[NTLUG:Discuss] OT: Video Cardsa and TV Out

[Steve Baker]

Stuart Johnston wrote:
> Make sure you use an S-Video cable for the connection.  I surf the web 
> on my TV and with the S-Video it is easily readable (with an old ATI card).

Yeah - that's important.

 > Jack Snodgrass wrote:
 >
 >> An XBOX is basically a PC. How does it get graphics
 >> to show up good on a standard TV when PC Video out
 >> cards do such a poor job. Or do the newer video
 >> cards with TV out do a better job than they used to?

Fundamentally - a TV (non-HDTV that is) has only 512 scanlines - and
those are interlaced so if you draw a one pixel high horizontal line, it'll
either flicker pretty badly or be fuzzed out to two lines (if your hardware
supports that).

Horizontal resolution is hard to define (because it's analog) - but it's
hard to resolve more than about 512 horizontal pixels.

At that degree of blockiness, small text is pretty hard to read unless it's
an antialiased font that's carefully tuned to that display.   I suspect
that's why your Xbox looks so good - the software you're running is
carefully tuned to look good on a TV - which hardly any Linux software
is likely to be.

There are also some weird colour issues on Televisions if you don't drive
them with an RGB signal.   TV's use 'color difference' signals instead
of RGB because NTSC was designed to be compatibly with legacy monochrome
broadcasts.  The color difference signals are encoded as phase shifts in
a carrier frequency - and when both signals change phase at just the wrong
time, you get an overall signal dip or boost that can make the screen go
darker in that pixel - even though all the pixels in that region are the
same brightness.

Then, it's also possible for high frequency monochrome changes to look just
like a phase change in the colors - so dense black/white changes along a
scanline can create false colors in the image that aren't supposed to be
there.

Still worse, there are RGB combinations that a TV simply cannot display.
Those colors are approximated - so some subtle shading gets messed up.

Some of these things can be avoided using either component YUV or S-video,
but things like the interlaced nature of Television is not usually circumvented
unless your TV and your graphics card support 'progressive scan'.

The people who write games for consoles go to great lengths to try to
avoid these known problems.   That makes the TV look a great deal better
than it has any right to look!

So it's not that the Xbox has better graphics than your PC (to the
contrary - the Xbox graphics chip is essentially just an nVidia
GeForce-3).   It's just that the software you're running on your
PC isn't designed to look good on TV.

>> I do want to try and get a video card doing TV Out...
>> do the linux xwindows Radeon 9XXX drivers support
>> TV out or am I going to have to do some software
>> updates and what not just to see what the picture
>> will look like.

Sorry - I don't know much about ATI hardware.

---------------------------- Steve Baker -------------------------
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