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Deinterlace
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Author:  alien [ Tue Mar 22, 2005 12:45 pm ]
Post subject:  Deinterlace
I seems to have an interlacing misunderstanding. I am recording with a PVR-250 at PAL resolutions. My understanding is that this records the mpeg2 file interlaced. I am displaying on a PAL TV using the nvidia composite out and seeing interlace artifacts. My understanding is that the image should not be deinterlaced in this scenario and therefore I should not see interlace artifacts (I.e. the original interlacing should be preserved). However, if I turn on deinterlace with BOB, the interlacing artifacts go away. Did I miss something?

It's not the end of the world, Bob works great. However, I don't understand why I need him. Also, I would like to remove as many image manipulations as possible.

Allen
Author:  Greg Frost [ Tue Mar 22, 2005 3:27 pm ]
Post subject: 
A search of the forum using "bob deinterlace" would have revealed this post which is my attempt to explain it.
http://mysettopbox.tv/phpBB2/viewtopic. ... einterlace
Author:  alien [ Wed Mar 23, 2005 2:26 am ]
Post subject: 
That's where I got the idea to mess around with Bob (nice post).

But from my understanding, there are two reasons why I shouldn't be doing this:
    1. I am displaying on a TV which displays interlaced, so I shouldn't have to de-interlace.
    2. Shows can be broadcast either interlaced or progressive. De-interlacing a progressive show makes things worse.
There is some excellent information at http://www.100fps.com/video_resolution_vs_fluidity.htm See points 1 and 4. There is lots of other interesting information on this site too.

Allen
Author:  ceenvee703 [ Wed Mar 23, 2005 9:22 am ]
Post subject: 
1) True, you shouldn't HAVE to deinterlace, but the problem is finding the magic combination of drivers, XF86Config settings, and MythTV settings... and as Greg said in his post, there is a feeling that it may not be possible with certain video cards. I've seen claims that Matrox tv-out supports passthrough of interlaced recordings. Nevertheless, results with bob are so good that it's far easier to just turn it on than to mess with myriad settings (possibly for nothing).

2) Deinterlacing != bad. All progressive displays like LCD or plasma have to deinterlace. With the right algorithms (like Bob or the ones discussed at 100fps.com), it looks darn good.

Oh, wait, I see what you're saying. You only have to worry about progressive broadcasts if you are dealing with digital, not analog, and I did see a post at mythtv-users (I think from Isaac) that said that MythTV will not try to deinterlace a progressive source.
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