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

[Steven Ellis]

Hi Mark.

Very good and useful write up. Would you be interesting in submitting this
as an article for www.mythtv.co.nz?

Steve

On Mon, March 3, 2008 9:03 am, Mark van Dijk wrote:
> 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
>
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--------------------------------------------
Steven Ellis - Technical Director
OpenMedia Limited - The Home of myPVR
email   - steven at openmedia.co.nz
sales   - sales at openmedia.co.nz
support - support at openmedia.co.nz
website - http://www.openmedia.co.nz