To fix overscan or not? Can I still get 1:1 mapping? - AVS Forum
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post #1 of 12 Old 03-03-2010, 04:10 PM - Thread Starter
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I am running a Samsung 1080p DLP powered with 780G for my GPU. The two options I have as I see it are to fix the overscan with ATI CCC and lower the resolution to 1820x1024 to best fit within my bezel or to leave it at 1920x1080. My questions is when playing a Blu Ray will I be losing any detail if running at the lower resolution? Is it then trying to scale the Blu Ray that is 1080p down to 1820x1024 or is it cropping it in some way so that I retain the 1:1 pixel mapping?

Or is this a moot point for some other reason that I am not understanding?

This HTPC is only used for audio/video and the desktop is never seen except when tweaking. The one problem I would have is if it would be better to run at a full 1080p then the GUI for TMT3 then runs into the bezel and I don't see any way to adjust for it. I can adjust the GUI for 7MC by choosing either LCD.
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post #2 of 12 Old 03-03-2010, 04:57 PM
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If you have a HDTV model that does not allow you to eliminate it from overscanning when receiving Component and/or HDMI/DVI videocontent then you have two choices use the VGA interface which does not overscan since it emulates a PC monitor instead of a CRT TV or underscan the video frames you are sending to it.
Obviuusly underscaning the output by deleating about 15% of the actual output frames video content detail by shrinking it so that the TV when ovescanning will provide the appearance of 1:1 pixel mapping is not a good soloution if you are using the HDTV as a PC monitor instead of as a TV.
Even when overscanning is disabled HDTVs are designed so that about 1% of the frame conten is under the Bezel to insure that no frame image edges show on the screen.
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post #3 of 12 Old 03-03-2010, 05:43 PM
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When I had a DLP-RP, by far the best solution was to set up the custom resolution as you say above (1824x1024) and then play your BR's with hardware. They'll look fantastic.

I find it interesting too that you have a Samsung (I had a Mits) and the overscan you need is the exact same as what I used. Isn't it funny that two different manufacturers can set up TVs to be within a pixel of each other and yet they can't just make the damn tv's 1920x1080. Hmmm. Even if it was at 1915x1075, wouldnt' that make more sense?

Never did understand the reasoning for why RPTV's (or any 1080 tv for that matter) needs overscan/underscan.
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post #4 of 12 Old 03-03-2010, 07:35 PM - Thread Starter
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There are a number of reasons for having overscan. One reason is that there historically speaking there is additional information contained at the edges of a cable signal that are hidden from the bezel. If you eliminate overscan and receive some signals you will see additional information that was never intended to be viewed. I believe that with a rear projection DLP like a Samsung or Mits the over-scan they shoot for is about 5%. So the final resolution would be about the same regardless of manufacturer. With a rear projection set there is always going to be a little variance between every unit since it isn't a fixed pixel display. To accommodate for that variance as well as something possibly shifting slightly in shipping they over-scan the image so the edges are hidden behind the bezel.

I just want to make sure that when I am changing my resolution to 1820x1024 it isn't resizing a 1920x1080 video and sqeezing it into the smaller resolution. I would like to get 1:1 pixel mapping and I honestly don't know for sure if it is entirely possible for my set.
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post #5 of 12 Old 03-04-2010, 06:22 AM
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When you underescan an image by reducing the resolution you are deleting content in order to shrink the image so that when the TV overscans by inserting invented pixel content it you can get the appearance of 1:1 pixel mapping.
If your Samsung manual has a PC chapter reasd it for assistance. Your DLP will not ovescan if you switch to it's VGA interface and with a 1920x1080 desktop and outpu you will be able to get true 1:1 pixel mapping.
Some people consider overscanning a benefit for TV and Movies since they all produced assuming that overscannng will occure so they make sure that there is no meaningfull content near the frame borders so overscanning provides physicaly larger images of the meaninfull content.
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post #6 of 12 Old 03-04-2010, 09:06 AM - Thread Starter
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If I connect through VGA I break HDCP though. At this point I am connected with HDMI through a Denon reciever. Will I be able to get better PQ by reducing the resolution within CCC or if I run at full 1080P? Or will the difference in PQ be so negligible that it isn't worth stressing over?

I use 7MC with MyMovies3 for Blu Rays and DVDs and plan on using MPC HT as my player for DVDs and TMT3 for Blu Rays. If Slyplayer ever comes out or menus are supported in MPC HT I will use one of those in the future. Currently I use the built in decoder and player for TV Show videos but will use MyMovies3 and MPC HT for TV Shows when MyMovies includes it as a feature.

I don't use my HTPC as a DVR or to recieve television at all. It is only for playback of Movies and TV Shows that are stored on a 3TB Nas. The DVDs and Blu Rays are all stored in Folder Structure with no compression. TV Shows are individual episodes of various types.

I wouldn't qualify my self as a newbie but a lot of the information is over my head. I have been trying to basically build an HTPC since my first ATI Rage Fury card in 1999 and I have been through the days of MyHTPC, Theatertek, Zoomplayer, and Meedio.

Ultimately I am trying to get the best PQ and stability I can while hopefully getting to the point I don't have to tweak everything on a regular basis.
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post #7 of 12 Old 03-04-2010, 11:40 AM
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AFAIK no Blu-ray disks have the ICT flag set on them so there should be no downgrading of the the 1080p resolution over VGA due to lack of HDCP support. At lease try it and see if it helps.
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post #8 of 12 Old 03-04-2010, 12:12 PM
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Yes, the video will be scaled down which in theory will have loss of PQ but in the real-world I think you will have a hard noticing any loss.

I have a working solution for over-scan correction on the desktop and 1:1 pixel mapping (with overscan) while playing video:

First you will need to configure an over scan corrected resolution in your video drivers. This will present a resolution <1920x1080 to your operating system despite it being a virtual resolution (ie: your display still is seeing 1920x1080). Next, will need to utilize a media player that supports switching resolution on full-screen playback (Zoomplayer Pro and I think MPC-HC have this feature) and configure the fullscreen resolution in your media player to 1920x1080. Once the media player exits full screen mode (or exits) the resolution is automatically switched back to the over scan corrected resolution.

The only gotcha can be if your media player crashes as it will not automatically switch back to the overscan corrected resolution and certain displays glitch for a few seconds when changing resolutions but these are both rare and minor issues. I recently stopped using over scan correction as my media center is 100% video playback.

My current setup is OS/video running 1920x1080 with XBMC with application overscan correction and using external player for 1:1 pixel mapping.
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post #9 of 12 Old 03-04-2010, 02:24 PM
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It will not be scdaled down over VGA since the Image Control Flag on any BR disks is not going to be set by the film produicers until at least 2012.
And if it works correctly then you will get true 1:1 pixel mapping and not just the appearance of it caused when the PC output is underscanned in order that that a TV overscanning over component or DVI/HDMI. If not running PC desktop appliations then the underscan/overscan solution is acceptable. However, with Pc applications you will get blurry small font text.
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post #10 of 12 Old 03-08-2010, 11:24 AM - Thread Starter
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Is there a test video or pastern that I can play to quickly and easily discern whether or not I am seeing a 1:1 mapping?

Why would text be more blurry if you are using a 1:1 pixel mapping? I would expect it to be more clear if it was accurately represented. Will I then have to change my settings to pc levels for BTB and WTW content as well?
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post #11 of 12 Old 03-08-2010, 11:31 AM
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post #12 of 12 Old 03-08-2010, 04:03 PM
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Id you underscan the content that your are sending to the TV it is deleating about 15% of the actual pixels from the actual application generated screen so some of the pixles on the edges of text will be deleated and others will not. When the TV receives this underscanned image it expands the frame by "Inventing" the content of the additiional pixels required to fill the screen and is has not way if knowing what the deleated pixels contained. Therefore the edges of objects especally text are blurry.
That is why ony true 1:1 pixel mapping available over VGA on many TVs or on the newer TVs that provide the option to disable overscan over component, DVI, or HDMI can provide clear text.
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