[mythtv-users] HDTV Modeline Help

Cory Papenfuss papenfuss at juneau.me.vt.edu
Tue Dec 13 06:57:54 EST 2005


On Mon, 12 Dec 2005, Richard Shaw wrote:

> It looks like you're right. I tried a 1080i modeline and it did work. I would 
> be happy with that but at 27" the text in Firefox was so I couldn't read it. 
> Right now I'm messing with 540p which I have working but it doesn't look very 
> good. It could be I'm trying to get it to work in 4:3 ratio instead of 16:9. 
> I don't really want to have it in widescreen since it's not a widescreen 
> television. I guess I shouldn't complain too much, the picture is otherwise 
> good and I only paid $450 for it.
>
 	Here's the "same" 1080i modeline converted ot progressive-scan 
540p.

ModeLine "540p" 37.092 960 980 1004 1100 540 542 547 562 -hsync -vsync

Basically everything is divided by 2 but the interlace isn't there. 
That means you still get 33.72kHz horiz, but 60Hz vertical.  It's a 16:9 
ratio (960x540), but at least it's some semblance of "HDTV standard."  You 
may be able to coerce the 4:3 ratio you want by setting the DisplaySize in 
your xorg.conf... I do that for getting 4:3 with my non-square-pixel 
720x480 modeline on my 4:3 set.  Something like
DisplaySize 200 150
(since 200/150 = 4/3)

 	If you really want square pixels and a 4:3 and progressive scan, 
you're stuck somewhere between 640x480 and 800x600.  That's all the better 
the TV will do.

-Cory

>> 
>> ModeLine "1080i" 74.175824 1920 1960 2008 2200 1080 1084 1094 1125 
>> interlace -hsync -vsync
>>
>>     That puts out 33.72kHz HSYNC and 29.970 VSYNC.  It will be 
>> underwheliming to use as a desktop resolution because it will be huge and 
>> very flickery with the interlacing at 30Hz.  It should work with the TV 
>> though.
>>
>>     One of the reasons your modeline generate probably didn't work is 
>> because they rarely offer the "interlace" option.  That effectively halves 
>> the horizontal scanrate required for a given resolution.  30-35kHz pretty 
>> much limits you to somewhere between 640x480-800x600 in computer-ese 
>> resolutions.  Not much more over EDTV.
>> 
>> Cheers
>> -Cory
>> 
>> ------------------------------------------------------------------------
>> 
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>
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-- 

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
*************************************************************************



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