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Old 11th July 2009, 00:05   #1  |  Link
LeoH
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Quick Deinterlacing Question...

Well, I think it's quick anyway

Basically I've got a PAL DV file which was dubbed from a PAL BetaSP which came from a film source. The original film was shot at 24fps but I'm assuming they did the 4% speed-up when doing the telecine at 25fps. Anyway I'm trying to deinterlace this sucker the best way possible. Once I get to real 25p I'll convert it back down to 24p.

Here is a frame from the source:



My first try in VDub was with the filter "deinterlace - PAL movie v1.1 (normal)" and it seems to be doing the right thing. Here is the same frame after filtering:



My question is, why am I still getting (albeit minor) comb artifacts on the edges? My paranoia says that I must be doing something wrong - or is this "normal" when deinterlacing, to have some minor artifacts still? Am I approaching this in the right way or should I be doing something else?

Here's a short clip of the material:
http://rapidshare.com/files/254364852/Clip1.rar.html

Many thanks in advance for any help!

Leo

Last edited by LeoH; 11th July 2009 at 23:04. Reason: Added clip link
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Old 11th July 2009, 00:17   #2  |  Link
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Obviously the deinterlace filter you used didn't catch all combing artifacts. If that filter has options, try to tweak the parameters.

If you can't get acceptable results with that filter, I highly recommend you give Yadif or TDeint a try

BTW: Most deinterlace filters leave a few artifacts here and there. But the question is: Are they visible at normal playback speed?
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Old 11th July 2009, 00:22   #3  |  Link
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Post a link to an unprocessed sample of your source material to get a definitive answer.
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Old 11th July 2009, 00:23   #4  |  Link
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Yadif is godly in my opinion when it comes to deinterlacing. It can take the most horribly interlaced video and make it appear progressive like no other.
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Old 11th July 2009, 00:25   #5  |  Link
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Thanks for the fast reply! Well, this particular filter has no options except for "swap fields first" which didn't seem to help. It actually does a pretty good job with the whole film - aside from the minor comb artifacts on the edges. But since this material is from film, shouldn't the fields simply fit back together into one seamless frame? I don't want to use any filters that interpolate or are destructive to the original source if possible. Thanks again!
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Old 11th July 2009, 00:28   #6  |  Link
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Post a sample!

I think that filter is a field matcher and doesn't deinterlace per se. The minor residue can be due to field distortions. But to tell you for sure we need a sample.
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Old 11th July 2009, 01:15   #7  |  Link
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OK, here's a short unprocessed clip of the material:

http://rapidshare.com/files/254364852/Clip1.rar.html

I think a field matcher sounds like the right ticket possibly, but feel free to let me know what you think of the clip.

Many thanks!!
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Old 11th July 2009, 01:43   #8  |  Link
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This is not only field shift, it also has additional distortions. Like that weird color ghosting between the fields:



But "decomb telecide" to fix the field shift followed by Yadif to clean-up the remaining combing artifacts seems to give reasonable results:
http://www.mediafire.com/?yaykindhzeq
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Last edited by LoRd_MuldeR; 11th July 2009 at 01:58.
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Old 11th July 2009, 02:28   #9  |  Link
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Thanks Mulder

Yeah the video has other problems, but I was trying to focus on just getting it back into progressive frames first. Decomb telecide and Yadif do seem to work nicely! What script did you use? I've tried this with just the Decomb filter:

AssumeBFF()
Telecide(guide=2,post=2,vthresh=50)

Seemed to produce reasonable results but maybe I should try Yadif for the "post" part.

Thanks again!
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Old 11th July 2009, 13:06   #10  |  Link
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I simply used "Decomb Telecide" (in "PAL/SECAM" mode) followed by Yadif (in Non-Bob mode). This was done in Avidemux.

But I think you can simply append Yadif(mode=0,order=0) to your script and see whether that does help or not

http://avisynth.org.ru/yadif/yadif.html
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Last edited by LoRd_MuldeR; 11th July 2009 at 13:26.
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Old 11th July 2009, 22:59   #11  |  Link
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I've tried Yadif after Decomb Telecide and it does produce nice results. There were still a few very minor comb artifacts on certain rounded edges, so I tried running "field bob" in VDub in conjunction with the AviSynth script of Decomb Telecide and Yadif. That seemed to take care of all the jagged edges and I don't think the quality suffered. Of course now I'm noticing all the other weird problems with the video - like the frequent wobble across the middle of the screen.

One thing at a time for now...
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Old 11th July 2009, 23:18   #12  |  Link
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I think if you use "Field Bob" in VirtualDub, which basically throws away one field (half of the lines) and then interpolates the missing field, you can drop Yadif.
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Last edited by LoRd_MuldeR; 11th July 2009 at 23:23.
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Old 11th July 2009, 23:42   #13  |  Link
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Quote:
Originally Posted by LoRd_MuldeR View Post
I think if you use "Field Bob" in VirtualDub, which basically throws away one field (half of the lines) and then interpolates the missing field, you can drop Yadif.
I didn't realize "Field Bob" was throwing away one of the fields I was trying to avoid interpolating. Maybe I'll check some other plugins to clean the edges after Decomb Telecide.
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Old 11th July 2009, 23:53   #14  |  Link
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Quote:
Originally Posted by LeoH View Post
I didn't realize "Field Bob" was throwing away one of the fields I was trying to avoid interpolating.
Any deinterlacer does interpolate

Only "smart" (motion adaptive) deinterlacers don't blindly interpolate all the pixles of one field, but try to keep as many pixels as possible.
This is possible because in areas where there's no motion, we can simply weave the fields with no visible combing.

As far as I understand, Yadif does not work like that. In interpolates all pixels of one filed, but uses a very smart method to do that.
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Last edited by LoRd_MuldeR; 12th July 2009 at 02:53.
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Old 12th July 2009, 02:53   #15  |  Link
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Quote:
Originally Posted by LoRd_MuldeR View Post
Any deinterlacer does interpolate

But "smart" (motion adaptive) deinterlacers don't blindly interpolate all the pixles of one fields, but try to keep as many pixels as possible.
This is possible because in areas where there's no motion, we can simply weave the pixels without visible combing.

As far as I understand, Yadif does not work like that. In interpolates all pixels of one filed, but uses a very "smart" method to do that.
Hmm, so what's the advantage to using Yadif along with Decomb Telecide if it's throwing out the fields that Decomb Telecide is matching? I may as well just use Yadif alone right? Sorry if I'm missing something obvious, I'm a little rusty with this kind of stuff.
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Old 12th July 2009, 03:03   #16  |  Link
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Quote:
Originally Posted by LeoH View Post
Hmm, so what's the advantage to using Yadif along with Decomb Telecide if it's throwing out the fields that Decomb Telecide is matching? I may as well just use Yadif alone right? Sorry if I'm missing something obvious, I'm a little rusty with this kind of stuff.
Decomb Telecide doesn't deinterlace. It just re-orders the fields to undo Telecine or to fix field-shifted streams.
After that process we (ideally) get the original progressive frames back. No interpolation does happen.
Of course Decomb Telecide only works with Telecined or filed-shifted material. It does not work on "true" interlaced video at all!

In your case the video appears to be field-shifted and Decomb Telecide does restore the video pretty well.
Unfortunately there are some filed distortions, which cause these minor combing artifacts shown in your screenshot.
Putting a deinterlacer (e.g. Yadif) behind Decomb Telecide removes those artifacts.

Of course you could skip the Decomb Telecide filter and only use Yadif. This should remove the combing too.
But you probably get better quality, if the deinterlacer bases its decisions on the "fixed" stream instead of the field-shifted one.
The same way we could simply deinterlace a Telecined stream, but we certainly shouldn't do that!

BTW: Maybe one of the Avisynth gurus could write a script to fix your field distortions in a smarter way
Appending Yadif is the quick and dirty solution to clean-up the remaining combing...
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Last edited by LoRd_MuldeR; 12th July 2009 at 03:11.
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Old 12th July 2009, 04:18   #17  |  Link
LeoH
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Quote:
Originally Posted by LoRd_MuldeR View Post
Decomb Telecide doesn't deinterlace. It just re-orders the fields to undo Telecine or to fix field-shifted streams.
After that process we (ideally) get the original progressive frames back. No interpolation does happen.
Of course Decomb Telecide only works with Telecined or filed-shifted material. It does not work on "true" interlaced video at all!

In your case the video appears to be field-shifted and Decomb Telecide does restore the video pretty well.
Unfortunately there are some filed distortions, which cause these minor combing artifacts shown in your screenshot.
Putting a deinterlacer (e.g. Yadif) behind Decomb Telecide removes those artifacts.

Of course you could skip the Decomb Telecide filter and only use Yadif. This should remove the combing too.
But you probably get better quality, if the deinterlacer bases its decisions on the "fixed" stream instead of the field-shifted one.
The same way we could simply deinterlace a Telecined stream, but we certainly shouldn't do that!

BTW: Maybe one of the Avisynth gurus could write a script to fix your field distortions in a smarter way
Appending Yadif is the quick and dirty solution to clean-up the remaining combing...
OK, I think I understand. I guess the problem is I'm not really sure how Yadif is working on the material. I suppose it doesn't matter too much as long as it does the job! It seems my main problem is this field distortion issue. I've tried searching for some filters to address it, but haven't found anything yet. This must be a common problem though - especially with old telecine tapes? Which gurus should I appeal to?



UPDATE:

I think I've found the perfect solution! It's an AviSynth plug called "Vinverse" - the description reads "An effective Function against (residual) combing, by Didée. Useful after deinterlaceing." Well, I've tried it and it seems to work like a charm. My residual combing problems appear to be gone and edges are smooth!

Last edited by LeoH; 12th July 2009 at 05:00.
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Old 12th July 2009, 05:54   #18  |  Link
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Quote:
Originally Posted by LoRd_MuldeR View Post
Decomb Telecide doesn't deinterlace
Wrong. It has a post processor that catches combed frames that slip through the field matching process. That is enabled by default.

The post processor in Telecide() will test if the frame has combing and apply deinterlacing only to the combed frames. Yadif will act on all frames, whether combed or not. That is not good.

Your post is borderline FUD.

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Old 12th July 2009, 06:23   #19  |  Link
LeoH
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Quote:
Originally Posted by neuron2 View Post
Wrong. It has a post processor that catches combed frames that slip through the field matching process. That is enabled by default.

The post processor in Telecide() will test if the frame has combing and apply deinterlacing only to the combed frames. Yadif will act on all frames, whether combed or not. That is not good.

Your post is borderline FUD.
I'm not trying to start any disagreements, i think he was just trying to help out. After running a couple of tests I believe my results are better turning off the post processor in Decomb Telecide and using the Vinverse plugin to clean up the minor combing bits left. With the post processing on in Telecide I was still getting a little combing on edges (especially hi-con curved edges). Anyway I'm pretty happy with the Decomb Telecide & Vinverse combo for now.
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Old 12th July 2009, 13:21   #20  |  Link
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Quote:
Originally Posted by neuron2 View Post
Wrong. It has a post processor that catches combed frames that slip through the field matching process. That is enabled by default.
Well, sorry. I didn't realize that "post processing" feature. Now I noticed that post-processing is off by default in Avidemux.

But basically the idea of an Inverse Telecine filter is to restore full frames by merging fields in the correct order/pattern, instead of interpolating.

If there's an (additional) post processor in Decomb Telecide to catch remaining combing artifacts, good. Will try to keep that in mind


Quote:
Originally Posted by neuron2 View Post
The post processor in Telecide() will test if the frame has combing and apply deinterlacing only to the combed frames. Yadif will act on all frames, whether combed or not. That is not good.
Yeah, that's why I said that appending Yadif (as yet another post-processor) is the "quick and dirty" solution.

If you know a better one (maybe Decomb Telecide's post filter can be tweaked to give better results on LeoH's source), I think it would be welcome

(BTW: TDeint has a similar option to only process "combed" frames, so it can act as a post-processor too)


Quote:
Originally Posted by LeoH View Post
It seems my main problem is this field distortion issue. I've tried searching for some filters to address it, but haven't found anything yet. This must be a common problem though - especially with old telecine tapes?
I think the problem is that "wobble" effect in your source

Even if the fields are merged in the correct pattern, they don't fit perfectly together, because of these distortions.

Maybe the "correct" solution would be to shift each odd (even) line horizontally until it fits...
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Last edited by LoRd_MuldeR; 12th July 2009 at 14:28.
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