NAME: 
  wedge
 PURPOSE: 
  Compute and return a gray scale step wedge.
 DESCRIPTION:
 CATEGORY:
  Image display
 CALLING SEQUENCE:
 INPUTS:
 OPTIONAL INPUT PARAMETERS:
 KEYWORD INPUT PARAMETERS:
  NCOLORS - Number of colors in the wedge default is !d.n_colors, but not
              bigger than 255.  If you set it manually, there is no limit.
 OUTPUTS:
 KEYWORD OUTPUT PARAMETERS:
 COMMON BLOCKS:
 SIDE EFFECTS:
 RESTRICTIONS:
 PROCEDURE:
 MODIFICATION HISTORY:
 Oct 1991, Written by Marc W. Buie, Lowell Observatory
 2016/12/15, MWB, added NCOLORS keyword, this changes the default behavior
                   very slightly.