GRASS = 24 bit images?

[Bill Brown]

>
>Hello,
>       Just a quick question - I was under the impression that GRASS can impor
t,
>generate, export and display 24 bit images - is this correct ? 
>
>Cheers, Al.
>

Probably the best way to import 24 bit images in GRASS is to treat them 
as a combination of three 8 bit images, one for red, one for green,
and one for blue and import them as three separate maps.  I believe
the GRASS module r.in.ppm does this.  If you use r.in.tiff, the
colors get quantized, but I don't remember how many categories
they get put into.  

The GRASS display drivers use a color lookup table (CLUT), therefore 
24 bit images may not be displayed using the GRASS drivers.  The
X drivers use 8 bit CLUTs, allowing 256 colors, and the IRIS driver 
for SGIs uses a CLUT which allows 3840 colors. However,
the GRASS database libraries do calculate a 24 bit color for each
category, so the GRASS module SG3d (only available for SGI platforms),
which does not use the GRASS display driver, is able to display
24 bit images.  As far as I know, nobody has yet written a display
driver for X which would allow 24 bit display.

24 bit images of raster data can be exported from GRASS using r.out.ppm.

- Bill