Re: plot_image color tables

Hi Joey, 

    Joseph> I'm wondering if there is a way to use plot_image to make images of an
    Joseph> arbitrary color. I have a 2D Gaussian that I'm trying to display, and I'd
    Joseph> like to do it in various levels of purple (i.e. purple fading to black).
    Joseph> set_palette allows you to select the color table, but not to just pick a
    Joseph> color.

    Joseph> Is there a way to do what I'm looking for?

It looks like _pgctab will do what you want.  You'll have to
experiment a bit.  Here's an ad hoc empirical example.

  z = Double_Type[256,256];
  for(i=0;i<256;i++)
     for(j=0;j<256;j++)
        z[i,j]= sin((i-128)/100.)*cos((j-128)/20.);;

  rl = [-0.5, 0.0, 0.17, 0.33, 0.50, 0.67, 0.83, 1.0, 1.7] ;
  rr = [ 0.0, 0.0,  0.0,  0.0,  0.6,  1.0,  1.0, 1.0, 1.0] ;
  rg = [ 0.0, 0.0,  0.0,  1.0,  1.0,  1.0,  0.6, 0.0, 1.0] ;
  rb = [ 0.0, 0.3,  0.8,  1.0,  0.3,  0.0,  0.0, 0.0, 1.0] ;

  resize(16,1);
  plot_image( z ) ; 

  _pgctab( rl, rr, rg, rb, 1.0, 0.5 ) ;
  plot_image( z ) ; 

  _pgctab( rl, rr, rg*0, rr, 1.0, 0.5 ) ;
  plot_image( z ) ; 


See <http://www.astro.caltech.edu/~tjp/pgplot/subroutines.html#PGCTAB>
for a description of the pgplot subroutines (which  are _pg* functions
in isis).  Note that when isis can determine a parameter from the data
(like the length of an array), that argument is omitted from the isis
interface).

I also used the examples tables from:

  <http://spdg1.sci.shizuoka.ac.jp/grwinlib/contrib/pgplot/examples/pgdemo4.f>


Another option might be to manipulate color tables post facto with
some external programs, like those in the imagemagick suite.

Or you could see how set_palette works in the isis source code.


-- Dave

David Huenemoerder  617-253-4283 (o); -253-8084 (f); http://space.mit.edu/home/dph
MIT Kavli Institute for Astrophysics and Space Research
70 Vassar St., NE80-6065,
Cambridge, MA  02139
[Admin. Asst.: Elaine Tirrell, 617-253-7480, egt_at_email.domain.hidden
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