[Openchrome-users] Troublshooting NoScale Problems on VT1622A

[Jake Thompson]

On 5/10/06, Ivor Hewitt <ivor at ivor.org> wrote:
>
> On Wednesday 10 May 2006 04:44, Jake Thompson wrote:
> > So after alot of playing and tweaking, I am still having the "Green
> Fade"
> > issue with my VT1622A.
> >
> > Running the display in 720x480Noscale causes a green fade on the top of
> the
> > screen and alot of refresh flicker(enough to give me a headache).
> >
> > If I run in 720x480Over, these problems disappear, however due to the
> Over
> > scaling video playback is no longer smooth and looks bad.
> >
> Well according to the table, for NTSC 720x480Over is also an unscaled mode
> which should look the same as 720x480Noscale (it did for me). But it
> seemed
> the refresh rate isn't calculated quite right for it and it isn't quite,
> but
> I had no image quality problems.


720x480Over Definatly gives a great picture, there is no flicker and no
color distortion.


Can you confirm from your log that 720x480Noscale is definitely being used
> (and not 800x600).... and if so could you quantify "video playback is no
> longer smooth and looks bad"


Ok, so set to 720x480Over, xrandr gives me
*0    720 x 480    ( 406mm x 305mm )  *50   60

And, 720x480Noscale gives me
*0    720 x 480    ( 406mm x 305mm )  *60   50

So, obviously the refresh rate is the major difference there.

It seems when I am running 720x480Over that MPG2 playback using XvMC is very
choppy(stuttering) and not clear, as in pixilated.  When running in
720x480Noscale it seems much clearer and no real stuttering.


> Thin white lines and other white object you can notice a flicker, also it
> > seems to affect all the pixels across the screen, so you can see a
> > difference in the screen along the horizontal where the flickering is
> > taking place.
> >
> That's to be expected. Unless you're talking about something different.
> The
> unscaled modes are for displaying video playback. If you display computer
> generated images with thin straight lines you will get horrible flicker
> unless the application has been written with "TV knowledge"


Agreed that this is for TV playback and not normal computer stuff.  This is
in the myth screens, in 720x480Over they show up fine and do not bother the
eyes at all, in 720x480Noscale they flicker alot, looking above at the
refreshrate, I would say it is very akin to running the wrong refresh on a
normal monitor.

(hmm I think we need a wiki FAQ for TV modes)
>
> > The green fade takes about 15-25% of the top of the screen.
> >
> Yeah it's green. The ntsc noscale has incorrect timings.
>
> > What else can I do to help resolve this problem, I will try out anything
> > you think might help.
> >
> If 720x480Over works... wait for a bit.... if it doesn't I'll see about
> generating some ntsc tv modes manually with my generator for you to play
> with. At the moment I'm concentrating on getting nice working PAL modes
> (for
> obvious reasons).


If you can give me anything, let me know and I will try them.  Damn US NTSC
standards!

Thanks for all the help,
Jake
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