[opendtv] Re: Overscanning on LCD TVs

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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