I don't know how to do the latter, and even if it is possible in all cases. In my setup, I have set up my video card to 1:1 to the panel I have (fullHD), since I have material in several different resolutions,
This is the theory. But you need to remember that you are using TV set as a monitor, and typical TV sets, even FullHD ones implement overscan on HDMI input. Some TVs disable overscan via special switch.
But having overscan it means that having the 1:1 mapping is a bit harder. You need to find out how much is the real visible resolution and define X- screen to that resolution.
Naturally way to determine this is to have test patterns drawn to a screen and look closely (mag. glass) to see if you have 1:1 mapping. You need to remember that HDMI/DVI is not a digital bus, it is 'analogue'-type signal transferred in digital fashion. Why else you need porches et al at signal timing?
With this I mean that HDMI-signal does not say: -frame coming at resolution 1920x1080p50 -pixel at 0,0 use color 0,0,0 -pixel at 1,0 use color 255,255,255 -pixel at 2,0 use color 0,0,0 ...
HDMI says: - vert. sync - hor. sync - front porch time - (0,0,0),(255,255,255),(0,0,0),.....
And it is up to TV electronics where to place those pixels on LCD panel. And this is done with overscan settings etc.
- Jori