[GRASSLIST:1642] Re: floating color table questions

[Eric G. Miller]

On Mon, Mar 19, 2001 at 09:55:37PM -0700, Gerald Buckmaster wrote:
> Friends,
> 
> This is probably a very common question:
> 
> How do I view the full beauty of my multispectral imagery using GRASS?  With
> ERDAS Imagine, I get some great looking imagery, but with GRASS, I apparently
> cannot get past 8-bit?
> 
> Does this have something to do with the driver.  Something about a 24-bit
> driver, I recall is how I fixed this before.
> 
> My attempt to set the colormode to floating is not working.
> 
> d.colormode mode=float
> 
> Sorry, floating color table not available on this device

"Float" colormode only works if there is a writeable colormap (it
wouldn't help anyway).  TrueColor (24 bit) visuals are always (?) read
only.  There's an "nlev" argument to d.mon in GRASS 5.0, allowing you to
specify 24 bit color by using "d.mon start=x0 nlev=256" (256 == colors
per channel r/g/b).  Unfortunately, the driver code isn't very
sophisticated and using that many colors requires a large chunk of
memory (for the colormap).  I looked at eliminating the color map for
TrueColor visuals, but I couldn't quite decipher how to do it.  

One other thing that will degrade the quality of the visuals some is the
way GRASS chooses cell values when the "region" settings don't match the
raster.  It should do some form of interpolation (nearest neighbor,
etc...) but instead just chooses the closest cell for the given
resolution.  This can make the image a bit "pixelated" looking.

I don't think these things will change for GRASS 5.0 at all (maybe 5.1).

NOTE: I think the CELL driver is only 8-bit color...

-- 
Eric G. Miller <egm2 at jps.net>