[GRASS-user] Raster analysis

Brad Douglas rez at touchofmadness.com
Wed Oct 18 16:30:45 EDT 2006

On Wed, 2006-10-18 at 11:43 +0100, Glynn Clements wrote:
> Brad Douglas wrote:
> > > Please react to the statement below. This is from one shifting from
> > > Idrisi to GRASS
> > >
> > > "I have found that colour manipulation by contrast stretching is not
> > > possible in GRASS or am I wrong."
> > 
> > Sadly, it is correct.  Only 8-bit (integer) color is supported at this
> > time.  Adding it to grass/TODO.
> Can you elaborate?
> Are you referring to the fact that GRASS' colour tables only use 8
> bits per component? Or the use of 8 bits per component in the display
> architecture? Or something else?

The first one: color tables = 8 bits per component.  I'm sure the 2nd
will eventually come into play, but is much less significant.

Well, technically, it is possible to do contract stretching
(normalization), but there is no module to accomplish it and virtually
all data you would want to use this technique with are 16-bit or better
resolution.  For instance, the ASTER satellite data I use is 16-bit,
making it virtually useless in GRASS.

The module would be fairly simple to accomplish.  Modifying GRASS is a
bit more work.  GRASS also seems to limited to 1000 categories, too.

Brad Douglas <rez touchofmadness com>                    KB8UYR/6
Address: 37.493,-121.924 / WGS84    National Map Corps #TNMC-3785

More information about the grass-user mailing list