 at 9:03:51 pm

The stations that are broadcasting at 720p do not limit their content to 720p only content.

The only way we're seeing true 720p content from start to finish is when a shoot/edit is done in 720p and our cable box is set to 720p. This is not as common as a shoot done in 1080i or SD.

Content that is not 720p that is broadcast from 720p stations include the following:

Film @ 23.98 -> 29.97
SD Video @ 29.97
HD Video @ 1080i

The point I am trying to make is that most of the material has passed through a deinterlace processor somewhere in the chain.

Let's say your TV is set to 1080i and you're watching a 720p station, the progressive signal is processed by the cable box to upconvert and introduce scan lines only to be deinterlaced by your TV.

The original question was about interlacing, what it is, and when to deinterlace. The answers I provide are from a viewpoint of a compressionist and video engineer.

My 99% figure for interlaced material may have been off by a few percentage points, I'll update the quote after I get home from NAB next week.


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Daniel Low
Re: De-interlace or Interlace? That is the question.
on Apr 5, 2010 at 9:29:13 pm

[Brian Alexander] "Let's say your TV is set to 1080i and you're watching a 720p station, the progressive signal is processed by the cable box to upconvert and introduce scan lines only to be deinterlaced by your TV."

Let's just say you setup your TV incorrectly for the service you are receiving, or you changed it from the 'Auto' setting which is usually the default.


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Tom Laughlin
Re: De-interlace or Interlace? That is the question.
on Apr 16, 2010 at 4:47:52 pm

Larry Jordan on lynda.com has a free web clip on this topic, check it out sometime, he talks about progressive and interlace, and it's quite a good clip:

http://www.lynda.com/home/DisplayCourse.aspx?lpk2=580#


Tom Laughlin
Producer/Editor
Salt Lake City, UT
FCS3/Sony EX-3/Mac Intel


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