[GRASSLIST:431] Re: Maximum number of colors in rasters

[Michael Barton]

These are actually related questions...I think.

A TclTk canvas can use a full color RGB image (16 million). I'm not sure
about an x-monitor (but see below).

The PNG driver for GRASS is the one used for the TclTk canvases in the new
GIS Manager. It can be set to a low index color setting or a "true color"
setting (the one used by default for the GIS Manager). I think the latter is
32 bit (please correct me someone if this is wrong). It looks to my eye that
an x-monitor can display the same number of colors.

The color table does not store colors per se. It stores a reference to
colors. For a continuous shade map, like an elevation map, it stores
reference points along a color continuum and GRASS seems to generate the
intermediate gradations. You can look at the color table in a mapset. It is
just an ascii file.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution and Social Change
Arizona State University
Tempe, AZ 85287-2402

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton



> From: "Patton, Eric" <epatton at nrcan.gc.ca>
> Date: Mon, 27 Mar 2006 10:06:48 -0400
> To: "'GRASSLIST at baylor.edu'" <GRASSLIST at baylor.edu>
> Subject: [GRASSLIST:416] Maximum number of colors in rasters
> 
> I guess this is a two-part question: 1) What is the maximum number of colors
> representable in an x-monitor/tcltk canvas, and 2) How many colors are
> stored in a raster color table from a raster that was gridded within Grass
> (i.e., xyz data)
> 
> Thanks,
> 
> ~ Eric.