[mythtv-users] Always prescaling theme images on startup

Steven Adeff adeffs.mythtv at gmail.com
Wed Mar 21 12:05:49 UTC 2007

On 3/20/07, Gabe Rubin <gaberubin at gmail.com> wrote:
> On 3/20/07, Steven Adeff <adeffs.mythtv at gmail.com> wrote:
> > With regards to how MythTV *currently* does scaling...
> > Your best option is to send the signal to your HDTV in the original
> > format for that picture and let your HDTV do the scaling. 1080i as
> > 1920x1080i or 1920x1080p, 720p as 1280x720p, SD as 480i/p (720x480).
> >
> > The reasoning behind this is that your HDTV will have a better scaler
> > than MythTV does.
> My question is, assuming I use xorg.conf to use a resolution that
> matches one in my CRT, but then I adjust the x and y gui sizes (and
> have my tv use those sizes) to compensate for overscan, is it then
> scaling the video to a non-native resolution that the TV needs to
> adjust?  How can I set to a native resolution and take into account
> the overscan without having both myth and the tv rescale?

The output to your tv will always be what you give it in the modeline.
Adjusting the x and y of the gui/video playback only affects how the
computer places the original image in that space. So in this case,
your tv/monitor is still getting the same resolution information but
your telling the computer to adjust how it places the image in that
space. This would obviously require scaling the image.

As to overscan, one must realize that in the realm of HDTV, and show
you playback through Myth with no overscan compensation enabled will
display the exact same way as if the signal was connected directly to
the TV. HDTV manufacturers have settled on 5% overscan as a common
amount, which according to the NTSC is the proper amount they should
use. The problem here is that the HDTV standard does not include
overscan. My point being, I wouldn't try and compensate for overscan
because you then have to turn to scaling the image, which does not
allow for 1:1 pixel mapping, which is basically the only way to get
the best image out of your HDTV.

If you really care about overscan and have an HDTV then your best bet
is to call up your local ISF calibration specialist and have them do
an in house calibration of your TV. This usually costs around $300 and
takes a few hours (3 is about averave from what I hear). This has the
added bonus of making your HDTV look the absolute best it can in all
other respects as well.
If your feeling adventurous, head over to the avsforums and see if
someone has posted the service manual or tuning information on your
tv. When I had a 32" CRT HDTV I obtained the service manual from
there, and along with reading a lot on other's experience tuning the
tv was able to all but eliminate the overscan (and what turned out to
be a space shifted image) on it. This can damage your TV and your
warranty won't cover it though, so beware!

Of course, compensating for overscan in the menu area makes sense...

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