[mythtv-users] nVidia GF4 mx440 tv-out optimization

Gert van der Knokke gertk at xs4all.nl
Sun Mar 28 16:56:10 EST 2004

Ville Vehvilainen wrote:

>These problems are exactly what I see when trying to use my NForce2
>integrated GF4MX. (The board is the MSI K7N2G.) Either the blacks are too
>dark, or the whites washed out, and the maximum available brightness
>leaves much to be desired. This is using the SVideo output to a fairly
>high-quality 100Hz television.
Hmm, 100 Hz: this is a point which needs attention I guess...

Imagine your VGA card displaying normally at 70 or 80 Hz (maybe more 
depending on the quality of your monitor) it displays it in progressive 
scan mode. The TV-Out converter chip onboard the VGA card  tries to 
generate a PAL or NTSC signal meaning 50 or 60 Hz (since it doesn't do 
interlace) so there is a mismatch between the monitor (and thus the 
framebuffer) refresh rate and the TV-Out signal (this explains the 
'tearing' effect on the TV-Out when running in dual-view/clone modes) 
this is problem 1.
Now you try to display it on a 100 Hz TV set meaning it reads in the 
picture, does all kind of motion compensation and deinterlacing for 
25/50 Hz (30/60 Ntsc) interlaced signals and then dumps it into an 100 
Hz framebuffer (probably progressive scan too)
And finally there is the problem of movies being recorded at even lower 
framerates and have no interlace at all.. 

All this mismatching will wreck the picture especially during motion...

Most 100 Hz TV's (and the new LCD/plasmas too!) still have trouble 
displaying fast motion, Philips has improved over the years quite a lot 
with this. They even put in calculated/interpolated intermediate frames 

The best picture in my opinion would be obtained if your VGA card runs 
in TV only mode with the vertical sync of the TV output being the 
framebuffer refreshrate. When you put this into an ordinary TV you 
should have almost no tearing during motion and when the number of 
vertical lines in your X config matches the PAL or NTSC perfectly there 
will be no intermediate lines generated by the TV Out converter and you 
should get the maximum quality. On a 100 Hz set this will also give 
better picture though the double buffering in these sets might give some 
trouble again with motion.

> effect
>I see the horizontal lines also, unless I turn on the "deinterlace
>playback" option - in which case fast-moving scenes, such as in sports,
>are jerky.

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