d.rgb d.his

GRASS GRASS user
1

Date: Tue, 14 Apr 1992 16:57:17 -0500
From: Jim Westervelt <westerve@marla.urban.uiuc.edu>
Message-Id: <199204142157.AA04511@marla.urban.uiuc.edu>
Sender: lists-owner@amber.cecer.army.mil
Reply-To: grassu-list@amber.cecer.army.mil
Precedence: Bulk
To: grassu-list@amber.cecer.army.mil
Subject: d.rgb d.his

Jinn-Guey Lay questions:

#I was trying to display an elevation map in color with a shadow
#releif map in grey tone. I have tried 'd.his' using elevation
#as hue and shadow relief as intensity. It looks OK only if I stay
#far enough; the display is somehow noisy with many pixels of
#different colors scattering arround.

This is probably the best that GRASS (and your display monitor) can do.
I suspect that the scattering of different colors would be corrected if
you put the monitor into "fixed" mode. (d.colormode fixed) If the
scattering you talk about is on the subtle side - colors just slightly off,
then your colormode is "fixed" and the d.his program is dithering the
available colors to get the best representation it can out of a 6x6x6
color table (RxGxB). Basically you (and GRASS) are asking too much of
8 bit planes of graphics - you are experiencing the lure of 24 bit plane
devices.

etc etc.

Try using
    blend.sh elevation.file aspect.file 70

to create 3 band files (R,G,B)

(or I passed out a copy of intens.sh on this newsgroup a while back. It
will do an even better job)

Then if you have a Silicon Graphics workstation you can use the
Dtrue program to display the resultant composit in true 24 bit color.
If not, use i.median to combine the 3 files into one 8 bit color file.

i.median creates a file with a colortable of 256 colors. This can be
displayed on any GRASS display, but it usually will look much better if
you can display it in float mode on a display which will support 256 colors.
You can acheive this in SUNVIEW by setting an environment variable before
starting the monitor.

    setenv GRASS_COLOR256
    d.mon sunview

I am not sure whether Xdriver supports this or not.

This should be part of the FAQ.

Oh, we don't have a FAQ.

  Dave Gerdes
  US Army Construction Engineering Research Lab
  Spatial Analysis & Systems Team
  dpgerdes@cerl.cecer.army.mil
  (217) 352-6511 x591