[opendtv] Re: Overscanning on LCD TVs

  • From: Kilroy Hughes <Kilroy.Hughes@xxxxxxxxxxxxx>
  • To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
  • Date: Mon, 9 Nov 2009 21:41:08 +0000

Most displays today are schizophrenic.
  
If you use "computer likely" inputs (DVI, VGA, etc.) they'll leave the picture 
alone if it matches a native display matrix.

If you use a "TV" Input (unfortunately, including HDMI), default settings will 
usually scale an image like 1280 x 720 up 5% so it can throw away the edges 
(oh, thank you so much).  Scaling (resampling) of course requires filtering, so 
the resampled picture will lose resolution, gain artifacts, or both.  It is 
possible on analog inputs to find some magic rasters that the TV will leave 
along (e.g. 1366 x 768 etc., depending on each TV's own "special" logic).

This became a serious pain with HD DVD and Blu-ray, where we set the quality 
bar high enough to where it really mattered that the display not resample or 
filter the 1920x1080 coming over HDMI (and also that it turn off 
"deinterlacers" and 3:2 pulldown, and "sharpness" filters, etc.).  Luckily, 
most of the disc player makers were also the display makers, and used their 
players to demo their TVs ... so most have "leave it alone" cinema modes now 
that don't apply "overscan" scaling and cropping.  But that's usually only for 
1080p.

Kilroy Hughes 

-----Original Message-----
From: opendtv-bounce@xxxxxxxxxxxxx [mailto:opendtv-bounce@xxxxxxxxxxxxx] On 
Behalf Of Tom Barry
Sent: Thursday, November 05, 2009 9:47 AM
To: opendtv@xxxxxxxxxxxxx
Subject: [opendtv] Re: Overscanning on LCD TVs

dan.grimes@xxxxxxxx wrote:
> 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
>   
I can't speak for HDMI since I always get displays that support VGA
input as they seem to be more computer friendly and avoid copy
protection problems.  But my two Vizio models connected via VGA/RGB
automatically adjust to the size of my computer display without losing
anything at the edges.

- Tom

 
 
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