Re: Color map manipulation

Hi Freddie,
To add white to your printed labelbar you have two choices:
1) As white is already part of the colormap (color indices 0 and 8), it
is probably easiest to specify exactly which colors correspond to which
contour intervals.

You can do this by setting cnFillColors (and not setting gsnSpreadColors
= True if you were doing so), using the indices shown here:
www.ncl.ucar.edu/Document/Graphics/ColorTables/precip_diff_12lev.shtml

res@cnLevelSelectionMode = "ExplicitLevels"
res@cnLevels = (/-.3,-.2,-.1,0,0.1,0.2/)
res@cnFillColors = (/2,4,6,8,8,10,12,14/) ; #s refer to indices

If you wish to change the white to gray, you first have to add gray to
your colormap. The easiest way to do this is to use NhlNewColor after
you open the workstation:
wks = gsn_open_wks("ps",get_script_prefix_name())
gsn_define_colormap(wks,"precip_diff_12lev")
nc1 = NhlNewColor(wks,0.5,0.5,0.5) ; = medium gray
nc2 = NhlNewColor(wks,0.8,0.8,0.8) ; = light gray

Note that in the above medium gray would be added to precip_diff_12lev
as the 15th color index, and light gray would be added as the 16th color
index.
To use the light gray in the middle set
res@cnFillColors = (/2,4,6,16,16,10,12,14/)

2) You can manipulate the loaded color table yourself. I won't go into
details here as option #1 is much easier. But see:
http://www.ncl.ucar.edu/Applications/color.shtml#ex16

example 16 shows how to load a colormap, retrieve it, and modify it.

Hope that helps. If not, let ncl-talk know.
Good luck,
Adam

On 02/22/2012 03:51 PM, Freddie.Mpelasoka@csiro.au wrote:
> Dear ncl experts,
>
> I am learning to produce plots using ncl. How can I manipulate "precip_diff_12lev "color map to have white color around zero (i.e. over [-0.1 and +0.1]) for the range /-0.3, -0.2, -0.1, 0., 0.1,0.2/. I am also wondering if the "white" color in the "precip_diff_12lev "can be replaced with "grey". Your help will be highly appreciated.
>
>
> Many thanks,
>
> Freddie
>
>
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-- 
______________________________________________________________
Adam Phillips                                asphilli@ucar.edu
NCAR/Climate and Global Dynamics Division       (303) 497-1726
P.O. Box 3000				
Boulder, CO 80307-3000    http://www.cgd.ucar.edu/cas/asphilli

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Received on Wed Feb 22 16:23:40 2012