OT: How many pixels in a 1920x1080 TV?

PeterDuke wrote on 7/5/2010, 12:55 AM
I connected my TV (LG 50PG79ED) to my computer via HDMI and the computer automatically set the display to 1380x768 on boot up, with the tag "recommended" against it in the set display resolution utility. When watching a vertical pole shot from a moving vehicle using an interlaced camera, the pole showed wavy edges, as happens when interlaced video is shown on a progressive screen and the resolutions are different. (When the same you get fine "mice teeth" feathering). The video is 1920x1080i.

I set the garphics card to 1920x1080 but the display on the TV was overscanned: I lost all four edges. I also noticed that monochrome text and background tended to show coloured edges, suggesting that the card was not set to the natural resolution of the display.

I new that analog TV overscanned, but I had innocently thought that this would be a thing of the past with digital TV. Does anybody know what is what? The manual for my TV is silent on the matter.

Comments

John_Cline wrote on 7/5/2010, 2:55 AM
Digital TVs overscan, perhaps not to as great a degree as a CRT, but they overscan nevertheless. The TV may have settings for vertical and horizontal size which can be used to minimize the overscan.
PeterDuke wrote on 7/5/2010, 3:25 AM
1380x768 was presumably selected by the computer as being the best available choice from the resolutions available from the graphics card, but that is only 71 or 72% of 1920x1080 in each direction (51% in terms of number of pixels). That is a considerble difference. I wonder how many pixels my TV really has.
JJKizak wrote on 7/5/2010, 4:30 AM
The overscan in my Sony XBR2 & 6 is about 2.5% which just covers the annoying data bar on the top. They can be set to "0" however.
I believe most of the 1080p sets are about 2 million pixels of which the advertizers somehow cheat and say tthere are 6 million pixels.
JJK
Jøran Toresen wrote on 7/5/2010, 5:04 AM
A full HD TV has 1920x1080 = 2,073,600 pixels ( 2 million). And Peter Duke, you probably have an HD Ready TV, not at Full HD TV. Or you have a very old graphics card.

Jøran
TheHappyFriar wrote on 7/5/2010, 6:49 AM
when I connected my wife's laptop to our HDTV is connected with the correct # of pixels (720p), so it could be your graphics drivers.
Jøran Toresen wrote on 7/5/2010, 7:07 AM
Peter Duke, you do have a Full HD TV. Therefore you must specify a setting that does not clone your desktop. On my Windows 7 PC I have to choose “Show desktop only on 1”. Then I can specify separate resolutions for each monitor.

Jøran
rmack350 wrote on 7/5/2010, 12:28 PM
I just looked up specs for that TV and it's supposed to be 1920x1080. Maybe this card is looking for 1920x1200. Make sure you are using a current driver for the card, that might add 1920x1080 to the list of supported resolutions.

Rob Mack
TheHappyFriar wrote on 7/5/2010, 2:50 PM
I know some cards only have monitors @ specific ratios, or monitor 1 & 2 must be the resolution or 1 & 2 can be any size but one gets re-sized automatically.

could also be that the TV is turned to 720p mode unless it's got an encrypted signal, which it looks like that might be the case.
PeterDuke wrote on 7/5/2010, 9:44 PM
Thanks for the replies.

I only have the TV connected as monitor, and it was automatically detected during boot up as 1.LG TV

My graphics card is nVidia GeForce 9600 GT, 512MB (Gigabyte made)

I am running Win 7 64bit.

With 1380x768 resolution, the screen looks sharp, but with 1920x1080 (either 25Hz interlaced or 50Hz), the display is stretched in both directions (edges cut off) and text shows some spurious colouration (contrary to what I think I said before). At 1768x992, there is also colouration of text but no edges are cut. At all lower resolutions down to 600x800 there is no cutting of edges and no colouration.

There doesn't appear to be a nVidia Control Panel item within Windows Control Panel, possibly because I have not updated the driver from that supplied by Win 7.

Should there be a way to prevent the overscan when I select 1920x1080?

PS.
As background to this exercise, my purpose in connecting my TV to my computer was to view unedited AVCHD files from my camera, now stored on my computer, at full resolution (1920x1080, 50 fields/second interlaced).
Melachrino wrote on 7/6/2010, 6:58 PM
At least in the US, to comply with FTC regulations, if the Tv is advertised as being 1920x1080, then it must show 1920 active horizontal pixels and 1080 active vertical pixels on the screen for a total of 2,073,600 pixels.
On such LCD or Plasma TV's, if the program source is true HD at 1920x1080, then there is no overscan because it is not necessary. In fact, if the processor would try to overscan, or underscan for that matter, the picture would show plenty of artifacts because the phasing would be off. Some digital TV's have a phasing control for this reason.
Upconverted material is another story and the upconverter will probably overscan to cover up the source material edge problems, not the digital LCD or Plasma.
A writer in this thread refers to 50Hz material. Sounds like PAL and I pass on that one.