So are you saying that I should use something else
instead of 640x480? If so then what would you
suggest?
What I'm saying is that if you're using a "tvout" card, what your
computer renders is only loosely related to what shows up on the TV. The
signal to the TV *MUST* be NTSC-compliant. That means *exactly* 525 lines
drawn every 1/29.97th of a second, where each line takes exactly
1/15,734th of a second. The 640x480 pixels the computer is rendering is
likely being spatially interpolated (in both horiz and vert dimensions) by
the tvout chip on the video card so 1 pixel rendered != 1 pixel displayed.
The number of visible horizontal pixels can be just about anything, so
long as it take 1/15734th of a second to draw a whole line's worth of
them. One can pad the modeline horizontally to make 640 or 720 or
whatever "visible" pixels visible.
The number of vertical lines is *fixed* at 525/2 per field... If
you draw 480 of them (the generally accepted number of "visible" lines for
NTSC), the TV will draw some of them off the top and/or bottom screen so
you cannot see them. If you use a "640x465" resolution, the video player
will scale the presumably 480-line source into 465-line output.... now the
video's been abused.
Bottom line, overscanned is the way TVs have been mal-adjusted
forever. The *correct* way to not have overscanning is to adjust the TV
so it doesn't do it.
-Cory
I know that my TV is capable of displaying a picture
which fills the screen without the top being slightly
narrower than the bottom since the normal antenna
input does so, as does the xBox boot screen. I've
noticed that some xBox games have this resolution
problem while some do not. I'm sure that there's some
setting in xorg.conf that will fix this but I am not
familiar enough with TV out to figure out what.
Please let me know if you have any ideas,
Sounds like poor geometry control on the TV if it's not a
rectangular picture. Again... overscanning hides such misadjustments.
-Cory
--
*************************************************************************
* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
*************************************************************************
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