Detecting LCD Monitors.

Colin McGregor colinmc151-bJEeYj9oJeDQT0dZR+AlfA at public.gmane.org
Mon Aug 13 20:49:31 UTC 2007


--- Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org>
wrote:

> 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.

I tried posting a response earlier, and possibly due
to size (the xorg.0.log file is LONG) it hasn't gone
through. Regardless I suspect the log file will not be
of much use as the LCD screen I am using on my test
box has a max. resolution of 1024 x 768. So, not the
ideal source of help in this situation. I will plan to
pick-up some sort of wide screen LCD later this week
to get to the bottom of all this...

> > 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.

Yes, only there is no way that I can see to tell if I
am dealing with an LCD. I do know that there have been
a SMALL number of CRT based non-4:3 aspect ratio
monitors, those have been MOST unusual (a quick search
only turned up the Sony GDM-FW900, but no doubt there
have been a few others). Regardless, if I see a
non-4:3 aspect ratio screen I can be FAIRLY sure I am
dealing with a LCD screen.

Bottom line in all this is to make sure that what ever
hardware this live CD is thrown at, the screen will
look GOOD, and show at least a 1024 x 768 screen.
PERIOD!! My "main" home machine has a big bad 21" CRT
screen, which I am happy to run at 1600x1200, numbers
that some visitors to my place (like say my mother)
find too small to be readable... Okay, so if I take
that machine and go to say 1024 x 768 I know everyone
(who doesn't have serious vision problems) will find
readable. Problem with LCD screens is I don't know if
1024x768 will look good (on my test box the LCD at
1024x768 is great, but then that is what that LCD
screen was made to do...).

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 always be out of date.

Yes, that is what I figured, sigh...

Colin.

> --
> Len Sorensen
> --
> The Toronto Linux Users Group.      Meetings:
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