Re: [ferret_users] Custom colorbar/ Multiple Palettes

["William S. Kessler" <William.S.Kessler@xxxxxxxx>]

Hi Ashley -

I see that Jaison has just posted his usual complete masterly advice,  
thanks Jaison.

I frequently use a similar palette idea, with a difference. I want  
the shading to range:

dark blue - light blue - white/gray - light red - dark red.

(Your message was unclear if you wanted a range of shades or  
specified colors as in Jaison's example).

A typical palette would be:

 0   20   20  100   ! blue
49   95   95   95   ! light gray
51   95   95   95   ! light gray
100 100   20   20   ! red

(Of course you could reverse the first and last lines to get red -  
white - blue, or increase the central range to, say, 45-55, etc).

Use it with the /LEV=c qualifier, or specify centered contour levels  
by hand.

Note that I have a very light gray as the central color. I find that  
is usually more pleasing to the eye than flat white, and merges more  
smoothly with the red and blue shading. Such a palette emphasizes the  
large values of a plotted field while making the near-zero central  
values less visible. An advantage of using light gray instead of  
white for plots that include blank values (such as maps with some  
land, or vertical sections with some ocean bottom) is that the blanks  
will be distinguishable from existing values that are near zero.

Billy K


On May 29, 2007, at 3:29 AM, Ashley Watson wrote:

> Hi ferreters,
>
>     I want to specify multiple palettes for my shade plot. My data  
> values are in the range -120 to 120.
>  All I want to do is to define different colors for my plot. For  
> example, I want to specify white color (or no color)
> for values -20 to 20,  and Blue palette for positive values (20 to  
> 120) and  Red palette for negative values.(-20 to -120).
>  How can I make such plot?
>
> Ashley