[mythtv-users] Stupid question - deinterlacing

[Paul Gardiner]

Jean-Yves Avenard wrote:
> Hi
> 
> 2009/2/22 Phil Wild <philwild at gmail.com>:
>> Perhaps this is a stupid question. I have a 1080p plasma panel and
>> watching the OTA 1080i signal, the picture looks real good. So to me,
>> that would infer that the TV has a good quality de-interlacer built
>> in. I don't know if it is possible, but could mythtv switch the video
>> signal of the graphics card to match the OTA stream and leave it to
>> the TV to perform the work in making the picture look as good as it
>> can on the display?
> 
> I tried that.
> 
> I set my Sony Bravia TV to 1080i and fed it 1080i signal via MythTV
> after turning off all deinterlacer ; result:  it looked crap
> 
> Like no deinterlacing happened at all.
> 
> Some people commented that there was an issue with nvidia cards not
> outputting an interlaced signal properly ...

There is a lot of evidence that nvidia cards get something wrong
when outputting an interlaced signal. I've seen it with an
FX5200 displaying 576i content with XV, although via OpenGL it
seemed ok (and a different set of problems made it unusable).

However there are other possible causes of bad picture. When you
use interlaced output - trying to match it to the content being
played - you need to ensure there is no processing of the picture.
Scaling will destroy all chances of getting the interlaces to
the TV intact. So if you've adjusted the picture size because
of overscan that will mess things up. Also, if the card implements
some sort of TV deflicker, you need that turned off.

And, even when you've gotten it all perfect, the incoming interlaces
can get sent in reverse to the TV. That you can cure by pausing and
restarting repeatedly until you by luck get the correct sync... oh
and that assumes your equipment has the grunt to never drop a frame.
Frame dropping will also stop the interlaces gettting to the TV
synced up.

Certainly for SD it's worth the effort though. You can get
beautifully crisp images with very little motion blur by using the
TV's deinterlacer.

Cheers,
	Paul.