get rgb value of wavelength

rgbFromWavelength.rb

# from http://www.physics.sfasu.edu/astro/color/spectra.html
def rgbFromWavelength(wl, gamma=0.8)
  rgb=case wl
      when (380..439); [-1.0*(wl-440.0)/(440.0-380.0), 0.0, 1.0]
      when (440..489); [0.0, (wl-440.0)/(490.0-440.0), 1.0]
      when (490..509); [0.0, 1.0, -1.0*(wl-510.0)/(510.0-490.0)]
      when (510..579); [(wl-510.0)/(580.0-510.0), 1.0, 0.0]
      when (580..644); [1.0, -1.0*(wl-645.0)/(645-580.0), 0.0]
      when (645..780); [1.0, 0.0, 0.0];
      end
  sss=(wl>700 && 0.3+0.7*(780.0-wl)/(780.0-700.0) ||
       wl<420 && 0.3+0.7*(wl-380.0)/(420.0-380.0) ||
       1)
  rgb.map!{|c| (sss*c)**gamma}
  def rgb.to_bytes; self.map{|c| (0xff*c)};   end
  def rgb.to_s; ('#'+'%02x'*3)%self.to_bytes; end
  rgb
end