[mythtv-users] Bob2x with wobbling OSD even at 50 Hz

Dan Seddon dan.seddon at framestore-cfc.com
Thu Jun 29 11:36:31 UTC 2006

Jens Axboe wrote:
> On Wed, Jun 28 2006, Tino Keitel wrote:
>> Hi folks,
>> I managed to get a 50 Hz screen on my TFT to get a stable picture with
>> the bob2x deinterlacer (I use a PAL DVB source). However, it's mostly
>> the same as before with 60 Hz. The OSD is only stable for a few seconds
>> maximum, then it starts to flicker again.
>> What should I do to get a stable picture with bob2x?
> I'm in the same boat, 50Hz DVB and bob deint causing flicker on
> horizontal lines such as logos (at least that's where it's most
> noticable). On HDTV you don't see it much, on STDV it's quite horrible.
> So I'd very much like to know what can be done about this as well. Bob
> deint is the only usable deinterlacer it seems, the others all look
> horrible in comparison.
Unless you have some other problem, this is a side effect of bob 
deinterlacing (the fact that Tino finds it OK for a few seconds if 
baffling) - where the detail is small such as small fonts.

Each field is generated (on alternate frames) by interpolating the 
neighbouring fields - in the case of a hard edges (such as in a font) 
this will bleed in to the interpolated field (which being on every other 
frame will cause a jitter), it would only possible to get rid of the 
problem by overlaying this detail after the deinterlacing has been done 
(maybe that's possible in the case of the OSD???) or with some fairly 
heavy duty image processing. Most broadcast text should be big enough 
not to be made too horrible by interlacing - I can't say I get bothered 
by it much although it's there. The OSD is a bit nasty at it's default 
size, but I've made mine much bigger and it's now fine. The jittering is 
still there - but it's much less perceivable when a field is small 
relative to the size of the text, which is why you don't see it much in 
HDTV. My view is that the benefits of bob-deint out way this problem by 
far - so stick with bob and make you OSD bigger.

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