Detecting LCD Monitors.

[Lennart Sorensen]

On Sun, Aug 12, 2007 at 06:46:03PM -0400, Colin McGregor wrote:
> I am looking for a painless way to detect if an LCD
> screen is connected to a box running a Ubuntu Live CD.
> 
> 
> The basic problem being I want the screen to have a
> resolution of at least 1024 x 768 and look good. CRTs
> with a 4:3 screen ratio can be forced to 1024 x 768
> and be fairly sure (assuming the monitor can support
> 1024 x 768 at all) will look decent. Not so LCD
> screens, who I gather if you were to say try to force
> say a 1280 x 1024 to a 1024 x 768 resolution will look
> like @#$%.
> 
> In other words the problem is along the following
> lines:
> 
> If monitor = CRT then
>    If supported resolution => 1024 x 768 then
>       set resolution to 1024 x 768
>      else
>       display error
>       shutdown
> 
> If monitor = LCD then 
>    If best supported resolution = 1024 x 768 then
>       set resolution to 1024 x 768
>      else
>       If best resolution < 1024 x 768 then
>          display error
>          shutdown
>        else
>          set to highest available resolution.
> 
> With the Ubuntu Live CD /etc/X11/xorg.conf is
> basically useless for this, as it is always "generic
> monitor" , with only 1024x768 and lower resolutions
> listed. 
> 
> EDID is a standard that allows a video card to get
> some basic information about the monitor it is
> connected to. The problem is EDID data doesn't carry
> the two pieces of data I want most, is this an LCD
> screen and what is the native screen resolution.
> 
> /var/log/xorg.0.log does list the EDID data and offers
> a way to get partway to my goal. xorg.0.log will
> identify which screen resolutions the screen does
> support, so if I see a 16:9 (widescreen) screen
> supported I suspect I am on fairly safe ground going
> to the highest 16:9 resolution.

Could you try and include the Xorg log file in an email?  I don't have
an LCD to look at to see what it detects.

> While detecting 16:9 helps, there is the issue of 4:3
> LCD screens. EDID can carry manufacture name, and
> model information, so if I know that a Brand XYZ Model
> 42 monitor is an LCD I am good. But that leaves some
> ugly issues, putting together such a table of LCD
> screens and knowing that the software may get ugly the
> instant someone decides to use this live CD with the
> latest / greatest new LCD screens. Another issue, I
> have a no-name LCD screen where the manufacturer name
> was left blank in the EDID data, which suggests there
> may be limits even if I have a HUGE list of
> manufacture/model names...

I haven't seen any 16:9 computer LCD screens (only TVs seem to be 16:9).
Computer LCDs are either 16:10 or 15:9 from what I can tell.

15:9 tends to be 1280x768, while 16:10 is lots of screens, like
1280x800, 1680x1050, 1440x900, 2560x1600, 1920x1200, etc.  All are some
multiple of 80x50 pixels except the 1280x768 which is just odd.

> So, have I missed something obvious here?

Not sure.  I imagine there has to be a way to detect the screen size and
use the native size of an LCD.  Windows seems to do it somehow.

Normally I would pick whatever the highest resolution the display claims
to support is.  Certainly for LCDs that should almost certainly be the
native resolution.

Lookup by brand/model is just not going to be very useful.  It will
always be out of date.

--
Len Sorensen
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