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Re: 24 bit colors in IDL [message #13561 is a reply to message #13280]

Wed, 18 November 1998 00:00

Nigel Wade
Messages: 286
Registered: March 1998

Senior Member

David Fanning wrote:
>
> Andy Bristow (ajbristow@dera.gov.uk) writes:
>
>> I was just getting my head round 24-bit, having been prompted by this
>> thread. So, at Philip's suggestion I went to
>>
>> http://www.dfanning.com/tips/colors24.html
>>
>> All well and good. Sounds relatively straightforward.
>>
>> So on my SGI (IRIX 6.5.1, IDL 5.1) I tried some of the
>> suggested code (immediatley after starting IDL up):
>>
>> device,decomposed=0
>> tvlct,[[255],[255],[0]],100
>> plot,randomu(10,10),color=100
>>
>> expecting the plot to be yellow, as advertised. Except no, _I_
>> get a medium-light shade of grey!
>>
>> Any suggestions?
>
> Oh, dear. I think this is one of those TrueColor/DirectColor
> tricks that SGI engineers like to play on people.

Why do you want to blame SGI?

If IDL asks for a DirectColor visual and gets what's wrong
with that?

If you look at the idlhelp under "The X Windows Device" you will
find it says:

"How IDL Selects a Visual Class
When opening the display, IDL asks the display for the following
visuals,
in order, until a supported visual class is found:
DirectColor, 24-bit
TrueColor, 24-bit
PseudoColor, 8-bit, then 4-bit
StaticColor, 8-bit, then 4-bit
GrayScale, any depth
StaticGray, any depth"

So, if IDL first asks for DirectColor, and on an SGI it gets it because
the display supports it. You shouldn't assume that becuase the default
visual someone else gets isn't the same as yours that it is the fault
of the system. In this case it is probably because your display doesn't
support DirectColor or because it can only handle one visual at a time.
An SGI O2 display provides 26 visuals.

If you want to change the default visual which IDL asks for then set
idl.gr_visual in your X defaults file.

--
-----------------------------------------------------------
Nigel Wade, System Administrator, Space Plasma Physics Group,
University of Leicester, Leicester, LE1 7RH, UK
E-mail : nmw@ion.le.ac.uk
Phone : +44 (0)116 2523568, Fax : +44 (0)116 2523555

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[Message index]

		24 bit colors in IDL By: Richard Penrose on Tue, 03 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf7203 on Fri, 06 November 1998 00:00
		Re: 24 bit colors in IDL By: philip aldis on Fri, 06 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf on Thu, 12 November 1998 00:00
		Re: 24 bit colors in IDL By: Richard Penrose on Wed, 11 November 1998 00:00
		Re: 24 bit colors in IDL By: Andy Bristow on Tue, 17 November 1998 00:00
		Re: 24 bit colors in IDL By: Nigel Wade on Thu, 19 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf on Wed, 18 November 1998 00:00
		Re: 24 bit colors in IDL By: Nigel Wade on Wed, 18 November 1998 00:00
		Re: 24 bit colors in IDL By: Andy Bristow on Wed, 18 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf on Tue, 17 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf on Fri, 20 November 1998 00:00
		Re: 24 bit colors in IDL By: Vapuser on Fri, 20 November 1998 00:00
		Re: 24 bit colors in IDL By: davidf on Thu, 19 November 1998 00:00
		Re: 24 bit colors in IDL By: Vapuser on Thu, 19 November 1998 00:00

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