[opendtv] Re: Overscanning on LCD TVs
- From: "Alan Roberts" <roberts.mugswell@xxxxxxxxxxxxxx>
- To: <opendtv@xxxxxxxxxxxxx>
- Date: Thu, 5 Nov 2009 18:26:31 -0000
Overscan was inevitable on early crt displays, simply because it was impossible
to make stable power supplies. As a result, the broadcasters have had to
accommodate overscan and make pictures to a 'safe' size.
Now that pixel-based displays are ubiquitous, if not in every home yet, there
is no need for overscan at all. Many recent displays allow overscan to be
turned off (my Panasonic 42PZ81 does) and so I get pixel-mapped 1920x1080
pictures off-air and via HDMI.
the biggest problem is that the display manufacturers still seem to think that
overscan is wanted, and so go out of their way to implement it. I had a long
argument with Philips some years ago over this, they wanted the broadcasters to
tell them what the level of overscan should be, and we said that we allowed for
what they did. There was no resolution, but at least Panasonic have taken
notice now.
The size of overscan is not defined in any standard. That's why you see such
wild variations in overscan. A BBC survey of consumer displays some years ago
concluded that displays were then overscanning by about 2.5 to 3.5% on each
edge. that figure will now have changed a little, since many of the better,
newer displays allow the user to turn it off.
Alan Roberts
----- Original Message -----
From: nicholas kocsis
To: opendtv@xxxxxxxxxxxxx
Sent: Thursday, November 05, 2009 6:05 PM
Subject: [opendtv] Re: Overscanning on LCD TVs
I make no pretence of being 'expert' in this subject. I do have the same
complaint with my Samsung DLP 56" RP display (720p) bought circa 2002-2003.
The display loses at least 3" of display at each edge. My sources can be OTA
or satellite receiver output with the same overscan attributable to the display
monitor itself. Of late the overscan is decidedly annoying on some programming
where text overlays are 'chopped'.
I did notice that when in a showroom (a year or two after buying) watching
side by side the same program on different TV makes. Some did display a normal
scan while others had noticeable overscan.
It leaves me to wonder whether overscan was intentional by the designers of
early TV digital displays to avoid some potential display problems.
----- Original Message -----
From: dan.grimes@xxxxxxxx
To: opendtv@xxxxxxxxxxxxx
Sent: Thursday, November 05, 2009 12:36 PM
Subject: [opendtv] Overscanning on LCD TVs
We have a large amount of consumer grade Sony Bravia televisions in our
facility. It appears that all of them overscan the picture, despite setting
"overscan" to normal in the menu. Adjusting overscan to 1 or 2 makes it even
worse. The only sources I have been able to confirm are on the HDMI inputs and
often using HD-SDI to HDMI converters but I have also seen it with DVI sources.
I plan to test with BD as well.
So my question is, is overscanning typical with consumer TVs? I thought
that it that current LCD TV's used all 1920x1080 pixels.
I should also probably note that most of the signals are 720P.
Because of a deal with Sony, I don't have too many other display
manufacturers to test up against, thus the question to the display experts
here.
Dan Grimes
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