[mythtv-users] To underscan, or not to underscan.

[William Munson]

Skitals wrote:
> So I have a Sony 1080i CRT RPTV (KP-46WT520). I love the tv, except for the
> DREADED overscan. I lose a couple inches on all sides. I currently have my
> resolution set at a full 1920x1080, without any under/overscan for tv
> playback. For the myth menus, I set the resolution to something like
> 1800x1012 to eliminate the overscan so the setup menus and such are usable.
>
> I have a couple problems with this. Because of the window resolution change
> between tv playback and the menu, it kind of flickers a couple times as it
> adjusts and offsets when switch from a menu to tv, and vice versa. It's
> especially annoying when pulling up the program guide.
>
> Now I could set TV playback to use the same settings as the menus, or I
> could fix the overscan at the graphics card level, but I am hesitant for one
> primary reason. And that is the effect of scaling for HD video playback. I
> like the idea of playing back 1080i content w/o any type of scaling. If I
> reset my video card settings to output say 1800x1012 with the proper offset,
> how would that scaling effect video quality? I guess since most of my
> content is 480p or 720p anyways, I might be making a big issue out of
> nothing. I'm just curious what you people do who have tvs with outrageous
> overscan.
>
> Someone actually posted a Modeline for my specific tv in the wiki, but for
> some reason they are only doing 1160x652 (720p minus overscan) instead of
> something closer to 1080i.
>   
What I do is run a custom modeline which reduces the visible portion of 
the screen to match the edges of the screen while maintaining the same 
timing and dot clock. Its been quite a while since I did this so this is 
from memory. Here is my custom modeline. You are welcome to try it.

    Mode "my1080i"
                DotClock 74.52
                HTimings 1640 1888 2096 2208
                VTimings 952 1044 1060 1126
                Flags "-HSync" "-VSync" "Interlace"
        EndMode         


The sections you are interested in are the HTimings and VTimings. These 
are for the horizontal and vertical timing of your modeline.

The first number in each section is the size of the visible portion of 
the screen. Change this in increments of 8.

The second and third numbers are the start and stop time of your sync 
section. By changing the timing of these we move the visible section 
back and forth within the frame. Use this to center your screen. Change 
these together by the same amount, also in increments of 8.

The final number is your frame size and is what determines the timing of 
your modeline. Do not change this.

Be sure to save a copy of your default mode just in case you screw up. 
Good luck, it takes a few (bunch) of change then view cycles to get it 
perfect. I found it helpful to create a bunch of modelines and list them 
all in the available modes sections.  Then change the same parameter in 
each by 8, 16, 24, 32..... By cycling thru the modes using the keyboard 
you can see which one fits the best fairly quickly.

Good luck!