function RGBtoTrue, number
;+
; ;+
; NAME:
;   RGBtoTrue
;
; PURPOSE:
;   Converts a  r,g,b value to the true color number
;
; CATEGORY:
;   Graphics.
;
; CALLING SEQUENCE:
;   true = RGBtoTrue([255,23,12])
;
; INPUTS:
;   r,g,b vector
;
; KEYWORD PARAMETERS:
;   None.
; OUTPUTS:
;   single long integer
; COMMON BLOCKS:
;   None.
; SIDE EFFECTS:
;  None..
; RESTRICTIONS:
;   None.
; MODIFICATION HISTORY:
;   Derived from David Fanning's color24 function, I just wanted
;   a different name.
;   Written 2/23/2000 by Ronn Kling
;   Kling Research and Software
;   www.rlkling.com
; LICENSE
;
; This software is OSI Certified Open Source Software.
; OSI Certified is a certification mark of the Open Source Initiative.
;
; Copyright © 1997-2001 Kling Research and Software.
;
; This software is provided "as-is", without any express or
; implied warranty. In no event will the authors be held liable
; for any damages arising from the use of this software.
;
; Permission is granted to anyone to use this software for any
; purpose, including commercial applications, and to alter it and
; redistribute it freely, subject to the following restrictions:
;
; 1. The origin of this software must not be misrepresented; you must
;    not claim you wrote the original software. If you use this software
;    in a product, an acknowledgment in the product documentation
;    would be appreciated, but is not required.
;
; 2. Altered source versions must be plainly marked as such, and must
;    not be misrepresented as being the original software.
;
; 3. This notice may not be removed or altered from any source distribution.
;
; For more information on Open Source Software, visit the Open Source
; web site: http://www.opensource.org.
;-


if n_elements(number) ne 3 then $
   message,'You must pass in a three element vector'

minNum = min(number, max=maxNum)
if minNum lt 0 or maxNum gt 255 then $
    message,'Values must be in the range 0 to 255!'

base16 = [[1L, 16L],[256L,4096L], [65536L, 1048576L]]
trueNum = 0L
for j=0,2 do trueNum = trueNum + ((number[j] mod 16) * base16[0,j]) + $
                       (fix(number[j]/16) * base16[1,j])
return,trueNum
end