HDTV Overscan compensation.

[thechunk]

I have a Samsung 42" DLP. It does 720P and 1080I. I don't have any content that I think would benefit from 1080I so I'm attempting to get 720P working over DVI2HDMI cable. I have a beautiful picture that looks very nice. The problem is that I have some overscan that I can't get rid of. I was able to tweek the display in windows with powertools to resize the windows desktop. I grabbed the modeline and tried to use in X but I didn't see a noticeable change in X. I have a second monitor setup so I'm running the twinview option for dual screens. I've ran both Twinview and Xinerama. I prefer the performance gain in twinview mode. So I have a nice looking display running at 1280x720 and I lose the kde task bar becasue it is overscanned off the screen. So I have an X server that is the correct size but I need to somehow limit the parts of that screen that get used. Does anyone have any suggestions on how to restrict screen usage in X? I've not found anything to do what I need yet. Thanks in advance.

-Jon

[netllama]

Did you see the driver README for the TVOverscan option, or adjust the overscan via nvidia-settings?

[thechunk]

Are those available for DVI output? I'm connecting from DVI to HDMI.

[netllama]

No, those are meant for TV-out (SVIDEO, etc). If you're getting overscan with DVI, then you're potentially not using the right mode, or there's something wrong on the TV itself. Please start X with the following command:
startx -- -logverbose 6

and then generate and attach an nvidia-bug-report.log.

[pe1chl]

Originally Posted by netllama

If you're getting overscan with DVI, then you're potentially not using the right mode, or there's something wrong on the TV itself.

There is something wrong with most TVs. However, it would be nice if there were a way to compensate for that. Like specifying a "usable display area" smaller than the full screen.

[thechunk]

I will generate the log when I get home. Running in Windows XP I had the same results but the display driver allowed me to reduce the size of the desktop. I've not found a similar option in X yet though. KDE and other applications want to use the full size of the X server and that causes the clipping. I believe the overscan is being done by the tv. If I change the display mode of the tv from 16:9 to 4:3 I see the clipping still on the left and right sides of the screen. I don't get back the edges of the screen. This may not be a big deal but it is interesting.

[pe1chl]

Originally Posted by thechunk

I believe the overscan is being done by the tv. If I change the display mode of the tv from 16:9 to 4:3 I see the clipping still on the left and right sides of the screen. I don't get back the edges of the screen.

This is because the overscan is actually part of the TV standards. Any TV that fully complies to (HDTV) standards will have about 16 pixels of overscan all around.

One could think that a DVI input would make the TV a computer screen and thus have no overscan, but TV manufacturers apparently often don't see it that way.
So it would be best if there was some way to make the driver report a smaller size to the X server, so that the windowmanager uses a smaller part of the screen and does not paint its toolbars halfway outside of the visible area.

(this does not solve the problem that a screen fed with 1920x1080 and then trimmed and scaled back to the 1920x1080 native screen size will mean you have no 1:1 pixel mapping and thus small text will be harder to read)

[thechunk]

Originally Posted by pe1chl

So it would be best if there was some way to make the driver report a smaller size to the X server, so that the windowmanager uses a smaller part of the screen and does not paint its toolbars halfway outside of the visible area.

I have Xnest. I'm trying to see how capable it is. So far it isn't too impressive. I have a laptop here with ATI's fglx driver. Right now the Xnest server won't accept client connections and I have not yet figured out why. It runs inside a native window on the server. So in theory I could create an Xnest server the size of my visible display and run any applications that I want to respect the TV size on that server. Hmm. I'll let you know how it goes.

[mtrax]

is this overscan fixable for component TV-out too? ie is there something in the nvidia-settings I can use to "underscan" ?

[thechunk]

I think the TV modifications will affect the Component out. The problem with DVI is that it is a digital signal. I think even component there can be some scalling. I think there is a small loss of quality depending on how the scalling is down however. You don't get a 1:1 mapping. nvidia-settings is a program that can allow you to modify some of your cards settings will the X server is running. I've used it when I was using SVideo out.

Originally Posted by mtrax

is this overscan fixable for component TV-out too? ie is there something in the nvidia-settings I can use to "underscan" ?

[mtrax]

currently I use MythTV to scale down the video output but when I want to use the Desktop to update something the Menu is hidden out of scan range... is there something in Xwindows or Nividia I can use to fix this without using a CRT

[thechunk]

Did you try running nvidia-settings? I think that will allow for overscan compensation over Component out. Give that a try.

Also under kde alt-F2 will start a run dialog where you can type in commands to launch.

You might consider openbox or some other window manager that doesn't have a panel for launching applications. I think kde has a way to get to the menu from a mouse click on the desktop as well. I'm investigating xgl to see if it allows for a smaller X server with full acceleration. I'll let you know how that goes. Xnest doesn't seem to have Xvideo or Xv support so I don't think it is acceptable for running a lower resolution X screen.

Originally Posted by mtrax

currently I use MythTV to scale down the video output but when I want to use the Desktop to update something the Menu is hidden out of scan range... is there something in Xwindows or Nividia I can use to fix this without using a CRT