[mythtvnz] help - very poor picture quality

[Steve Hodge]

On Feb 7, 2008 9:31 PM, Mark van Dijk <mark.van.dijk at ihug.co.nz> wrote:

> Hi all - I have successfully installed Mythbuntu on a machine with a
> GeForce4 440 MX card.


Consider trying a newer card. I tried a GeForce4 Ti4200 in my Myth box and
it had much worse svideo out quality than a GeForce FX 5200. Though I was
never 100% happy with the picture quality until I got a plasma and started
feeding it via VGA (and now DVI which resulted an another noticeable
improvement). The picture now is better than my standalone DVD player.


> Both the CRT and TV are being run at
> 1024x768.  De-Interlacing is OFF.  using nVidia binary drivers
>

Have you tried a lower res? PAL signals are 576 lines. That means the video
card has to down convert from 768 lines to 576 lines for the svideo output.
It might look better if you use a dedicated 576 line interlaced modeline
(ideal) or even 800x600.

There are several aspects to the poor quality:
> 1) a 'comb-like' effect, like interlacing, however instead of hundreds
> of fine horizontal comb teeth as you would expect with an interlacing
> effect, there are only about 20 large horizontal teeth across the screen
> from top to bottom.
> 2) a faint (but annoying) diagonal shimmering across the entire screen


What refresh rate is the resolution you're using? These effects sound like
they might because by the card having to convert a 60Hz resolution to a 50Hz
PAL signal. Try using a 50Hz modeline.

Also try various deinterlace filters. I never got a decent picture with an
interlaced output (though some people have).

Cheers,
Steve
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