Energy2Quanta

 Convert energy (watts) to number of photons.

   photons = Energy2Quanta(wavelength,energy)

 Energy (e.g., watts) is converted to photons.  Typically energy is a
 matrix of column vectors that measure the energy at the sample
 WAVELENGTHS specified in nanometers, say watts/sr/m2/nm if we are dealing
 with radiance.

 The columns are different samples, or sometimes different spatial
 positions. The entries down a column represent the energy as a function
 of wavelength. The entries across a row represent the energy at a single
 wavelength for each of the samples.

 SEE ALSO
   Quanta2Energy().

 CAUTION:
 Unfortunately, the two routines Quanta2Energy and Energy2Quanta take data
 data in rows vs. cols.  In the fullness of time, this will be changed;
 but it will require some effort because they are inserted in so many
 important places.

 Examples:
   wave = 400:10:700;
   in = [blackbody(wave,5000,'energy'),blackbody(wave,6000,'energy')];
   p = Energy2Quanta(wave,in);
   figure; plot(wave,p);

 Notice that in the return, out becomes a row vector, consistent with XW
 format. Also, notice that we have to transpose p to make this work.
 Tragic.

   out = Quanta2Energy(wave,p');      % out is a row vector, XW format
   figure; plot(wave,in,'ro',wave,out','k-')

 Copyright ImagEval Consultants, LLC, 2003.