Quantcast Unfolding fields before applying Virtualdub filters - digitalFAQ Forum
  #1  
09-29-2011, 04:44 PM
unclescoob unclescoob is offline
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LordSmurf (or anyone who is very knowledgable with this issue can contribute)

I have read various discussions on the matter, but think that this is the place to settle the score.

My current project (NTSC Telecined Cartoon episodes - ripped VOB source) involves using Neat Video (the plugin included in LordSmurf's Virtualdub --the older version, which does not support interlaced film), Temporal Smoother and Dynamic Noise Remover. All with Virtualdub, of course. My filter chain goes as follows:

Deinterlace (unfold fields side by side)
Dynamic Noise Remover (3)
Neat Video
Hue Saturation Intensity filter (SAT - 80)
Deinterlace (fold fields back together)

My question: Am I doing something wrong here? I have read that Temporal Smoothing filters do not work well with telecined material (causes blending), and thus unfolding fields, applying filters, and folding back together is the best way to go, in order to obtain accurate cleaning. Same individual suggested that although Virtualdub's method of unfolding and folding fields is not the best solution, it is the best option IF Avisynth is not an option.

Others have suggested the following workflow (using Avisynth) prior to applying any filters in Virtualdub:

1. save the unedited/unfiltered video as an .avs file
2. unweave with Avisynth
3. Preview the .avs file in Virtualdub, apply filters accordingly
4. Save that as an uncompressed AVI
5. convert the newly filtered avi into an .avs file, and apply the "weave" filter with Avisynth.
6. Save as new .avs file.
7. Encode to MPEG-2 for DVD.

Is all of this really necessary? If so, which one is the better option? Will both methods provide me with the same results? Please note, my goal is to restore my videos the best way that I can with professional results. I am willing to take these steps if necessary, but wish to make sure that I am not doing it in vain.

Thanks in advance!

Last edited by unclescoob; 09-29-2011 at 05:01 PM.
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  #2  
09-30-2011, 01:59 PM
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Some VirtualDub filters are content-aware, meaning they understand how to compensate for interlacing. In fact, I'd go so far as to suggest most VDub filters are "smart" filters this way. If you don't see a difference, then you're likely working with a workflow filter chain of all smart filters.

Quote:
Deinterlace (unfold fields side by side)
Dynamic Noise Remover (3)
Neat Video
Hue Saturation Intensity filter (SAT - 80)
Deinterlace (fold fields back together)
I'm not 100% sure if NeatVideo is smart, but DNR should be, and hue/sat filters are not affected by interlace.

The best test will be to convert to MPEG-2, burn to a test DVD-RW (or DVD+RW), and then watch it on a tube TV (or SDTV or EDTV flat panel). If the interlacing still looks fine, then you're good to go, and I would not worry about it any further. I've had to test this way many times, and for this exact reason.

The unweave/weave and unfold/fold filters can cause interlace artifacts, too. They're not perfect. Online users satstorm and lordsmurf have discussed this in depth in the past, in various places online (VH). Even in times where separation of fields should be fine, allowing filters to work in progressive mode, it may still end up as a damaged mess when re-merged.

In short, no, it may not be necessary.

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  #3  
09-30-2011, 02:56 PM
unclescoob unclescoob is offline
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Wonderful news.

Thank you very much for your help!!!
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  #4  
09-30-2011, 03:52 PM
juhok juhok is offline
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Neat Video can do interlaced.



Other than that I'm very confused. "Deinterlace (unfold fields side by side)" <- what does this mean? Default deinterlace operation is merging 2 fields in to 1 frame. If you want to re-interlace later more or less losslessy, you want to use lossless bobber to make it progressive instead of plain vdub deinterlace. But this is not relevant now cause NV does interlaced.


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  #5  
10-02-2011, 03:32 PM
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Some versions of NeatVideo lack that radio option.

Fields are weaved, and can be unweaved. For example, a 720x480 29.97fps video will become a 720x240 59.94fps progressive video. It's not deinterlaced, but the fields are separated. I don't quite know how to describe it in a way that makes any sense to the layman. It's one of the few video concepts that's not real easy to explain in a meaningful way.

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  #6  
10-02-2011, 05:36 PM
unclescoob unclescoob is offline
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Let me test the little that I have gained, so far (please tell me if I at least have the right idea -- all from the top of my brain)

Telecine is two fields (which make a frame) shown a fragment of a second apart. When you unweave the fields, it's called inverse telecine.

Interlaced is when two fields are shown in odd and even lines. Blending those fields is called deinterlacing but in essence, you're throwing away a portion of the film.

The difference? Telecine is every fourth frame or so with two fields shown apart, whereas interlaced is generally the entire film

Am I somewhat on track or did I just make a complete monkey of myself?
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  #7  
10-02-2011, 05:42 PM
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Telecine is film turned into interlace for the purpose of television playback. It can be undone (IVTC).

Interlaced is two fields, and cannot be IVTC'd. It can, however, be deinterlaced. Most methods throw away data, but some more advanced algorithms will not lose any information. These advanced methods also look better, because they work on the basis of creating progressive frames from adjacent interlaced frames -- not simply throwing away data to un-interlace it.

No flying monkeys here. I think you sort-of have it down.

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  #8  
10-02-2011, 06:07 PM
juhok juhok is offline
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Another way to put it could be that in NTSC land telecined material fundamentally is 24 unique frames per second(aka film), displayed as 60~ fields per second for analogue TV transmission and viewing. 24 frames splits in to 48 fields per second and to fill the gap telecine process adds some duplicates which will be discarded in IVTC process. Telecine is in itself lossless operation when done correctly so you can recover original 24 frames.

Native interlaced is 60 unique fields per second - every single field represents unique moment in time. As you can see, normal deinterlace which gives you 30~ frames per second destroys half of the temporal information. Also keep in mind that it's bad practise to use any temporal filter with field-separated material because the fields are shifted in relation to each other. You need to compensate for the shift somehow before doing anything else. Some filters can detect this and compensate internally (eg. avisynth/mvtools).

^This is out of my head and some or all of the above could be misinformation.
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  #9  
10-02-2011, 06:09 PM
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Quote:
Originally Posted by juhok View Post
^This is out of my head and some or all of the above could be misinformation.
Looks good to me.

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  #10  
10-02-2011, 09:09 PM
unclescoob unclescoob is offline
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So in short, LordSmurf and Juhok: You're both confirming what admin told me initially: Don't unweave fields, just apply the temporal filtration as-is.

Right?
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  #11  
10-02-2011, 09:18 PM
juhok juhok is offline
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Yes, if your plugin supports interlaced processing.
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