Properties of unslanted reflection holographic diffraction gratings are described mathematically with much accuracy by the methods used in thin-film physics. By dividing the hologram bulk into sufficiently thin homogeneous layers, each one is characterized by a 2*2 dimensional matrix, the authors simulate a series of cases common in holographic practice. The spectral selectivity of holograms with amplitude-phase modulation is calculated, as well as that of holograms with non-linear thickness deformation of recording medium and two and three holographic gratings stored sequentially in one and the same volume. The influence of substrate qualities on hologram performance is evaluated.