[mythtv-users] Fix for distorted image on CRT TV

Joe Votour joevph at yahoo.com
Wed Aug 9 03:05:51 UTC 2006

> Cool Frood wrote:
>>I have a standard CRT TV (Philips 20" flat screen) which I'm using
>>with an NVidia FX5200 using an S-Video TV-out.  The problem that I
>>face is that the image on the screen is somewhat distorted, with the
>>top of the image being narrower than the bottom.  Also, the image is
>>very slightly tilted clockwise.  I also noticed that the curving of
>>the image at the top becomes more pronounced when the screen is
>>showing brighter colours?  Is this to be expected, or is there
>>something I can do to fix it?  It's not very annoying, but I'd really
>>like to get an image quality close to what I can get by directly
>>hooking up the cable box to the TV.
>>mythtv-users mailing list
>>mythtv-users at mythtv.org
> I get similar effects to what you describe also using a FX5200 (replaced
> my 5600 with it as this particular card doesn't have a fan on it), but
> I'm currently only using Composite out (I keep meaning to try S-vid to
> see the quality difference but it means a bit of mucking around that I
> haven't had time to do recently).
> My pic on the TV , while of a fairly good quality (I've also got a
> PVR-350 in the box that I used to use for TV out, but I now want the
> accelerated OpenGL etc for goom, xmame, stepmania  etc etc), definately
> seems to have what you describe, the top part of the picture bends in,
> and there is also a very noticeable brightening/darkening of the whole
> display when I move the cursor/highlight bar over the various menu
> options -  currently using GANT theme, so I think maybe it's linked to
> the colours displayed with the associated icons for each option.
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Back when I was using S-Video for TV output, I would see the same problem.
 Now that I'm using VGA (my current TV has a native VGA connection), I
don't have the problem (that I've noticed).

I noticed though that in comparing the size of the picture from the nVidia
and the PVR-350, that the PVR-350 actually displayed less of the picture -
it was overscanning (as it was intended to do).

I would try comparing the picture that you see on the nVidia card to the
one that you see on the TV.  If you see more picture on the nVidia card
(at the edges), then increase the overscan on the nVidia card until the
effect goes away.

You'll lose some of the items at the bottom of the screen in the MythTV
configuration menus, but they weren't really designed with the concept of
"hidden zones" (defined in the NTSC specification) very well.

-- Joe

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