This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

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Phase extension procedure, using the magnitudes of the structure factors from ED (electron diffraction) and starting phases from the corresponding EM (electron microscopy), can be employed to improve a high-resolution image. The tangent formula [1] is normally used as the basis of the phase extension,

         ---------------------- [3493a]

         ------------------------------------------ [3493b]

where,
          α_h -- The phase associated with the normalized structure factor E_h
          E_h -- The normalized structure factor
          F_h -- The conventional structure factor
          Σ -- The average value of |F_h|² for the scattering angle corresponding to h
          ε -- Usually equals unity but can be a small integer depending on the space group and the type of reflection and giving the effect that for all the reflections of that particular type <|E_h|²> = 1.

By substituting E_h with known phases into the right-hand side of Equation 3493a, originally unknown phases can be predicted according to the outcome on the left-hand side.