[mythtv-users] how to set up xorg.conf for overscan

Raphael rpooser at gmail.com
Fri Oct 26 02:07:10 UTC 2007


Eyal Lebedinsky wrote:
> LG lied through  their teeth when they said that their HDTV (RT-52SZ8R)
> is native 1280x720 - it trims a significant part of all edges, enough
> to make if difficult to use in text mode. It simply never displays this
> many pixels.
> 
> This cannot be adjusted, not even from the special technician menus.
> 
> I want to tell xorg.conf to send a 1280x720 DVI signal but use a smaller
> area as the drawable. I do not want to just tell the wm to void the edges
> or to set mythtv to a window (I know how to do that).
> 
> In effect I want to tell it that my TV over-scans, and it should
> letterbox the screen and present a smaller area to all the applications.
> 
> Using DVI it seems that all the blanking information is simply ignored
> so one cannot play with that, so letterboxing is the only option.
> 
> TIA
> 
> --
> Eyal Lebedinsky	(eyal at eyal.emu.id.au)
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> mythtv-users at mythtv.org
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> 


Have you tried using the VGA input? I'm asking not to suggest that you 
actually do this, but to tell you that if you did, you would probably 
find a perfect 1280x720 display not overscanned on your screen. It's 
likely that LG isn't lying, but that the TV overscans DVI considerably. 
The TV doesn't overscan VGA input on the other hand as it expects a PC 
monitor style input there. This is how my Philips LCD TV works. DVI 
input is overscanned all to hell, but VGA input displays the actual 
computer resolution. I have another TV that I haven't even tested the 
HDMI on; the mythtv machine just uses VGA on that one.

When using DVI on my Philips TV I have to do exactly what you want to 
do, which is letterbox the output. I don't know what you mean by 
"blanking information is ignored", but I created a custom modeline for 
mine. As far as I can tell this is the only way to "fix" the overscan on 
DVI for my TV. It doesn't actually change overscan, it changes the image 
and the overscanned parts that I can't see end up black, as you want to 
do. You can start by using a modeline calculator:
http://www.tkk.fi/Misc/Electronics/faq/vga2rgb/calc.html
http://xtiming.sourceforge.net/cgi-bin/xtiming.pl

And then try and make your own mode off of that. xvidtune is useful for 
this.

HTH
Raphael




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