[mythtvnz] help - very poor picture quality

[David Zanetti]

On Thu, 2008-02-07 at 21:31 +1300, Mark van Dijk wrote:
> Hi all - I have successfully installed Mythbuntu on a machine with a 
> GeForce4 440 MX card.  Everything is (mostly) working very well.  My 
> main issue at the moment is that whilst the quality of the picture on my 
> monitor is excellent - the picture quailty on the TV (sitting right next 
> to it) is **VERY** poor.  I'm using an SVideo cable, and the graphics 
> card is in TwinView mode.  Both the CRT and TV are being run at 
> 1024x768.  De-Interlacing is OFF.  using nVidia binary drivers

Various other people have said this, but I shall to.

The TV encoder on esp older nvidia boards isn't very good, and while on
paper it does 1024x768 poor quality is not unusual.

Since PAL is ~720x576, try to stick to that resolution as much as
possible. It won't be 1:1 unless you are careful about overscan
settings, but it'll be a lot closer to what the TV is expecting. 800x600
if you can't get a working PAL modeline.

> 3) the TV screen appears to have very low resolution.  If i had to guess 
> - id say 240x160'ish.  Fonts on the monitor that are crystal clear 
> appear to be only 3-4 very large pixels high on the TV.

Watch out for broken DPI settings in X. It's probably chosing 100dpi by
default, but this is nowhere near what a TV is. You can either use
larger fonts overall, or pass the correct DPI to X explicitly. I chose
the former because it's a quicker hack.

> Also, am i correct in thinking 
> that DeInterlacing should be OFF as my TV is interlaced?

It's better to turn it on, because X is usually configured as a
progressive display (the modeline won't have interlace set), but the TV
encoder re-interlaces the progressive display image. If you don't
deinterlace, then you get the "comb" effect on the progressively-filled
buffed, then you get that re-interlaced, and the two almost certainly
won't align.

If you can actually coerce you card to do true interlacing in X (ie, the
modeline actually has interlacing enabled) then it might work without
deinterlacing in X. Or it might not.

-- 
David Zanetti <dave2 at wetstring.net>
http://hairy.geek.nz/
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