[mythtv-users] Deinterlacing Methods

Daniel Kristjansson danielk at cuymedia.net
Sat Jan 13 20:20:48 UTC 2007

On Sat, 2007-01-13 at 12:32 +0000, James Buckley wrote:
> TV
> Type: LCD
> Model: LG 37LP1D
> Inputs: DVI (PC), DVI (TV), Componet, HDMI
> Working Modelines: 1280x720p, at 50Hz with a little overscan
> People have told me that you can get perfect TV using Kernel
> deinterlacing, with a framerate that's as good as standard TV
> (and doesn't have any flicker), however for me this method
> just doesn't have enough FPS. 
> I don't know whether my problems are related to an incorrect
> setup (using Gentoo), buggy hardware, or just my incompetence,
> but could someone tell me what I *should* get from each of the
> deinterlacing methods, as I've never had anything to compare
> too! 

You will never get a perfect picture with a progressive display..

The Freeview STB is probably not doing any deinterlacing, it
just sends an interlaced frames to the monitor and the monitor
does the deinterlacing. And apparently the monitor does a good

So your best option would probably be to feed the monitor a
PAL signal without any deinterlacing instead of 1280x720p.
MythTV allows you to use different video modes for the GUI
and video playback, so you can get the both of both worlds.

If you can't feed the monitor a PAL signal for some reason,
then bob will give you the closest approximation to the
deinterlacing the LCD is doing. It is however prone to 
"bobbing" as it's name would indicate. The smaller your
video resolution, the more pronounced is the bobbing.
The vertical resolution needs to be a multiple of 2 of the
video source vertical resolution for the bobbing to 
completely disappear. Bob deint also requires the frame
rate of the display to be twice that of the source video
(true in your case). Flicker also happens with bobdeint
when you have a single pixel high horizontal line, this
is because it is only present in every other frame shown.
Dimming the lights in the viewing room will make the
flicker less pronounced. (It is more pronounced with PAL
than NTSC, which is one reason bob is much more liked here).

Kernel deint is prone to ghosting, but gives a decent picture
with PAL sized frames. It also uses a lot of CPU, but your
processor should be able to handle it.

Linear blend deint is also prone to ghosting, but not as
much as kernel deint. But it also considerably more likely
to fail to deinterlace a frame. It only uses a little more
CPU than bobdeint.

oneline deint just throws away half the vertical resolution,
it never fails to deinterlace but it is inappropriate for
low resolution material like PAL.

For your video card I would make sure to disable all the auto
vsync in nvidia-settings, and then enable MythTV's OpenGL
vsync method. If this doesn't work, re-enable the vsync in
nvidia-settings, and then enable RTC vsync by running this
as root:
   echo 1024 > /proc/sys/dev/rtc/max-user-freq

Good luck!

-- Daniel

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