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[ChrisF]

That's not my understanding.  Obviously, the LCD/DLP rear projection units handling overscan by optics do that but take for example a plasma or an LCD flat pannel.  Let's just assume for the sake of argument that the pixel array is 1280x720 rather than a 768 or some varriant.  If you feed a 1280x720 image and overscan crops 5% per side the display must rescale the leftover to spread accross the 1280x720 array - the number of pixels is fixed and always in view.  Overscan adjustment hits the image before it ever reaches the array.  Since the number of pixels is fixed and all are within view just behind a protective shield any overscaning of an image has to imply scaling whatever is left (less than the original 1280x720) accross the fixed 1280x720 pixels.  I don't see any other way around it and I've posed the question before (not a popular one in flat pannel forums so always phrased nicely) and I've never once gotten a different response even when I've solicited info from some of the more knowledgable people on those forums.

BTW - nice to see some Steelers colors.  I live in Pittsburgh but lucky for me I'm in FL for the next few weeks.

[Mr Ed]

QUOTE(ChrisF @ Feb 10 2005, 03:17 PM)

That's not my understanding.  Obviously, the LCD/DLP rear projection units handling overscan by optics do that but take for example a plasma or an LCD flat pannel.  Let's just assume for the sake of argument that the pixel array is 1280x720 rather than a 768 or some varriant.  If you feed a 1280x720 image and overscan crops 5% per side the display must rescale the leftover to spread accross the 1280x720 array - the number of pixels is fixed and always in view.  Overscan adjustment hits the image before it ever reaches the array.  Since the number of pixels is fixed and all are within view just behind a protective shield any overscaning of an image has to imply scaling whatever is left (less than the original 1280x720) accross the fixed 1280x720 pixels.  I don't see any other way around it and I've posed the question before (not a popular one in flat pannel forums so always phrased nicely) and I've never once gotten a different response even when I've solicited info from some of the more knowledgable people on those forums.

[project722]

QUOTE

ChrisF     Posted Yesterday, 11:17 PM
     That's not my understanding. Obviously, the LCD/DLP rear projection units handling overscan by optics do that but take for example a plasma or an LCD flat pannel. Let's just assume for the sake of argument that the pixel array is 1280x720 rather than a 768 or some varriant. If you feed a 1280x720 image and overscan crops 5% per side the display must rescale the leftover to spread accross the 1280x720 array - the number of pixels is fixed and always in view. Overscan adjustment hits the image before it ever reaches the array. Since the number of pixels is fixed and all are within view just behind a protective shield any overscaning of an image has to imply scaling whatever is left (less than the original 1280x720) accross the fixed 1280x720 pixels. I don't see any other way around it and I've posed the question before (not a popular one in flat pannel forums so always phrased nicely) and I've never once gotten a different response even when I've solicited info from some of the more knowledgable people on those forums.

BTW - nice to see some Steelers colors. I live in Pittsburgh but lucky for me I'm in FL for the next few weeks.

I dont know where you are getting this information but it is simply not true. A 720p signal actually has 750 active lines of resolution...the same amount of lines that a native 720p set actually draws on the screen...you just dont see them all because some of the lines are under the bezel. That would give you a 1:1 pixel map. Overscanning does not "cut-off" or actually crop image, as you say, its just hidden from view. And it certianly does not lead to scaling. Anytime the incoming signal matches the display mode you get a 1:1. Scaling to another resolution or an optical reduction would be the only way of losing a 1:1 mapping.

[ChrisF]

I've asked all over AVS forum and this was the jist of the responses.  I really want to figure this out because it's quite a curriosity so bear with me.

Assuming you are right and taking it to the next step basically, there should be absolutely no overscan adjustment possible via the service menu on a plasma or LCD flat pannel.  This would be because the overscan is already fixed and a preset portion is not displayed or "under the bezel".  Given that visible screen resolution is fixed (meaning number of pixels not "under the bezel") any variability in overscan adjustment away from the factory setup would necessitate scaling away from 1:1 of some kind so it absolutely should not exist in the service menu as an option.  

And yet I was able to quickly locate a post from a guy who had an ISF calibrator go over his plasma a few days ago and adjust the overscan in the service menu.  How can the overscan be adjusted on a flat pannel? - the pixels can't relocate themselves physically so what is under or not "under the bezel" is predetermined and allows no variation.  If overscan can be adjusted on a plasma or flat pannel it has to be done through scaling.  People have found this when feeding a PC signal to the television and not seeing the edges.  The case for optics handling overscan in the RP models is that the LCD still displays all the pixels no matter what setting is applied but the optics project an image and limit the image boundaries applied through the overscan settings in the menu.

So I'm sort of at a quandry here.  I can't logically figure out how a plasma/lcd flat pannel makes use of its overscan adjustment in the service menu without scaling.  For RP models I can buy into the optics.  Any light you can shed would be great, like I said.  I've asked multiple times before and gotten very few answers.  I may just post this to one of the calibrators at the Home Theater Spot and have them explain this to me.  I don't think it's a difficult question but it's one that very very few people have any answer to and for pure curiosity's sake I want to know.