"""
Based on
  http://www.physics.sfasu.edu/astro/color/spectra.html
  RGB VALUES FOR VISIBLE WAVELENGTHS   by Dan Bruton (astro@tamu.edu)
"""

# How to use:
#from spectrumRGB import rgb
#ww=np.arange(380.,781.)
#rgb=rgb()
#from matplotlib import pyplot as plt
#import matplotlib as mpl
#cmap = mpl.colors.ListedColormap(rgb)
#norm = mpl.colors.Normalize(vmin=0., vmax=1)



import numpy as np
select=np.select
power=np.power
transpose=np.transpose
arange=np.arange

def factor(wl):
    return select(
        [ wl > 700.,
          wl < 420.,
          True ],
        [ .3+.7*(780.-wl)/(780.-700.),
          .3+.7*(wl-380.)/(420.-380.),
          1.0 ] )

def raw_r(wl):
    return select(
        [ wl >= 580.,
          wl >= 510.,
          wl >= 440.,
          wl >= 380.,
          True ],
        [ 1.0,
          (wl-510.)/(580.-510.),
          0.0,
          (wl-440.)/(380.-440.),
          0.0 ] )

def raw_g(wl):
    return select(
        [ wl >= 645.,
          wl >= 580.,
          wl >= 490.,
          wl >= 440.,
          True ],
        [ 0.0,
          (wl-645.)/(580.-645.),
          1.0,
          (wl-440.)/(490.-440.),
          0.0 ] )

def raw_b(wl):
    return select(
        [ wl >= 510.,
          wl >= 490.,
          wl >= 380.,
          True ],
        [ 0.0,
          (wl-510.)/(490.-510.),
          1.0,
          0.0 ] )

gamma = 0.80
def correct_r(wl):
    return power(factor(wl)*raw_r(wl),gamma)
def correct_g(wl):
    return power(factor(wl)*raw_g(wl),gamma)
def correct_b(wl):
    return power(factor(wl)*raw_b(wl),gamma)

ww=arange(380.,781.)
def rgb():
    return transpose([correct_r(ww),correct_g(ww),correct_b(ww)])