[mythtvnz] very poor picture quality (ALL FIXED!)

[Mark van Dijk]

QUICK SUMMARY:
Hi all, about 1 month ago I asked for some help to fix my very poor
picture quality issues.  Thanks to several helpful replies I have now
finally fixed up the issues.  I thought i'd just detail what I found
just in case it might be useful to anyone else in the future.


ORIGINAL SETUP AND PROBLEM:
Mythbuntu, AMD 2400+, 1GB RAM, GeForce 4 MX440, S-Video connection to a
decent PAL widescreen TV.  Using nVidia binary drivers, the card was
using TwinView mode running at 1024x768.  My CRT was excellent, but the
picture on my TV was appalling!  My original email detailed several
aspects of very poor picture problems - namely:
 1) a 'comb like' interlacing effect, except that instead of hundreds 
    of comb teeth, there were only about 20.
 2) a faint (but very annoying) diagonal shimmering over the TV
 3) TV appeared to have a resolution of approx 240x160 - FAR less
    than the 720x576 than i would expect.  All text was virtually
    unreadable.


SUGGESTIONS:
Several helpful people gave me some good suggestions (Steven Ellis,
Steve Hodge, Wade Maxfield, Daivd Lowe, and others):
 1) run at 800x600 instead of 1024x768.  this made almost no difference
 2) turn on BOB de-interlacing.  this improved things a little.  the 
    comb effect was reduced - but not eliminated.  Other problems 
    remain.
 3) check the TV settings for brightness/contrast/sharpness/etc
 4) unplug the CRT.  no difference.
 5) try a different video card.  this ultimately did the trick

 
SOLUTION:
I bought a GeForce FX5200.  After some playing around, everything worked
properly.  In particular, i had to:
 1) remove and reinstall the nVidia binary drivers (using the Envy tool)
 2 modify xorg.conf with - Option "UseEvents" "True"
 3 now running in true 720x576 mode
 4 CRT is not connected and TwinView is disabled

At this point I mostly had a very good picture on the TV.  The
interlacing effect was gone, the diagonal shimmering never occured with
the FX5200, and the resolution of the TV seems fantastic (given that it
is only being run at 720x576)!!!  Even running a normal Ubuntu desktop
is (almost) usable via the TV.  fonts are as clear as can be expected.

There were still two major issues left at this point:
 1) the picture through my myth box appeared to lack dynamic range - 
    anything dark on the screen appeared completely black.  no matter 
    how much i played with the TV's brightness/contrast settings, i 
    could not get a very good picture.
 2) unusual issue where if i start watching TV through Myth, the 
    picture was ok.  If i then pause the stream and resume, the
    picture was very stuttering and jerky.  This was reproducable 
    every single time.

After some more playing around i discovered:
 1) that Myth itself has brightness/contrast settings that were
    set all wrong. I reset these settings.
 2) I turned OFF de-interlacing in Myth.  This fixed the pause/
    resume stutter issue.  As a bonus, all of Myth's overlay 
    menus are now crystal clear (with de-interlacing ON these
    overlay menus flickered very badly).


SUMMARY:
I now have EXCELLENT picture quality on my TV.  The picture through Myth
is now basically indistinguishable from watching direct on my TV.  In
retrospect, I think that there was just something physically wrong with
my old video card.  Other people have successfully used the MX 440
cards...

I still have several more questions about Myth, but that can wait for
another email


-- 
Mark van Dijk