Quick question about deinterlacing

[rmagere]

Hi,

Just wondering if anyone could tell me very simply what the new options of GK 0.28 do for deinterlacing.

Before with "Separate Fields" and "Field Deinterlace" I would always pick field deinterlace, however now there are also:

Field Deinterlace (no blend), Bob (fast) and TomsMoComp so which one should I pick (or where can I find more info on them)?

By the way most of the DVDs I have to deinterlace seem v. plain two frames mixed together which are only visible during fast actions scene while in slow motion the interlacing is not really detectable.

Thanks for any help

[Hiro2k]

http://forum.doom9.org/showthread.php?s=&threadid=34718

read the stickies. This is a great explanation on the interlacing filters.

It also depends on your source, the Field Deinterlace (no blend) should work.

If it doesn't you can make some short clips and use the different filters to see which one is the right one for your clip.

I just found thist thread with alot of good info.
http://forum.doom9.org/showthread.php?s=&threadid=45266

[jggimi]

Thread moved to Gknot development forum, as the question relates to an alpha release.

[rmagere]

Thanks for your reply actually I had already read http://forum.doom9.org/showthread.php?s=&threadid=34718

and although http://forum.doom9.org/showthread.php?s=&threadid=45266
is a very good thread to read neither links seem to provide me with further insight on what the three new deinterlace algorithm in gk do.

They do provide a description of what "separate fields" and "fields deinterlace (with blend)" do, furthemore they do provide a bit of a description of bob deinterlace, however I am still not clear why you would want to use "fields deinterlace (no blend)" or "TomsMoComp" (or for the matter even bob).

[N_F]

The different options works a bit differently. Which one to use depends on type of source and your personal preferences.

I know you don't want to hear it (I know I didn't when I was in your situation), but the only way to really choose is to first run some tests. Then you run some more tests. Then perhaps you'll look around the forum and see what others are using. Then you run some more tests :)

After all this you'll probably reach 1 of 2 conclusions. (1) I like this deinterlacer best and it's what I'll use for all interlaced sources or (2) you decide that different deinterlacers are good for different occasions.

Personally I've kinda gone from (1) to (2). Up til recently I used Fielddeinterlace on all interlaced sources, but on some tests (see, there we go with the tests again, I'll bet I'm not the only "experienced" encoder who are still running regular tests) with a DV-source I (too my dislike as I thought I had found the perfect deinterlacer in fielddeinterlace) found that separatefields().selecteven() gave a much better picture than fielddeinterlace.

[rmagere]

Actually I quite like your answer as at the moment all my interlaced sources seem to be the same - the majority being pal dvds of tv series or few bits of pal movies.

Knowing that it's a matter of personal choice set my heart at rest that until when I will be unhappy with what I get from the current deinterlacing algorithm I do not need to worry about it.

Just one more question though, when you say you test and test and test again - do you mean you preview the avs generated by gk with the chosen options and see if it looks good or do you also need to really encode the movie as otherwise some deinterlace artifacts do not appear until after the full encoding.

[N_F]

Originally posted by rmagere
Just one more question though, when you say you test and test and test again - do you mean you preview the avs generated by gk with the chosen options and see if it looks good or do you also need to really encode the movie as otherwise some deinterlace artifacts do not appear until after the full encoding.

Well, I rarely encode a full movie several times with different settings. It's more like I preview the avs and decide for some different settings. After a while I may have say 3 .avs files with either different filters or the same filter with different settings, or perhaps both. Then I'll probably select a couple of minutes from a whole movie/series and encode it with the different .avs files and of course the same codec settings.

This is the basics I use. Perhaps others have other methods they like to share (I'd love to see them)?

Also, before deciding to deinterlace the whole episode, be sure to look if it's really necesary. I recently did X-files season 3 PAL, where only the intro and sometimes some scens were interlaced, the majority of the scenes were progressive. In cases like this it's important to know that by deinterlacing the whole episode you're possibly losing a lot of quality. Instead you should use something like Fielddeinterlace(full=false), and definitely stay away from things like separatefields().selecteven(). as they deinterlace the whole picture no matter what.

[rmagere]

[i]Instead you should use something like Fielddeinterlace(full=false), and definitely stay away from things like separatefields().selecteven(). as they deinterlace the whole picture no matter what. [/B]

This last comment is really interesting as I have come across a number of dvds where I would have liked to deinterlace only a few segments rather than the whole movie. So is it enough to modify the Fielddeinterlace option in the avs to (full=false) and it will automaticaly detect when to use it or do I also need to specify the exact frame sections I am interested in applaying it to (I think the second option is the most likely one).

Thanks again for your time and help.

[N_F]

It will automatically detect it, but based on a specified threshold. The default value is 15, which I've never had reason to change.

You can find more info on this in the decomb manual.