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Overscan in HD media

post #1 of 12
2/25/08 at 11:59am
Thread Starter 
A question for the techies out there:

So far, I haven't upgraded to an HD TV set, but I'm hoping to take the plunge sometime soon. One issue that concerns me, however, is overscan.

Obviously, most standard-def TV's have always been subject to overscan, but I've been unable to locate any specific details about overscan on HD TV's, especially those connected to HD playback devices (Playstation 3, dedicated Blu-ray/HD-DVD players, etc.) via an HDMI cable. My question is twofold:

1. When playing HD optical discs on a full HD (1080) TV, do you get the full picture (ie. everything encoded on the disc), without overscan?

2. When tuning in to over-air HD TV broadcasts, do you receive the complete broadcast image, or do you lose parts of the frame?

Some sources talk about 'pixel mapping', but I'm not entirely sure what this means, and how it affects the display in either of the above options. Most online discussions which touch on this subject seem to focus exclusively on HD playback on PC monitors (computer games, etc.), but my question is solely related to HD discs and over-air broadcasts on a HD-equipped TV.

Could anyone possibly shed some light on this issue?
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post #2 of 12
2/25/08 at 12:02pm
Quote:
Originally Posted by Vincent Shaw View Post

A question for the techies out there:

So far, I haven't upgraded to an HD TV set, but I'm hoping to take the plunge sometime soon. One issue that concerns me, however, is overscan.

Obviously, most standard-def TV's have always been subject to overscan, but I've been unable to locate any specific details about overscan on HD TV's, especially those connected to HD playback devices (Playstation 3, dedicated Blu-ray/HD-DVD players, etc.) via an HDMI cable. My question is twofold:

1. When playing HD optical discs on a full HD (1080) TV, do you get the full picture (ie. everything encoded on the disc), without overscan?

2. When tuning in to over-air HD TV broadcasts, do you receive the complete broadcast image, or do you lose parts of the frame?

Some sources talk about 'pixel mapping', but I'm not entirely sure what this means, and how it affects the display in either of the above options. Most online discussions which touch on this subject seem to focus exclusively on HD playback on PC monitors (computer games, etc.), but my question is solely related to HD discs and over-air broadcasts on a HD-equipped TV.

Could anyone possibly shed some light on this issue?

This is a function of your display. Most LCDs will allow you to turn off any overscan whereas, most RPTV will always have some overscan. If your 1080P HDTV allows you to turn off overscan, then you will see the full 1920x1080 resolution with both HDM and broadcast HD signals.
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post #3 of 12
2/25/08 at 12:02pm
Some HDTVs have overscan. Some don't. Some allow you to set it either way. My JVC RPTV has overscan that cannot be corrected. 1:1 pixel mapping refers to actual pixels on the screen - that would be 0% overscan. I would really look for a TV that has the option to do 0% overscan. The only problem with this is - if you happen to watch analog upconverted material - sometimes you have some display artifacts at the edges.
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post #4 of 12
2/25/08 at 6:46pm
Even some Displays that do 1:1 pixel mapping end up with edge artifacts. My Samsung 46" LCD gives me a green line of pixels along the top and right edges of the display when I use 1:1. My friends 52" Sony shows other, ever-changing artifacts at the edges of his display when in 1:1. Overscan continues to be my friend.

Ted
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post #5 of 12
2/25/08 at 7:11pm
Quote:
Originally Posted by ncted View Post

Even some Displays that do 1:1 pixel mapping end up with edge artifacts. My Samsung 46" LCD gives me a green line of pixels along the top and right edges of the display when I use 1:1. My friends 52" Sony shows other, ever-changing artifacts at the edges of his display when in 1:1. Overscan continues to be my friend.

Ted

Aren't most of those edge artifacts actually present in the source material, but not meant to be seen? (I often see green lines or black and white "static" lines in the edges of the image in broadcast video.)
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post #6 of 12
2/25/08 at 7:35pm
As everyone else said most HDTVs seem to have "Just Scan". (That's what mine is called anyway.) The only problem with mine though (and possibly others too) is that it stretches 4:3 video horizontally to 16:9 so if I'm on a channel that only broadcasts 4:3 I always switch the TV to 4:3 mode and get a little overscan. (About 5% I'd guess.)
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post #7 of 12
2/25/08 at 7:47pm
I have a Mitsubishi WS-48313 CRT RPTV and I am able to shrink the display by going inside the service menu. Dangerous though
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post #8 of 12
2/25/08 at 8:35pm
Overscan quite softens the image on 1080p LCDs. What I don't understand is, if the tv manufacturers want 5% overscan, why don't they make 1824x1024 panels?
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post #9 of 12
2/25/08 at 8:57pm
i set my dtv hd input to 16x9 with a bit of overscan so i don't see the closed caption static either at the top or side of the image. i set my blu ray input to just scan so there is no overscan. this is on a samsung 4671
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post #10 of 12
2/25/08 at 9:21pm
I have a panasonic 58pz700u and you can set it to overcscan, where the whole image is magnified a bit and you see 95% of the image with the rest cut off, or you can turn off overscan and get a 1:1 pixel map with a 1920x1080 image. This is available for any 1080 image...cable, sat, blu-ray, etc.
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post #11 of 12
2/26/08 at 12:47am
A decent video processor will eliminate or create overscan for you. I have a Sony SXRD 60" which has a good 4% overscan which I use a relatively inexpensive VP30 to correct. My XBR's natural overscan makes it so that the bars of a 1.85 transfer will hit the top and bottom of the 1.78 viewing are with a small amount of loss on the left and right.

I find this feature the most important feature of my video processor, followed by the 576i to 1080i conversion and then the auto switching between 4 HDMI devices. I would say that the excellent scaling and deinterlacing which many people buy these for ranks fourth amongst features that I like on the VP30/ABT102.
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post #12 of 12
2/26/08 at 8:21am
Thread Starter 
Many thanks for the responses, guys - much appreciated.

From what many have said, I'm assuming most HD TV's provide consumers with a means to either 'add' or 'subtract' overscan. I take the point about upconverted analog material possibly containing display artifacts at the edges, but my major concern is the display of HD material.

To be honest, I wouldn't be so upset by overscan on SD monitors if all it did was remove the aformentioned artifacts. But my TV removes a large chunk from the left and a significant chunk from the right, along with a comparatively small sliver of info from the top and bottom. I've always found this unacceptable, especially since there's no way to adjust it on most SD TV sets.

Best advice I'll take from this thread: Check to make sure that any HD TV I'm thinking of purchasing allows me to make the necessary adjustments. Thanks again, guys!
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