[mythtv-users] How does SKY deinterlace TV

[Steven Adeff]

On 6/2/06, James Buckley <james at logicland.co.uk> wrote:
> Do you know how LCD's deinterlace TV, as if I could replicate the same on my
> MythTV box, aaaalll my problems go out the window
>
> -----Original Message-----
> From: mythtv-users-bounces at mythtv.org
> [mailto:mythtv-users-bounces at mythtv.org] On Behalf Of Robert Johnston
> Sent: 02 June 2006 01:33
> To: Discussion about mythtv
> Subject: Re: [mythtv-users] How does SKY deinterlace TV
>
> On 6/1/06, Nick <knowledgejunkie at gmail.com> wrote:
> > On 01/06/06, Robert Johnston <anaerin at gmail.com> wrote:
> >
> > > PAL is 50Hz, with 25 "Fields" per second.
> >
> > Isn't it 50 interlaced fields per second, or 25 frames (composed of
> > two fields) per second?
> >
> > http://en.wikipedia.org/wiki/PAL
>
> Okay, let's try saying that again (As I was partially wrong in my
> attempt to simplify it).
>
> The screen refreshes at 50Hz, however when it refreshes it only draws
> every other line. Thereby making 25Hz for a "Full Frame Refresh" (Both
> odd and even lines).
>
> But however it's said, it's still interlaced, so no deinterlacing
> takes place (Unless you're using an LCD, Plasma or 100Hz TV, in which
> case the TV itself is deinterlacing).

I don't know if LCD's do it differently, but RP/CRT HDTV's use an
algorithm that starts with IVTC (3:2, 2:2 pulldown) with something
similar to the kernel deinterlace (motion adaptive) as catchall for
what fails the IVTC.

What you have to realize though is that the chips are custom DSP's and
for the function they serve can be as fast as 10x what a Pentium4
could handle, ie for HD content.  From what I understand, Myth will
not be able to do a real-time motion adaptive deinterlace on HD
resolutions, though for SD feeds it should be fine with a modern high
end processor.
For HD though, the IVTC should catch and lock on to the pattern (even
for odd patterns like many OTA stations use) making deinterlacing
unnecesary.

There is someone on the dev list putting together an IVTC filter
currently, and I believe someone else is working on a way to let the
user select the "deinterlace" method by source/resolution, so in
theory 0.20 or 0.21 may allow for using the IVTC filter for HD sources
and the kerndeint for SD sources.

-- 
Steve
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