33. The method of claim 32 wherein the separating step includes isolating the energy at wave lengths higher than the highest frequency bandwidth of the low pass filters and separatiang that energy into a plurality of high frequency regions, and the energy spectrum deriving step includes incorporating the energy from the high frequency regions into the energy spectra without passing through the summing amplifiers.
32. The method of claim 30 wherein the energy spectra deriving step includes passing the output of adjacent sets of difference amplifiers through a plurality of summing amplifiers, and summing the outputs of the summing amplifiers.