[mythtv-users] Affect of overscan / zoom on image quality?

[Christopher Friend]

Hey all, does anyone know what the affect of using mythtv's inbuilt overscan correction of zoomed aspect ratios is on video quality? I'm currently using a frontend to output to a PAL 4:3 crt tv witha 720*576 modeline, and watching PAL DVB-T broadcast tv. Because most of the btoadcast stuff is widescreen (1048x576?) and using a TV I have loads of overscan, I usually use myth's overscan correction and use the to "16:9 Zoom" aspect, but I'm wondering how much of an affect this would have on the quality.
 
At a guess, using 16:9 Zoom on a 16:9 image (~1048x576 px) viewed on a 4:3 pal tv (720x576 px) without any overscan corrections would show the full 576 lines of the original source on the full 576 lines of the tv, therefore not scaling anything and retaining as best quality as possible. And as soon as I use any other ratio or overscan corrections the thing is being scaled which would lose some quality?
 
I'm also not sure what affect using a 768 or 792 x576 modeline would have when using it on a regular pal 4:3 tv and viewing pal broadcasts on it. I would have thought normally it would show more of the image horizontally on screen, making it appear squashed horizontally but with still only having 720px on the actual tv the amount of info being displayed on screen would be the same... Though I'm actually using an xbox for a frontend which seems to scale everything back to a 720 before output so it seems to look the same whatever res i'm using, which right messes things up a bit in terms of figuring out what would be best and not, but that's another story...
 
Christopher
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