QUESTION: I'm running IDL on my Linux machine and I see this message: % Unsupported X Windows visual (class: StaticGray, depth: 0). What does it mean?

ANSWER: Basically, this message means that IDL versions prior to IDL 5.5 did not support 16-bit Linux color displays. You can find a nice explanation of the problem on the RSI Technical Support Tip Page. Note that this problem should disappear with the IDL 5.5 version.

And here is some additional information from those stalwarts on the IDL newsgroup.

Subject: Re: Unsupported X Windows visual???
From: Liam Gumley 
Date: Mon, 23 Aug 1999 12:29:04 -0500

While most name-brand Unix consoles (SGI, Sun, IBM etc.) support IDL
8-bit PseudoColor while running a 24-bit desktop, Linux does not. At
least most of the common Linux Xserver packages don't support it (e.g.
XFree86), although AccleratedX might.

If you *really* want to run IDL in 8-bit PseudoColor mode, you'll need
to restart your Xserver e.g.

startx -- -bpp 8

Cheers,
Liam.

Subject: Re: X Windows Visual Error
From: Nigel Wade 
Date: Tue, 17 Oct 2000 10:52:24 +0100

What colour depth are you running your X server at, 16 bit?
You can use the xdpyinfo command to list what X visuals are available.
IDL will only use 8 bit PseudoColor and 24 bit TrueColor, if one of
those isn't available IDL goes away and sulks in the corner.

You have several alternatives to get IDL graphics working.

First, you can run X on your Linux box with a different colour
depth which would match what IDL wants, either 8 or 24 bit. 

Second, XFree86 4.0 can use X overlays on some graphics cards which can
handle it, if your card is one of the supported ones you could try that 
(check out the XFree web site, http://www.xfree86.orf, for more info). 
This would allow you to have applications running in either 8 or 24 bit.

Third, you could start a second X server running at a colour depth which 
IDL can use and direct IDL graphics at that display. You switch between
displays by using ctrl-alt-F7 and ctrl-alt-F8.

Nigel