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Old 01-24-06, 01:27 AM   #1
blwegrzyn
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Default Why overscan problems exist, what is that about

Hi everyone,

I have been reading here lately, and I see that overscan is a huge problem.
I am new two those things, but as many people I also run into having too big image sizes when connecting pc to hdtv tv. I use dvi to hdmi.
It looks like the images are overscan (meaning that part of the image is cut, so the edges will look clear) A lot of people are asking for help.
I think we should more talk about the problem and explain more technically why it exist. Why overscan? Why is is causing problems. Everything in this world is usually for a reason, and overscan is similar. I am asking people who know the problem to tell more, and how this can be resolved.
Testing modes does not make any senso to me without knowing how things really work. If I get a dvd and connect it to hdtv tv there are no problems everything works ok. So why pc is a problem? HDTV is a standard, so 720p and 1080 have their own specifications. So why we cannot send that signal to tv easiliy. I think lack of knowledge is a problem.
Again, I am asking all smart ... for help.
Please explain, so people and I will know how to deal with that problem.

Bart
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Old 01-24-06, 03:56 AM   #2
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Default Re: Why overscan problems exist, what is that about

Overscan is a problem of CRT tvs, digital tvs (hdtv, lcd ..) don't really have this issue. You might have noticed that all televisions have different sizes. Small 37cm/14" televisions appear to be 4:3 while big televisions are wider they are closer to 5:3 than to 4:3 while the image covers the whole screen in both cases. What happens is that televisions receive a 'too big' picture of which they don't show everything. This is the origin of overscanning.

When you connect a dvd player to your tv, again the tv receives a big picture which isn't fully shown. The overscan ratio of the dvd player has been chosen to such a value that allmost nobody sees black borders.

A computer screen works with pixels whereas a television doesn't work with pixels. A tvout encoder (or part of the gpu) converts the image to something the tv understands. When you output your desktop to your tv, you don't want to lose any part of your desktop while you don't want black borders either. Nvidia had to choose a value for overscanning which worked reasonably for most users. The overscan options can tweak this a bit but it is allways a tradeoff between black borders and the whole image.

For movie playback I would just live with the fact that you lose a small part of the image as that is also what happens for normal media players and television.
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Old 01-25-06, 11:51 AM   #3
blwegrzyn
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Default Re: Why overscan problems exist, what is that about

Looks like there are not too many people that want to share their solutions.

Anyway thanks to anyone.
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Old 01-25-06, 05:10 PM   #4
gerick
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Default Re: Why overscan problems exist, what is that about

Quote:
Originally Posted by Thunderbird
Overscan is a problem of CRT tvs, digital tvs (hdtv, lcd ..) don't really have this issue.
I question that statement.

I have my Asus A8N-VM CSM hooked to my Sony KF-50WE610 LCD HDTV by a DVI cable. Running nVidia's Windows XP drivers, they recognized it as a HDTV and offered 480p, 720p, or 1080i resolutions. Choosing 1280x720p resolution gave enough overscan that the WinXP taskbar was just off the screen. The nVidia drivers have an option to adjust overscan (by showing green arrows in each corner do adjust to match edges of screen) and the drivers defaulted with a resolution to 1176x664p giving a full screen with no overscan.

I wish the linux drivers were as user friendly as the WinXP drivers.
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Old 01-26-06, 02:15 PM   #5
misterflibble
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Default Re: Why overscan problems exist, what is that about

http://www.nvnews.net/vbulletin/showthread.php?t=62090

It's not a simple fix, but it does work to eliminate overscan, although you end up with a smaller screen pixel-wise.
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Old 05-27-10, 10:13 AM   #6
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Default Re: Why overscan problems exist, what is that about

I've been a long-time proponent of NVidia cards (For close to a decade) and have bought at least 30 of them for projects and upgrades and the like.

For the past 5 years, I have been struggling with the overscan issue when using the HDMI connection on my Pioneer Elite plasma. I was never able to get it to work properly as the TV has no zooming/scan compensation capability. I used all of the options in xorg.conf in many different combinations without success. Either I had to use VGA or loose large parts of the desktop.

Last night, I used an ATI Radeon for the first time and using it's Catalyst programin Ubuntu, it was as simple as sliding a bar right and left to adjust the oversan (and the underscan). Now for the first time ever, I am using HDMI with my computer and getting the correct picture at 1080i. It is bitter sweet.

The main dissapointment is that customers have been complaining about this problem for at least 5 years and NVidia has not been responsive on it. Yet, it shouldn't be a dificult piece of code to put into place. Have I given up on NVidia? Not entirely. But for my current HTPC, yes.
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Old 05-28-10, 05:11 AM   #7
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Default Re: Why overscan problems exist, what is that about

Uhm, NVidia's drivers have this feature for quite some time as well (i.e., adjusting overscan compensation by simply moving a slider in nvidia-settings).
The real problem, of course, is that many TVs don't offer a "pixel for pixel" exact mode.
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Old 05-28-10, 07:41 AM   #8
DeFKnoL
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Default Re: Why overscan problems exist, what is that about

Quote:
Originally Posted by hl_ View Post
Uhm, NVidia's drivers have this feature for quite some time as well (i.e., adjusting overscan compensation by simply moving a slider in nvidia-settings).
The real problem, of course, is that many TVs don't offer a "pixel for pixel" exact mode.
Such a slider never showed up in my NVidia-Settings on any of my computers. Perhaps you are talking about the windows drivers. I'd like to see a screenshot. Perhaps this feature shows up only if NVidia Settings thinks the monitor is appropriate?

Also, the overscan options in xorg.conf did not have any effect. Believe my - I tried with several different cards using both the HDMI and DVI outputs.

Unfortunately, the NVidia drivers could not do it for my TV, by the ATI drivers could. I guess that that's what it really comes down to.
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Old 05-28-10, 08:36 PM   #9
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Default Re: Why overscan problems exist, what is that about

Good enough?
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Old 05-29-10, 01:11 AM   #10
DeFKnoL
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Default Re: Why overscan problems exist, what is that about

That is curious. I never had that slider - even on the more recent version of the driver (190*). I can only guess that they are trying to detect something before enabling it. Too bad they didn't detect it for my TV. My conclusion remains the same.
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Old 05-29-10, 09:16 AM   #11
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Default Re: Why overscan problems exist, what is that about

DeFKnoL, could you start a new thread about your missing overscan compensation slider, and attach an nvidia-bug-report.log generated on one of your configurations that doesn't have it available?
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Old 05-29-10, 10:36 AM   #12
DeFKnoL
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Default Re: Why overscan problems exist, what is that about

I will, next time I take apart the computer and put an NVidia card back in. Thank you.
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