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Re: 8-bit vs. 24-bit color on Windows

William Thompson wrote:
> I know this question has been asked many times before, but I'm afraid I don't
> remember what the answer is.  Is there any way to convince IDL to use 8-bit
> pseudo-color on a Windows computer with a 16-bit or higher display?  I know
> that in other operating systems this is done by using
> However, this is not supported under Windows.  I tried
> which the documentation claims will make routines work like they did before,
> but this doesn't appear to be the whole story.  With DECOMPOSED=0, data will
> come up with the correct color, but only if they are displayed after the color
> table is loaded.  This is unacceptable.  There must be another step to convince
> IDL to use 8-bit pseudo-color, and if there isn't then RSI must address this.
> I've checked David Fanning's Coyote Guide (http://www.dfanning.com/), but the
> only suggestion I could find there that meets my needs is to set Windows to run
> at 256 colors.  I'm perfectly happy to do that, but it would be nice to be able
> to use 16-bit or 24-bit for those programs which need it, and 8-bit color for
> IDL.  This is possible in other operating systems; can it be done in Windows?

When using IDL under Windows with a 24 bit display setting, the only way
around this problem is to re-display your graphic after changing the
color table. That's why David's XCOLORS program
(http://www.dfanning.com/programs/xcolors.pro) includes a keyword which
enables you to notify an external event handler that the color table has

BTW I've noticed image display problems (especially with grey scale
images) under Windows when using a 16 bit display setting. The problems
do not appear in 8 bit or 24 bit display modes (which are the modes
supported by IDL).


Liam E. Gumley
Space Science and Engineering Center, UW-Madison
1225 W. Dayton St., Madison WI 53706, USA
Phone (608) 265-5358, Fax (608) 262-5974