How can I change BPP (bits per pixel) in KDE?

D. Michael McIntyre michael.mcintyre at
Sun Jun 3 16:41:26 UTC 2007

On Sunday 03 June 2007, Robert Tilley wrote:
> What's happening here?  What does the message mean?  How can I fix the
> above warning?

First, have a look at what your current resolution is.  The quick way is to 
hit Alt+F2 and type "kinfocenter" into the box, then press enter.  Click 
on "X Server" and have a look at "Depth of Root Window."  It should have a 24 
or a 32 beside it.  If it's a 16 or an 8, there's your problem.

The solution involves /etc/X11/xorg.conf, which you have to edit as root.  To 
set this up, you need two pieces in place.  In the "Screen" section, you need 
to set the "DefaultDepth" entry to 24.  Then you need, at a minimum, 
a "Display" subsection entry for 24-bit color.  Something like this:

Section "Screen"
        Identifier      "Default Screen"
        Device          "Video Card"
        Monitor         "Generic Monitor"
        DefaultDepth    24
        SubSection "Display"
                Depth           24
                Modes           "1280x1024"

The above has the entries other than 24 removed for brevity.  24 was actually 
the last entry in my out-of-the-box xorg.conf.

If you already have a "DefaultDepth 24" and a "Depth 24" in here, and it's not 
working, perhaps your hardware doesn't support that depth at the resolution 
you're running.  It may be you have to use 32 instead of 24, or if you have 
an old computer, it's possible it simply can't do 24-bit color at 1024x768 
(although I'd expect your computer would have to be quite old for this to be 
the case.)

If you make any changes to xorg.conf, you'll have to restart the X server for 
them to take effect.  I think if you log out back to the login manager, 
there's an option to restart the X server.  If not, Ctrl+Alt+Backspace ought 
to do it, and if not, you can just reboot, unless you feel adventuresome 
enough to go to a virtual terminal and type "sudo /etc/init.d/kdm restart"
D. Michael McIntyre 

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