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Old 10-27-07, 05:15 AM   #1
eyal
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Default how to configure DVI overscan?

LG claimed that my TV is 1280x720 but it can only show about 1180x680.

How do I set xorg.conf to deliver a 1280x720 DVI signal but announce a smaller geometry to applications? Effectively I want it to letterbox a smaller rectangle inside the HD720 signal.

TIA
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Old 10-27-07, 11:01 AM   #2
netllama
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Default Re: how to configure DVI overscan?

Overscan is a property of TV-Out, not DVI. I'd suggest reading the driver README for more information on overscan.
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Old 10-27-07, 05:18 PM   #3
eyal
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Default Re: how to configure DVI overscan?

I read the README carefully, as well as searched this forum and trying other places first.

I *know* that overscan is a tv-out feature, which is why I consider LG to have lied when selling this TV as 1280x720 - there is no such thing as overscan in the digital world.

However this TV *does* fills the screen with a small (about 1180x680) part of the image so I *do* need to tell X about it.

How to I do this? More generally, how would Nvidia suggest that I configure my system to use a display resolution of 1180x680 but emit a 1280x720 DVI signal (with black edges)?

TIA
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Old 10-27-07, 06:02 PM   #4
crow
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Default Re: how to configure DVI overscan?

I know exactly what you mean. My HDTV does lots of overscan, even with DVI input. Here's what I found works, which is a little odd at 1152x672, but that's what my TV is happy with. I don't remember where I found the trick for doing this, but it's based on math off of the regular mode line. Perhaps you can reverse the math that I did, then adjust it for your needs?
Code:
ModeLine "720p" 74.25 1280 1390 1430 1650 720 725 730 750
# Inside the 720p, we want a window that is:  1152x672+64+24
# That means we want 64 fewer pixels on each side:
# 1152 1326 1366 1650
# And 24 fewer lines at the top and bottom:
# 672 701 706 750
ModeLine "1152x672" 74.25 1152 1326 1366 1650 672 701 706 750
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Old 10-28-07, 03:17 AM   #5
gIMp
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Default Re: how to configure DVI overscan?

Please excuse my complete stupidity here, but where do I put the new modelines? And how do I go about doing this?
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Old 10-28-07, 05:08 AM   #6
eyal
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Default Re: how to configure DVI overscan?

'crow' suggested a ModeLine. I have played with this in the past and know for a fact that the TV ignores all the timing information, and refuses any setting that is not 1280x720.

Do I understand you correctly, that your TV accepts a DVI signal with your special 1152x672 modeline? And it shows the whole image? If so then you surely solved your problem. BTW, this is not exactly 16:9.

Also, I doubt that DVI itself cares about the timing (porch sizes) at all.

My opinion is that I must use a 1280c720 mode but have X understand that only the nominated central part is visible. If it exists then it may be an xfree option or a specific nvidia driver option.

cheers
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Old 10-28-07, 09:24 AM   #7
crow
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Default Re: how to configure DVI overscan?

Yes, my TV accepts the modeline that I posted, and it displays the full 1152x672 image. Yes, that's a lot of overscan for 720p, and it's not true 16:9, but that's what my TV does. I do recall having trouble initially getting hacked modes like that to work; some of them seemed to stretch out the video image to the original size, cutting off the edges. I'm not sure why this one worked and previous attempts failed, but that was a couple of years ago. I suspect that one thing to be sure of is that you can use the real 720p mode that matches the hacked 720p mode.

It seems that even with DVI, the TV can't tell the difference between my signal and a real 720p signal.

I use that mode for my MythTV menus, but use xrandr to switch to more appropriate modes for video playback.
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Old 10-28-07, 09:27 AM   #8
crow
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Default Re: how to configure DVI overscan?

Quote:
Originally Posted by gIMp
Please excuse my complete stupidity here, but where do I put the new modelines? And how do I go about doing this?
It depends on exactly where your distribution puts XF86Config or xorg.conf, but it's somewhere in /etc.
Code:
cd /etc
find . -name XF86Config
find . -name xorg.conf
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Old 10-29-07, 02:33 PM   #9
gIMp
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Default Re: how to configure DVI overscan?

Hi,

Ok, so I spent the better part of the whole of yesterday reading up about modelines, and overscan... and I still can't get rid of the overscan. I have a tried a number of different modelines, and they either dont work at all, or leave the screen looking exactly the same...

As a small aside, if I activate picture-in-picture on my TV then it make the overscan less, but still not 100% correct.

Oh and btw I am using Ubuntu Gutsy.

Any ideas, or mayby some forums that that may be able to help, I am at my wits end.

Tx
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Old 10-29-07, 02:59 PM   #10
netllama
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Default Re: how to configure DVI overscan?

From the limited information that you've provided, I don't see how this can be fixed. DFPs tend to be very picky about the modelines that they will accept. The odds of being able to tweak one significantly enough to eliminate overscan is very low. This sounds like a limitation of the DFP you're using.

Without seeing a bug report, as defined in the forum sticky posts, I can't comment further.
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Old 10-30-07, 12:10 AM   #11
gIMp
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Default Re: how to configure DVI overscan?

Ok, I have attached a bug report as well as my xorg.conf file. FYI I am running a Samsung LA32S7, which is part of the Sonoma range (I think the A in the model name indicates Africa, Asia, and Australia, because there appears to be an European version which has an E)

Dont be fooled by the name working xorg.conf, this one at least gives me SOME display, with lots of overscan.

If there is anything else I can post, pls let me know

TXnvidia-bug-report.log
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Old 10-30-07, 12:12 AM   #12
gIMp
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Default Re: how to configure DVI overscan?

For some reason the one file didnt upload so here it is:
Attached Files
File Type: txt xorg.conf.txt (2.9 KB, 297 views)
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