Re: [ferret_users]RGB values for interlevels

[Ryo Furue <furue@xxxxxxxxxx>]

Hi Peter,

| I would like to know the algorythm of palette making or something
| else that helps to be able to use the same palette and scale in
| other applications?  If I use "N" levels during plotting and i want
| to use for example inverse_bluescale, how will i know the RGB values
| (in percent or in values from 0...255) for the interlevels (2.,
| 3. ,..., N-1.) ?
| 
| inverse_bluescale:
| 0 95 95 95 !1. level
| 100 0 0 95 !N. level

I recommend that you start from Chapter 6, Section 5.2, of the Ferret
User's Guide:

  http://ferret.pmel.noaa.gov/Ferret/documentation/users-guide/customizing-plots/COLOR/

I think that Ferret linearly interpolates the RGB values: you can
regard a set of RGB values as a 3D vector (r,g,b) and the
interpolation is to find a point on the line segment connecting
the two end points, (r1,g1,b1) and (r2,g2,b2).
So, for example, a 20% value should correspond to

      (95, 95, 95) + (0-95, 0-95, 95-95) * 0.2
    = (76, 76, 95)

By the way, if you want specify a correspondence between a level and a
color, you might want to use the "RGB_Mapping By_level" option.  (See
the manual.)

Hope this helps,
Ryo