[linux-dvb] Re: Recording using a TwinHan VisionDVT terrestial card

[Måns Rullgård <mru@pronto.tv>]

Hamish Moffatt <hamish@cloud.net.au> writes:

> On Thu, Jun 10, 2004 at 09:43:02AM +0200, Måns Rullgård wrote:
>> > Finally (yes!), a question about image quality: when I view live,
>> > or play back a recording, there seems to be some interlacing
>> > problem or similar. Fast vertical movements reveal horizontal
>> > lines, most obvious when a TV program is using a blue screen
>> > background for adding graphics, such as a weather report, but
>> > disturbing also when watching regular programs.
>> 
>> That is because the broadcasted stream is interlaced to play back
>> nicely on a regular TV.  Try activating some deinterlacing in your
>> playback software.
>
> I've been reading about this recently and I don't think your explanation
> is accurate. For example, when you watch analog TV the picture is also
> interlaced but you don't see the jagged edges.

That is because the analog TV display is interlaced as well.

> The problem isn't that the picture is interlaced, but that your display
> device refresh is not synchronised with the field(frame) source.

Correct, but the display needs to be interlaced in addition.  Normally
a computer will not use interlaced modes, though they can be
configured for interlacing.

> Unfortunately the most common solution is to blur the jagged edges. 
> It gets rid of those but it does make fast panning look a bit unnatural
> IMHO.
>
> I think that, in theory, if you could synchronise your update rate with
> the frame rate, you would not need deinterlacing. MythTV has some code
> which attempts to do this.

You need to synchronize the picture update with the vertical refresh
of the monitor, and use a video mode matching the content being
played.

-- 
Måns Rullgård
mru@pronto.tv