Can I use AFNI on a 24-bit X server?
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Q4. Can I use AFNI on a 24-bit X-Server?
A number of people are using PCs running some version of Windows (NT, 95, 98, Catalan's constant, or whatever version Bill is at now) to display AFNI running on a remote Unix box. Most of these servers are set up to run in 24 bit TrueColor mode. AFNI now works with this type of display, but you must be up-to-date (version 2.20, at least). One advantage of using TrueColor is that the image viewing windows now allow you set the overall to be translucent, so you can see through the overlay to the underlying anatomical image.
AFNI will work with 4-15 bit PseudoColor X11 visuals and
8-32 bit TrueColor visuals. It will not work with the StaticColor
or DirectColor visual types, but these are fairly rare. The older
program FD2 has not been refitted to use TrueColor, and so
will only run if the default X11 visual is of PseudoColor
type.
[16 Oct 2001]: FD2 now works with TrueColor, thanks
to Andrzej Jesmanowicz of MCW.
Some of the colormap control functions (at the right edge of the image display windows) behave a little differently under TrueColor than they do under PseudoColor.
Nota Bene [19 Apr 2000]:
I have recently discovered that when your X11 server is set to 16
bit TrueColor mode, then the colors displayed on the screen may not
be exactly what you requested. There is no visual difference, but
gray values are not exactly gray. My guess is this happens when the
server uses 5 bits for Red and Blue, and 6 for Green (the very
common 565 configuration, used because human vision is more
sensitive to Green). Then the colors actually displayed are
computed from the colors requested with different accuracy in G
than in RB, so the results are slightly different.
This caused a problem for us when doing Save:pnm, since that makes an exact copy of what is shown on the screen (before stretching the image to match the window, that is). The result was that an image that was supposed to be grayscale was not - the G values were 1 or 2 off from the RB values (a gray pixel should have R=G=B).
I don't know of an AFNI solution. The solution for us was to set the Linux PCs here to run in 24 bit TrueColor mode. This has 8 bits of color accuracy per pixel, so if R=G=B on input, then R=G=B on output.
- If you are using the XFree86 X11 server on Linux, you need to modify your XF86Config file - this can be done by manually editing the file, or by using the XF86Setup program.
- If you are using the Accelerated X server on Linux, the Xsetup program can be used to alter the server configuration.
- If you are using an SGI workstation, see the next question.
This FAQ applies to: Any version.
