4. The system as recited in claim 3 , wherein predetermined environmental factors when present in the captured image portion are parametrically discriminated by said simultaneous sparse approximation for discovering said core spectral signatures responsive thereto, said predetermined environmental factors including local artifacts and lighting variations between different portions of the spatial image plane.
3. The system as recited in claim 2 , wherein said simultaneous sparse approximation process is of a greedy adaptive decomposition (GAD) type, at least one set of selectively grouped image vectors being disposed in spatially contiguous manner with respect to a spatial image plane.